[AMRadio] Pw Supply

Jim Candela jcandela at prodigy.net
Wed Dec 6 18:24:27 EST 2006


   I don't have a good explanation except I tried this once at a high power level, and the results worked until we put a clamp on Ammeter to look at the combined primary current. 

   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!


----- Original Message ----
From: John E. Coleman (ARS WA5BXO) <wa5bxo2006 at pctechref.com>
To: Discussion of AM Radio in the Amateur Service <amradio at mailman.qth.net>
Sent: Wednesday, December 6, 2006 3:28:44 PM
Subject: RE: [AMRadio] Pw Supply

Jim: (JKO)
    That is an interesting statement which I had never thought of
before.  Using two XFMRs like Jack said, seems at first to be a good theory
but as you pointed out each transformer will be looking into a half
rectifier circuit so that the duty cycle on each core and primary would be
alternately 1/120 of a second.  I'm just not sure how that computes to heat.
The primary current of one XFMR would high for 1/2 of the cycle and low on
the other half and alternating half cycles for the other XFMR if phase
wiring was proper.  If the primary windings were in parallel then the sum of
the primary currents would equate to a proper sine wave and the total
current of the two would be more that if there was one due to the losses
being double but I wouldn't have thought it to be  2X more.  

    This may seem like a dummy's question but is it the unbalanced
magnetic swings and DC current through the secondary that would cause the
extra loss?

I can see where a full wave bridge circuit for each supply and connecting
the two power supplies in series would solve this.

Elucidated some more please!
John, WA5BXO

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