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Re: Solid-state tesla circuit



On Mon, 30 Sep 1996, Tesla List wrote:
> pulse widths from voltage measurements - I know I need a scope
> but I'm reluctant to spend (L300 new - L100 second hand) and if I
> did I'd be reluctant to use it near the coil!). It must be either the current
> feedback loop or bouncing power lines.

Or resonances at the transformer!! The worst of the early tries I had
showed about 1MHz resonance which was 1/3 of the main signal amplitude!
That certainly did disturb everything up! At high turns ratio one has
to be very careful of huge reflected secondary capasitance and leakage
inductance will lead to lots of problems.

BTW, I told you I did drive some 20A peak sine to the system. Guess
how I know the current? :) I had the coil about 1-2m away from my
scope. A proper setup ment no problems. At lower powers I did have
the scope at a very short distance from the coil. Just for the
record: I still use the same scope and it works.

> Yup and the source is capacitively coupled to the gate - sending 
> more current into the driver chips.

So is drain. In some cases those capasitances can lead to problems
like spurious turn-ons etc.

> At the moment I'm running at about 100kHz - and there is 
> heat from the wire - rather than the core - I was going to put the cores
> physically together and make a single large bobbin - rather than use
> 2 seperate transformers. But I need to think a bit more about this -

That is a good idea. You may also want to use more thin wires in
parallel to reduce the resistance of the wire. (Proximity effect
and skin effect!) You can also always submerge it in a cooled oil
bath or use a fan :)

> >That's why people use resins with good thermal
> >conducting properities in transformers. Silicone is not quite ideal.
> 
> Is there a commonly available resin that will beat silicone?

Lots of them. You may even use something like common epoxy or
some other resin you have. Very good resins can probably be obtained from
some transformer manufacturer.

> IMO2 - I've only seen zero voltage switching for things like triacs in lighting
> control.
> I rememember from your earlier comments that Phased Locked Loops weren't too
> clever in this application.

I did not use it right. I know it now. I was trying to lock it into
a point which was not possible. ZCS and ZVS seem to be the way SMPSUs
are going right now. Lots of nice literature on subject has been
published in 1990s.

> Pity - back to the careful winding of transformers - I'm using multiple wires
> rather than thick wires in the primaries - too fiddly for the secondaries.

Copper foils is also nice for primaries. Usually no good for the secundary
in tesla systems becouse it will add a huge interwinding capasitance.
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