Running 60 Hz Motor On 50 Hz Supply

[dooroy]

I live in Ireland and I imported a 4 post car lift from the USA.

The motor that drives the hydraulic lift pump has 208 - 230 v on the plate . (220 supply in Ireland )

However when I began to operate the motor when setting up the lift I noticed it was getting very warm .

I asked an electrician to check it for me and he discovered it was drawing 45/46 amps - the plate on the motor said 15.0 -18.0 amps . The rpm on the plate was 3450 .

He had come across this before and figured that while the motor was 60 Hz on the plate the supply was 50Hz - and the maximum achievable revs at 50 Hz was approx 2900 .

For this reason the centrifugal switch was not disconnecting the start up capacitor - causing the high current draw and the heat .

The suppliers have not been able to offer any help - even though they say they supply lifts worldwide and should have encountered this problem elsewhere .

The electrician says he can get around the switching problem by mounting an external electronic timer to disconnect the start up capacitor as he has done this successfully before .

What he's not sure about and would like advice on is :

would there still be a tendency for the motor to overheat due to the Hz difference ?

I operated it a few times before I became aware of the problem - but only for 30 secs or so and it was then drawing 45/46 amps . Would it then be safe to assume that it would operate OK if the start up cap was disconnected as intended ?

I note from the FAQ that there would be a 20% drop in rpm - I am hoping this would not make too much of a difference to the speed of operation .

I don't want to fit electronic timer etc if there is a strong possibility that the motor will still overheat .

[marke]

Hello dooroy

 

Welcome to the forum.

 

You have three issues.

1. The motor operates slower on 50Hz than 60Hz, so the start winding is not being disconnected by the start switch. This will cause the start winding to fail.

2. The motor is designed to operate at 230 V 60Hz and you are operating at 220V 50Hz. This means that the motor will be over fluxed and will over heat. If you want to operate that motor on 50 Hz, you must reduce the voltage by the frequency ratio, so the maximum voltage at 50Hz is 230 x 50 / 60. which is around 195 volts at 50Hz.

3. If you operate a 60Hz motor at 50 Hz with a reduced voltage applied, the KW rating of that motor will be reduced by the frequency reduction.

 

You would be best to replace the motor with one designed for operation at 220V 50Hz.

 

Best regards,

Mark.

[dooroy]

Hello dooroy

 

Welcome to the forum.

 

You have three issues.

1. The motor operates slower on 50Hz than 60Hz, so the start winding is not being disconnected by the start switch. This will cause the start winding to fail.

2. The motor is designed to operate at 230 V 60Hz and you are operating at 220V 50Hz. This means that the motor will be over fluxed and will over heat. If you want to operate that motor on 50 Hz, you must reduce the voltage by the frequency ratio, so the maximum voltage at 50Hz is 230 x 50 / 60. which is around 195 volts at 50Hz.

3. If you operate a 60Hz motor at 50 Hz with a reduced voltage applied, the KW rating of that motor will be reduced by the frequency reduction.

 

You would be best to replace the motor with one designed for operation at 220V 50Hz.

 

Best regards,

Mark.

 

Thanks Mark - very clear answer , which I have not been able to get elsewhere .

Looks like a replacement motor designed as you say for 230V 50Hz is the most sensible option .

Padraig .

[Bysikmode]

Thank you for your posts! Very interesting!

[Alvin78]

Using a 60Hz motor in 50Hz duty.

w) It will turn 20% slower.

x) Cooling will drop dramatically.

y) The load's horsepower requirements will drop, possibly dramatically.

z) V/f will increase possibly causing a large increase in current draw.

Make sure the load will still do what is required of it when running slower. For instance, a fan load would now move less air. Still enough?

The cooling will reduce dramatically. Is it enough to matter? This depends on how the load has decreased. If the hp requirement dropped because the load has decreased the current will drop and less heat will be released internally. You would want to take temperature measurements until the motor reaches a steady state temperature running in its new frequency application.

The motor's hp will drop because hp is a function of speed x torque. The motor's torque doesn't change but its speed has dropped so it is now a lower hp motor. If you change pulley sizes to return the load to its original speed your motor will likely be undersized, possibly seriously. Example: A 10 hp motor is now an 8 hp.

The most serious issue is the V/f issue. The V/f will increase. Likely enough to cause a large increase in the motor's current. This coupled with the reduced cooling may cause rapid overheating. However the V/f problem can be fully mitigated! You reduce the voltage to the motor by the amount required to return the V/f back to its original value. This removes the hazard of excess current from an increased V/f.

Example: A 60Hz 240Vac motor is going into 50Hz service.

V/f = Y Hence: 240/60 = 4.0

So if Y x f = V then by plugging in the new frequency of 50 we see:

4.0 x 50 = V

V = 200

Running the motor at 200V at 50Hz will remove the V/f problem.

Another way to think of this is:

New voltage = Old voltage x 50/60

New speed = Old speed x 50/60

New Horsepower = Old horsepower x 50/60

hr conveyor belts hope i offered some help

Alvin

[rotomoulder]

A failure of the centrifigul switch would not have occured to me but it will do so in future.

 

Question. If a timer was fitted accross the switch then would it not be like reducing the delay time on an SD changeover switch with all of the possible associated problems?

Terry