davycrocket,
Thanks for the detailed explanation. I think our motors here in the states differ from yours, though, in that the TYPICAL three phase dual voltage motor is a nine lead motor and your approach demands a twelve lead motor. Here our nine lead motors are wye connected with one set of three windings permanently connected at the center to form the initial wye. I suppose you could dig around in there and find the connection, unsolder it and bring the leads out, but this is NOT a simple reconnection, where nicely numbered leads are mated with wire nuts.
I'm still not sure where the odd voltage of 414 comes from. I'm familiar with 110, 120, 208, 220, 240, 440 and 480. Looking at this now, I suppose I might have just answered my own question. 480 is 2x 240. 440 is 2x 220. I guess that makes 415 an approximation of 208x2. I'm not sure what I'd do with 415 volts, though, since the motors want 480 to run properly and 414 isn't even close to 10% under.
I watched the video and was unimpressed that the guy is using a VFD in conjunction with the Frankenmotor. Now, if I could use this basic setup with a few capacitors and minor additions to run a three phase 480 motor just like I'd run 240 or 208 motors with a plain RPC (bodge-style as Clive might say) then I'd be impressed enough to give it a try. But if I've got to mess around with a spaghetti-wired motor AND a VFD, sorry, I'll just get a single phase 240/480 transformer of appropriate KVA and use that to single-phase a derated VFD and be done with it. As has been pointed out on PM before, 480V VFD's are comparatively inexpensive and plentiful. Transformers, too, can be found at reasonable prices, making for a dependable and simple converter.
Looks like I've got some more curiosity satisfying to do. I am not ready to accept that what Clive refers to as a UK/Euro rotary phase converter, based on a delta-connected motor, is any more capable of producing clean and balanced three phase power than our wye-connected bodger. I'm not arguing that this is NOT a better converter, I am merely saying I need convincing.
One thing's for sure, the bodgers are not as bad as Clive makes out, and I'm sure many PM membrs can attest to this, having used home-brew converters successfully for many years without allowing any smoke to escape. If it can be shown conclusively that the delta converter is superior to the bodger (I like that word) I will consider hacking into a hapless victim motor to bring out the remaining three leads to make a super converter.
To some extent, though, this series of posts has satisfied me in one regard. Now if I describe the Frankenmotor setup to someone and they say I am an idiot and that such a scheme could never work, I can prove them wrong, on a demonstration level if not a practical one.
Thanks all for the interesting and stimulating conversation.
Steve