Things to do with high voltage and capacitors and other stuff

Ever since I was a young boy I wanted to work with electricity.

Now that I am older and have access to whatever I can afford (or whatever I can salvage without worrying about making my parents angry since I don't live at home), I have discovered a fondness for high voltage and other impressive displays of power derived from home brew and salvaged parts. You would be surprised at what you can play with on a zero/ low dollar budget. One of the first things I used was an ignition coil from an automobile. These are easy to find if you ask someone you know for one, or if you go to the local auto store and ask for their cheapest coil. There are several ways to make sparks with one of these, the easiest being to use a relay with 2 sets of contacts one wired as a buzzer, and the coil's power being switched by the other set.

I used this configuration in my childhood and later in my 7th grade science fair. It is primitive but it works, just remember not to go with a voltage much higher than 20 volts DC or you may damage the coil. The next easiest auto coil based sparks come from using a special automotive coil called a HEI used by Chevrolet, it is not oil filled like the older kind and it runs on a higher voltage, it's design is more advanced and it is encapsulated in epoxy. A driver that runs this coil is easily constructed from a fan control and a capacitor. Your local hardware store sells variable fan controllers that are much like lamp dimmers only more robust (Lutron makes nice ones). All you have to do is take one of these and put a capacitor in series with your coil's primary winding and wire it up as if this assembly were the fan, and the power connects to the normal spot. The capacitor should be .2 Uf at 250 VDC, and not electrolytic, this can be changed so experiment with values to get what is right for your preference. The setting on the "speed" control actually varies the pulse width along the ac waveform going to the coil more than the voltage, or the speed of your pulses. Set it to whatever you like best. You can upgrade the triac in the control module to carry heavier loads for longer runs, in fact I would recommend it because you will blow controllers pretty fast if you don't (change to a 15-25 Amp triac). You can also put in a series of 250 Volt MOV's across the transformer/ cap combo's input wires to clamp voltage spikes coming back to the triac when the field collapses on the coil. REMEMBER, this stuff with 120 volts AC can be deadly, and will be deadly if you do something careless.

Other designs for coil drivers may use heavy duty power transistors or amplifier designs to form oscillators that induce an ac signal to the primary/ secondary. From my experience I only have seen sparks of an inch or two in length from these coils, perfect for a beginner or someone who does not like to live life on the edge . These coils will also prove a good power source for feeding rectifiers, charging capacitors and running voltage multipliers. (more on these devices later) They also will prove useful in experiments involving ionization of gasses, home brew plasma globes, and any other experiment needing a high voltage/ low current power source.

Next in my list would be the TV flyback transformer type circuits, I messed with these for a while but found them hard to get as a young boy. They are the round high voltage transformers used to provide power to the picture tube in a television's horizontal circuitry. Today with the abundance of dead computer monitors and cheap color televisions, you should have a dozen within a month if you scrounge on pick-up day, or ask family/ friends for dead monitors. These can be used in circuit for a really crude high voltage supply by just pulling off the suction cup looking thingy on the side of the picture tube (WATCH IT, this wire probably has high voltage on it even though the thing is unplugged so discharge it to ground before messing around) Taking this wire and a wire connected to the monitor's metal chassis will produce inch and a half sparks that buzz and just sound mean as heck. DON'T get bit by this one either, it will hurt pretty badly. I don't know how long this type of power source will last because it wasn't really designed to work without a picture tube connected. It produces a pulsing DC voltage around 30, 000 volts but at a higher current than the AC of the ignition coil. It is recommended that one removes the flyback transformer and builds a driver for it with power transistors and a little modification, it will last longer this way and it takes up less space in your lab. (diagram to come) As an added bonus to flybacks, they are also sometimes connected to high voltage diodes and multiplier modules that provide DC from their AC input, used by us experimenters as a cheap means of rectification or voltage multiplication, for general experimentation it can be considered a performance booster in that sometimes larger sparks (and hotter sparks) can be produced by these devices.

A typical relay that could be used for the buzzer circuit

The guts of a monitor showing the high voltage suction cup anode connection.

Here is my makeshift lamp dimmer/ HEI ignition coil setup, you should make your's better! Beside that is a makeshift plasma globe made from a large light bulb connected to a high frequency high voltage source, the photo is a bit blurry because of the lighting conditions.

I used a metal heat sink on my replacement Triac to hopefully keep it from blowing up, it should be isolated and kept where it can't be touched accidentally because the tab on the part is probably at a potential difference with you and ground.

Inverters, somewhere in the middle of this all are inverters made by taking a step down transformer and hooking it up backward and driving it with a low voltage/ high current source to provide a few hundred volts of pulsing low current power. The most common I would say is the 6 volt filament transformers used in tube stuff. IT was designed to make 6 volts from the 120 volt line current to power tube filaments, one can also use 9 or 12 volt transformers depending on what you have on hand. When connected in reverse with 6 volts going in you get 120 volts out. 12 volts in you get 240 volts out etc... Transformers, being ac devices need a pulsed source, a simple timer or transistor circuit will fill this need well and provide a safer source of medium high voltage power for ionization and other "shocking" devices. (I do not advocate the use of any devices here as defense or practical joke implements, discretion must be used at all times and it should be known that long term exposure to high voltage shocks has not been studied and may prove to have a cumulative damaging effect on the nervous system etc...) Here is a simple circuit using a step down transformer wired backward (diagram to come)

Neon sign transformers/ oil ignition transformers.

Above is a typical neon transformer. This unit is capable of producing 12,000 volts and 30 miliamps.

This breed of transformers are intended to run big neon signs found in windows. They are a robust power source that can be used for many things including Jacobs ladders and tesla coils. These transformers are usually powered directly from the AC line and are current limited meaning that they require no ballasting (more on ballasting later). Don't be fooled by the new models of "solid state gaseous tube supplies", they are inverter circuits that will probably shut down after an overload (r.e. any use except for neon signs). I have one of these, they typically come in plastic housings and weigh a lot less than a real transformer. This isn't to say that the solid state ones are useless, they just require special attention to their uses since they are more complex. Neon sign transformers can be found for free at local sign shops in used and untested condition, some will only have output from one of their terminals to ground because it is "1/2 blown" , some will only have one terminal. Cost of a new large sign transformer can get pretty steep (about $75-$120) They can also be found on ebay but shipping will be more than the price due to it's weight. I have a local sign dealer who sells me a trunk load every few years for about $40 if I give him cash. This is a nice step up from the old ignition coil setup. Once again, these devices are quite mean when you get on their bad side, so don't use one if you aren't sure of your skills/ safety procedure. And whatever you do, don't sue anybody if you get hurt. This world is filled with examples of people's stupidity and the consequences when legal action is involved usually takes the fun away from everyone else who can take responsibility for themselves. (speech over)

That said, we can now move on to the ever so frightening and awe inspiring Microwave oven transformer. This transformer requires ballasting and produces about 2,000 volts at nearly a full amp! If you plug it into the wall directly it will blow your breaker in your fuse box. This is why it is best to have 2 transformers, one to ballast the other, ballasting limits the current that the MOT (microwave oven transformer) can pull. There are other methods of ballasting if you search the net for them, the way I describe is simply to hook both primaries in series and short the secondary of one of them, it just acts like a big inductor. This transformer should be used with discretion, it is unforgiving in it's ways and you probably won't live to learn the lesson it will provide about high voltage safety. This can be used for tesla coil powering with certain provisions and Jacobs ladders as well. Due to it's low voltage and high current output it acts like an arc welder, you need to get the contacts on the output really close to draw an arc, then pull them apart slowly, you will see a 5 inch flaming , sizzling, and blinding arc. I will include a photo if I can get my girlfriend to hold the camera in the same room as my demonstration. You can also get these for free on garbage day, just find a microwave, open it up, look around and you can't miss it.

Here is a photo of one of my microwave oven transformers.