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05-09-2008, 12:07 AM #1
How do I rewire a 2 speed, 3 phase 440 volt motor?
I have 220 3 phase in my shop. I have a 2 speed 3 phase 440 volt motor (3/4 hp) on a small Hardinge lathe that I would like to use. Can I rewire this motor or is it a 440 volt only? On the name plate it states.......440V...1750 rpm....875 rpm...etc
Can I find a 1750/875 rpm 220v 3 phase motor? I didn't see anything in Graingers either. Your help is appreciated
05-09-2008, 03:26 AM #2
"On the name plate it states.......440V...1750 rpm....875 rpm...etc"
Hardinge lathes almost always have a two-speed 1750/875 rpm six-wire single-voltage motor.
Hardinge mills almost always have a two-speed 1750/875 rpm eighteen-wire dual-voltage motor.
Both are rated the same, as to HP.
A six-wire motor is a "consequent pole" motor, operating with four real poles in 1750 rpm mode and with four real and four "apparent" poles in 875 rpm mode.
The only way to change voltages is to rewind.
About $440 for a 0.75/0.375 HP motor.
Probably cheaper to install a 220:440 transformer.
05-11-2008, 08:37 PM #3
I'm in the same predicament with a DSM lathe. I'm wondering what's the smallest 3 phase 220-440V transformer that can be used in this situation? I've found a 3KVA for $325 which is less than the rewind and simpler to implement since all the other controls and heaters are 440. Does a 1.5KVA even exist in 3 phase?
The frame on the motor is 184 but the shaft size is special.
05-11-2008, 09:46 PM #4
Don't need a three-phase...
You don't need a three-phase in 1.5kva... and you'd probably be alright with 1kva...
lessee... 1kva @ 240v is about 4A... using three single-phase transformers, that's a whole lotta power for a 3/4hp motor...
Take a look at the motor plate and see how many Full Load Amps it draws at 440-480... multiply that by two to get FLA at 240v... and then multiply that to get VoltAmpres...
and then divide that by three to determine how many VA you'll need in each of a trio of single-phase transformers.
One other way to accomplish it, is to get a 440v Variable Freq drive... about 2hp... and feed it with just ONE 240-480v transformer (backwards- line to the 240v side, 480 out the other end, to the VFD) and call it done... much less iron involved, and you get variable-speed, forward-reverse, and dynamic braking to boot!
I've been doing quite a bit of this kind of thing lately... For what it's worth, you should be able to find a good used transformer for under $50, and a 2hp 440 VFD for under $75... check HGR's website for transformers, and E-pay, and any of the drive warehouse places for VFDs. The solution shouldn't cost you over $150.
Last edited by DaveKamp; 05-11-2008 at 09:49 PM. Reason: Adding costs...
05-11-2008, 11:06 PM #5
If you're wedded to this motor than transforming the voltage is your only hope. Single voltage motors have to be operated at their designed voltage +/- 10%. This is easy to do on a motor that small. If he price of a 230/460 volt step-up transformer is out of reach (looked at the used market?) then three 1 KVA control transformers conncected in delta will work as well. The transformers don't even have to match too well and depending on what the wiser heads here have to say you may get by with an open delta two transformer configuration.
I'm a VFD guy so naturally I'd push a VFD at you but you'd still need a transformer.
05-15-2008, 11:01 AM #6
i recently had exactly this problem with a 3 speed 3 phase motor. I was lucky that in the event I got it all working with an auto-transformer converter I had kicking about and all three speeds work without the need for an idler motor which is handy.
I was considering picking the star points out of the windings enable me to re-connect the motor to run from a 240V inverter and got a lot of useful information about how such motors are connected internally here:
Either download the whole manual, which is quite large, or browse to the section on Pole Changing Motors -> Motor windings.
It should be 'do-able' but depends on how careful/confident/persistent you are and how desperate you are to avoid another route.
BTW for the prices quoted earlier in the thread I'd just pay the man the money and get on with it unless 'playing' with the motor has some interest value. Here in GB a decent 240-415V inverter is going to be around GBP350 ie US$700!! so you're getting off pretty lightly.