Rewinding microwave transformers

I have no picture but this is a quick description

To rewind microwave oven transformers.

The primary in North America is 115 volt a/c. It usually has tabs to
connect the 115 volt power that is controlled by a black, square triac
that is mounted metal for a heatsink.
The primary wire is fairly heavy and you can identify it quickly as it's
wire size is much larger than the secondary. I would guess #12 or 14 wire..
Keep the primary coil in place as it is engineered for the transformers
size and output. You only are changing the output from high to low voltage.

The secondary wire is quite fine. The secondary is a high voltage coil
that outputs high voltage to run the microwave tube. The secondary coil
is physically bigger than the primary because of the large amount of
wire needed to create the high voltage. Hacksaw it out.

The space left in the high voltage side is bigger than the space needed
by the primary. This allows lots of room to wind the secondary as even
at 48 volts, you only need half the turns that the primary uses. Most of
us don't need to have full output from the transformer so real heavy
wire is not neccessary.

For those experimentors who like to research the details, Here is a
great site that will give you the math to calculate wire sizes.
It has everything you need to know and more.

http://members.tripod.com/~schematics/xform/xformer1.htm

<Hi Jan, Now that I know #12 is AWG I can consult my Zeus for sizes.

<I am now going to show my ignorance of things sparks & smoking.

<Our mains is nominal 230 volts AC, it is really 240 but I am being politically correct. If there is this greater voltage across the primary does the figure of 1 turn per volt change? I would also guess that enamel copper wire is the stuff to use?

<Regards,Terry

If you are using a microwave oven tansformer that has a primary of 240
volts, you can check the turns per volt by winding a temporary coil of
10 turns of light wire on the secondary side, load it with a junkbox
resistor and measure the output with an a/c voltmeter as you power up
the primary for 30 seconds.
It will give you a quick and easy output measurement for a 10 wind
coil. If you get 10 volts a/c out, you will wind it 1 turn for 1
volt. If you get 5 volts output, you must wind 2 rounds per volt.

When you wind your coils, remember that peak voltage to your storage
capacitor will be 1.4 times the RMS measured voltage of the coil. When
you are not running or when the motors are not loaded, the voltage will
approach the 1.4 times measurement.

Enamel wire is best. Household wire is easy to get. You choose. Just
watch that it doesn't overheat. The inside of the transformer will be
hotter than the outside. Monitor it for heat buildup for the first few
hours of use.

My rewind unit heated up as it ran. I place it in a toolbox with a fan
at one end to cool it. The air ran over the output FETs of my drivers,
then ran across the power transformer before exiting. Household wire
worked for me.

I wound my coils in 5 and 10 volts steps. I brought out the wire to a
junction strip where I could series connect the coils to select whatever
voltage I wanted to experiment with at the time. I can test the motors
at low voltage, then as I have the system operating properly, I change
the taps to boost voltage and speed up the motors response.

These transformers also make great battery chargers for boosting car
batteries and replacing lead-acid car batteries for 12 volt appliances
in your recreational vehicle when you are parked on holiday. If you can
find an extension cord in the camp ground, you won't run your car
battery down running your fridge or appliance.

P.S. Integrated circuits run on smoke. If you let the smoke out, they
stop working.

Walter