I need 3 VDC filtered about 50 amps.

[gary350]

Mot's have 2 spacers between the pri and sec, usually a few plates of silicon steel about 30 x 15mm wrapped in tape, also the e's and i's are all aligned, this is done deliberately to increase leakage flux.

Magnetrons are dangerous powered and unpowered, the liquid stuff in your eyes will boil in less than a second with a blast of rf from a magnetron, and the pink ceramic insulators are loaded with beryllium which isnt very friendly.

Your correct with the universal transformer equation, used it many times, and some transformers have a thermal fuse, however I fail to see any relevance in your other comments.

All the MOTs I have taken apart (about 15) have EI laminations like all other transformers with no shunts. Shunts are for current limiting like 15k 30ma neon transformers. If you cut the high voltage coil off a MOT with a hacksaw 10 turns of #1 wire is good for 12v 120a. The MOT EI laminations are sized smaller than most transformers a 1400 watt transformer is close to being maxed out at 1400 watts. The MOT small EI core is the current limiting factor. If you wrap a copper U shape strap around the EI core of the MOT volt meter reads 120v 11.66a on the primary winding, .8v on the U shape copper, amps should be about 1750 amps. Some transformers do have shunts but I never saw any in MOTs. The factory that builds MOTs weld the EI laminations together I can cut them apart in the milling machine but for only a few turns of wire on the secondary no need to take the laminations apart. Sometimes I wind good primary coils to make better transformers I built one that is 120v primary 48v with CT secondary the new primary has 200 turns of wire I got rid of the original factory primary coil. No shunts to be found in that MOT either. Has anyone on this Forum actually seen shunts in a MOT ? I like to use the 1400 and 1200 watt MOTs I have some that are 900w but never taken one of them apart. If I build a lower power transformer I use fewer EI laminations to get the watt rating in need it makes a much lighter weight transformer not to use 75% of the laminations for a 300 watt transformer.

 

[Mosaic]

As I recall I have seen shunts in 2 of the 3 MOTS I have cut open. In order to reduce the xformer heating (unloaded) I added extra primary turns. If you don't expect the xformer to run unloaded you don't need to do anything except wind the secondary for the voltage/current you want or have a muffin fan on it.

 

[dr pepper]

The current limiting factor of a transformer is largely governed by magnetic shunts if fitted, the coupling constant and winding resistance.
In an ac transformer the core is largely concerned with voltage not so much current, the critical parameter being dv/dt.