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| Rewiring old 3 phase motor for low voltage |
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| NickG:
Useful thread this, I thought you needed the motors that were 220/440v to run from an inverter, does this mean you should potentially be able to re-wire any 3 phase motor in delta? Cheers Nick |
| BillTodd:
--- Quote from: NickG on October 27, 2012, 06:31:53 AM ---Useful thread this, I thought you needed the motors that were 220/440v to run from an inverter, does this mean you should potentially be able to re-wire any 3 phase motor in delta? Cheers Nick --- End quote --- Potentially yes, but the problem with rewiring, is that it is not always possible to find the star point without risking the destruction of the motor wiring; I had a go at finding the star point on my HLV-H speed control motor, a small 1/8 hp device. The windings were so tightly bound and bonded with epoxy it would have simply broken the copper wire if I had tried to pull it apart. In the end I choose to drive it in star mode at 415vac from the main motor's VFD In the case of my Hardinge 2 speed (dual windings) main motor, the rewiring would have been so complicated by extra wire, that it just isn't worth it; Stepping up the 240 mains to 415 with a transformer and using a high voltage (=cheaper on ebay) VFD was easier and meant I didn't need to touch the, awkward to get at , motor at all (nor did I need to disturb the motor's 0.0003" balance!) . Stepping up the mains voltage and using a high voltage VFD is easy :) Bill |
| awemawson:
There are another couple of issues with running 'non-inverter designed' motors on an inverter. The fast rise time of the chopped square waves can lead to insulation break down in the wires due to the high frequency component of the waveform, and also the cooling fan will really only be intended to shift enough air at standard rpm. In practice I've never had problems with the voltage break down, but the cooling at lower revs is definately to be watched. |
| loply:
Oddly, this particular motor doesn't have a cooling fan of any kind, which I found odd. It does have several kilos of metal enclosure though, perhaps they expect it to simply conduct away. |
| NickG:
Thanks guys, I thought the cheap type inverters wouldn't do the high voltage and you needed a proper phase converter to use them ... it has been a while since I looked, was looking into it when I bought my harrison lathe, but because it wasn't a dual voltage motor I thought I could either pay the high cost of a phase converter or swap for a single phase motor - so I put a single phase on. Still got the big 3 phase, looks a good quality motor! |
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