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Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
hey,
yesterday i removed the secondary, the filament wires, and the magnetic shunts etc. from my MOT, and today i did a test my winding a secodary, and everything seemed fine, till i realised, that, at 60v input (using variac) the current drawn when the transformer is idling, is 0.15A and at 120v, it is 0.3A, but after about 200v, the current rises dramatically, and at 240v in, it is drawing 5A!, and the core, and primary are heating up, although not *too* much, i tried grounding the core, it didnt help :S
maybe there is an arc, or insulation breakdown? :(
there is a twist though, when i measured the power with my power meter, it read 177 watts, at 5A, 240V maybe something irrelevant to do with power factor?
Registered Member #3781
Joined: Sat Mar 26 2011, 02:25AM
Location:
Posts: 701
Your MOT is getting saturated, the more voltage you put into it, the faster it will saturate and the more amps it will waste as heat energy. Try using a ballast
Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
Camp Badger wrote ...
Your MOT is getting saturated, the more voltage you put into it, the faster it will saturate and the more amps it will waste as heat energy. Try using a ballast
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
The problem with MOTs is that they use huge flux density, and are already beyond saturation at "rated" voltage. Removing the shunts makes this even worse. Try winding around 20% more turns, or use a series step-down transformer (a "buck transformer").
Registered Member #2727
Joined: Tue Mar 09 2010, 02:39PM
Location: Montevideo - Uruguay
Posts: 33
Do not worry about the transformer, which has no any short circuit. The quick explanation for this phenomenon is: these transformers were made to cost little money and be used in intermittent conditions and full power. Too much flux density. Furthermore, as the transformer is at no load condition in your test, I would not rely much on reading the power or ampere meters if they aren't true RMS meters, because the current harmonic content is enormous.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Actually, every time I've measured an MOT I meter a no load (magnetizing) current of 5 amps or so. 60hz transformers are crap like that, and that's why we use switch mode supplies now.
Registered Member #3925
Joined: Fri Jun 03 2011, 10:50AM
Location:
Posts: 121
Grenadier wrote ...
Actually, every time I've measured an MOT I meter a no load (magnetizing) current of 5 amps or so. 60hz transformers are crap like that, and that's why we use switch mode supplies now.
ahh right, of course P=VI, doesnt apply here, cuz although in theory it should be using over 1kw, it is only using 180w! so it aint as bad as i thought lol i have wound about 6 meters of mains cable on the transformer (20cm per turn, if the wire could cling to the laminations perfectly) and i am getting about 24v, so now i must squeeze another 3 meters of wire in to this critter :D i am winding it, with taps, so it will supply 12, 24 or 36v to my zvs driver, (dont wanna wear out the fbt unneccessarily)
i have this image in my head of it all being in a nice wooden box with knobs and buttons on it, but itll probs end up, as always, in a tangled heap of wires hahaha
btw has anyone tried discharging a hv cap through a piece of nichrome wire? it gives a nice effect, if the voltage is high enough to melt the wire, it breaks into hundreds of glowing balls of metal. lol.
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microwave oven transformer buzzing loudly
