Date: Tue, 19 Nov 2024 16:17:44 -0800
From: "Luis A. LLambias" <lallambias@verizon.net>
To: amps@contesting.com
Subject: Re: [Amps] Need to have a 6KVA plate transformer rewinded
<Thank you again for your input Don. I just spoke with Araceli from
<Magnespec, and they only
<manufacture transformers for the Military, nowadays.
<I thank the suggestions of the other members of the list but, at 81, I
<don't feel brave enough to do
<the Hipersile rewinding myself...
<Any other places that could rewind or make this transformer?
<Thank you guys
<Luis? AI6FK
Is this for the BTI with the 2 x 8877's ?? Is your 6 kva xfmr internal to
the BTI....or external ? Who made the 6 kva xfmr ? If it was a Dahl
xfmr, they can probably re-wind it for you. The cores are expensive, and
can easily be re-used. With the steel bands removed, and both tops of the
cores removed, the pri + sec windings will slide right up and out.
The new pri + sec windings are wound on a jig, which supports the inside
of the pri. Once wound, the 'fingers' on the jig contract, and the
completed pri/sec windings slide out....which are then slid over the pair
of C cores. Tops of C cores put back on, then on goes the steel bands.
Sounds more complicated than it is.
Be careful with the insulation ratings. There is magnet wire..and there
is magnet wire. You can get magnet wire from 75C up to 225 C . You can
get magnet wire with 300-500 V ratings.... up to 15 kv rated.
Dahl specced his plate xfmrs at a 55 deg C temp rise over a 40 deg C
ambient = 95 deg C. Then deep inside the core, it's another 10 deg C
hotter. Total is 105 deg C = Class A insulation. Dahl used Class B
insulation = 155 deg C.
My theory on why these various xfmr fail is..... with the sustained heat,
the insulation eventually breaks down...and then poof, there goes the V
rating too...at which point it will arc from sec winding to the frame.
For new xfmrs, Dahl is good / expensive. Heyboer is another xfmr maker,
that is also good. https://www.heyboertransformers.com/
Jim VE7RF
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