7.5HP Three Phase Motor Conversion


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oztules

Guru

Joined: 26/07/2007
Location: Australia
Posts: 1686
Posted: 09:53pm 25 Sep 2008      

Good to see I could help a bit.

I now have a lathe chuck that attracts iron particles from everywhere, and a range of tools to match. The chuck is the killer though, gets particles stuck in the spiral race, and seizes it up.... I blame a certain Dutchman for this.... measure the volts/rpm in the lathe.... don't do it.

Being a four pole may help keep the inductive reactance component at a much higher RPM than with a 12 pole.

Conversely, 12 pole would give you better scope to negate it with capacitors with it's higher frequencies..... why is everything with wind such an inter-related compromise

Sparweb "Okay, four poles isn't a lot, but I've been noticing that the size and weight of these motors goes up rapidly with the pole count. Why is that?"
You have to pack in more wire with more poles. Same turns and current for each, but smaller spans.... this of course means more poles packed closer which then adds to leakage between the poles, so they tend to make the rotor larger in diam physically. I think after 12 poles, the leakage flux and slot harmonics is so great they stop (plus the power factor falls away as well), unless you opt for a much larger rotor.

I wound a 36 pole induction motor.... got hot and some harmonic crawl, but that was all. With 18 pole a much better crawl, but no real running, with 12 I got it to run reliably, but inefficient, with 8 we were away.

.............oztules Edited by oztules 2008-09-27
Village idiot...or... just another hack out of his depth