Coil Driver HV Generator

[xyz]

I recently made an ignition coil driver and thought I would post some pics of it. I know it doesn't really fit the topic of improvised weapons as it need to be plugged in but this board is where PYRO500 posted his pulse capacitor briefcase and this topic doesn't really fit anywhere else.

Here is a pic of the whole coil driver set up, the big silver thing with the black top that's standing on a stack of tiles is a car engine ignition coil, the tiles are to stop it from arcing into the ground,and the top has been coated in hot glue to stop it arcing up there. The other two things are a 2Kv 1.1uf capacitor (from a microwave) and two dimmer switches to control the output (the kind used for lighting, this circuit will still work with only one but I put 2 in for better output control). The pic is about 40kb.
<a href="http://www.boomspeed.com/theprodigy/xyzcoildriver.jpg" target="_blank">Coil Driver</a>

Here is a pic of the fury of sparks which jump rather noisily between the output wires, the gap in the photo is about 3cm wide but the sparks can jump up to about 5cm. This pic also about 40kb.
<a href="http://www.boomspeed.com/theprodigy/xyzcoildriveroutputs.jpg" target="_blank">Coil Driver Output Wires</a>

The parts are quite easy to find and any capacitor in the range of 600v upwards and about 0.5 - 2 uf will work (different capacitors give different frequencies and spark lengths) although when I tried a 350v 120uf camera flash capacitor it thermally failed quite spectacularly filling the garage with smoke :) .
These things are useful for frying just about anything that contains electrical circuitry (I already tried a toy bob the builder walkie talkie :D )and will punch a tiny hole through anything non conducting and thin enough that gets in between the terminals (sheets of paper or thin plastic.

[PYRO500]

Incase you or anyone reading this dosen't know how this thing is woking this circuit uses the light dimmer witch clips the waveform of the wall ac to cause lights to go dimmer, this clipped ac charges and discharges the capacitor through the ignition coil causing it to resonate and saturate the coil and you can thus draw power from the output.
I think the most practical use for these devices is a charger for an electric defense shield although I don't think that you should let one of these run for an extended period of time as I think it could wither damage the dimmer unit, the coil or cause a fire or something.

[xyz]

I thought dimmer switches are just variable resistors that serve to increase or reduce the power, it still works when they are both set to have no effect (i.e. set to full power, their range is 14% to 100% of the total power). The coil is a large one and I have noticed no change in temperature after the circuit has been on. If any part were to get damaged I would expect it to be the dimmer switches or the operator :D . BTW I just thought I would also mention something that you forgot to say Pyro, the coil works by building up a magnetic field and then collapsing it, so it sparks once when the current is turned on and once when it is turned off again, I think PYRO500 mentioned that the capacitor is what turns it on and off very fast by charging and discharging.

Edit: Spelling

<small>[ July 19, 2002, 06:08 PM: Message edited by: xyz ]</small>

[PYRO500]

While a variable resistor would work for dimming a light it would not only get hot but it would not give linear dimming. I mean by liner dimming in that when you turn the knob the bulb's dimming would be continuously variable by the amount you turn it and it would not dim faster or slower at lower or higher settings.

The way these dimmers work is by clipping the top and bottom of the ac wave causiing the peak voltage to be reduced. the capacitor charges and discharges with ac where as with dc it will charge then block the current.

[xyz]

Ok then, I'll remember that. They have coils of wire inside them (you can see them from the outside, I haven't dismantled one) which is why I assumed they were variable resistors. I have potted the coil in wax now to insulate it from the ground and it's surroundings and to prevent all arcing (the hot glue wasn't doing a satisfactory job) and I am currently waiting for it to cool down and solidify so I can test it.

Edit: Just adding that I can see it's potential as a very powerful (and probably lethal) electric fence, you could simply make a wire fence that was well insulated from the ground and then connect the positive terminal of the coil to it. When something touches the fence while it is also touching the ground, BZAAAP :) . You could also use the dimmers to adjust the fence to anything from Ouch, my finger! to Oh No! I'm Dead or seriously injured by a 50 Kv electric fence!

<small>[ July 19, 2002, 09:53 PM: Message edited by: xyz ]</small>

[PYRO500]

I would try using diffrent capacitors instead of changing the voltage. the way the circuit works is that it continuously charges and discharges the capacitor every cysle so less capacitance means less energy. To reduce capacitance you could hook the capacitors in series witch would allow you to use higher voltages (although you won't be) and will cut the capacitance in half.

[xyz]

It works well with no arcing whatsoever now the wax has cooled. Smaller caps does mean smaller discharges but I'm pretty sure it also means more rapid ones because it takes less time to charge and discharge, why bother changing the caps when you just turn the dimmer dial down and the sparks are smaller and less powerful but just as rapid.

<small>[ July 19, 2002, 11:08 PM: Message edited by: xyz ]</small>

[PYRO500]

As far as I know the frequency of the sparks in this circuit cannot be determined by the capacitor, you must change the input frequency to change the output frequency witch under us power is 117V average (around 170 peak).

[xyz]

The site where I got the plans (these are not plans for US power, they are designed for use in the UK, Australia, New Zealand, Or anywhere else tha uses 240v 50hz)said that different caps give different frequencies. Mine makes about 25-30 sparks in a second and is definitely slower than the 50hz that our mains power supplies. The cap in the plans was a 600v 1uf and I am using 2000v 1.1uf which I think is why I am getting slower sparks. I should get 100 sparks a second with 50hz mains power (the rate it sparks is double the frequency because the coil sparks once when turned on and once when turned off again so turning on and off 50 times a second gives 100 sparks a second).

[PYRO500]

Technichly you should get the same amount of pulses no mater what capacitors you use beacuse the capacitor is being driven by the line pulses witch continually charge and discharge each cycle, it's possible that the pulse is switched off or something but I can't remember what the waveform of these looks like. I think with a smaller amount of capacitance you should be able to get a higher voltage at a lower energy allowing you to have a safer HV supply.

[xyz]

2000v 1.1uf IS high voltage low capacitance (and a lot more so than the 600v 1uf one which was recommended for this circuit). Anyway, I found it to be extremely good at destroying CDs, when a CD is placed between the teminals the electricity arcs all over it burning off all that shiny material and after about 2mins or so you have a perfectly clear plastic CD :) .

[PYRO500]

It does not matter what voltage capacitor you use in your setup as long as it exceeds the maximum voltage of your circuit.
A bit here on the energy in capicitors, The energy in capacitors is determined by the formula (0.5C)(V^2) or if your calculator dosen't screw order of operations up 0.5*C*V^2=J .
In that formula C=capacitance in farads (caps are usually marked in micro farads)J=joules (Watts*1second) and V=voltage.
If you look at this formula carfully or even plug some numbers into it you will see that the voltage has an exponential increase in energy as the voltage increases while the capacitance (witch is halved to start with) is only having a liner effect on the energy.

If you were to plot a capacitor's energy while charging with this formula (energy=vertical voltage=horizontal) you would see a line that formed a curve that would become increasingly steeper untill it eventually became almost vertical and impossible to graph by hand.

I'll do some math for you to show you an example of the energy in this cap:

your capacitor is 1.1UF so C= 0.00000011/2 (that's 0.000000055) and the maximum voltage is 2000V so that squared is 4000000 and 4000000*0.000000055= 0.22J

now that's at maximum charge of 2000V but your capacitor can only charge to say around 200V when you have the dimmer on at a safe setting so I'll spare you the math and tell you that the energy at that it has at 200V is 0.022J witch is the energy per spark witch you say happens around 30 times a second witch means .66J in one second, not necessarily lethal but sure to be painful.

<small>[ July 20, 2002, 03:03 AM: Message edited by: PYRO500 ]</small>

[xyz]

I have both dimmers set at full power all the time as I have noticed no heating up or anything like that after the circuit has been running. You can smell the ozone quite strongly after about 2 mins.

0.66 Joules a second isn't very much :( (about the same as being shocked from a camera flash cap),I'm sure it must be more than that because it takes 4.2 joules of heat energy to raise the temperature of one ml of water by one degree celsius and I have watched it burn the coating off CDs at a reasonable rate not to mention that lots of the electrical energy is expended as light and sound as well as heat.

Also, If the capacitor can be any value so long as it is higher than the circuit, and the circuit is 240v with a possible maximum of 250v, how come my 330v flash cap blew when I tried that?

[PYRO500]

I think I may have had a small error in my math, I neglected to take into consideration the reverse charging of the capacitor during discharge, so that's 1.12 J witch is less than a camera flash cap the most common ones in disposable are around 6.5J. But remember now, your camera flash circuit makes quite a bit of noise it self when shorted and pts out a fair amount of energy. your coil on the other hand is high voltage witch can take that energy and push it through conductors your 330V camera flash can't go such as through the metalic layer of a cd by arcing through it.

The capacitor can't really be any value, for one the camera flash capacitors aren't AC rated, in fact the fit in a catagory of capacitors called electrolytics witch only are supposed to be charged in one polarity( the negative side is indicated by either a stripe down the side or a negative sign on that side or both), by hooking the tiny photoflash capacitor you basicly took a capacitor that was designed for a very quick pulse once in a while that also was supposed to be charged in one direction, and you set it up in a circuit that it was continuously charging and discharging in opposite directions 100 times a second. You never did show me the circuit that you were using, just to be sure I have the right idea about your device can you show us a link?

<small>[ July 20, 2002, 08:34 AM: Message edited by: PYRO500 ]</small>

[xyz]

Here is the circuit diagram for my coil driver:
<img src="http://www.boomspeed.com/theprodigy/coildrivercircuit.gif" alt=" - " />
The original circuit had only one dimmer and used a 600v 1uf capacitor. Polarity is not marked on the coil because my coil is marked for use in a car engine and doesn't say positive and negative, I just make sure that the wire coming out of the top of the coil is the one that wants to ground itself (i.e. is the one that shoots purple sparks into the floor when placed above the floor and the coil driver turned on)
I also think that it may possibly set someones clothes on fire if they got stuck on it for more than 2 seconds, it takes about 2 seconds to set paper on fire when it is placed in between the terminals.

[Anthony]

Uhhh, the coil on a car engine *does* stay at the same polarity. The casing is connected to negative, the centre connection in the top is HT out, then there's a positive trigger from the distributor, usually to the side.

I think I remember seeing a similar circuit, but without a capacitor. I presume this would still work as the magnetic field in the coil should still collapse on every cycle? Or does the cap serve to rectify the AC to DC and the coil will only work if fed DC?

[PYRO500]

I think it'd be a good idea to keep the capacitor. The capacitor is what limits the power every pulse to twice the energy of the capacitor. This works by the AC cycle charging the capacitor one way then on the voltage reversal the power discharges the capacitor and charges it the other way and so on.

[xyz]

Anthony, what I meant is that the coil is not marked positive and negative, one side is marked as battery and one side as something else. I can still use it fine without the markings anyway.

When I had just started building this and hadn't yet got hold of a suitable capacitor, I tried it without the capacitor, it sparked once (rather weakly as well) and then the circuit breakers tripped and cut off the house's power supply. It needs the capacitor and the dimmers to work (tried it without the dimmers out of curiosity and it did nothing at all).

The coil works fine when fed AC (I have run it on 12 volt 15 amp AC, it worked but the sparks were only about 0.3cm long and it only sparked once when turned on and once when turned off as there was no capacitor to pulse it)and I don't think that the capacitor serves as a rectifier.

[PYRO500]

You shouldn't run these things from AC for one the reason it didn't arc very far is that it needs pulsed power from a source such as a light dimer.

[xyz]

I don't use the 12v AC because I have my capacitor and dimmers now and can run it from 240v.

<small>[ July 23, 2002, 05:47 AM: Message edited by: xyz ]</small>

[ETCS (Ret)]

The Incandescent Lamp Dimmer circuit is based upon a Thyristor (Triac) which is adjusted to change the angle of conduction of the incoming AC current. By rotating the adjustment potentiometer on the dimmer, the incoming AC sinusoid waveform is is blocked until the Triac is triggered "on" at the desired angular position of the waveform, thereby reducing the time of current flow during each half cycle.

The output waveform of the dimmer, at other than full brilliance, is more like a pulse than a sinusoid; at the instant of "turn on" when the Triac goes into conduction the output voltage instantly jumps to the insantaneous value of the input voltage, and the output voltage continues along the sinusoidal track of the input until it reaches zero volts which will switch the Triac "off" until the next half cycle turns it on again at the set point of the dimmer adjustment.

To power an induction coil (Ignition Coil) with a Dimmer it is absolutely necessary to use a Capacitor in the current path to the Coil. The Capacitor must be "Non Polarized" and capable of use in Alternating Current applications.

A DC Electrolytic Capacitor will not work as it will be destroyed by the Alternating Current flow.

The brief "charge" and "discharge" pulses of the capacitor through the primary of the coil is what produces the high voltage discharge at the output terminals of the coil.

For best and safest operation the Capacitor should be One to Two Microfarads with a Voltage Rating of more than 250 Volts for 120 Volts AC operation.