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Electric Motor Conversion European - USA

dodulation

Mar 25, 2017
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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 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?
 

Bluejets

Oct 5, 2014
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You will be lucky if you have not damaged the motor running on low voltage. The clicking sound would have been the centrifugal switch which is designed to operate at the correct speed and turn off the start winding.
As it stands like I said you' ve more than likely burnt the start winding and insulation to boot.
Best option would be just get a motor suitable for the supply as converters etc will cost big bucks.
Good choice of lathe by the way... I have just finished restoring an ML7 from the early 50's ( by serial no.) and my other ML10 has done a great job for the last 30 years now.
 

kellys_eye

Jun 25, 2010
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Get hold of a UK site transformer - the big yellow 'bricks' used to use 110V power tools on a 240V supply.

Used in reverse - perfectly acceptable - it will provide up to 3kW of power and no issues.
 

Minder

Apr 24, 2015
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perfectly fine on the European 240 Volt / 60 Hz 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.

For one it is the other way around, N.A., is 60Hz which means your motor will run that much higher rpm, which is also dependant on the pole count of the motor, 2 pole or 4 pole..
You cannot run it on NA 120v, you do have the 240v available which should be fine for that motor unless you have already blown it by trying it on 120v.
BTW, the motor does not care about having a neutral,
The N.A. 240v is virtually identical to the European 230v, except for the N.A. 60Hz.
M.
 

hevans1944

Hop - AC8NS
Jun 21, 2012
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BTW, the motor does not care about having a neutral,
The motor may not care, but the actual wiring of the "reversal switch" may include a "frame ground" from the European installation. Connecting one of the two "live" 240 V AC 60 Hz mains lines to this "frame ground" is a recipe for disaster.

I agree with @Minder that the "clicking" sound is the centrifugal switch that engages the start winding on the motor. The motor will reach sufficient speed to disengage the start winding centrifugal switch (hence the click) but the 110 or 115 or 120 VAC that is then applied to the run winding is insufficient to maintain sufficient speed and torque under load. Therefore the rotor speed drops and the centrifugal switch re-engages the start winding (hence another click). Wash, rinse, and repeat until the windings overheat, their insulation melts, and the resulting short-circuit current fries the motor.

There are two possible solutions: purchase an isolation transformer that converts the American 120-0-120 VAC distribution to 0-240 VAC, or purchase a motor rated to run from a 0-120 VAC circuit. In either case, motor speed will be significantly greater operating on 60 Hz instead of 50 Hz.

BTW, where did @dodulation get the totally incorrect idea that Europe uses 240 VAC, 60 Hz power distrubution whereas the American standard is 110 VAC, 50 Hz? Europe power distribution is at 50 Hz. American power distrubution is at 60 Hz. Power to residences in the United States is generally provided from a center-tapped "pole pig" transformer with the center-tap designated NEUTRAL and connected to earth-ground at the service entrance. The ends of the transformer secondary winding provide 120 VAC with respect to NEUTRAL and 240 VAC with respect to each other. There is no "ground" associated with the 240 VAC distribution.
 

Minder

Apr 24, 2015
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I was a practicing electrician in the UK and I don't know of any configuration where the reversing switch would normally be (re)-referenced to 'frame ground'?
As in N.A. the neutral will not be referenced or taken to ground anywhere in the installation apart from the originating source. They are kept completely separate,
IMO the 240v available in N.A. service should be perfectly sufficient and capable of operating this motor.
M.
 

Bluejets

Oct 5, 2014
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I was a practicing electrician in the UK and I don't know of any configuration where the reversing switch would normally be (re)-referenced to 'frame ground'?
As in N.A. the neutral will not be referenced or taken to ground anywhere in the installation apart from the originating source. They are kept completely separate,
IMO the 240v available in N.A. service should be perfectly sufficient and capable of operating this motor.
M.

I was about to say the same for Aus.
 

Minder

Apr 24, 2015
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A couple of considerations when using it in N.A. is to make any disconnect D.P. to take care of what was previously a N and is now a 'live' conductor L2, Like wise it should also be fused in tandem to the other live L1.
IF there was any 120v to 240v transformer used, One terminal on the secondary would have to be taken to the service ground connection in order to set up a local Neutral.
Then it could be used as original.
M.
 
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