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Subject: [Amps] Fw: TRANSFORMER-TEST
From: "Harold B. Mandel" <>
Date: Sun, 12 Jun 2005 15:23:23 -0400
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Dear Ken,

You did a great job in investigating the transformer!

Let's see: My PWD monster that took three tries to get right
from Peter is 12" high by 11" wide by 10 inches across, and weighs
167 pounds. It is a "hypersil" object rated at 0 - 1800 - 3000 volts,
at 3 amperes CCS.

Peter had to do it over and over because he didn't wind a 3 ampere
CCS piece and I caught it when it arrived.

Since I build monster power supplies I have learned the hard way
about component ratings, (almost electrocuting myself last Fall.)

The one feature I see on your iron is that the windings are not 
potted. This means the unit, as it heats and cools, absorbs moisture
from the air around it, said moisture settling in the paper laminations
in the wiring.  To forestall disaster, I myself pot HV stuff, especially
transformers, chokes and coils.

I found that the best stuff isn't too expensive: Dolph's Synthite AC-41.

It's about 25 dollars a gallon and is made for HV insulation potting, and
the consistency of plain old varnish, but with much better breakdown
characteristics. There are several distributors and the stuff is made in
Monmouth Junction, New Jersey (732) 329 - 2333.  For my 10KV
plants I use about 10 layers, either brushing or dipping.

The test jig you set up is perfect for doing a preliminary examination. 
Once you place the transformer into service I would suggest using 
a mighty fan such as a Tarzan 320CFM, 230vac to move air around
the structure. 

>From your temperature observations I would concur that this is a 2 ampere

However, the acid test will be to actually construct a load bank.  Your
of 6719.33 vac, after filtering, would yield 6047.40 VDC. (Applying the
0.9 factor).

Since the power factor comes out to 12KW using around 3K of resistance, I
know if you want to invest in a bunch o' resistors to do the test, but
let's figure
this transformer was made for broadcast use.

Two 4-1000A's would need 2 amps at 6KV.

You'll not probably melt the transformer down at 2 amps CCS, but if you
jump to
three amps and run AM 'Phone or RTTY it will get plenty hot.

Just choose your rectifier bank carefully, Ken. Build it for 18KV,
minimum, at four
amps, minimum.  Cool the diodes with that Tarzan fan, and then, let's
talk about
capacitors.  Please don't tell me you're going to use photoflash
oil-filled caps
unless you see their voltage rating at 30% of what's written on the cans.
One screw-up
and the blown cap takes out your diode string and the transformer.  I had
a huge argument
with my capacitor supplier about this and ended up backing up my argument
written evidence.  The end result was that for the same money I was
shipped three times
the actual units to make up a 100 percent Working Voltage Direct Current
instead of a Peak Voltage Direct Current filter. Your filter better be
rated at 12KV

Work Safely!


Hal Mandel
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