[AMRadio] Re: Pw Supply

Geoff/W5OMR ars.w5omr at gmail.com
Thu Dec 7 16:48:16 EST 2006

Gary Schafer wrote:
> I am not so sure the correct answer was given and there was no explanation
> of why two separate transformers would not work other than the "primary
> current seemed higher". 
> It seems this would make a much better topic to argue about than some other
> recent ones.

You didn't see Jim's post?  That's not what he said.

> We needed 60 volts CT at 200 amperes with 208 vac primary. The secondary isolation from the primary had to withstand 200,000 volts DC. The core was a large 'C' core, and the whole thing sat in a oil tank. The layered layers of mylar insulation resulted in considerable leakage inductance within the transformer. Before we built the beast we tried two 30 volt @ 100 ampere standard transformers to power up a big electro-magnet. It worked but the primary I was 2X what it should have been. Maybe the Tripplett clamp on ammeter was miss-behaving from the every half cycle current draw, but I also recall blowing circuit breakers, and darkening portions of the building. The boss was concerned to say the least. After building the 60v CT transformer prototype, everything worked fine, and had expected primary current. So was it core saturation from high DC current one way only, a power factor issue, or something else? I really don't know, and since that was 1981, my recall could be put in question. After all , over 50 now, so CRS is a fact of being an OM!  ;-) 
>   I had to make a 0-200amp DC linear series regulator for that supply. A large water cooled heatsink and 32 TO-3 2N6258's in parallel.  What a monster that was!

I don't have a good reason as to why, either.  I can't explain to you 
why the primary current of two power supplies doubles, when the output 
of the two supplies are in series.

Meaning, I draw 3 amps from the power supply, when running 1500v @ 300mA 
on the final, and the modulator biased off at 150mA (0v bias @ 1500v), 
but if I turn on the second supply, and bias the modulator back to 150mA 
(with 2700v instead of 1500v) the primary current on the two supplies 
jumps from 3 to around 8.5 or 9amps.

'Splain that one?

73 = Best Regards,

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