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Best way to run 400v 3ph motor on 220v

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Jak2g21/06/2022 17:08:25
40 forum posts
12 photos

Hello everyone

I've recently began restoring an exe surface grinder. I had anticipated running the 3ph motor using a VFD; however, on receipt I noted that the motor is single voltage (400/415v) and not as straight forward to swap over to delta so that I can hook it up to a 220v VFD (I think)...

At this stage, I don't really know how well the machine will run once set up and I don't want to drop £500 on a rotary converter or 220 to 400v VFD without first seeing the machine run. Catch 22 situation I suppose. What makes it worse is that I have a single to three phase VFD with an output of 220 volt that I was hoping to use...

Are there any options that I am missing? Here is a photo of the motor badge, and what is inside the wiring box.



Edited By SillyOldDuffer on 21/06/2022 18:33:19

Clive Foster21/06/2022 18:06:10
3173 forum posts
113 photos


For testing purposes simply connect the 440 volt motor to the 220 volt VFD. It will run just fine but power will be reduced to something between 1/2 and 2/3 rds of nominal nameplate output. Basically at 220 volts the motor enters its constant power region at 29 hz rather than 50 hz so it can't get up to full nameplate power.

As a surface grinder is more about free spinning than hard driving the reduced power may do just fine for you.

Inverter Drive Supermarket have a blog post explaining what is going on. Excellent, clear, information as usual from IDS. **LINK**

If you do decide to open up the motor to find the Star point and convert it you will find that NECO make a nice motor with the junction clearly accessible.


peak421/06/2022 18:23:29
1785 forum posts
193 photos

As said above, you can convert the motor from star to delta yourself, or it is possible to get 220V single phase in 380V 3 phase out inverters. Look for AT4, rather than the more common AT1

Alternatively, you could have a word with Newton Tesla, as I've read elsewhere, that if you buy an inverter (package??) from them, they will assist in digging out the star point on your existing motor.


Edited By peak4 on 21/06/2022 18:24:27

AJAX21/06/2022 19:03:15
395 forum posts
42 photos


My Eagle surface grinder came with a 440V motor that was hard wired star configuration. After a test run using a 240V VFD I stripped the motor down and dug out the star point from the windings. I then rewired in Delta configuration. It was a relatively quick and easy job.

I'm not the only one to have done this. Whereabouts are you? Someone may be able to assist.

not done it yet21/06/2022 20:35:40
6888 forum posts
20 photos

A super little surface grinder, if in good condition, but you will need that full motor power to operate sensibly - or use narrow/smaller diameter wneels.🙂

He is somewhere near Leeds. The Eagle motors are an easy conversion - this one may be more finicky.

I was looking for an EXE, when I was watching the market, but they were a little too expensive.

Edited By not done it yet on 21/06/2022 20:36:10

Jak2g15/07/2022 14:10:12
40 forum posts
12 photos

Thank you all for coming back to me. I must admit that I didn't realise any replies had been posted (it usually emails me but not this time!!).

I decided to go for a 220 to 410 VFD. I did try it on my 220 VFD and the motor ran fine, so at least I know the motor should be ok at full speed!


john fletcher 115/07/2022 14:23:23
805 forum posts

A few years ago there was an excellent thread on here, complete with several picture on locating the Star point and bringing out the three extra wire, converting a 3Ph motor from 415 volts Start to 240 Delta. Often a simple job and well worth a read. John

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