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Re: [Amps] Microwave Transformers?

To: amps@contesting.com
Subject: Re: [Amps] Microwave Transformers?
From: Steve Thompson <g8gsq@eltac.co.uk>
Date: Wed, 11 Mar 2009 07:49:34 +0000
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Microwave oven transformers can be very different one from 
another, even when the original appliance had the same nominal rating.

A lot have quite high resistance windings for the power rating, so 
will give poor regulation and run hot on continuous load. Most 
also have too few turns on the primary for continuous 
energisation, and get very hot from that (in most ovens they are 
fan cooled, even though on for only short periods). You can add 
extra primary turns in the space from the heater winding and 
shunts to help with this, but that increases the resistance. 
Measure some and use the Duncan Amps PSU Designer to see what 
performance they will give.

All I've toyed with can be used with the secondary disconnected 
from the frame - one out of eight or nine needed a bit of kapton 
tape for insulation on a hipot test.

Steve

> Ok, after reading some of the excellent links that the reflector members 
> sent me I see that now.  Makes total sense after finding the right info!
> 
> Hmm, I could scrounge two of them, but I don't know if its worth all the 
> trouble when I can buy a new toroidal transformer off eBay for about $60 
> with a 1a 800v secondary.  That puts me at a lower plate voltage then I was 
> shooting for but it would still give me a respectable max output.  I'm only 
> shooting for about 3-400w on 2m SSB which should be easy at that voltage 
> with the GI-7B.
> 
> 73,
> 
> Scott
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