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Registered Member #223
Joined: Mon Feb 20 2006, 06:42PM
Location: Ottawa, Ontario, Canada
Posts: 125
Well I never really much liked 'calculations'. I'm more of a Edisen guy just try different things untill it works. From what I know unmodified mots when shorted will draw 20-30A on 120VAC(limited by there internal shunts).. So the maximum avalible current would be 20-30A. Just put an AC ammeter in series with the shorted mot or use and amp clamp to messure the MAX current.. Of coarse the current actually drawn will be less than this when the mot ballast is connected to a load.
I think there are some fancy formulas that can do this but you would need to know the primaries reactance at 60Hz. an inductor can be use in a freqency dependant voltage divider. see here , This should help you find the reactance of the primary at 60Hz. Now I think you can get away with just plugging the reactance into ohms law I=V/R.
Registered Member #227
Joined: Mon Feb 20 2006, 10:47PM
Location: Cambridge Ontario, Canada!!
Posts: 127
damn, I was reading about that last night(all the formulas) and today all my book have been moved 45 minutes away, I'm so lost without my books. check out google, they where very short formulas, or You could do it hands on and shove in a good AC ammeter in there. I have a 5 amp ballast for mine now, It pulls more than 5 amps from the mains but I dont worry too much.
Registered Member #157
Joined: Sun Feb 12 2006, 08:00PM
Location:
Posts: 76
Well rather than using dan's aaproach. what can i expect to get for a current draw while using a MOT as a ballast? What have you all gotten on averge for current draw while using a MOT as a ballast?
Registered Member #79
Joined: Thu Feb 09 2006, 11:35AM
Location: Arkansas
Posts: 673
Average is not an easy thing to come up with. It varies widely on the size of the stack and the MOT ballast. All the ballasts I have have a different value.
Just measure the impedance. That's real easy. Just hook a low voltage (5-12V) AC across it and measure current draw.
Then V=IR,
12=Current*impedance
Now you know your impedance, just work it back in:
120V=Current* impedance
That will give you the maximum current allowance for the ballast.
5 min, and you'll have your answer. You can even figure out the inductance, but I don't remember the formula. 'Cause now I got a meter.
You'll actually not draw as much current as you'll calculate because the MOT's in the stack will be self ballasting somewhat.
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MOT Ballast
