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Re: Microwave Oven Transformers (MOTs)

At 07:29 AM 28/04/00 -0600, you wrote:
>O.K., two questions:
>
>Actually, I have two different MOTs, one is higher in power than the other,
>does this pose a problem?  Or is it because the winding directions of the
>coils may be different, making phasing difficult to know?  If it is the
>latter, is there a way of finding out the phasing?  Does it matter if I get
>the phasing wrong, will it destroy the MOTs?
>

My first thoughts on this are that it probably would be better if the
two MOT's where the same.  Not neccessarily the same manufacturer but
at least the same voltage and current ratings.

>
>The second question is with regard to connecting the two cores together, are
>we talking about some real metal work here or just a sensibly sized metal
>straps or something?
>

A metal strap or even some heavy braid like the shield from a length
of RG-213 coax would be fine.

>
>With reference to the above question regarding phasing, and assuming that
>if I get this wrong the whole thing does not bow up in my face, would the
>following procedure work?
>
>Connect the two primaries together in parallel with a 100 watt bulb in series
>with the connected-together primaries.  If the bulb is dim, then the phasing
>is wrong and the primary leads of one of the MOTs need to be swapped round to
>correct the phasing.
>

If you try to draw an arc between the two high voltage leads and the bulb
stays dim and you get no arc, then your phasing is wrong.  If the bulb
gets brighter and your arc is good, then you've got it right.

> 
>If you connect together the secondary leads of an MOT, does this not turn
>the transformer into a resistance?  The magnetic field in the core
>generated by the primary would induce a current in the secondary, which in
>turn induces an opposing field back into the core.  If this is so, then
the >device is no longer an inductor as it is unable to store energy in the
form >of a magnetic field.  If this is the case, all you are left with is
the DC >resistance of the primary coil?  Or am I wrong?
>

You've got me on that one.  I'm no transformer expert, but I think that
even with the secondary shorted there is still inductance in the
primary, which will limit the current to your MOTs.  I do know
that it does work, as others have reported so.

> 
>Regards,
>
>Gavin, U.K.
>



73, Weazle, VE3EAR/VE3WZL

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