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

[Paul Brodie <paulb.brodie@xxxxxxxxx>]

I have tons of experience with auto alternators both as a mechanic and
building "stuff." I have a setup with a 6.5hp gas engine driving a 60A
alternator and I built a new voltage regulator for the field windings so I
can change the output throughout a large range. If you Google Lindsay books,
they have a small pamphlet they sell that contains details about how to
build the voltage regulator and how auto alternators function. I think it
costs about $6. If you will contact me off list, I will be more than glad to
share my experiences with alternators and the cheapo Harbor Freight
inverters, which work great and no failures, yet.
Paul
Think Positive


On Sun, Jan 2, 2011 at 11:46 AM, Jonathan Peakall <jpeakall@xxxxxxxxxxxx>wrote:

> Steve,
>
> Sorry for the late reply. I fill in at a small Fire Department sometimes
> and had a 72 hour shift.
>
> I can look around for low input imedeance MOSFETS, but is the layout going
> to be super cranky?
>
> I'd love to play with the IGBTs. I've never used 'em. I've built a couple
> of switchmode DC to DC converters that make around 200V, for nixie tubes,
> but nothing that can handle more than 50mA or so. Any links on makind a
> converter that has enough beef?
>
> The thing for me is I am self taught. I;m good at building, have a couple
> of 'scopes and know how to use 'em. However, without a design to work from,
> I'm lost.
>
> Going to go give your site a good look-over. Not only would I love to build
> one to play with, but it would be fun to take it to the local high school.
> I'm always worried that I'm going to backfeed nasties into their mains. It's
> never happened, but I'm always a little relieved when the show is done and
> everything at the school still works.
>
> Jonathan
>
> ----- Original Message ----- From: "Steve Ward" <steve.ward@xxxxxxxxx>
>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Thursday, December 30, 2010 10:35 AM
>
> Subject: Re: [TCML] Off grid, medium size, 12V battery powered TC
>
>
>  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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>
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