[Amps] Microwave Oven Power Transformer

[Carl]

So if you take a MOT with a 120V primary and series it with an identical MOT 
and plug it into 120V we have solved the flux problem.... correct?

Now the issue is what is the resultant individual secondary voltages, how 
are we going to connect those windings, and what rectifier circuit do we 
want?

Having never bothered with a MOT I'll leave the final answers to others but 
when something is free it begs a solution.

Carl
KM1H



----- Original Message ----- 
From: "Manfred Mornhinweg" <manfred at ludens.cl>
To: <amps at contesting.com>
Sent: Monday, November 19, 2012 1:13 PM
Subject: Re: [Amps] Microwave Oven Power Transformer


>I can very well understand the temptation to use MOTs, since they are so 
>widely available for free, and let's face it, most of us are cheapskates!
>
> But please do understand what MOTs are:
>
> They are the absolutely cheapest possible implementation of a 
> current-regulating transformer, designed to work always at fixed full 
> power, for a few minutes at a time, in the airstream of a fan.
>
> And for a ham linear amplifier you want:
>
> - NOT a current regulating transformer, but one that is the exact 
> opposite: As stable a voltage as possible.
>
> - A transformer that idles very well, since typically at least 80% of the 
> time a ham amp transformer will be idling.
>
> - A transformer that can stay energized for the 48 hours of a contest 
> weekend, or the two weeks of a DXpedition.
>
> So the requierements for a ham amp transformer are diametrally opposed to 
> those for a MOT, and it's just not very convenient to adapt MOTs for ham 
> amplifier use. Better use purpose made transformers for ham amps, and 
> leave the free surplus MOTs for other hobby applications to which they are 
> better suited, such as small spot welders to weld those battery tabs, 
> light effect setups using gas discharge tubes, Jacob's ladders to scare 
> away your mother-in-law, and the like.
>
> It's perfectly possible to recover just the core of a MOT and rewind it as 
> a normal transformer with good efficiency, but this requires throwing away 
> the wire, which is the expensive part, to recover the iron, which is 
> rather inexpensive, and then do all the winding work. On top of that many 
> MOTs have the cores welded together, so they are damaged when taken apart. 
> And a 1500 watt MOT will only make roughly a 200 watt, normally efficient 
> transformer!
>
> This is basically an option for people who can't buy transformer 
> laminations new. If you can buy them new, better do that, because the 
> laminations contained in a MOT would be worth only about 3 dollars! And 
> from a scrap yard, less than one dollar...
>
> Manfred
>
>
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