Re: MOT Primary Current Question

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Christoph Bohr" <cb@xxxxxxxxxxxxxxx>

Hello Justin.

> Experience and my gut tell me that an open secondary will draw very
> little real current on the primary side.
this is usually true, though weak transformer design can in some cases
mess things up, saturation at higher voltages etc.

> *why* that's true because from one POV that primary should be a low
> resistance short circuit and current should be through the roof!
This would only apply to the DC resistance of the coil and with DC current
flowing through it. The resistance to 60Hz AC is comparatively high,
gained through the mass of metal inside the coil.

> Is it the impedence of the coil + core that keeps things from going
> bananas?
it is, its basicaly all about using the current to move the iron "particles"
and using these in turn to induce current in the secondary.

>My gut also tells me that if I simply make a coil out of wire
> and stick it in my wall outlet the current would definitely be there.
Hm, that could be a real "hands on" experienceto better not try ;-)
But it depends on the coil. If you just wind up wire, you will need
a pretty big coil. However, if you have an laminated iron core,
you will end up with a coil, that looks dramaticaly like a transformer,
cause it is one. If you have an old MOT you can play with, you
can try this:
Connect it to a variac and mesure currents with open load, load
and / or short curcuit carefully.
Open the welds of the transformer and remove the I-part of the core,
repeat above mesurements.
Maybe even remove the primary and measure again, currents will
be high with only the coil, take care when you crank the voltage up.
The key value is the inductance of the coil, which rises with the
iron core.

regards
Christoph Bohr