oldswamm said:You don't have to go into detail here, just post a link that will explain WHY a motor won't work unless all the windings of any phase are in series. It's been over 30 years since I studied motor theory, and I honestly don't understand why the windings can't be paralleled. I always just assumed it was because they didn't want to make 2 splices for every winding, which you have to admit would make motor assembly WAY more difficult.
Seems like it should work to me as long as all the parallel sections are equal. You might have a little tendency for unequal current if the resistances aren't matched exactly, but that would tend to equalize with resistive heating. It would be much easier than tapping each pole winding, that's for sure.
Triacs have a quite a bit of voltage drop and would need very large heat sinks to run 100A, for example.
FETs could do better, but you'd need a swarm of them and driving the gates would be challenging.
I think relays or a mechanical switch are the only practical ways to switch the windings at higher power levels.