Neon John wrote:
see originsl post

It's popular to use several MOTs to build an arc welder. This works quite
well specifically because these transformers are constant-current devices -
exactly the characteristic stick welding needs. If they were conventional
transformers, the first time the rod touched the work and shorted the
secondary, fault current would flow and the breaker would trip or blue smoke
would leak out.

Along similar lines, one can cut off the high voltage secondary and replace it
with a suitable number of turns of heavy wire, connect a bridge rectifier and
have a nice constant current battery charger. Select the turns carefully and
it'll do the bulk/absorption stages of the smart 3 stage charging algorithm.

Another use for defunct MOT's, even those with a bad HV winding, is
using two as a line isolation transformer. Just remove the HV winding,
and connect the two magnetron heater windings together. The normal line
winding on the second transformer then supplies your workbench with
power isolated from the line. (You might need to modify the "shunt" core.)

With a Variac on the input, this is a handy for working on line operated
devices that might have a line-to-chassis defect.

--
Virg Wall