The last time I used a pole pig was almost 50 years ago. However, It had a
tap switch on the primary (HV side) which was connected to taps between two
windings. Both windings appeared to have about the same number of turns. Now,
back then it was common to use a center tapped transformer with choke input
filter and mercury vapor rectifiers. I never tried to use it as a center tapped
transformer suspecting that both windings were not exactly the same since one
was of a larger diameter than the other. But thinking back, it would seem
practical to remove the switch and use a single winding with a full wave
rectifier. I don't know how pole pigs are made these days and if they have the
split HV windings and tap switches.
73
Bill wa4lav
________________________________________
From: Amps [amps-bounces@contesting.com] on behalf of Jim Thomson
[jim.thom@telus.net]
Sent: Wednesday, July 22, 2015 1:10 AM
To: amps@contesting.com
Subject: [Amps] HV transformer and Variac
Date: Tue, 21 Jul 2015 14:55:24 -0700
From: "Hardy Landskov" <n7rt@cox.net>
To: "'Steve Wright'" <stevewrightnz@gmail.com>
Cc: <amps@contesting.com>
Subject: Re: [Amps] HV transformer and Variac
Steve,
Don't be surprised if you see large swings in plate voltage. A "pole pig" is
not designed to be run backwards. It wants secondary current to be low and
primary current be very high. I ran one as a kid in California because
that's all I could afford. It worked but I only used it on CW.
73 Hardy N7RT
## I have never seen bad regulation in a hypersil pole-pig. I checked this
out a few yrs
ago and 90% of the available xfmrs could be run at 100% of their ratings...run
backwards.
The remaining 10% could be run backwards at 90% of their ratings.
## The problem is..with a 7200 vac xfmr, with a fwb, you end up with 10.1
kvdc no load.
And 5.1 kv with just 110 vac applied to the 220 v primary. To get it down to
say 3800 vdc,
you would have to drop the primary down to just 82 vac.
## About the lowest v I have seen on a pole pig is the 4160 / 4800 vac
variety. You will still
require a heavy duty variac to run the mess. Use too small a variac, and V
regulation will suffer.
## The difference between the hypersil pole pigs and say the dahl plate xfmrs
is... on the pole pigs,
the primary is the 7200 vac winding.... which is called the primary. The
primary always goes on the inside
of the core..with the secondary wound on top. Sec of course is the 240 /120
vac side.
## on the dahl the 240 side is the primary..and is wound 1st..with the HV sec
wound on top.
## On a pole pig supply I built years ago,,,,we used a 10 kva ccs type, 4800
vac sec. removed
from oil and weighed 120 lbs. 6700 vdc no load, I had an extra dpdt 50 amp
relay in there, so I could
feed 120 vac into the 240 vac primary, to drop the B+ down to 3350 vdc.
All the relay did was toggle
between neutral and one of the hot legs. Regulation was good either way.
Its currently being used
on a YC-156 amp...with a 150 uf filter.
## two identical 0-130 vac @ 20A variacs can be ganged together...to
operate on 240 vac.
A longer shaft is used. I used AL tubing...and simply bolted the variacs nose
to tail, flush to each other.
A longer shaft used, and only one knob of course. Both variacs cranked fully
CCW, b4 tightening down the
shaft set screws.
I have seen as many as 3 x variacs nose to tail... for 208 3 phase service. (
3 x 0-240 vac variacs used).
## since the pole pig has the HV winding on the core 1st.... with the 220 vac
on top.... there is no way
to remove HV turns.
## u might want to try and find a lower HV winding if a pole pig is to be
used. Flip side is... u could easily test
what u have with a variac, and a simple FWB diode board, and an oil cap... + a
B+ voltmeter. Don’t use too small
ga wire in the 240 side, ditto with any relays etc. You don’t want V drops
on the low V side. Since u only need
aprx 82 vac to run ur xfmr, IF u can find a BIG 0-120 vac variac, it may
work well. Since u need a FWB + HV cap
anyway, it’s a easy test .... provided u have a variac.
Jim VE7RF
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