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Re: Solid-state tesla circuit
Thanks for the input Hari
>> I get two distinct peaks one at about 1/2 way and the other
>> at about 80%. Needs a bit of twiddling. This happens regardless of which
>> output transformer I'm using.
> That must be some sort of resonance or something. I definately think
> you should wind a current transformer for investigating the problem
> (with a scope, you'd definately need one). Current transformers
> are also pretty nice becouse of very low losses.
Yes the 3825 part of the circuit performs exactly as anticipated with
no power to the Mosfets - everything is very smooth ( I have to infer
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.
>OK. On low side you gotta be very careful with resistors. They raise
>the source level above the ground!
Yup and the source is capacitively coupled to the gate - sending
more current into the driver chips.
>They also must be of very low
>inductance (no usual 4W wire-wound ones). Metal foil resistors work
>well.
Eek! I must check the inductance specs for the resistors I'm using.
>I wonder if many cores are needed. At coiling frequencys (say 250kHz)
>a supprizingly small core should do for 1-2kW. However, make sure
>all the 3 coils share the current equally if you make a 3-core system!
>Have either primaries or secundaries in series. That is a fool-proof
>method for having the same current in each one.
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 -
and make careful comparison between the 100kHz coil (bucket sized)
and the 200kHz coil (4" pipe). I have more than doubled the spark length
by moving to a higher inductance coil.
>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?
> That's why I'm more into zero
>voltage switched resonant converters in my design. ZCS in not too easy
>to impelement in coil driver IMO.
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.
>Those rods can hve pretty low permeability too! They can also be made
>of materials ok for low flux (like a MW receiver but way
>too lossy for high power at higher flux.
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.