Re: Power Transformers

To: tesla-at-pupman-dot-com
Subject: Re: Power Transformers
From: "David E, Sharpe" <sccr4us-at-erols-dot-com>
Date: Tue, 19 Nov 1996 23:49:21 -0800
Tesla List wrote:
> 
> >From jim.fosse-at-bdt-dot-comTue Nov 12 22:45:27 1996
> Date: Wed, 13 Nov 1996 05:27:07 GMT
> From: Jim Fosse <jim.fosse-at-bdt-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Power Transformers
> 
> >Date: Sun, 10 Nov 1996 22:45:37 -0800
> >From: Bert Hickman <bert.hickman-at-aquila-dot-com>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Power Transformers
> >
> [snip to save chip]
> >
> >In order to keep the size and cost down, the ballast inductor should use
> >some type of laminated iron core.
> Good post Bert,
> > Wire size should be
> >large enough to keep I^2R losses manageable - #6 or #8 AWG will be good
> >up to 50 Amps for intermittent duty. The solenoid could be wound from a
> >pair of #10 AWG wires in parallel to achieve about the same ampacity.
> >
> I'm using dual #19 on a 3" pvc former filled with "Is" from some old
> transformers I had wound years age.  It works well (-at-20A) for a few
> tens of seconds before the IR losses heat it to the point where the
> PVC former starts to smell;)
> 
> > Other alternatives include ballast inductors for high-power arc
> >mercury or sodium vapor lighting, or even some types of microwave
> >transformers with the secondaries shorted.
> 
> also shorted Neon sign transformers.
> 
> > Large arc-lighting ballast
> >inductors can often be found at scrapyards for $10-20 (since they have a
> >fair amount of copper and iron). I just purchased one at the local yard
> >that handles 6.5 KVA and weighs 52 pounds for about $20.
> >
> I've got 2 small ones that limit at about 10A each with their
> secondaries shorted. Mine are 1 KVA autotransformers with current
> limiting shunts between their primary and secondary.
> 
> >Note that high-power shunting resistors are essential to keep voltage
> >transients down to a manageble level when the gap is quenched. These can
> >be space-heaters, hot-water heater elements, or oven elements, but must
> >be capable of safely dissipating up to several kilowatts of heat. Not
> >using these can mean that inductive kickbacks will get back into your
> >power mains and wipe out your computer, VCR, answering machine, etc...
> >
> Also include a "PFC" cap between you ballast and any RFI filters that
> you use, otherwise the inductive kickback will blow the common mode
> caps in the RFI filter AND any unhardened electronics connected to
> your power mains. ( I've blown 2 light timers just doing ballast
> experiments;(
> 
>         jim

I have used a motorized liquid rheostat for 4 years consisting of 
3 plates of 316 stainless steel operated by wind shield motor powered 
lead screw in a rubbermaid 5 gal plastic container.  The electrolyte
used was baking soda (sodium bicarbonate)and water.  The rheostat has 
successfully handled power levels up to 5kW for several minutes
(Richard Hull and Alex Tajnsek of TCBOR has witnessed and has been 
videotaped).  Advantages are:
1.  Extremely inexpensive (less than $30 for a 10kW unit) :-)
2.  Extremely robust (try blowing up a liquid rheostat, the
    railroads used them in early electric traction very successfully)..

Dave Sharpe, TCBOR