"Fun with MOTs"

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Date

06-22-2008

Posted by Bob Engelhardt on June 22, 2008, 9:32 pm

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Since building a spotwelder with 2 microwave oven transformers (MOTs), I
have fooled around with them and found other uses:

http://www.metalworking.com/dropbox/FunWithMOTs.pdf

It's 1.09 MB. Sorry, dialup readers.

Bob

Posted by RoyJ on June 22, 2008, 9:50 pm

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Very good. Properly filed. Will come in handy for some project.

Bob Engelhardt wrote:

> Since building a spotwelder with 2 microwave oven transformers (MOTs), I
> have fooled around with them and found other uses:
>
> http://www.metalworking.com/dropbox/FunWithMOTs.pdf
>
> It's 1.09 MB. Sorry, dialup readers.
>
> Bob

Posted by Winston on June 22, 2008, 11:21 pm

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Bob Engelhardt wrote:

> Since building a spotwelder with 2 microwave oven transformers (MOTs), I
> have fooled around with them and found other uses:
>
> http://www.metalworking.com/dropbox/FunWithMOTs.pdf

Very cool, Bob. Thanks!

--Winston

Posted by ff on June 23, 2008, 4:46 pm

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> Since building a spotwelder with 2 microwave oven transformers (MOTs),
> I have fooled around with them and found other uses:
>
> http://www.metalworking.com/dropbox/FunWithMOTs.pdf
>
> It's 1.09 MB. Sorry, dialup readers.
>
> Bob

Here's another project for a rewound MOT:

http://www.aaroncake.net/circuits/inverter.asp

Posted by Artemus on June 23, 2008, 6:55 pm

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This circuit is not a good design.

1. There is the obvious problem of the capacitor polarity being
reversed.

2. The snubbers (D1-R2 & D2-R1) are suitable for a flyback
circuit but not a push-pull circuit like this one is.
Consider: When Q1 is saturated, Q2 is cutoff. Q1 pulls the
voltage on the right primary connection to 3V (Ic=10A). The
voltage on the left primary connection will be +21V.
But D1-R2 shunts this to the 12V CT. 9V / 10ohms = 0.9A of
wasted current. Good designs use RC combinations for snubbers.

3. C2 charges to 19.5V (21V - 1.5Vbe). When Q1 switches off
this places -16.5V on it's base. The max spec for Vbe is -7V so
the design far exceeds the 2N3055's ratings.

4. A collector current of 10A requires a base current of around 3A.
Yet R4 limits it to (12V -1.5V) / 180ohms = 58mA.

5. There is no provision for a dead time. During switching Q2 must
turn on before the base drive can be removed from Q1 to turn it off.
This causes collector currents of both transistors to spike very high for
a short time and is just piss poor design for high power inverter circuits.

Art

----- Original Message -----
"ff" wrote in message

>
> Here's another project for a rewound MOT:
>
> http://www.aaroncake.net/circuits/inverter.asp

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