Just mulling over the next project (wind generator if you must know!) I
need to find the field winding CORE (the steel, not the copper!) that
surrounds the armature. The thought is to buy a suitable scrap motor,
cut the copper out, (sell it!!), cut the field core apart and rewind to
my specs. I really only need about an inch of core but roughly 12"
inside diameter and 24 to 32 poles.
So the questions: what size motor do I need to look for that uses a 12
inche diameter rotor? How many poles will I find on same?
I think 25 hp is a reasonable minimum. A really old fashioned motor (the
kind it would be a pity to strip) might have a 12" rotor in a 25 hp
machine. My 2.5 hp Laurence Scott motor from 1931 has a 7" rotor if I
remember correctly. Modern TEFC motors tend to have smaller rotors
working at a higher flux density. I've seen four pole 50 hp motors with
rotors smaller than 12". Lower speed motors also tend to have larger
rotors for the same horsepower rating to provide the additional torque.