Preface

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DISCLAIMER

Introduction

Reducing the Clutter in Land Fills

Many dead appliances, and consumer electronic and computer equipment contain parts and subassemblies which are not only neat and interesting, but useful for various experiments and projects.

• I bet you tossed that big heavy slow 5-1/4" hard drive in the garbage when you upgraded, didn't you? Admit it! Did you know that if it was a high performance drive, it contained several of the most powerful permanent magnets you would ever be likely to find anywhere? And, they would have been free!

• That big old microwave oven? Too bad. More magnets, nice high voltage power transformer, rectifier, capacitor. Electronic or mechanical timer, fans, other motors, etc.

• What about that dot matrix printer? Too bad - at least two stepper motors, a nice power supply, and various other electronic and mechanical components.

• More steppers in floppy drives. Also, probably a regulated speed pancake motor.

• Old TV or monitor? Another mistake. The high voltage power supply was probably good for 12 to 30 kVDC at 1 or 2 mA. This is useful for many high voltage experiments, plasma globes, negative ion and ozone generators, bug disintegrators, starters for really LARGE HeNe lasers, etc.

1. Where to obtain a particular type of part like a powerful magnet.

2. What dead consumer electronics, computer equipment, and appliances yield in the way of useful parts.

3. Unconventional uses for subsystems or common replacement parts or modules from such equipment.

Safety Considerations

Before thinking about experimenting with anything using or producing high voltages or connected to the AC line - even opening up a disposable camera that may have been laying around gathering dust (the capacitor can still be charged - arggh!), see the document: Safety Guidelines for High Voltage and/or Line Powered Equipment. A large percentage of equipment that is perfectly safe from the outside has dangers lurking inside. In addition to electrical dangers, there might be sharp sheet metal, wound up springs, powerful magnets, and other potential risks to your outer surface integrity like CRT implosion - just to name a few. Something that looks innocent can really ruin your entire day!

For really high voltage equipment, also see: Tesla Coils Safety Information.

Places to Obtain Sacrificial Equipment

Of course, don't overlook high tech flea markets as well as ham and computer fests. Regular flea markets are usually overpriced (where do you think they get the stuff??) but sometimes you will be able to negotiate a great price because they have no idea of what they are selling!

Yes, we are a strange bunch. :-)

Neat Magnets

Sources of Extremely Powerful Magnets

• Microwave oven magnetron tubes. Go to your local appliance repair shop and ask - they just toss bad ones. Each one has two ring shaped ferrite magnets about 2-1/4" in diameter with a 7/8" hole, magnetized N-S on the faces.

  Surplus places typically charge $3 to $6 each for one of these magnets.

  Note: A few older magnetrons used AlNiCo magnet assemblies or even possibly electromagnets which are not nearly as interesting. However, you probably won't see any of these.

• Large hard disk drives - especially full height 5-1/4" high performance types - e.g., Seagate WREN series or Micropolous boat anchors (the rare earth magnets in these are wicked). The magnets in small drives are even stronger but are, well, much smaller. :-) A typical size for a large drive is about 1" x 1-1/4" by 1/2". Since almost no one wants such large slow drives anymore, they are often found at swap meets or yard sales for next to nothing. These magnets are a few thousand Gauss compared to 10 to 15 K Gauss (1 to 1.5 Tesla) for a medical MRI scanner (of course, the field of the MRI scanner's superconducting magnet is uniform over a volume of several cubic FEET! The disk drive magnet's field decays quickly as you move away from it.)

  Surplus places may charge $12 or more for ONE of the magnets from a large disk drive (there are typically 2 to 6 such magnets in a disk drive)!

  I have a monolithic clump of 40 or 50 of the magnets from full height 5-1/4" SCSI drives. I figure there is a black hole growing inside but haven't dared to look. :) The only way I was able put the clump together with minimal damage to flesh was by using a hard wood ramp to gently guide each new magnet into place. I haven't figured out how I'll ever get them apart though!

  Here is a quick easy experiment to try with these powerful magnets: Slide one such magnet over a thick aluminum plate. What do you feel? Or, let a 1/8" x 2" x 12" aluminum plate drop through the intact yoke from a Seagate WREN series 5-1/4" full height hard drive positioner. What happens? Why? What material might produce an even more pronounced effect? Why?

  For more things to do with these neat magnets, see: Neodymiumarium.

CAUTION: Both these types are powerful and will squash flesh as they suck all the bits off of your magnetic media! I am not kidding about the part about squashed flesh - with some you actually need a small crowbar to pry the assembly apart!

You will find that some of these magnets are painted. This provides some resistance to chipping though this material may be on the verge of flaking off or has already done so in spots. In any case, I further recommend that you add additional layers of a tough enamel (e.g., Rustoleum) or the plastic/rubber dip used to coat tool handles. Otherwise, chipping damage (at least) will result all too easily and the chips are just as powerful as the rest of the magnet.

Additional Disclaimer: I will not be responsible when your spouse or parents come home to find the microwave or PC missing some key components and as dead as a brick!

(From: Terry Sanford (tsanford@nf.sympatico.ca).)

Magnets salvaged from scrapped computer drives are strong!

• We use them to hold old blankets that cover a vintage car stored in garage.

• Useful for finding nail locations in plasterboard walls. Strong magnet will 'stick' to wall at the nail location. better than those weak magnet 'dippy indicator' things! You can leave magnet parked on the nearest nail head after each use!

• Use magnet to pick up wrench/spanner dropped off boat wharf into ten feet of sea water! Also fished wrench out from under patio deck other day; main problem was finagling wrench through the gap between the deck boards. Used bent coat hangar which kept sticking to the magnet; darn!

• Also you can 'feel' if current is actually flowing to an electrical appliance by holding a strong magnet next to the wiring! It detects 'flow' not the presence of voltage.

PS: After WWII, strong horseshoe ex radar magnetron magnets were sold surplus for about two and sixpence each. Someone took his into a pub on way home and everyone had a great time with it until people starting checking their (then magnetic) watches. He wasn't too popular after that I can tell you!

Other Sources of Fairly Powerful Magnets

• Spent laser printer toner cartridges where the entire developer assembly is part of the cartridge (e.g., EPS-2 for Canon engines). These include a page-width ferrite magnet. However, expect to make a mess disassembling the cartridge as there will still be considerable toner remaining inside.

  WARNING: The toner is a possible health hazard. A good dust mask should be used while working on these. Also, do not vacuum what remains - static can set off a dust explosion - use wet rags or paper towels to clean up the mess! The coating on the photosensitive drum may also be a hazardous material.

• Loudspeakers.
  • Smaller or older speakers use AlNiCo type magnets which are usually in the form of a cylinder (about as tall as it is wide). AlNiCo is an extremely hard metal alloy.

    AlNiCo magnets are not as powerful as ferrite or rare earth types and are easily demagnetized (but just as easily remagnetized). Passing a stack of these through the center hole of a strong ferrite magnet will increase their strength dramatically - until they are separated from each other!

  • Modern loudspeakers use ring shaped ceramic ferrite magnets (similar to those in a microwave oven magnetron - see the section: Neat Magnets) glued to the pole piece (yoke) assembly within which the voice coil moves. The ferrite is extremely hard but very brittle so care must be used to extract these from the yoke assembly - see the section: Disassembling Loudspeakers to Get at the Magnets.

• Permanent magnet stepper and servo motors. These will use ferrite or rare earth magnets usually in strange shapes. Note: Removing the magnets may result in partial demagnetization (reduction in magnetic strength) as the rotor is part of the magnetic circuit. Therefore, I do not recommend this source. There is generally no practical way of remagnetizing the strange shapes involved.

• Optical (laser) pickups from CD players, CDROM drives, and other optical data storage devices. These may have some very tiny, but strong, rare earth magnets in the focus and tracking actuator. However, it seems a shame to sacrifice the beautiful mechanics in such a device just to get the magnets! CAUTION: Tiny magnets even more fragile than bigger ones!

Disassembling Loudspeakers to Get at the Magnets

(From: Arie de Muynck (ademu@pi.net).)

For the normal black ceramic ring shaped magnets (and likely for some Ticonal 'iron colored') the trick is: heat the complete assembly slowly using a paint-stripper gun, or in an oven (thermal, not microwave!). The glue will weaken and with a screwdriver you can SLOWLY work them loose. Protect your fingers with an old cloth. Never apply too much force, the ceramic would chip or break.

Do not overheat them above the so-called Curie temperature or the magnet will loose it's power irreversibly. That temp depends on the material but should be way above the 120 C or so to soften the glue. If you want to experiment with this effect: use a piece of iron attracted towards a magnet, heat the iron with a flame and above a rather sharply defined temperature it will not be attracted anymore. The effect is used in some Weller soldering irons to stabilize the temp.

Note that the force of a bare ceramic magnet is not as strong as you might expect, the magnetic lines of the large area of the ring have to be bundled and guided though iron to a narrow gap to provide a proper magnetic field.

How do I Make a Harddrive Motor Spin?

(From: Bob Weiss (bweiss@carroll.com).)

These motors are usually brushless DC, and can be a pain to figure out. Windings are usually 3-phase wye. DC power applied to center tap of wye, and ends of windings go to output transistors/fets in the driver. Driven by 3 pulse trains 120 degrees apart. Other leads are for hall effect sensors that measure rotor position and time the drive pulses to the relative positions of the rotor magnets and stator coils. Not an easy driver to build from discretes! Some motors contain all the driver electronics, and only require +12VDC and a TTL enable signal to run. The Disc drive you took them out of will contain appropriate parts to build a controller, probably a driver chip from SGS or Sprague UCN series. Look up the chip in a databook for suggested circuitry. Best way to learn this field is reverse engineering!

High Voltage Power Supplies from Dead Equipment

You are Surrounded by HV Equipment!

• TVs, monitors, and computer terminals all contain a source of high voltage for the CRT. Depending on the particular model, up to 30 kVDC or more at 1 to 2 mA will be available assuming the deflection/HV subsystem of your sacrificial equipment is in operating condition. However, you cannot (or at least should not) just string HV wires from the back of the family's 35 inch TV to your lab. :-)
  • How much circuitry you actually need (and what you will have to add) depends on design but figure on the mainboard with the deflection drive and flyback, and probably the yoke (to keep the system properly tuned though this may not be essential).

    Some capacitance on the HV output may be needed as well (though the ones I have tried were happy enough with just the stray capacitance of the wiring). Originally, the CRT envelope provided this capacitance.

    See the section: Why the Yoke is Needed to Keep the Horizontal Deflection System Happy.

  • Power will either be the AC line (WARNING: Very dangerous) or a DC supply (typically 12 to 24 VDC). They will usually operate on somewhat lower input voltages with correspondingly reduced output.

  • A 555 timer based oscillator or other horizontal sync source may be needed as well if the system doesn't free-run at close to the normal horizontal scan rate. This is probably easier where the guts came from a monitor or terminal (since a separate TTL compatible horizontal drive input is likely to be available) but it should be possible to fake out a TV as well.

  • Depending on design, these may require signals like 'HV Enable' and/or a feedback or reference voltage to operate properly.

  • Small B/W TVs, mono computer monitors, and computer terminals will provide about 12 to 15 kV.

  • Large B/W TVs and Color TVs and monitors will provide 15 to 30 kV. Even more from projection sets!

  • Some larger high performance color monitors may have a separate self contained HV module. One particular type (found in a 19 inch workstation monitor) is rated at 25 kV, 1.1 mA (and produces several other voltages) from a 26 VDC, 2.5 A power supply. However, by tweaking some internal pots, over 30 kV is available. See the section: High Voltage Power Supply Module from Monitronix EZ Series Monitors for one example.

  One key advantage of using predesigned circuitry is that you are less likely to destroy power transistors and other expensive parts - and I have blown my unfair share. :-(

  See the section: Sam's Super-Starter(tm) for a specific example of this kludge, um, err, approach for starting large HeNe laser tubes. :-)

• The high voltage power supplies from plasma globes, electrostatic dust precipitators, photocopiers and laser printers, bug zappers, negative ion and ozone generators, electric fences, cattle prods, electric chairs, and other 'common' equipment may be pressed into service for your applications.

  Since these HV generators are not combined with anything else, they are likely to be self contained modules and very easily used by themselves.

  However, available current from some of these sources is generally less than from TVs or monitors. Details are left to the highly motivated student. :-)

  • Plasma globes: Pulsed (not rectified or filtered) 10 to 15 kV.

  • Electrostatic dust precipitators: 5 to 10 kVDC.

  • Photocopiers and laser printers: Two outputs at 5 or 6 kVDC.

  • Bug zappers: 10 kV???.

CAUTION: Since these power supplies were designed for a specific purpose under specific operating conditions, their behavior when confronted with overloads or short circuits on the output will depend on their design. It may not be pretty - as in they may blow up! Take care to avoid such events and/or add suitable protection in the form of fast acting fuses and current limiting to the switching transistor.

Note about X-rays: Improper use of these sorts of devices may result in shock or electrocution, but at least you will not be irradiated at the same time unless you connect them to a something which includes a vacuum. In order to produce measurable X-ray radiation, electrons must be accelerated to high velocity and strike a heavy metal target. A high vacuum such as in a CRT or other vacuum tube (valve) is best but there may be some X-ray production from a low pressure gas filled tube. There is virtually none in sparks or arcs at normal atmospheric pressure. However, there will be UV and ozone which are both hazardous.

Sam's Super-Starter(tm)

The entire horizontal deflection and high voltage sections of a long obsolete and lonely ASCII video display terminal were pressed into service for starting larger HeNe tubes. A source of about 12 VDC at 1.5 A is needed for power and a 555 timer based oscillator is needed to provide the fake horizontal sync:

• The deflection circuitry was all on one corner of relatively small board (about 3 x 6 inches). The flyback transformer is a plug-in unit. I left the other circuitry (vertical, video) in place since it is not powered by the same supply and therefore is pretty inert. However, if you want to recycle the parts.....

• The horizontal deflection yoke is needed to 'tune' the system - performance is much better with it installed. This wart looks a bit strange but is the easiest way to avoid modifying the design. See the section: Why the Yoke is Needed to Keep the Horizontal Deflection System Happy for more info.

• Horizontal drive is provided by a 555 timer in astable mode running at about 16 kHz (the original horizontal deflection rate of the terminal). A 10K ohm pot allows me to fine tune this for maximum HV output.

  Well, it turns out there was an unused spot on the board ready made for this circuit (well almost, at least there was a pattern for a spare 8 pin DIP! So, once the thing was basically working, I built the oscillator onto the board to reduce the clutter!

• Power requirements are modest - 10 to 15 VDC at just over 1 A. Over this range, the output varies between about 10 and 15 kV (what a coincidence!). Input down to about 5 VDC produces correspondingly reduced output but the circuit is not particularly stable over this lower range of voltages.)

I guarantee that "Sam's super-starter(tm)" - or its big brother, "Sam's hyper-starter(tm)" using parts from a color TV or monitor - will start ANY HeNe tube that can possibly be started! These also make nice self contained HV sources for other experiments. :-)

Why the Yoke is Needed to Keep the Horizontal Deflection System Happy

(From: Jeroen Stessen (Jeroen.Stessen@philips.com).)

Of course that doesn't work. The flyback capacitor is tuned for the presence of both inductances: line transformer and deflection coil. If you remove the deflection coil then the remaining primary transformer inductance is about 5 times as large. So, rule-of-thumb, you would have to decrease the flyback capacitor by a factor of approximate 5. But that's not all:

Without the deflection coil, a lot less current runs through the horizontal output transistor. So, in all likelihood, it will now be overdriven. So you need to reduce the base drive. But that's not all:

If you remove the picture tube capacitance and the deflection coil then all peak energy demand must be delivered from the primary winding of the line transformer. Even the shortest peak load will cause saturation. The parallel deflection coil will at least lend some temporary energy, and the picture tube capacitance does an even better job. A good high-voltage source without the benefit of a deflection coil is more expensive...

If you *must* get rid of the 'ugly' deflection coil, then you may want to replace it with an equivalent 'pretty' coil. But:

• It must be able to carry the peak current without saturation (a deflection coil has such a huge air gap that it can not possibly ever saturate, but a smaller coil can).

• It must have a low enough dissipation so you might have to wind it with litz-like wire (multi-stranded isolated), do not underestimate the losses in high-frequency coils, mostly due to skin- and proximity-effect.

• Yes, it can be done, good luck.

And you might want to add a discrete high-voltage capacitor. How to isolate the wiring (corona discharge!) is left as an exercise to the reader... (We pot them in convenient blocks).

High Voltage Power Supply Module from Monitronix EZ Series Monitors

It is fully enclosed in an aluminum case about 1-7/8" x 6" x 5" with a 9 pin connector for the low voltage wiring and thick red wires with HV connectors - suction cup and Alden type - for the CRT 2nd anode and focus voltage respectively.

• Manufacturer: Toyo, Corp., Japan
• Model: HVP-1208A1-26L.
• Input: 26 V, 2.5 A max.
• Outputs:
  • High Voltage: 25 kVDC, 1.1 mA
  • Focus: 4.5 to 7.65 kVDC, 15 uA
  • G2: 200 to 1000 VDC, 5 uA
  • AUX: -200 VDC, .5 mA

      ___________
     /           \
    (  o3  o6  o9 |
     >            |  View of connector on case.
    (  o2  o5  o8 |
     >            |
    (  o1  o4  o7 |
     \___________/

• Pin 1 - G1: -200 VDC (-184 VDC measured), white or yellow.
• Pin 2 - DC+ in: 26 VDC, 2.5 A max, green or brown.
• Pin 3 - Power Gnd, black.
• Pin 4 - Shield Gnd, bare or black.
• Pin 5 - NC.
• Pin 6 - NC.
• Pin 7 - Enable (low) TTL, orange.
• Pin 8 - NC.
• Pin 9 - G2 (+200 to +1000 VDC), red.

In addition to the Focus and G2 pots, there is an unmarked adjustment accessible via a hole in the case. At first, this appeared to have no effect on any output.

When I opened the case, 2 additional pots come into view. While I do not really know their exact function, by advancing them clockwise, the HV could be boosted significantly. With both fully clockwise, the externally accessible control will vary the HV between about 27 and 32 kVDC regulated (only HV probe meter load).

High Voltage Transformers

Types of HV Transformers and Where to Get Them

• Neon sign or luminous tube transformers (same thing): 10 to 15 kV at 15 to 60 mA, current limited. Some may be higher. There are also smaller ones.

  Current limited means that the transformer will deliver the rated current (Io) into a short circuit and produce the rated voltage (Vo) with no load. In between, it is designed to produce a somewhat constant current up to a substantial fraction of its no-load output voltage. This is somewhat similar to being in series with a resistor equal to n*Vo/Io (where n may be 2 or 3 or more) over this range but implemented without silicon as the magnetic design of the core and windings with no extra power dissipation. (It isn't really this straightforward but will serve as a first approximation.) Therefore, a short circuit on the output will not blow a fuse or trip a breaker (though the transformer will overheat if left this way for too long).

  Sources: Your local sign shop, demolition company, or salvage yard. New: $100 or more. Used: $5 to $50 or free.

  Both iron (an actual transformer) and electronic (high frequency inverter) types are available. The iron types are more robust and will survive repeated abuse that may destroy the others but they are heavy.

  WARNING: Though current limited, the available current from neon sign transformers - especially the larger ones - is far into the range where lethal consequences are likely under the wrong circumstances.

  (From: Jason Freeburg (egraffiti@iname.com).)

  "A used neon sign transformer should not cost more than $20 or so. Find a neon shop in your area. They usually have the used ones stacked up somewhere and will sell cheap. The 60 mA models are usually somewhat cheaper than the 30 mA type if you buy them used from a neon shop because they are really too hot (e.g., provide too much current) for running neon and they cause staining and premature burnouts. It all depends on the particular shop you go to. I don't suggest buying new for something like this, the performance will be the same but the price much higher. A new 15 kV, 60 mA transformer lists for about $80.

  BTW, the best name to look for in neon sign transformers is France. These things are ruggedly built like and will take a lot of abuse without dying. The name to avoid is Actown - their transformers are wimpy and usually don't deliver the rated current."

• Oil burner ignition transformers: 8 to 10 kV at 10 to 25 mA, current limited. (See description for neon sign transformers, above.)

  Sources: Your local HVAC contractor probably for the asking as the ignition transformers are thrown out along with old oil burners when they are replaced. Of course, you will probably have to take the entire icky smelling disgusting burner assembly as part of the deal. :-) However, there is will be a nice motor and small oil pump in there as well. ;-)

  WARNING: Though current limited, the available current from oil burner ignition transformers is still more than enough to kill under the wrong circumstances.

• Microwave oven high voltage transformers: 1.5 to 3 kV at 0.25 to 0.5 AMPS.

  Sources: Dead microwave ovens (the transformer is rarely the problem). Try your local appliance repair shop. However, you will probably have to cart away the entire oven - but other useful parts inside. :-) See the section: Dangerous (or Useful) Parts in a Dead Microwave Oven.

  WARNING: The electrocution danger from microwave oven transformers cannot be overemphasized. They are not current limited, and even if they were, could be instantly lethal given the least excuse for a suitable path through your body since the rated current is a substantial fraction of an AMP at several thousand volts. Normally, one end of the high voltage secondary is bonded to the core - which must be grounded for safety. However, it may be possible to disconnect this and construct an isolated HV power supply (which will be only marginally less dangerous).

• Automotive ignition coils: 25 to 75 kV (depending on model) at low current.

  Sources: Your 1997 Honda. Just kidding. :-) Auto repair shops or parts stores, salvage yards.

  WARNING: While unlikely to be lethal, the HV output of an ignition coil can still result in a seriously unpleasant shock and possible collateral damage.

• Flyback transformers from TVs, monitors, computer terminals, or other HV power supplies. Little teeny ones in CRT based camcorder viewfinders and older Watchman TVs. Output from less than 3 kV to over 30 kV at 1 to 2 mA depending on model. Most include a high voltage rectifier though some may use an external one or voltage multiplier (also a useful and neat device).

  For many hobbyist uses, the only portion of the flyback that is important will be the high voltage winding (and rectifier, if present). It is a simple matter to add your own drive and feedback windings on the flyback core. This eliminates the uncertainty of determining the number of turns and wire size for the existing windings.

  Sources: CRT based equipment tossed for failures NOT caused by a defective flyback. However, sometimes even a bad flyback can be used for HV projects. This will be the case if the problem is:

  • Shorted primary windings. With some flybacks, the primary windings are on a separate bobbin and can be removed. Even when buried, they can sometimes be extracted without affecting the HV winding (just don't lose the HV return!).

  • External arcing due to cracks or pin-holes. Try coating with RTV silicone or HV sealer (allow ample time to dry completely). Plastic electrical tape may work temporarily at least. Note: Try to get the type of RTV that is non-acidic. The normal kind (that smells like viniger when curing) may be corrosive to the wiring. However, I haven't seen problems with this.

  • Breakdown in focus/screen network. This section may be removable with a hacksaw or small chisel! Then, insulate the exposed HV terminals as above.

  • Shorted HV rectifier (rare). Just add an external HV rectifier if needed.

    If you really want AC, this is an advantage! In fact, it might be possible to deliberately short the HV rectifier where you want an AC source by passing excessive (DC) current through it and/or violating its PIV rating (but that may be tough as other parts are likely to fail first!).

  • Broken or cracked core. Substitute the core from another flyback or glue or clamp the pieces together (broken edges in close contact). Don't lose the mylar/plastic spacers and replace them (if needed) when the repair is complete!

  No one actually buys flyback transformers for experimentation!

  WARNING: Flyback transformers are capable of producing shocking experiences. However, when run at high frequencies, your first hint of bodily damage may be via your sense of smell - from burning flesh. Keep clear!

Also see the section: Driving Automotive Ignition Coils and Similar Devices.

Basic Ignition Coil Circuit

                                    T1 +-------o HV Out
                       Rb       Bat ||(
         +12 o--------/\/\--------+ ||(
                                   )||( Ignition Coil
                                   )||(
                      Cp           )||(
                 +----||---+----+-+    +-+
                 |         |    |        |
                 | S1 _|_  |    +--------+
         Gnd o---+----o o--+
                    Points

• T1 is one of those round metal can ignition coils widely used in automobiles when there were actual points. If you have a modern one, that should work also as long as there isn't other 'stuff' inside.

• Rb is a current limiting ballast resistor. I used the nichrome element from a defunct waffle baker but an auto headlight or any other high power resistor will work just as well. The nice thing about the heating element is that it is easily adjustable by just moving a crocodile clip lead.

• Cp is essential - not just to protect the switch contacts ('points') but to provide a buffer so that current flow isn't interrupted so suddenly that a low voltage arc forms across the switch contacts. Without Cp, there will be next to no HV output. Think of it this way: without Cp, as the points open, the inductive kick-back from T1 results in an arc forming across the switch contacts. This is relatively low voltage and essentially kills any output from the coil. With Cp present, current continues to flow into Cp until the contacts have opened wide enough that they no longer arc and a high voltage can build up (probably a couple hundred volts). The accompanying field collapse results in a nice juicy spark from the ignition coil! See additional comments below.

  I used a .1 uF, 400 V capacitor for Cp. You can try smaller capacitors (but at least the same voltage). Too small, however, and that annoying arcing will return and you will barely be able to light a tiny neon indicator lamp!

• S1, the switch ('points') should be a 'fast break' variety - not a knife switch. The faster the contacts move apart (and the better the insulating medium is if it isn't air), the smaller Cp can be and still result in reliable operation. Smaller Cp should result in higher output voltage. Just touching some wires was erratic - a large pushbutton 'micro-switch' was much better. Of course, using a power transistor and 555 timer to drive it would be even more way cool. :) See the "Adjustable High Voltage Power Supply" in the document: Various Schematics and Diagrams. It can easily be adapted to use an ignition coil instead of its flyback transformer.

• The power supply was a no-name far-East 200 W unit for a PC clone. You will likely need a load on the +5 to keep it happy - an automotive headlight works well. The second half of a dual-beam headlight can be used for Rb (though you may want to go to a lower value and it isn't adjustable like the heating element, above).

(From: Jonathan Bromley (jsebromley@brookes.ac.uk).)

The voltage across the coil is L*dI/dt. Voltage across the coil HT winding is the same, but larger by a factor of (turns ratio) which is typically 50 to 100 in ordinary car coils.

When the points are closed, the coil current will progressively increase because the full battery supply appears across the primary. This will incidentally put around 1kV across the secondary, not enough to jump the gaps in spark plug and distributor. The points dwell time (or the behaviour of the electronic points-substitute controller) will be such as to allow the coil current to reach some sensible value.

When the points open, if no capacitor then current would instantaneously collapse to zero giving a very high coil voltage (huge dI/dt). But this happens JUST AT THE MOMENT THE POINTS OPEN, when the points gap is tiny. So the high coil voltage will immediately strike an arc at the points as they open. This provides a fairly low-resistance path which will be sustained as the points open further. dI/dt is therefore not so big after all, just enough to maintain the few tens of volts across the points arc. Therefore, not enough voltage on the HT winding to fire the proper spark, and all the stored energy in the coil goes into the arc at the points.

So, the (rather small) capacitor is there to allow the coil current to continue to flow, without a big voltage appearing across the points initially. Basically this C is there to give the points time to open before the coil primary voltage reaches its peak value of a few hundred volts. The C is chosen to resonate with the L of the primary so that the peak voltage is delayed just long enough so that the points are open wide enough that the 500V primary voltage DOESN'T arc across them, but the 50*500V = 25kV secondary voltage DOES jump the plug/distributor gaps. It's therefore the breakdown voltage of the plug/distributor gap that controls the highest voltage reached across the points. Typically this will not be high enough to allow much of the coil's energy to be transferred into the capacitor. Any energy that _is_ stored in the capacitor will eventually find its way into the spark by the reverse- current mechanism that you describe - the spark current will oscillate for a while. But the oscillations are fairly heavily damped by the loss of energy into the spark.

The story is slightly more complex in reality because of finite resistance of the coil windings and their distributed capacitance, but this simplified account is not too far from the truth.

(From: George Nole (gnole@brisbane.dialix.com.au).)

In the operation of the Kettering ignition system three clearly defined stages or phases can be identified.

1. Points closed.
2. Points open, but no gas discharge or spark has been initiated.
3. As per (2) but discharge has occurred.

Before proceeding with an analysis, a few notes on the ignition coil. The ignition coil is a transformer with very high leakage inductance. This because the core of the coil is not a closed magnetic circuit, but a straight piece with both ends open. The turns ratio is of the order of 100 or so. Recent measurements on a 6V coil revealed primary inductance with secondary open -no discharge- of 4mH, and with the secondary loaded -gas discharge- of 1mH. These values vary considerably from coil to coil.

Now the analysis which you can do yourself. Don't take my word.

1. With the points closed a current flows and energy is stored in the inductor (primary inductance).

2. When the points open, the circuit consists of a capacitor or condenser in series with the inductor. The other terminal of the capacitor is connected to chassis, and so is the other terminal of inductor via the ignition switch and the car battery.

   This forms a series resonant circuit of finite Q with energy stored in the inductor, and will start to oscillate. The voltage across the inductor -and the capacitor- will be much higher than the voltage across the series resonant circuit and in practice it is of the order of a few hundred volts. This is important because, with a transformer ratio of -say- 100 and a secondary requirement of 20kV, the primary voltage has to be 200V.

3. Before the oscillation can reach the first peak the gas discharge commences and the inductance changes to that of the leakage value, with a quenched oscillation continuing at a higher frequency than the frequency before the spark.

End of analysis.

What would happen if you tried to start the car without a condenser? If you do the experiment, please let me know the result.

Driving Automotive Ignition Coils and Similar Devices

"I have some questions about automotive ignition coils. I'm referring to the cylindrical "universal" type which has two 12 V terminals and one HV terminal in the center of the cap.

What is the typical peak output voltage and current?

What is the maximum average power input that such a coil can tolerate? I'm aware that the cross-sectional area of a transformer core dictates power handling capability. Judging from the skinny core in a spark coil, I'd place the maximum continuous duty input at around 50 watts. Am I in the ball park on this?

Is there an optimum pulse rate?

Do ignition coils employ any sort of current limiting?

Do "high-performance" coils with 45-75kv outputs offer significant increases in output power, or just higher voltage?"

First, be aware that the coil does not act as a transformer as such, even so called "Hot Coils" have only a 1:100 turns ratio which would give only 1,200 volts from a transformer. If you were to energize the coil with an AC voltage like you would with a transformer this is what you would get. An automobile ignition is more properly referred to as an "induction coil" Its output voltage is defined, not by the turns ratio but rather by the differential equation:

                        V = L di/dt

• V is the output voltage
• L is the inductance in Henrys
• di/dt is the rate of change of current flow as the field collapses in the coil.

Hot coils have a heavier primary so that they can pass more current, hence a higher di/dt.

The maximum pulse rate is determined by the time taken for the current to build when the points close (due to L it rises slowly until it reaches a steady state) and the time for the field to collapse when the points open. (the voltage to generate the spark occurs only after the points open and the field is collapsing)

I have never thought about the power in the spark but I suppose it would be:

P = (L di/dt)^2 / R where P is the power in watts and R is the total resistance of the coil secondary, the plug wire and the ionized spark gap. (Some Professor of EE is welcome to comment here).

As for current limiting, many coils employ a series resistor in the primary which limits current and is shorted out during starting.

(From: Mark Kinsler (kinsler@froggy.frognet.net).)

I use a 12 volt battery and it works pretty well. Probably the best high voltage power supply for careless amateurs is the one I designed, which could be found on my Web page if I knew how to do schematics but I don't. But it's simple enough.

I've been driving my old 12 V coil (bought as a replacement for the one in my Econoline but never used) through a buzzer-type interrupter made from an old relay. I put a capacitor across the contacts for good luck, and for the most part it works pretty well. It'll give me about a 1/2" spark, which is all I need for my illegal spark transmitter and the spark plug in my famous "One Stroke Engine" demonstration. However, it yields some amusing effects, to wit: blue sparks dancing around on the battery lead and the battery itself, extremely strange noises, copious production of ozone, and the occasional puff of smoke. I have the whole mess mounted inside a plastic 2-liter cola bottle. On the advice of my friend Dewey King, who restores old gas engines from oil rigs, I've purchased a Chrysler ballast resistor to put in series with the battery and thus keep the coil healthy.

All you need to do is make a trip to the local auto junkyard:

Buy a used but fairly viable car battery, an old-fashioned ignition coil (i.e., before electronic ignition came out in the '70's), an ignition condenser (capacitor) from out of a dead distributor, and the heaviest 12 volt spdt relay you can get from Radio Shack. DPDT is okay, too.

1. Figure out how to connect the relay so it buzzes.

2. Connect the capacitor across the contacts

3. Connect the primary winding of the ignition coil in parallel with the relay coil.

I've found that only a car battery has sufficiently low internal resistance to run the thing: my big old bench power supply won't do it. So keep a trickle charger on the battery. It seems capable of giving a 3 cm or so arc depending on conditions.

(From: Pamela Hughes (phughes@omnilinx.net).)

I did something like that only it plugged into the wall. Don't remember the circuit but it was a 33 uF, 630 VAC mercury vapor ballast cap connected to a rectifier in a linear fashion (much like using a cap for an AC resistor only the rectifier prevented bidirectional current flow...). This was connected to an 800 V, 6 A SCR and a neon lamp for a diac in a trigger circuit. Adjusted the trigger point so the scr would fire at a certain point in the AC cycle and discharge the cap through the primary of an ignition coil. If you adjusted the trigger point right, you could get about 3" to 4" sparks. Connected that to a 40 kV TV rectifier and a cap made from a window and some aluminum foil and to a 2" spark gap. Wouldn't fire unless something was placed in the spark gap, but then it went off with a bang that would put any bug zapper to shame.

BTW, I took the ignition coil apart, disconnected the common lead connecting the primary and secondary and then used the secondary and core for a giant sense coil for monitoring changes in magnetic fields... thing would make the volt meter jump if you brought a magnet anywhere close to it, but mostly it just fluctuated with atmospheric effects like lightning.

(From: Pierre Joubert joubertp@icon.co.za).)

1. Use a monostable-based circuit which gives the maximum 'on' time for current in the coil. As revs go up, many older systems produce reduced spark energy simply because the rate of rise of current in the coil prevents full current from being reached before the current has to be switched off.

2. Use one of the coils which is designed to operate normally with a series resistance, which is conventionally bypassed during cranking to help get a better spark on the reduced battery voltage. But instead, limit the current in the coil to a safe value by setting a current limit around the switch transistor. This prevents the coil overheating (which it would if you used it without the resistor in a conventional system.

3. Look around for the 'best' coil you can find; you might find a better match to your needs by using a coil from a different model or even make of car. If you know the R and approximate L you can model the current buildup and estimate the energy available. Generally the more energy the better, assuming that the transformation ratios of most coils are roughly the same, which was true way back when.

I have characterized a 'typical' car coil, and found it rings best around 1 kHz with the steel core in, and around 8 kHz with it out (no capacitive load on secondary). As you can imagine, leakage (coupling) get worse without the core out, but Q is a little better. Q is under 10, more like around 4. The secondary is around 20 Henries (core in) and 4 H with it out, and primary is around 5 mH. Step up ratio is around 60. My thermal guestimate said continuous power should be under 300 watts in oil. Disappointing.

Mark's Comments on High Voltage Lab Conditions

So how do you make your high-voltage laboratory safe? Well, you just assume that anything you build is likely to catch fire and/or arc over, and design your lab space accordingly. Stay out of the way of capacitor strings, though when these blow up the shrapnel is generally pretty harmless. I've gotten stung by exploding carbon resistors, but again, it's no big deal if you're well away from them. In general, take the same precautions with high-voltage or high-current components that you would with small fireworks: avoid flammable environments and stay well away from them. If all else fails, take the stuff outside.

My advisor at Mississippi State University observed that if you never damage any equipment and you don't have fairly catastrophic failures, you're probably not doing any research. That helped justify the 6" crater I blew in the concrete lab floor (a record that still stands--his crater was only 4", though there were several of them produced at once.)

Discharge Display Gizmos

Plasma Globes

Recent Sci-Fi movies and TV series seem to have latched onto plasma globes as high-tech replacements for the old-fashioned Jacobs Ladder. :-) (E.g., certain episodes of "Star Trek the Next Generation" and "Star Trek Voyager".)

One such product is called "Eye of the Storm".

It should be possible to construct these gadgets with salvaged flyback transformers, power transistors, and a few other miscellaneous parts using a large clear light bulb - good or bad, doesn't matter - for the discharge globe (However, I don't know how good these actually are for this purpose).

Of course, purists will insist on fabricating their own globe (and official ones can also be purchased at exorbitant prices as well).

As far as I know, these will work with just regular air (though the expensive ones no doubt have fancy and very noble gasses!) and the vacuum is not that high so a refrigeration compressor should be fine.

See The Electronic Bell Jar vacuum technology articles for info on using refrigeration compressors as vacuum pumps.

However, since large clear light bulbs may also be satisfactory (though I don't which ones to recommend), there is may be no need to mess with a vacuum equipment. :-) And, of course, you have a wide selection of inexpensive types to use for experiments, and dropping one or blowing it up isn't a disaster!

Excitation is usually from a high frequency flyback transformer based inverter producing 12 to 15 kV AC at around 10 kHz. Its HV terminal attaches to the internal (center) electrode of the globe or light bulb. The HV return is grounded. Ionization of the gas mixture results from the current flowing due to capacitive coupling through the glass.

For a power source, either the "Simple High Voltage Generator" or "Adjustable High Voltage Power Supply" would be suitable. See the document: Sam's Schematic Collection - Various Schematics and Diagrams for circuit ideas.

However, note that its output must be AC so there must not be any internal HV rectifier in the flyback transformer (which may be hard to find these days since most flybacks have internal rectifiers). (If a flyback with an internal rectifier is used, the globe will just charge up like a capacitor which is pretty boring after a few milliseconds!)

(From: Don Klipstein (don@misty.com).)

As for common gas fills, Radio Shack's "Illuma Storm" sure looks like neon and xenon. I have seen others that had neon-krypton or neon-xenon-krypton. I have seen one in a science museum that looked like plain argon. Other lightning display type things with brighter basically white sparks have xenon.

(Portions from: Steve Quest (Squest@mariner.cris.com).)

A $20 air conditioner repair hand-pump is fine. If the colors of plain air are not 'pretty' enough, let me recommend what is used in commercial units: a mixture of low pressure argon and neon. If you want to be extra fancy, try all the inert gasses, or a mixture of them all, helium, neon, argon, krypton, xenon, radon. :) Of course, radon may not be safe/legal, or even available. You could just toss a chunk of radium into the globe, it will generate the daughter isotope Rn(222) thus slowly, over time, enhance the color of the gas mixture. Just a thought.

The power supply needs to be dielectrically isolated (using the glass as the dielectric), otherwise you'd have direct emission from the metal, and it would be more of a light bulb than streaks of color. Plus, people touching it would feel a tingle while the dielectrically isolated is less likely to shock. What this means is that a direct connection to the filament lead wires is not that great as you really want glass in between the driving source the center as well as the outside globe.

• If you are making your own 'globe', one way to do this is to fuse a glass test tube into the center and coat its interior with conductive paint. This then becomes the center electrode.

• For a light bulb (which isn't really recommended anyhow), you can try to use the filament directly or cut the lead wires as close to the glass as possible and insulate them with RTV or HV putty. Then coat the remainder of the interior of the glass filament support structure with conductive paint to use as the center electrode.

However, I would highly recommend using a commercial flyback! You just need to find one without an internal rectifier. To wind your own flyback requires several thousand turns of super fine wire in 50 to 100 nicely formed layers with the whole thing potted in Epoxy for insulation. Not a fun project.

(From: John Drake (jdrake_deja@deja.com).)

Here is a simple trick:

1. Find some clear light bulbs. Burnt out ones are fine. Any size will do, from a small turn signal light for a car, to a head lamp for a car, to whatever.

2. Attach any Tesla coil output or other low current high voltage source in the 10 to 100 kV range to one of the filament leads. Leave the other lead alone.

3. Turn on the power and watch. Touch with your hand, if you dare. Plenty of lightning in a jar. Eventually, the lightning will poke a hole in the glass, and let the air in. Game over. Get another bulb.

Sparks patented his device, and overseas companies literally ripped off the patent wholesale. (Most of the $49 plasma globes you see use his exact circuit from the patent, including a couple of unnecessary parts, etc.) He was trying to get some money out of the whole thing, but I don't know if he ever did or will. Alas.

Of course, if you are just going to make plasma globes and not sell them, you aren't necessarily violating the patents. The underlying idea was well known for a long time before Sparks patented his "globe with controls".

If you want to make your own globes, you can make them lightning compatible by either just sucking the air out, or sucking the air out then adding gas in. Common gasses to use are argon, neon, and krypton. Helium might work (haven't tried), and it's easy to get and use; you can replace the air in the bulb with helium since it's lighter than air.

Lum(n)glass Lightning Plates

A basic description can be found in U.S. Patent #5383295: Luminous Display Device. The abstract reads:

"A luminous display device which includes a fused assembly of three flat members, behind the first of which a chamber partly defined by an opening in the second of said members is formed, a quantity of beads and an ionizable gas being disposed in said chamber, a source of high frequency voltage being connected to an electrode through an opening in the third of said members to form myriad discharge paths throughout said chamber."

By adjusting the voltage and frequency, using gasses (other than air), phosphor type materials on the beads, colored beads and/or glass, higher or lower pressure, and other changes in drive or construction, the size, color, character, and dynamics of the resulting display to be varied over a wide range.

I would suggest making the assembly out of a pair of pieces of plate glass (though even Lucite/Plexiglas might work - it shouldn't get hot during operation). The plates don't even need to be circular though this isn't really difficult with a glass cutter and template. The outer ring which serves to space the glass plates and also to seal the chamber may be the greatest challenge if made of glass. The space is filled with glass beads, or frit, which, in conjunction with the outer ring, also prevents the thing from imploding. Drilling the hole in the center of the bottom plate for the electrode can be done with some abrasive and a tile or glass bit.

The patent describes a construction method that fuses the entire assembly together at high temperature. This may not be needed unless you intend to seal the device permanently (and even then, a good two-part Epoxy will likely be adequate).

Cheap Sources of Magnet Wire

However, a nice source of fine magnet wire is relays and solenoids - many have very fine wire - #40 for example - and miles of it (well thousands of feet at lest). These are very often not varnished so they unwind easily (just don't let them unwind all over your junk drawer!).

Ideas for Things to do with High Voltage

• Jacobs Ladder, Tesla Coil, CO2 and other home-built lasers, ersatz plasma globe(s) from clear light bulbs; investigate (or at least observe) spark and spark-gap behavior between electrodes made of various materials; Use of spark as an ignition source - for igniting paper, black powder, flash powder, firecrackers. combustible liquids, gases and mixtures of gases; with a rectifier (few bucks from surplus places) - DC phenomena, electrostatic precipitator

• If you have a vacuum pump in that "well-stocked workbench" collection, and you get hold of a rectifier, you are set to investigate all sorts of high-voltage discharge phenomena in partial vacuum and/or reduced pressure - that could keep me amused for weeks.

• Spark travel and propagation over surfaces (kind of a sub-set of my earlier suggestion about spark phenomena in general).

• Flame phenomena: Flames are highly ionized (hence, charged) and react in various ways to high voltages applied to them in one way or another.

• Spark-gap transmitter: Revisit the very earliest days of of radio by duplicating on a small scale the work of Hertz, Marconi, Fessenden, et. al. (Note that the operation of a spark-gap transmitter is unlawful in most jurisdictions - but - if you keep the power way down; use a small antenna; work in the dead of night; and keep transmissions very brief -

• High-voltage and photography: Great opportunity to combine two hobbies. Lictenberg Figures and Kirlian photography. There are also Kerr cell shutters, and microflash - both for ultra- brief bullet-stopping photographic exposures. There is also X-ray flash and microflash (for a photo of a bullet actually entering and traveling inside of - whatever - a block of wood -- a side of beef).

• I guess I may as well mentioned X-rays. Of course you need a small X-ray tube. Some of us have been successful in finding, begging, borrowing, such. They can of course be bought - but usually we claim to have no money. :) 10 kV (actually 14.14-kV peak) gives rather soft (but still usable) X-rays, which brings me to:

• Voltage multipliers, impulse generators (a la Marx, Cockcroft-Walton, and many others). You need rectifiers and (homemade perhaps) capacitors. Multiplications of 3X and 4X are attainable without too much effort, 6x, 7x maybe achievable.

• Kissing-cousin to spark-gap radio transmitters is the singing-arc. Although it is an arc phenomena rather than a spark phenomena, you can use your transformer all the same to good advantage. A singing- arc circuit is essentially the same as that for a spark-gap radio transmitter except it is tuned for audio frequencies. (You can imagine the rest).

• There's always Van DeGraaff Generators - the kind charged by an external high voltage power supply. Of course you need a rectifier to get the DC required.

• Crystal phenomena: Certain crystals, such as those of Potassium Chloride, develop what are called color centers when exposed to prolonged, intense, high-voltage fields (and for that matter to strong x-rays as well).

• There is also X-ray crystallography to be investigated when you get that X-ray tube. Fortunately it does not require much power or hardness from the X-rays/tubes. Investigators have spent an entire career in this field alone - it ought to keep you occupied for at least a couple of weekends.

• Plant growth: Are you any kind of a gardener, whether inside or out? Plants are greatly influenced by the presense of an electric field - AC, DC, positive polarity, negative polarity - hey each have their effects. (Watch your fingers as you do the watering!)

• Ozone generation. Be careful. Ozone is considerably more toxic than many realize. It's approximately the same as hydrogen cyanide (HCN). Fortunately Ozone has a much stronger aroma in small concentrations.

Dangerous (or Useful) Parts in a Dead Microwave Oven

Some may feel there is nothing of interest inside a microwave oven. I would counter that anything unfamiliar can be of immense educational value to children of all ages. With appropriate supervision, an investigation of the inside of a deceased microwave oven can be very interesting.

However, before you cannibalize your old oven, consider that many of the parts are interchangeable and may be useful should your *new* oven ever need repair!

For the hobbiest, there are, in fact, some useful devices inside:

• Motors - cooling fan and turntable (if used). These usually operate on 115 VAC but some may use low voltage DC. They can easily be adapted to other uses.

• Controller and touchpad - digital timer, relay and/or triac control of the AC power. See the section: Using the Control Panel from Defunct Microwave Oven as an Electronic Timer.

• Interlock switches - 3 or more high current microswitches.

• Heavy duty power cord, fuse holder, thermal protector, other miscellaneous parts.

• High voltage components (VERY DANGEROUS if powered) - Typical HV transformer (1,500 to 2,500 VRMS, 0.5 A - see the section: Microwave Oven Transformers), HV rectifier (12 to 15 kV PRV, 0.5 A), and HV capacitor (approximately 1 uF, up to 1,500 to 2,500 VAC (4,200 to 7,000 VDC).

• Magnetron - there are some nifty powerful magnets as part of the assembly. Take appropriate precautions to protect your credit cards, diskettes, and mechanical wristwatches. See the section: Neat Magnets and the document: Notes on the Troubleshooting and Repair of Microwave Ovens for more info.

DOUBLE WARNING: Do not even think about powering the magnetron once you have removed any parts or altered anything mechanical in the oven. Dangerous microwave leakage is possible.

Microwave Oven Transformers

However, these transformers are designed with the bare minimum of copper so without a load, they still draw several amps from the power line. Therefore, they are most suitable for applications where a heavy sustained load is involved - not for that isolation transformer used mostly for testing (20 W) laptop switchmode power supplies! Figure things like arc or spot welding, battery charging, shaker table drivers, aluminum ring levitation (remember that science museum demo?), and other low voltage high current experiments. I am not recommending these for your 1 kW class A audio amp because of they are not generally rated for continuous duty and tend to hum - but you could try especially if you add some cooling.

Note that very few microwave oven failures are due to transformer problems. And, even those that are, likely mean that the HV or filament windings are to blame - neither of which you will likely be using (unless you want the 1.5 to 2.5 kVRMS at 0.5 A or so they put out).

Aside from the dead microwave oven(s) you may have around the house and your friends' and relatives' houses, try the local dump and repair shops - but you may have to convince them that you know what you are doing and of course be willing to haul away the entire carcass, not just the transformer!

WARNING: The intact microwave oven transformer is extremely dangerous when powered. (When not powered, about all it can do is smash your foot.) That 1.5 to 2.5 kVRMS at 0.5 A or more is an instantly deadly combination. Take extreme care if you have any idea about using the transformer without modifications. In addition, since it is so LARGE, any windings you add are also going to be capable of high current and could quite easily end up arc welding or burning things you didn't intend!

Assuming you are not using the HV or filament windings, the first step is to remove them. The filament winding is only 2 to 3 turns of heavy wire and easily extracted. However, the HV winding is likely to require the services of one or more of the following: a chisel, hacksaw, ax, blowtorch, heavy cutters, drill. (And, make sure your accident insurance is paid up for the required trip to the ER to stitch up your hand afterwards.)

Once these windings are gone, there is plenty of core area to wind your own new ones.

• Confirm that the primary is good. Power the transformer at normal line voltage and make sure it doesn't draw excessive current. As noted above, with no load, a few amps due to magnetizing current and core saturation is normal. However, it shouldn't trip your 15 A line fuse!

• Determine the V/turn rating. This is likely to be around 1 V/turn for the typical design which uses just enough copper to prevent excessive overhating. Just wrap 10 turns of insulated wire on the core, power up the primary at normal line voltage, and measure the voltage across your 10 turn secondary with a multimeter. Divide this by 10 to determine the V/turn rating.

• For each secondary, determine the wire size you will need based on your current requirements. A rough guideline would be to keep the total heat dissipation for the secondary to under 25 W. As an example, suppose you want 25 VRMS at 40 A. Then, R needs to be less than .015 ohms. Assuming a 1 V/turn transformer with an average turn length of 10 inches (36 feet of wire), this results in a wire size of at least #6 AWG (or 4 'strands' of #12 AWG wire). Fatter wire won't hurt if it will fit.

• Wrap the core with insulating tape. For light duty use, this can simply be plastic electrical tape. However, proper transformer insulating material should be used for serious applications.

• Wind your secondary or secondaries. For maximum fill, the use of proper magnet wire - even special square wire - is desirable. However, for a couple of turns here and there, any insulated wire of suitable size will do. For extended operation, make sure the insulation is rated for high temperature use.

Using the Control Panel from Defunct Microwave Oven as an Electronic Timer

The output will control a 10 to 15 A AC load using its built in relay or triac (though these may be mounted separately in the oven). Note that power on a microwave oven is regulated by slow pulse width modulation - order of a 30 second cycle if this matters. If it uses a triac, the triac is NOT phase angle controlled - just switched on or off.

The Zap in Scripto Lighters and Gas Grill Ignitors

The result is several thousand volts on demand with its output available at a couple of terminals. This can be used to trigger xenon tubes or even to start helium neon lasers (with the addition of a pair of high voltage diodes to form a charge pump). Or as a prod for small cattle, but I didn't say that. :-) For a discussion of the HeNe laser application, see the document: Sam's Laser FAQ.

Detaching the piezo assembly only requires bending back and removing the sheet metal shroud at the top of the lighter. The entire piezo unit then just pops out.

Gas grill ignitors are similar - and even more powerful. These are available as replacement parts at your local home center or appliance store. (Don't steal the one from the family gas grill - your dad won't be happy.) Ditto for piezo matches. Once the gas is used up in these, you're the only one who will want them anyhow. :)

Useful Parts in a Battery Powered Electronic Flash

For information on how these things work, see the document: Sam's Strobe FAQ - Notes on the Troubleshooting and Repair of Electronic Flash Units and Strobe Lights which also includes many many sample circuits. Two popular designs from Kodak disposable camera flashes are:

• Kodak Funsaver with Flash Schematic.

• Kodak MAX Flash Schematic and Photo. Many newer Kodak disposable cameras including the "Funsaver Sure Flash" appear to use a similar if not identical circuit though some parts may be surface mount. I've heard that some APS (Advanced Photo System) "ADVANTIX" are powered by a pair of AAA cells instead of the single AA used in most other units, so their design may differ somewhat but I haven't disassembled one of those as yet.

For detailed instructions on disassembling the Kodak MAX camera to safely remove the flash unit and some simple modifications, see Don's Hack Kodak MAX to Strobe Page. Details on other cameras will differ but this information should alert you as to what to avoid touching.

WARNING: The energy storage capacitor in even the tiny flash from a disposable camera may hold a painful, if not lethal, charge for days or longer. Always remove the battery first and then make sure to check and, if necessary, safely discharge this large capacitor before touching anything!

The major parts present in all units include:

• Chopper transistor - high gain power transistor to drive the inverter. For pocket cameras, typical part numbers are: 2SD965, 2SD879, 2SD1960, etc. These are low voltage (20 to 40 V) NPN (though some may use PNP), high current (e.g., 5 A), with Hfes in the 400 to 600 range.

• Inverter transformer - Generates the 300+ VDC to charge the energy storage capacitor. Includes a primary drive winding of 5 to 15 turns, similar feedback winding (maybe), and 1,000 to 2,000 turn high voltage secondary.

• Energy storage capacitor - 120 to 500 uF or more, 330 to 400 V, photoflash rated (rapid discharge) electrolytic. Note: These usually do not have a high temperature rating - 55 DegreesC typical. WARNING: Can be lethal if even partially charged!

• Neon (normal or 200 V breakdown) or other ready indicator.

• Trigger transformer - generates a 4 to 8 kV pulse to fire the xenon tube from a small 150 to 300 V capacitor discharge. Includes a primary of about 12 turns, secondary of 350 to 450 turns.

• Xenon flashtube - usually between 1 and 2 inches in length. These require a 300 to 400 V energy storage capacitor, 4 to 8 kV trigger, and can handle 10 to 30 W-s flash energy.

And, in the disposable cameras, there is likely to be a very nearly fresh Alkaline cell unless the place you obtained them from knew this and beat you to it! :)

Automatic types will have additional components including the following:

• Quenchtube - looks like an oversize neon light bulb but filled with xenon and triggered in a similar way to the main flashtube.

• Trigger transformer for the quenchtube - similar to the main trigger transformer.

• Thyristor (SCR) - in series with the flashtube used in energy conserving automatic flash unitsx.

• Photosensor - used to read light reflected from scene to set exposure.

There will also be a variety of other small electronic components possibly including fancy microchips in TTL (Through The Lens) programmable units.

Note: To remove individual components without destroying either the PCB or the component, you must use a proper desoldering technique. If too much heat is used for too long, I've heard that the HV winding inside the transformer may become detached which renders it useless. And, the PCB will certainly be damaged. I generally use a desoldering pump like Solda-Pullet(tm), (not the cheap short one) but this can still damage the fine PCB traces. The use of copper braid with rosin like Solder Wick(tm) may be gentler.

Also see the document: Sam's Schematic Collection - Various Schematics and Diagrams for possible useful modifications to inverters like the one from the Kodak MAX Flash.

Useful Parts in a Non-Working VCR

• Motors: 1 to 6 motors of various types. Mostly these are cheap DC permanent magnet motors but the main capstan motor may be a high quality brushless type with electronic control on-board. The video drum motor is likely three phase with its own controller.

• Power supply: Outputs various voltages and may be used intact but will always contain useful components like transistors and diodes, transformer(s), and large capacitors.

• Tuner. Whether you can make this work without the rest of the VCR is problematic but worth a try.

• RF modulator. This usually accepts a DC voltage for power, a control voltage to select TV/VCR, and will output on channel 3 or 4.

• IR receiver module (for remote control). It is usually possible to power this from a DC supply (5 or 12 VDC typical) to convert the IR signal from remote controls (probably not just the one that came with the VCR) to a logic level output.

• Miscellaneous electronic components including crystals, delay lines, video and audio ICs, pots, connectors, etc.

What can you build with it? One can never tell! :-)

Useful Parts in a CD, DVD, LaserDisc, or Other Optical Disc/k Device

• The laser itself - For really old LaserDisc players, this is a helium-neon gas laser tube (probably linearly polarized) and high voltage power supply. All the others use diode lasers which require current limited drivers to prevent instant destruction. The output power of these lasers is usually less than 5 mW except for writeable optical drives which may go up to 30 mW (but IR) or more.

• Optics - May include lenses, mirrors, beam splitters, 1/4 wave plates, diffraction gratings, and other unidentified optical elements. Depending on the application, these may be optimized for the laser's wavelength. Thus, an IR mirror may actually look more or less transparent. The objective lens and/or other mirrors may be on electromagnetic positioning devices.

• Motors - For spindle, sled movement, drawer open/close, etc. Some are common DC permanent magnet types while the spindle motor may be a brushless DC type. Some CDROM and other use storage drives linear motors to directly position the optical pickup sled.

• Mechanical parts - Gears, racks, rails, pulleys, belts, etc.

• Power supply components - Transformer, regulator(s), transistors, capacitors, etc.

• Other electronic components - Microswitches, opto-interrupters, solenoids, etc. Ironically, the high-tech chips are probably not work unsoldering. :(

WARNING: In addition to electrical and mechanical dangers, the laser may emit levels of visible or invisible radiation that is potentially harmful to vision.

There is much more info on their laser and optics Sam's Laser FAQ.

Wayne's Notes on Salvaging Parts from Pioneer LaserDisc Players (From: Equinox (eso@pacific.com).)

I have taken apart several of Pioneers old video disc units, I cannot remember the model #'s right now.

The units I had contained the following items that I found of value and kept. Yours should be the same or similar, as all units that I took apart, internally were very similar.

• The laser - A bare HeNe laser tube producing a red beam rated at 1 mW or less, about 8 "long.

• The laser power supply - A small circuit board with a flyback transformer with obvious high voltage white rubbery wires going to the laser tube.

• Large transformer - The laser power supply gets it's input voltage from the main stepdown/up transformer of the entire system. it put out around 700 VAC to work the laser power supply, as well as the analog and digital DC voltages for the rest of the player. Keep it! Your laser power supply board may be useless without it.

• Small X-Y galvo - Dual voice coil assembly to deflect the beam. (In some models, this may be similar/identical to Meredith's GAL-2.)

• Small diffraction grating in round brass housing producing 3 beams if I remember correctly.

• Beam splitter, 2 adjustable mirrors, photo detector and preamp, other optics.

• Voice coil actuated focusing assembly - This looks like a speaker magnet with a hollow center with a lens. It sort of looks like a mechanical eyeball from the top - Used to focus the beam on the disc.

• DC motor with analog tach output - drove the disc Small geared down DC motor - found near and controls the assembly that houses the optics controlling the translation of the beam/optics across the disc.

With care and the forethought that you are working with 110 VAC, 700 VAC and more than a kV for the laser, you can measure the voltages in, and enable/disable the safety interlock and see which line it triggers. The interlock switches (2?) were a metal tab activated switch in the back of the lid, and I think part of the latch gizmo near the front of the system had one.

(From: Chris Hoaglin (choaglin@aol.com).)

Inside Maxoptix magneto-optical drives, there are quite a few small mirrors, lenses, beam splitters, etc. The models I've taken apart have been the Tahiti II model. These drives also have a very nice actuator. The laser diode isn't even on the part which emits the beam against the disc, it's mounted on the frame of the drive and reflected against the disc by a mirror mounted on the bottom of the part that moves back and forth. The actuator assembly might be useful for experimentation as well, since It's very sturdy (It rides on two metal shafts and has small metal wheels which keep in contact with the shafts). It has a coil and magnet arrangement on each side. All the optics are on small removable mounts as well, so they'd be easy to put to other uses. I believe the wavelength being used is IR, but they might work for visible stuff as well.

How and where to find them: The drive is a full height 5.25" drive. Looks a bit like an ESDI drive, except for the slot on the front to insert the MO disk, of course. A good place to look for them might be places which do data storage, or use workstations (DEC, Sun, etc.) I don't think they're used much on the PC platform.

Also, I noticed today while reading Lasers and Optronics that several outfits are offering OEM modules which incorporate 400 nm diodes. Sooner or later people will start scrapping equipment that uses them, although probably not for a few years.

Useful Parts in a Laser Printer or Laser Fax

• Laser - Usually semiconductor laser diode mounted in assembly with collimating lens and other optics. Its output is a nearly parallel beam 1 or 2 mm in diameter.

• Laser diode driver - Usually a circuit board in close proximity to the laser diode which provides power and modulation capability. Reverse engineering and luck may be required to figure out how to use it.

• Thermo-electric cooler - I don't know how common this is but some laser printers have/had a nice little Peltier device to maintain the laser diode at a constant temperature. There would be an electronics board associated with the actual device.

• Multifaceted scanner - A polygonal mirror (usually metal coated) on a high quality brushless DC motor. The constant speed controller may be a part of the motor assembly with only a few interface signals to power and run it.

• Objective lenses - 2 or 3 lenses that look cylindrical may actually be just relatively thin sections of normal lenses or anamorphic with different focal lengths in the two axis. Due to their shape, they may be of questionable utility for other purposes.

• Mirrors - 1 or 2 long strip mirrors that may be metal coated (with a copper tinge for IR laser printers) or dichroic coated. Note that while these appear to be planar, they may in fact have a slight curvature along the narrow axis. The dichroic types may be of very high (laser resonator) quality but if frosted on the opposite surface, of limited utility since any transmitted beam is dispersed.

• Fiber optic sensor - Canon engines have this situated at the one end of the scan line to detect the beam and provide a time reference.

• Motors - In addition to the scanner, there will be a main AC line driven for paper movement. There will also be 1 or 2 fans.

• Mechanical parts - rollers, gears, pulleys, clutches, bearings, you name it - lot's of useful stuff.

• HV power supply - Usually a self-contained module which generates the corona voltages. Up to 6 kV or more but microamps of current.

• LV power supply components - Depending on whether a switchmode or linear power supply is used, there could be a variety of useful parts and possibly the complete power supply as a separate unit.

• Toner/Developer - There will be a long, moderately powerful magnet associated with the toner distribution system, probably inside an aluminum cylinder. The toner cartridge or built-in mechanism will also include other useful parts but is extremely icky and messy to disassemble.

• Fuser lamp and power supply - Quartz halogen lamp and triac controlled power supply with temperature sensor.

• Other electronic components - Again, the high-tech parts may be less useful than the simple things. :)

• Fax machine components (where applicable) - Include a cold cathode fluorescent lamp for the light source and linear CCD image sensor with associated electronics.

See the document: "Notes on the Troubleshooting and Repair of Printers and Photocopiers" for information on how this equipment works as well as warnings and precautions with respect to the hazards of toner dust.

WARNING: In addition to electrical and mechanical dangers, the laser may emit levels of visible or invisible radiation that is potentially harmful to vision.

There is much more info on their laser and optics Sam's Laser FAQ.

Useful Parts in a Photocopier

Items in place of the laser of a laser printer include:

• Light source - a linear quartz halogen lamp is most likely. Some may use a special fluorescent lamp instead. In either case, the needed power supply or ballast will be included - don't miss it!

• Optics - Several mirrors and a high quality objective lens. The large tempered glass plate on which the material to be copied sits is also useful.

• Additional mechanical parts - Include those for paper selection and sorting, two sided copying, and so forth.

Useful Parts in a Barcode Scanner

Looking through the glass of the scanner, it may appear that all sorts of stuff is arranged at random. However, this is not the case. :) For more information on how barcode scanners operate, see the chapter: "Laser Instruments and Applications" in Sam's Laser FAQ.

• Laser - The source of the beam is either a low power helium-neon (HeNe) or diode laser. Older (and larger) scanners tended to use HeNe lasers. However, size alone is no sure indication until you get to very small (6 inch cubes or hand-held wands) which are almost always based on diode lasers (if they use a laser at all). A better test is to check the color of the beam - the light from HeNe laser based scanners appears orange-red (632.8 nm) while that from diode laser based scanners tends to be a deep red from the 670 nm wavelength which is less expensive (but just as effective). Just explain that you are doing scientific research when the people in the white coats come to take you away for staring into the scanner! :)
  • HeNe lasers are typically 1 to 3 mW (mostly near 1 mW) using tubes between 5 and 10 inches in length. The tube will probably be mounted on brackets and will be easily replaceable. Some scanners use HeNe tubes with larger than diffraction limited divergence to simplify the optical system down the line. Where an external lens is actually glued to the output mirror of the HeNe tube, it can probably be removed with a suitable solvent or heat leaving a low divergence tube. See the chapter: "The Home-Built Laser Assembly and Power Supply" chapter of Sam's Laser FAQ for more details. Or, simply locate the collimating lens that is present in the scanner or one of your own and use that to adjust the divergence as desired.

    The HeNe laser power supply may be a self-contained 'brick' or built onto the mainboard.

  • Diode lasers are typically 670 nm (deep red) with 5 mW maximum output. A collimating lens and possibly some other optics will be part of the diode laser assembly.

    The laser diode driver circuit will be in close proximity to the laser diode itself and may be on a separate board. However, it is most likely part of the mainboard. and difficult to determine correct use without a schematic.

• Variable attenuator - A graded density filter may be present immediately following the laser's output to adjust the beam intensity to compensate for variations in laser power (mostly for HeNe lasers - diode lasers will have a pot for this purpose).

• Turning mirror(s) - There may be one or more high quality planar first surface or dichroic mirrors to direct the beam. Their mount will probably be adjustable in X and Y to some extent.

• Main objective combo - This consists of a large (probably plastic molded) convex lens with a hole in its center in which a prism, mirror, and/or lens may be inset.

  The components of the this part can generally be separated to use individually using a combination of brute force and solvents. For example, to remove the lens and prism from the combo in the Orien 300, a pad of tissue paper is inserted in the hole followed by a wooden dowel that just fits. A couple of whacks to the dowel with a small hammer while holding the assembly should result in the prism/lens popping free. They can then be separated by soaking in acetone.

  WARNING: Acetone and its vapors are flammable and toxic.

  CAUTION: Acetone will also damage many plastics including most likely, the large plastic lens, so don't let it contact that or other plastic optical components.

• Multifaceted rotating mirror - The collimated outgoing is deflected by a 3 to 6 facet polygonal mirror directly driven by a speed regulated brushless DC motor. The motor/scanner assembly is generally a separate module in older equipment requiring only DC power and an enable signal to run. However, newer ones may be mounted directly on the mainboard.

  Unlike those in a laser printer, the mirror facets are large since they have to reflect the diffuse return beam as well as the tiny spot of the outgoing beam. They are fabricated as individual mirrors glued to a cast metal wheel type affair and are all set at slightly different angles so that each rotation of the mirror wheel results in scan lines at 3 to 6 slightly different locations depending on the number of facets.

• Multiple planar mirrors - These are usually decent quality aluminized first surface mirrors and could find all sorts of other uses. Although generally shaped as strange 4 sided polygons, they can be subdivided into more useful sizes using a glass cutter from the rear or a water-cooled diamond cutoff wheel.

• Photodetector - A silicon photodiode, often of moderate area (typically 2x2 mm, good for a laser power meter) There may be an additional focusing lens and/or red ambient light blocking filter associated with the photodetector.

• Electronic components - Include a microprocessor, RS232 or other interface, etc. However, these may not be very useful for other purposes.

• Power supply - Depending on the model, these may plug directly into the AC line or be powered from a wall adapter.

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