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Author Topic: Dumb idea for using microwave power transformers?  (Read 7967 times)
K1ZJH
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Posts: 1185




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« on: August 28, 2012, 07:36:06 AM »

Take two identical microwave power transformers... knock out the current limiting shunts, and wire the primaries in series to reduce magnetizing current. Parallel the secondaries to yield about a 1000 volt AC.  Use a full-voltage doubler to eliminate half cycle loading, which should improve transformer current rating. Any unbalance in the secondaries should equalize out since the transformer doing the most work will increase the primary voltage in the other transformer, and force the other transformer to take more of the load. Is this worth doing?

Yeah, it is raining and I am bored... Grin Grin Grin Grin

Pete
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K8AXW
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« Reply #1 on: August 28, 2012, 08:13:02 AM »

Pete: I'm not even going to address "If it would work."  What I would like to point out though, is that hams have been doing this very thing for decades with varying degrees of success.

As for the "Is it worth it"  Only you can answer that Pete.  If I wanted a power supply that provides that voltage and I had no other means except to salvage parts from a microwave, I'd go for it.  Rather it works or not would remain to be seen.

If I could afford or had other means to build a power supply with those parameters, I'd no doubt go that way simply because of the greater chance of success.

Ham radio is great and great fun partly because of our desire or need to innovate.  Go for it.
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K1ZJH
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« Reply #2 on: August 28, 2012, 08:27:47 AM »

I have enough salvaged iron in the basement that I've collected over the past 50 years Smiley It was more of an academic question. If had two identical microwave transformers I'd be tempted to try it just to prove the validity of the idea.

Pete
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W9GB
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« Reply #3 on: August 28, 2012, 09:02:31 AM »

Pete -

Tom, K8ERV is a good resource, he designed some of these -- and wrote patent on in-rush relay protection.

Here you go, with photos for main steps in process.

Modifying a Microwave Transformer
I used a transformer from a 750 watt Sharp unit but any transformer from a microwave oven having a larger power output can be used. The smaller units use 1.2 turns/volt meaning that the 18 volt secondary needs 22 turns. The larger units from 1kW 'nukers' have bigger cores and use 1 turn/volt (18 secondary turns). The problem with most modern microwave transformers is that the cores have been welded together and cannot be disassembled for rewinding. Some other method has to be found for quickly removing the secondary winding.
http://www.users.on.net/~endsodds/psrewind.htm

DC Power Supply built from this "new" transformer
http://www.users.on.net/~endsodds/ps20.htm

Microwave oven transformers
Jochen's High Voltage Web Page
http://www.kronjaeger.com/hv/hv/src/mot/index.html

« Last Edit: August 28, 2012, 09:10:58 AM by W9GB » Logged
KJ6HYC
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Posts: 103




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« Reply #4 on: September 01, 2012, 08:32:22 PM »

Not sure about the transformer, it looks like it would have its difficulitys.
How about the switcher powered microwave ovens, would they have a sutiable supply for a amplifier? Assuming you could find a amp tube match to the switcher HV output. Could be plauseable. Most full size ovens are at least 1200W.
« Last Edit: September 01, 2012, 08:35:10 PM by KJ6HYC » Logged
K1ZJH
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Posts: 1185




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« Reply #5 on: September 12, 2012, 12:58:17 PM »

After some reflection, a full-wave doubler is out of the question due to one side of the secondary being grounded.

Pete
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