From: John De Armond
Subject: Re: Autotransformer to run Well Pump?
Date: Sat, 24 Mar 2007 00:17:09 -0400
On Sat, 24 Mar 2007 00:06:51 GMT, "N9WOS" <N9WOS@nobug.sbcglobal.net>
>If you live near any decent size town you should be able to find a scrap
>dealer. Bloomington Indiana (which would be considered a suburb in
>California) Has two large scrap dealers that i know of. Kroots and JB
>There has to be some place where they take all the stuff from the old
>buildings they rip out. Hopefully they don't just throw everything into the
>dump. That would be a depressing thought.
Generally good advice but I have to add some more details. Dry type
industrial/commercial transformers tend to be much more lossy than
utility transformers. The prime spec for these is cost and that means
less iron and copper. OTOH, transmission losses have to be eaten by
utilities and so they spec the lowest loss transformers available.
Remarkably low, as a matter of fact.
The common ordinary pole pig, that round thing that hangs on the pole
and steps down the high voltage distribution voltage to 240/120 is
VERY efficient. Indeed, the low voltage secondary makes an excellent
voltage splitter autotransformer. Just disconnect the high voltage
primary side inside the can and leave it disconnected under the oil.
Apply the available 120 volts between the neutral and one leg of the
secondary and get 240 off the ends. Or apply 240 to the ends and get
two 120 volt legs to neutral.
Used pole pigs are dirt cheap. In fact, many utilities will give away
lightning damaged ones just for the asking. Pigs are used in reverse
to generate the high current high voltage necessary to process neon
tubes so there is a demand for 'em. I've helped a number of folks get
and adapt pole pigs for various purposes.
The most usual lightning damage to a pig is blowing the primary high
voltage fuse contained inside the insulator horn. Of absolutely no
consequence to its use as an auto-transformer.
Here's a photo of a pole pig in a domestic setting :-)
Pigs are very popular among tesla coilers for the higher powered
coils. The three low voltage taps that you're interested in are on
the side facing forward. The high voltage horns are on top. For your
purposes, the band around the top would be loosened, the top removed
and the leads disconnected from the horns. They'd be secured to some
of the insulating structure inside the can. The can is almost full of
insulating oil. The high voltage leads remain below the surface where
the oil insulates them.
That's a 15kva pig in the photo. More usual for single house service
is the 20kv version. Very occasionally one can find a 5KVA pig
designed for substation lighting duty. Any of these will work great
for your application. Pigs can withstand 200% overload indefinitely
and typically start to saturate at 250% rating.
In addition to being super low loss, a pole pig is completely and
totally protected from the effects of weather. Just hook 'er up and
forget 'er. The case is hermetically sealed with a pressure release
valve located somewhere on the case. Transformer location gets
flooded? No prob. When the water goes down, fix everything else that
flooded and you're pig will be ready to go to work again, no attention
needed. Outbuilding burn down? No prob. Clean off the soot, replace
everything else that burned up and your pig is ready to rock.
If you can't schmooze* one from your local utility, there are a number
of companies that sell used utility apparatus on the net. Last time I
looked a used 20KVA pig sold in the <$200 range. Heck, they're only
about $600 new, utility cost, so not all that much money involved
* In my experience, the best results come from rural cooperatives and
not city utilities. The best approach is with the line or maintenance
foreman/supervisor. Hanging around the employee parking lot at shift
change time will get you the correct person's name.
Much less successful is walking in the front door and officially
asking. I've gotten feedback from people that this approach has
actually worked but generally the do-nothing front office types tend
to start thinking about lawyers and liability and all that rot and
besides, it's easier to say NO than to investigate.
The utility I normally get mine from is paid $20 apiece core charge
from the company that hauls off the "bad" ones for refurbishment.
Coincidentally that's what I have to pay :-) I go out to the laydown
yard where they store their bad pigs, equipped with my DVM and a
megger and start checking. Many have nothing wrong at all (lineman's
motto: when in doubt, change 'em out). Others have blown primary
fuses. If the can is intact then the transformer inside likely is
also, even if lightning has danced a jig on the outside.