Date: Tue, 03 Feb 2015 13:41:44 +0000
From: Manfred Mornhinweg <manfred@ludens.cl>
To: amps@contesting.com
Subject: Re: [Amps] Variac Question
Larry,
My suggestion is to save that Variac for better uses, and reduce your high
voltage by removing a suitable number of turns from the HV transformer's
secondary! Depending on the transformer's construction, that might be very easy
to do. Or you might be unlucky, and find the secondary is wound under the
primary. In that case it would be necessary to first unwind the primary, then
remove turns from teh secondary, then wind a new primary (with new wire!). That
would probably be too much effort to be worthwhile. But if the secondary is
accessible, you may be able to remove turns without even disassembling the core.
Another option is to trade that transformer for another of the proper ratings,
if you manage to find any way to d such a trade.
Manfred
## heres the easy way to do this V redux. Obtain a small xfmr with a
120 vac primary.... and a 20-50 vac, high current secondary. Wire the
20-50 vac secondary IN SERIES with one of your existing legs of your
oem plate xfmr primary. Either leg will do, pick one. The 20-50 vac
xfmr will be used as a buck transformer, knocking your 240 vac line
voltage way down... by 20-50 vac. Your small variac will be used
and wired to the 120 vac primary of the 120 /20-50 vac xfmr.
## presto, now you can easily adjust the buck voltage any where
from zero...up to 30-50 vac.
## IE: say u used a small xfmr with a 50 vac sec. Ok, now you can
dial up your line V from 190-240vac..... and anything in between.
## The caveat is the sec of the small xfmr will have to have a sec current
rating of at
least the same as what your big plate xfmr will suck out of the wall. lets
say its 15A.
And the small xfmr is say 50 vac. You will need a 750 va rated small xfmr .
15 x 50 = 750vac.
## Just work out how much V u need to dump.. and use the correct V on the
small xfmr.
## The above procedure works, and has been used in the past.
Jim VE7RF
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