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Re: 10KVA FET coil
Thanks Mark,
For the specs on the FET coil. I certainly agree with going for a lower
frequency. At 220kHz I am having problems with FET switching and
heating, and also the speed of the PWM chip, which is operating
at the top of its range. Currents rise faster, so current limiters need
to act quicker, inductive effects in wiring are more severe......
Mark our gallons are different sizes, but I visualise a drum 18" diameter,
3 feet high close wound with 22awg (I'll avoid teflon coating -
I have enough problems getting to grips with this!). Is this right, and
how high was the primary?
I've blown another fet after what I thought would work better worked worse.
Intense 3 - 5" arc from the dicharge point to an earth point. White arc,
rather than the purple stuff, but too much heat inside - zap.
However the ground point is now on the rail connecting the PSU capacitors
Next to the electronics, 2" wire instead of 2'.
Jim Fosse gave me a number of suggestions for dummy loads, and I think
this is the right way to go. I need to know if the problems are due to the Tesla
secondary, or due to the driver design.
My circuit is struggling at 150v, and I think I'll
go back to 75v, get something that works, to drive the 4" secondary and try
to complete that as a project.
I'm trying a new chip set tc4421, (serious fet driver) and 3527, (pwm chip.)
We shall see.
Then build a big coil (a couple of friends are looking out for
pipes and barrels). Aim for <100kHz and a more ambitious
driver. Probably end up with a heavy duty fet blower!
Have fun,
Alan Sharp (UK)
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>The secondary was wound with 22awg teflon wire around a standard size
>55 gallon polyethylene barrel (talk about slippery!). It resonates at
>80KHz. This lower frequency is much easier on the FETs because they
>get to enjoy a longer on/off time compared to the time spent in
>transition. The primary was 20 turns of 1/4 inch copper tubing in a
>straight helix, 30 inches in diameter, placed at the bottom of the
>secondary. Flashover problems were severe and dielectric was needed
>between the windings. I would do it again with a larger diameter
>primary.