I have a piece of machinery that does not match my power supply and I do not want the expense of putting in 3-phase. Can I change out the motor to single phase without incurring significant switching/wiring problems/expense?
Responding to Jay’s 23-Nov (11:22) query… yes, a 3-phase motor can be operated with a single-ph supply!
It can be easily done, and at very little expense! Of course you must be aware that size impacts success. Therefore, I suggest you search the Control List archives. There are a number of topics on the conversion procedure!
Another good tactic is to use an unloaded 3 phase motor, fed single phase, as a rotating 3 phase generator. But, as Phil says, size impacts success. If you need 20 HP pay for the 3 phase; you'll be happier in the end. You can look up "phase converter" and start browsing. Or look on eBay and people sell new, fully warrantied, manufactured phase converter units. But if you really want cheap there's a bunch of web sites with how-to instructions.
If you're a controls systems guy, and you happen to have an unused VFD (with the right input voltage) hanging around from a previous job you can just single phase the VFD and let it produce 3 phase for you. You'll have to derate the power considerably, since you aren't really supplying it with the "normal" input power. But all the VFD does is rectify the 3 phase input to the internal DC bus and then produce the variable frequency output from the DC bus. You can get the internal DC bus energized on a single phase just fine. I doubt you could get more than 1.5 HP from a 5 HP VFD, but it will work. And if you need to control frequency then you'll have that capacity, too.
Your original question about whether you can change out the motor I think you're going to have to determine locally. What does it look like it will entail? Does it look like a mess, or not to bad? All a motor does is power the rotating shaft. If you *REALLY* wanted you can hook it up to an old grist mill water wheel, but that's probably *REALLY* a lot of trouble.
From your post, it looks like you already have single phase and have acquired some 3 phase equipment. Going from 3 phase to single phase is certainly possible. In our part of the country, rural Quebec, Canada, the utilites have a limit of 7.5hp for single phase motor applications. Above that you must go to three phase. You can appreciate that the higher power single phase motors constitute a significant inductive load to the grid. The utilites are not fond of large unbalanced loads... does crazy things to the distribution network and gives rise to unstable voltage for everyone in the area. Also the higher power single phase stuff has significantly larger wiring and contactor requirements which could also influence your decision.
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