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Electric Motor Conversion European - USA

Convert Myford ML7 to USA

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Jeroen V22/07/2018 06:06:03
1 forum posts

I moved from Europe to the USA a while ago and I took my Myford ML7 Lathe with me. This machine has a Brook Crompten (KP7575) 3/4 Hp motor on it which worked perfectly fine on the European 240 Volt / 60 Hz AC network. I plugged it in the American 110 Volt / 50 Hz outlet and it will work although it makes weird speed variation intervals and clicks every couple of seconds during these intervals. I think that is caused by the electromagnetic relay in the reversing switch which is bouncing on the lower voltage.
Anyway, besides those intervals it has absolutely not enough power to be be considered usable so I have to find a more powerful source.
So, I thought to use the 220 Volt outlet in my garage knowing that this is actually a 2 x 110 Volt outlet without a neutral line. Nothing happened at all, most likely because the electromagnetic relay in the reversing switch doesn't work without that neutral line.

Although I haven't tried them I read about the options available to use a Voltage convertor or just change the whole electric motor. Does anyone has any suggestions how to convert my machine to this 220 Volt outlet without exchanging the motor or using a step-up convertor? And are there people out there who have experience with step-up convertors on 3/4 electric motors?

not done it yet22/07/2018 08:29:01
1959 forum posts
11 photos

I would think the speed variation and clicking is caused by the start windings continually being switched in and out by the centrifugal (centripeta?) switch on the motor shaft. The motor is not getting to sufficient speed for the main windings to accelerate the motor shaft to normal running speed.

Motor should work if the 220V supply is connected properly, but not sure about that, or how. Motor speed will be rather higher due to the supply frequency (and different value of start capacitor may be needed?).

Step up transformers are little different than the step down ones used on buiding sites in the UK, I would suggest.

Hopper22/07/2018 08:51:50
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2798 forum posts
44 photos

You're in America. You should be able to get a half or 3/4-horsepower 110volt motor cheap enough before you blow yourself up experimenting with fatal voltages. If it's like everything else in the USofA, there should be plenty of good condition used stuff around to choose from if you can't afford new. I lived off of the locals' cast-offs when I lived there for some years.

I don't know how long you've been there but if you explore around a bit I'm sure you will be as gobsmacked as I was at the sheer volume of "stuff" lying around available for next to nothing.

Edited By Hopper on 22/07/2018 08:54:12

richardandtracy22/07/2018 08:56:54
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938 forum posts
10 photos

I think you'll find the 220V outlet is a delta connected 3 phase outlet with 110V between phases - in the same way we have 415V three phase and 220/240V between phases in Europe/UK.

What can you do about it? Well, I'd be tempted to replace the motor with a US 3/4hp motor, keeping the old one available for a move back to Europe if there's the slightest chance it'll happen, or discard it if the move won't happen. It's unlikely it'd be worth selling the motor - postage costs would be prohibitive. If you have a motor re-winder locally it may be a viable alternative to buying a US motor.

Regards

Richard.

John Haine22/07/2018 10:43:23
1986 forum posts
112 photos

Er, in the UK we have 230 V nominal neutral-to-phase voltage, or ~400 V phase to phase. Nominal voltage in the US is actually 120 V phase-to-neutral (according to Wikipedia), which gives 208 V nominal phase-to-phase.

I would have thought the lathe starter should not be able to tell the difference between a "real" neutral and a phase connection on your 220 V nominal supply. If there is an earth leakage breaker on that supply it may be showing up an earth fault in your machine that might not cause a problem in the UK because the neutral voltage is normally very close to earth volts.

I can understand that the motor wouldn't run on "110 V" - the volts are only half or less what it's expecting.

Undoubtedly the best approach is to buy a 3/4 HP 110 V 60 Hz motor and replace the existing motor with that. As mentioned by Hopper it might be quite cheap if you can find a used one. You could even get a 3 phase version and fit a US spec VFD, though that probably wouldn't be usable if you move back.

Michael Gilligan22/07/2018 10:44:06
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11457 forum posts
492 photos

Jeroen,

I have no practical experience of U.S. mains socketry:

The principles seem simple enough, but the practice seems designed to confuse !

The 220/240Volt outlets come in 3pin or 4pin versions and are wired a little differently.

This **LINK** appears to cover things reasonably well.

http://www.applianceaid.com/electrical-testing-tips.php

From what I can see; your motor [wired appropriately] should be useable.

MichaelG.

.

Edit: Quoting from the opening post ... "So, I thought to use the 220 Volt outlet in my garage knowing that this is actually a 2 x 110 Volt outlet without a neutral line. Nothing happened at all, most likely because the electromagnetic relay in the reversing switch doesn't work without that neutral line."

Edited By Michael Gilligan on 22/07/2018 10:46:54

Ian S C22/07/2018 11:39:34
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6909 forum posts
224 photos

 They wire in split phase 220 V, and use that for domestic stoves, hot water cylinders, clothes dryers and other things that use over 1500W, and split the out put for the rest of the house at 110V. By shuffeling the phases around down the street they try to get somewhere near a balance. You should be able to wire things up for your motor, but best to ask around. the Americans don't like our high voltage stuff, although I don't think a shock from 110V would be much less fatal than 230V.

Ian S C

Edited By Ian S C on 22/07/2018 12:15:20

larry phelan 122/07/2018 11:53:26
171 forum posts

Have never lived over there,but I would seem that the simplest answer would be to replace the motor.

Motors are not that dear,despite what people say,and it gets you up and running straight away,with no messing. Also,I bet there are loads of second hand motors that size to be had for half nothing over there. Ask around.

Ian S C22/07/2018 12:34:58
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6909 forum posts
224 photos

There is a colour code that may help, black and red are live, and white is neutral. If you have the "Popular Mechanics do it yourself encyclopedia", go to vol 5 page 885, and that will give a simple run down on US domestic wiring.

Ian S C

Muzzer22/07/2018 12:43:59
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2792 forum posts
441 photos

I don't know what the problem was in your case but every US / Canadian house has 120-0-120V supply so that high loads such as cookers and heaters can be sensibly operated. You don't get 3-phase in domestic installations there any more than we do here. So it's 240V, not 208V.

When I moved to Canada, obviously I took all of my UK workshop equipment and simply wired a multi-way extension lead into the consumer unit in exactly the same way as you would a tumble drier or cooker there. Everything worked fine, as you'd expect. Technically the motors spun about 20% faster (60Hz vs 50Hz) but that worked for me(!). The welders etc also didn't need any adjustment. Really nothing clever required and certainly no need to over think it.

You will find that any US / Canadian kitchen wired up in the last 15 years or so has so-called "split receptacles" whereby each of the twin outlets are actually connected to opposite phases, so in fact you can find 240V between the correct pair of wires. That's so you can run a kettle and toaster (for instance) simultaneously without tripping the 15A MCB. You can replace such a split receptacle with a US / Canadian 250V receptacle (different pin-out but same size plate) which will enable you to run a "proper" 3kW UK kettle - the US ones are feeble, being limited to 1.2kW. Then you don't lose the will to live, waiting for the damned thing to boil. When you next visit the UK, make certain to come back with a couple of 3kW kettles.

So have another go. You don't need the neutral connection - connect the motor L & N between the 2 opposite phases.

Murray

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