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Author: Subject: Electric Motor Help (3 phase/Single phase)

posted on 10/4/19 at 06:20 PM Reply With Quote
Electric Motor Help (3 phase/Single phase)

Right full disclosure, I'm a clanky and struggle a bit with the sparky, electrical danger side of things.

Long story short I have purchased a new lathe, a Harrison 140 with a 1.1kw 3 phase motor see picture 1.

I need to run it off the available 16 amp supply in my garage and am wondering what my best option is.

Is there a single to 3 phase inverter available so I can use the machine as is?
The second alternative i suppose is to replace the motor with a suitably powerful single phase one. I have a brand new 1.1kw one already left over from an old project. See picture 2

It would appear i need a horribly expensive rotary converter to run a 420 polyphase motor from a 240 single phase supply. So it would seem my best option is to use my single phase motor on hand.

Any advice gratefully received.

I anyone is interested I'll be selling my well tooled Myford ML7 to make way for this lathe either send me a U2U or watch out for the For Sale thread in the next couple of days.

Many Thanks

Liam Mc

[Edited on 10/4/19 by liam.mccaffrey]

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posted on 10/4/19 at 08:36 PM Reply With Quote
Power and speed rating seem to match, so if they are physically similar and can be adapted if not, then yes, it should be a suitable replacement.

Watch out though - how is the 3ph motor controlled? Reversing a single phase motor is different and will require a different arrangement. 3ph just swaps two of the phases over, single phase requires one coil to be reversed, but not the other (IIRC). The manufacturer's data sheet will give you the information you need for each motor.

Are there any other controls and if so is the 3ph supply used for them or are they taken from just one of the phases and neutral or from a transformer?

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posted on 10/4/19 at 08:53 PM Reply With Quote
That's really helpful. I've been studying this tonight and had sort of come to a similar conclusion. The lathe has a big mechanical 4 position off/run/off/reverse lever which would appear to be connected to some sort of reverse swithh. Unfortunately I can not inspect this yet as I am not taking delivery until Tuesday.

As the primary drive is the only electrical control I will probably bypass it all with an external single phase reversing switch until I can work out how or even if I can use the lathe mounted lever

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posted on 10/4/19 at 09:05 PM Reply With Quote
I have lived through this... You might change to single phase for a stop gap but...Single phase motors are horrible on a lathe. The difference is best explained by comparing a harley engine with a straight 6. That shows up in your surface finish. For the same reasons as you I had a single phase on my Harrison but reverted to a three phase in delta with an inverter. You will gain a soft start and simple reversing if that is your bag... Inverters are now cheap as chips (well posh french fries).

Your alternative is a 415v inverter - they are not.....toooooo.....expensive...ok well a bit

A further alternative is to locate the star point on your existing motor and convert to delta and hence 240v - google it, it is not that bad a job

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mark chandler

posted on 10/4/19 at 10:43 PM Reply With Quote
I had a similar dilemma on a couple of three phase tools.

Huge donkey saw, had a 3hp motor, I made up the third phase with just capacitors, had a starting switch so put in more to get the thing fired up then backed down the far ads until it ran smoothly - it worked perfectly well.

Meadings bench drill, 1/3hp this just has 1 capacitor, it takes a little time to speed up - is a bit down on power works well.

Milling machine, 1hp motor, ran this with a single to three phase converter - it was down on power this was an old fashioned box basic circuit and some coils.

Car lift, could not even get the 3hp motor on this to work with any power, I now have a 5hp single phase motor to run this, took a bit of thought to wire up

Harrison L5 came with a 3hp Clarke motor like your new one, it works very well, purchased a simple switch to reverse - cannot comment on finish as this is all its had in my hands.

I did try making a static 3 phase convertor with an old slave motor, gave up on that pretty quickly.

Bottom line, stick on the single phase if easy, as the harrison has a clutch you could get away with just capacitors I recon and see how that goes, just keep adding until it runs smoothly under load.

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posted on 10/4/19 at 10:55 PM Reply With Quote
Just going through a similar process.

I'm converting a Denford Viceroy lathe from single phase to 3 phase

Just bought one of these from Ebay LINK

For a 1.5kw motor.

It does need a Delta motor (230V)

If you look at the motor connections and there are 6 terminals, with on side of three shorted, then you may be able to re link it to 230V

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posted on 11/4/19 at 07:06 AM Reply With Quote

I fitted an inverter, much easier and "free" reversing and speed control too.

mechanically means that no other changes are required,

to paraphrase a meerkat "simples"


Fisher Fury was 2000 Zetec - now a 1600 (it Lives again and goes zoom)

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posted on 11/4/19 at 06:47 PM Reply With Quote
Thank you everyone for their suggestions. I have decided ro remove the original motor and replace with a slightly more powerful 3 phase motor and inverter sourced from the electric motorman.

Extremely helpful chap.

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