Re: [TCML] Off grid, medium size, 12V battery powered TC

[Steve Ward <steve.ward@xxxxxxxxx>]

Jonathan,

Without doing a serious investigation (via simulation and part hunting), i
suspect there is some viability in making a DRSSTC operate from 12V nominal
bus.  You'd need a tank impedance that is roughly 10-20X less than a typical
DRSSTC that might make 2 foot sparks.  For example, a "small" DRSSTC might
use something like a .05 to .1uF tank cap at 150khz Fres, which is a tank
surge impedance of 10-20 ohms, so for similar performance from 12V, you'd be
aiming for a ~1uF tank capacitor.  The current would be about 10X higher
than typical, so something in the 3000-5000A peak range.  The things to
investigate are 1) can you make a 1 turn primary to tune with a 1uF tank
cap?  2) can you parallel enough MOSFETS (note i specify MOSFETS and NOT
IGBTs due to the voltage loss) to handle the 3-5kA peak currents with
reasonably low loss?  Even at 1m ohm, that would be a 3-5V drop which is a
sizable fraction of the bus voltage, so its best to get it down to <100u
ohms or so per switch.  Should be feasible with big groups of low voltage
(40V?) high current MOSFETs, but is it reasonable for you??

A more realistic solution would involve stepping up the voltage to at least
150V i'd say, but if you are to build a solid-state converter, you may as
well step up to 350VDC where 600V IGBTs would be perfectly happy and deliver
plenty of power.  But this becomes a new project in itself.

Another, better option still, may be to design a 12V to 12kV converter.
Using a full-bridge of MOSFETS switching 12V into a ferrite step-up
transformer to get about 6kV peak.  This could feed a voltage doubler to get
12kV, which should be plenty for a SGTC of the variety you seek.  The thing
only has to convert a few hundred watts, so it shouldnt be terribly
difficult, though even at 12V this could be 50-100A range, so not trivial.
There are some special "topologies" (or types) of converters that are
specifically useful for charging capacitors, i discuss one of them (the SLR
converter) on my website, though its designed for 350V to 12kV to charge a
5kJ pulse cap at a few kW peak.  The principals are similar and require some
scaling of components to achieve proper operation at just 12V input.

http://www.stevehv.4hv.org/ccps1.htm

I could offer more help if you thought this was a suitable route for you to
take.

Steve




> It's a little discouraging though. A lot of work to make some sparks. Such
> a bummer there is no way to use the battery bank, so much power there and
> easy to charge back up. And I know that if Terry was here, he could figure
> out a way. ;-)
>
>
> Jonathan
>
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