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.
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 :-).
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 - outch!), see the document: Safety Guidelines for High Voltage and/or Line Powered Equipment. Something that looks innocent can really ruin your entire day!
For really high voltage equipment, also see: Tesla Coils Safety Information.
We will not be responsible for damage to equipment, your ego, blown parts, county wide power outages, spontaneously generated mini (or larger) black holes, planetary disruptions, or personal injury that may result from the use of this material.
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.
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)!
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 pronouced effect? Why?
For more things to do with these neat magnets, see: Neodymiumarium.
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!
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.
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!
(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.
(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!
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.
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. :-)
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 :-).
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.
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:
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!
If you unplug the yoke (even if there is no interlock), while the system may still work to some extent but performance will be poor. High voltage will be reduced and parts may overheat (and possibly blow up).
(From: Jeroen Stessen (Jeroen.Stessen@ehv.ce.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 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.
_________
/ \
< o3 o6 o9 |
> | View of connector on case.
< o2 o5 o8 |
> |
< o1 o4 o7 |
\__________/
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).
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. This is somewhat similar to being in series with a resistor equal to Vo/Io but implemented as a loose magnetic coupling so there is no additional 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.
Sources: Your local sign shop, demolition company, or salvage yard. New: $100 or more. Used: $5 to $50 or free.
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.
Sources: Your local HVAC contractor probably for the asking as they are thrown out along with old oil burners when they are replaced. However, 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.
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).
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.
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:
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!).
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.
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
Where:
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.
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)).
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.)
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 Generator" 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!)
(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.
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!).
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:
The output will control a 10-15 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 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.)
These units are found in both pocket cameras (regular 35 mm, older 110 or 126, as well as disposable 'single use' types), and external flash units. Larger, more sophisticated models will have proportionately larger components but the basic circuits are very similar. The major parts present in all units include:
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