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Registered Member #2422
Joined: Tue Oct 06 2009, 02:41AM
Location:
Posts: 85
What sort numbers do I need to get a reasonable model of a standard MOT (no shunts) in a simulator?
I've been using the "coupled inductor transformer" with 53.8mh pri, 17.65h sec, k=.99 and a 5 ohm resistor in series with the primary, but this seems to draw unrealistic currents (8A) with an open secondary.
I assume someone has at some point needed to simulate one of these things and still has the data lying around... (thanks in advance btw)
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
I don't have a MOT here to test, but this model seems reasonable. Maybe with smaller coupling. It is a transformer, and this model is the model of a linear transformer. The inductance ratio and values seems to be in the correct range. The primary resistance is too high.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Using your model, what is the wattage of the transformer with the open secondary ?.
If the transformer had 53.8 mHy in series with 5 ohms, the load at 120V60Hz would be 5+j20 ohms;, for all intents just inductive, and it would draw about 6 amps and dissipate 180 watts Cu.
It the secondary is open, it might as well be not there.
Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
8 A input current with no load is not a crazy value -- I have measured over 6 amps in one 120V MOT. (Are you talking about a 120V or 230V MOT?).
But 5 ohms in series with primary is not a realistic way to model the current limiting effect. In service, with more than 12 amperes of primary current, most of the input power would be lost there.
Much more realistic, in a simple linear model, is to set primary and secondary series R's to match the measured DC resistances - probably less than 1 ohm on primary. Then dial down the k factor substantially, to the point where with secondary shorted, primary current is around 30 A and secondary current perhaps 1.5 A. With k much less than unity, you are modeling the deliberate leakage inductance created by the magnetic shunts.
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what is a fairly realistic model for a MOT in SPICE?
