"Fun with MOTs"
 

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

"Fun with MOTs"
 

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

"Fun with MOTs"
 

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

"Fun with MOTs"
 

"Bob Engelhardt" wrote in message
...
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

"Fun with MOTs"
 

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 **** 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

"Fun with MOTs"
 

"Artemus" wrote in message
. ..
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 **** poor design for high power inverter
circuits.

Art


Is that why this was posted in the comments section of that site?

"I built this and it immediately exploded the tantalum caps. They were
the exact value and voltage rating as those listed."

"Fun with MOTs"
 

"ff" wrote in message
...

"Artemus" wrote in message
. ..
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 **** poor design for high power inverter
circuits.

Art


Is that why this was posted in the comments section of that site?

"I built this and it immediately exploded the tantalum caps. They were
the exact value and voltage rating as those listed."



I didn't read the comments, but yes all polarized caps don't take kindly
to having reverse voltage applied to them.
art