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Single phase verses 3 phase motor

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Philip Slater09/02/2019 16:49:21
12 forum posts

Hi all

Not sure if this is a good place to direct this question or not but here goes.

I'm fairly new to model engineering and am in the process of building up a Tom Senior M1 milling machine to which I've grafted a Rambaudi vertical head. I now need to fit a motor to the vertical head and was looking at fitting a 1 1/2 HP type. I was going to go for a 3 phase motor with a VFD but it occured to me I could make the job a bit cheaper and fit a single phase motor.

Does anybody have any thoughts on this? I would think the 3 phase motor would be smoother running and I like the idea of a soft start but I can save the cost of a VFD if I go single phase.

Gary Wooding09/02/2019 17:01:14
545 forum posts
127 photos

I fitted VFDs to my Centec - smooth start and variable speed is far better than 1-phase.

Brian Oldford09/02/2019 17:17:30
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530 forum posts
4 photos

IMHO good solid 3 phase motors of that capacity can often be picked up S/U for a song. With all the advantages of Soft Start, Infinitely Variable Speed and even Over-speed a VFD is a no-brainer.

I have them fitted to both my mill and lathe and wouldn't go back to single phase machines.

duncan webster09/02/2019 17:53:35
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2109 forum posts
27 photos

Wouldn't go back to single phase for all the tea in China. 1.5 HP single phase is going to be quite a lump as well, as Brian says you'll get S/H 3 phase if you search. Try Gavin Oseman who sometimes advertises on **LINK**. Never dealt with him but I know a man who has.

Pete White09/02/2019 18:23:29
52 forum posts
6 photos

Double post, instead of edit, as below.smileyangry

Edited By Pete White on 09/02/2019 18:27:47

Pete White09/02/2019 18:26:22
52 forum posts
6 photos

I am lucky to have 3 phase in the workshop, never used a VDF, but do you need to ensure your motor is a six ends out so that you can make sure the voltage is correct, or already suitably wired?

There was single phase motor on my wood lathe when I bought it., it was hopeless with all the stopping and starting leading to over heating. Sorted by fitting a readily available cheap three phase option. Maybe the motor had a problem but convinced me that single phase is not for me.

Pete

Mike Poole09/02/2019 18:40:13
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1965 forum posts
46 photos

I would not hesitate to go with the three phase solution. Three phase motors do run more smoothly and the flexibility of the variable speed is sure to be found useful, in my opinion running a VFD at the extremes of its range is to be avoided as this compromises motor performance but it will still save a lot of belt changes and it is easy to find the best speed for the cutter and material being used. Even if I had a three phase supply I would still like a VFD as it enhances the usability of a machine.

Mike

Philip Slater09/02/2019 19:14:32
12 forum posts

Preety conclusive then!! I hadn't thought of running the VFD beyond 50hz but as suggested you would have to be a bit careful doing this. VFD and 3 phase motor here I come then.

Thanks for the rapid respones

Brian Oldford09/02/2019 21:26:07
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530 forum posts
4 photos
Posted by Pete White on 09/02/2019 18:26:22:

I am lucky to have 3 phase in the workshop, never used a VDF, but do you need to ensure your motor is a six ends out so that you can make sure the voltage is correct, or already suitably wired?

There was single phase motor on my wood lathe when I bought it., it was hopeless with all the stopping and starting leading to over heating. Sorted by fitting a readily available cheap three phase option. Maybe the motor had a problem but convinced me that single phase is not for me.

Pete

Actually Pete, so long as the stator windings aren't epoxy potted, on a three post machine (415v only), if you're not afraid of a bit of motor open heart surgery, you can almost always get to the star point and open it up. Carefully noting the phase relationship you can rewire it to delta and they'll invariably run beautifully. Getting the phase relationship is crucial (don't ask!).

Hollowpoint09/02/2019 21:43:36
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187 forum posts
27 photos

Looks like you have already made your mind up but here's another vote for 3 phase. I converted my boxford a while back and it runs so much better now! yes

Pete White10/02/2019 10:25:57
52 forum posts
6 photos
Posted by Brian Oldford on 09/02/2019 21:26:07:

Actually Pete, so long as the stator windings aren't epoxy potted, on a three post machine (415v only), if you're not afraid of a bit of motor open heart surgery, you can almost always get to the star point and open it up. Carefully noting the phase relationship you can rewire it to delta and they'll invariably run beautifully. Getting the phase relationship is crucial (don't ask!).

Thanks for that Brian, I have never stripped a motor but thought the star point would be like looking for hens teeth. I might have have a go. I am not afraid, I used to run motors and a mig welder, form an oil cooled welder and very big capacitors capacitors years ago. I think I am to afraid these days to do that again. lol

Pere

.

Sandgrounder10/02/2019 11:36:39
161 forum posts
2 photos
Posted by Brian Oldford on 09/02/2019 17:17:30:

IMHO good solid 3 phase motors of that capacity can often be picked up S/U for a song. With all the advantages of Soft Start, Infinitely Variable Speed and even Over-speed a VFD is a no-brainer.

I have them fitted to both my mill and lathe and wouldn't go back to single phase machines.

The same here, also fitted one to my Meddings Pillar drill which makes things so much easier when countersinking a hole after drilling, I don't have unscrew the pulley guard, loosen the motor, move the belt, c'sink the hole, loosen the moter, move the belt, lever it back to tension the belt and replace the guard.

Ian McVickers10/02/2019 16:06:42
122 forum posts
69 photos

Yes vfd and 3 phase motor all the way. Some wiring and a few buttons and switches and you can choose from fwd/rev. High/mid/low speed or fit a pot and vary the speed to your hearts content.

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