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Re: [TCML] MOT stacks

On 12/25/11 8:30 PM, jhowson4@xxxxxxxxxxx wrote:
Hello all and Merry Christmas,

How necessary is it that MOTs be of exactly the same type when stacking them in a MOT stack. I am planning on putting 2 in series and 2 series pairs in parallel. Or 3 in series and 2 sets of 3 in parallel. I have plenty of mots, but they are a hodge podge mess of them, only 2 of which are exactly the same. Should I just ball park it and try to make each mot somewhat symmetric to each of its paralleled counterparts?

Have you got a way to measure the output voltage?

(preferably under load?)

You don't want to be hooking up a 2kV transformer to a 3kV transformer. However, these things have a fair amount of leakage inductance, so often, you can parallel two with somewhat different unloaded voltages without disaster.

The other thing to think about is whether you could do some sort of buck/boost on the primary side to equalize the output voltages. In general, since MOTs are pretty ragged edge in terms of core cross section and saturation, you'd want to reduce the voltage of the higher voltage transformer, rather than increase the voltage of the lower one.

These things have integer number of turns on the windings... maybe you could add windings to the primary side (Remove the filament winding to make room?) or remove some turns from the secondary side?

I don't know how hard it is for you to get more MOTs, but it might be easier to just get a huge pile and pick and choose to find good pairs.

Or, use it as an educational exercise.. Measure the transformer performances and use a modeling tool to figure out which ones to mate up.

Measuring all the transformer parameters can be done with a voltmeter, ammeter, a variable voltage source (variac) and a suitable resistor.
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