pcmhacking.net

So I got a deal on 20 TDK old stock door nob caps at 300 USD. 50Kv and 2000pf

Better than paying 80 odd each for them lol

vlad01 wrote: I plan to run pretty high frequency, about 10-20KHz. Stringing lots of little diodes has little success due to flash over and cascade failures. Seen heaps of youtube video of strings like than in the CW generator, lots of the videos end in a whole string burning up. Can run a limiting resistor in series but it all gets messy when you have at least 1000 diodes to solder together, and very expensive!

FWIW ...

Too high freq. for 1N5062's. There are high speed alternatives, but I can't say if these would last. The 1N5062 is rugged, not really little, and designed for series operation, 100 of them gets you 80kV. Avoid sharps to prevent corona and possible flash-over. Potting could also help.

I say I can't say if high speed alternatives would last, because when I experimented with some high speed 15kV low current diodes (diode stacks, really) some years back, I found they would spontaneously die for no apparent reason, even series resisitors didn't seem to help. But these ones were little diodes and definitely intended for potting. Perhaps beefier high speed diodes will fare better.

Joe.

Im thinking of using either 80Kv 200ma diodes or 50Kv 3A diode. Im not sure what sort of voltage V6 coils output normally, but 50Kv sould be fine as the caps are rated at 50Kv, only the 50Kv diodes are expensive, 34 each and will need 20 of them.

Also the other little dilemma is I'm trying to find a circuit design that can drive the coil in an AC configuration, firing square wave with alternating polarity.

There are a number of good designs including ones using IGBTs but only operate single polarity waveform, ie, the -ve peak would be at 0V and +ve peak at rail voltage.

Not sure if it matters or not though since the 2 posts of the coil aren't tied to anything but the multiplier works on AC waveform, giving DC at the output.

I have also decided I will make an acrylic tank to house the multiplier ladder and immerse it in oil for reliable operations and more voltage!!

vlad01 wrote: and immerse it in oil for reliable operations and more voltage!!

If you are going to put it in oil I'd use a coil with normal stud and nut connections, not the V6 coil with it's spade receptacle. Might be more reliable.

not putting the coil in oil, just the multiplier. the coil is low voltage so no need to.

Hell if a big job to get that extra hot spark with a 10mm plug gap....

Simon

you mean 500m spark gap lol

vlad01 wrote:you mean 500m spark gap lol

Does that go with the new block that has wider bore spacing, runs on hydrogen and makes 10,000HP?

Simon

vlad01 wrote:Im thinking of using either 80Kv 200ma diodes or 50Kv 3A diode. Im not sure what sort of voltage V6 coils output normally, but 50Kv sould be fine as the caps are rated at 50Kv, only the 50Kv diodes are expensive, 34 each and will need 20 of them.

Also the other little dilemma is I'm trying to find a circuit design that can drive the coil in an AC configuration, firing square wave with alternating polarity.

There are a number of good designs including ones using IGBTs but only operate single polarity waveform, ie, the -ve peak would be at 0V and +ve peak at rail voltage.

Not sure if it matters or not though since the 2 posts of the coil aren't tied to anything but the multiplier works on AC waveform, giving DC at the output.

I have also decided I will make an acrylic tank to house the multiplier ladder and immerse it in oil for reliable operations and more voltage!!

Wow! That's some voltage you're aiming for!

Conventional ignition coils operate in flyback mode. I presume the modern ECU-controlled ones do too. If it were forward mode, dual polarity would be a bit easier to arrange, but alas ...

Peak flyback/output voltage depends on the energy built up in the coil (ie. inductance and peak current), the turns ratio, the load impedance and the winding capacitance. This voltage is also reflected back at the primary, though reduced by the turns ratio. The switching circuit needs to accommodate this reflected flyback voltage.

To achieve dual-polarity drive, you'd probably need a dual-polarity power supply and a switching circuit to drive the coil from the positive and negative rails in turn, say a PNP/PMOS circuit and an NPN/NMOS circuit. Since the flyback voltage will occur in both polarities and the two circuits will both connect to the coil, you'd need each to have a series diode to block reverse conduction through the transistors. In other words, the collector/drain of the PNP/PMOS circuit would have a diode "pointing away", while the collector/drain of the NPN/NMOS circuit would have a diode "pointing toward".

The coil would also need a series capacitor to ensure that any small imbalance in the drive waveform wouldn't accumulate over multiple cycles and cause the coil flux to saturate. The duty cycle will also need to be such that most of the flux has collapsed before the next half-cycle is begun. Of course, the duration of the switching pulse, the applied voltage and the coil inductance, together determine the peak current mentioned previously.

Joe.

Edit : Actually, with a series capacitor driving the coil, you don't really need a dual-polarity supply, just alternate switching from the positive and negative rails, so as to drive the coil in both directions.

I see virtually everyone who builds these normally use a coil and drive it in flyback setup, but I don't know how their multipliers seem to work well from what I understand would only be a single polarity HV at the coil. Perhaps others aren't getting full potential from their multipliers because of this?