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Re: Flyback charge pump for TC PSU
On 26 Jul 00, at 12:17, Tesla list wrote:
> Original poster: "LOCKWOOD, Chris J." <clockwood-at-orbeng-dot-com.au>
> Does anyone have any experience with flyback converters as the main PSU for
> small/medium power TC?
Yes - they're great. Obviously, coil output is going to be a
function of the power the flyback can deliver. Flybacks in the
TV/ignition coil range are great for small tabletop coils. For
serious work have a look at the DC charger Marco Denicolai has
built - not a flyback but a quasi-resonant topology.
> My initial impression is that this would be a fantastic way of delivering
> adjustable power to a coil, without the dramas of big heavy xfmrs /
> I built a coil using 3 car ignition coils, running off a 30V 15A PSU in
> flyback configuration- through a simple cct using IGBTs. The secondaries
> pumped up the tank cap through a series of 50 1kV 200ns diodes (resistored
> etc). This was decoupled through a ~10mH inductor, and 1nf ceramic cap stack
> to save the diodes (from excess dV/dT), and prevent power being pulled back
> out of the tank.
> The idea was to get a higher peak power (for longer sparks?) with a lower
> rep rate by using a big cap.
> The results aren't anywhere as impressive as I would have hoped. My tank cap
> is 100nF (quite big)- an oil-filled type scored from a university physics
> dept throw-away. I can only get 15-16" at around 20 zaps/sec, when the coil
> is tuned to ~150kHz (static gap, ~30cm diam primary, tapped at 4 turns
> (+-1/8 turn) for best results)...
> I'm thinking that perhaps the cap is crap. After discharging from 10KV
> (shorted for a second) the voltage rises again, to approx 1kV. Is this
> normal for a HV oil cap???
It is a sign that the dielectric suffers from hysteresis
losses and is not the best for TC applications.
> Does the rep rate affect the spark length significantly?