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Re: MOT Primary Current Question



Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,

Mot's have very poor saturation characteristics. At say 120VAC in, they will draw substantial open load current. 10 amps seems high, but not surprising. If you graph the current vs. input voltage you can see where it saturates the core.

I guess this is fine for its real use in the oven. Or they are trying to save weight and cost so they cut it right to the edge. But your MOTs are typical.

Cheers,

        Terry


At 08:52 PM 6/11/2006, you wrote:
I measured the primary current of a small 120 VAC MOT.  To my surprise the
primary current was 10 Amps with the secondary open!  The MOT is about 4" x 3"
x 3" and came from a 1000 Watt oven.  Is the MOT bad, or do these transformers
just have a low primary inductance?  The primary wire is aluminum and the
secondary voltage was measured by me at about 1800 Volts.  Also, I also
measured a much larger transformer from (I think) an older oven with a copper
primary and it drew 6 Amps.  The small transformer was very beat up and it is
possible that there is a short in the primary.  If you guys out there think
that the primary must be shorted then I will rewind it, but if the transformer
is acting normally then rewinding it will not reduce the current.