Electronics > Beginners

Microwave transformer reversed?

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chiken:
Hello, does anyone know what could be microwave's transformer secondary coil inductance, to measure impedance?So if transformer is connected reversely (secondary coil to mains 240V (resistance in ohms is 200, dont have meter for inductance nor impedance) ), what could be output at "primary", i connected it and voltage is 24V, but im interested how many amps (or better VA)

Ian.M:
The answer to the VA question is not a lot!   Its got a 10:1 ratio and you shouldn't exceed the original secondary current when using it as the primary.  Assuming its out of a nominally 800W oven at 80% efficiency, the secondary must have been about 415mA RMS @2.4KV, so its only good for at most 100VA which is 4.15A @24V intermittent duty cycle (e.g. 1/2 hour on 1 hour off). , with fan cooling!  For other oven power ratings, scale proportionally.

chiken:
If thats true, that is EXACTLY what i need, max 3AMPS @ 24V,
but, why would it heat so much with misserable amperage as that?

Cliff Matthews:
I've never hooked one up in reverse, but the shunts should be removed before connecting it to a 6-ohm load. As I understand it, shunts pre-load (regulate?) so the HV is stable. Judging on core weight, one might expect to get 200VA* without high temps.

*edit - Well, I was wrong. I just tested a 700 watt MOT with a "114 ohm primary". I had to turn my Variac to 140v to get 2.7 amps through a 100 watt  1 ohm resistor (it was 7v unloaded..) even shorted, I could only measure 6 amps.

Summary: These HV windings have potential and nothing more..

chiken:
ehmmm,
So you connected 120V to 100-Ohm "primary" @ 60Hz
maybe with 240V on 200-Ohm @ 50Hz would provide a bit more current, since lower frequency, lower impedance..
I guess ill need to wait a bit more and try it directly
But if i get a bit more than 3A then i dont even need fuses  :-DD :palm:

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