Electric motor help

[stuwindsurf]

Hi,

I am thinking of swapping the single phase AC electric motor on my hobby lathe for a DC brushless motor with a variable speed controller. The thing I'm concerned about is matching or improving the power of the current motor.

The current motor is as mentioned single phase AC motor, 240v rated at 550w. The brushless DC motor I am looking at to replace it is 220v rated at 1000w and is approx a third of the size of the AC motor.

Because of the different motor types are the watts still comparable? or are there other considerations to be taken in to account?

Thanks Stuart

 

[rjenkinsgb]

From the figures alone, it should be fine.
The only thing to possibly be wary of, if the new one seems too small for the stated power, is if it has a "Duty cycle" rating on it, less than 100%? Some applications only allow a motor to run for a short time then it can cool down for a while, or only occasionally put it under high load, so the motor does not have to be big enough to continuously dissipate the full heat it produces when working hard..

It may just be that the original motor is an older design and over-size by comparison to newer types.. Without full data it's a bit of guesswork.

As long as the motor speeds are compatible, I'd say just try it and keep any eye on the motor temperature while cutting, to start with.

 

[stuwindsurf]

From the figures alone, it should be fine.
The only thing to possibly be wary of, if the new one seems too small for the stated power, is if it has a "Duty cycle" rating on it, less than 100%? Some applications only allow a motor to run for a short time then it can cool down for a while, or only occasionally put it under high load, so the motor does not have to be big enough to continuously dissipate the full heat it produces when working hard..

It may just be that the original motor is an older design and over-size by comparison to newer types.. Without full data it's a bit of guesswork.

As long as the motor speeds are compatible, I'd say just try it and keep any eye on the motor temperature while cutting, to start with.

Thanks for your reply. I don't believe it has a duty cycle and it is sold as a kit specifically for a lathe.

I'll take your advice and keep a close eye on the motor temperature

Thanks Stuart

 

[rjenkinsgb]

it is sold as a kit specifically for a lathe

That should be fine & not have any problem at all then.

I was just being cautious in case it was a generic secondhand motor off ebay etc.

 

[Diver300]

Is the top speed of the DC motor comparable with speed of the AC motor? It's probably not very critical, as there is twice the power, and you can change the gearing on most lathes, but if the speed is very different then the DC motor might not have enough torque.

 

[stuwindsurf]

Is the top speed of the DC motor comparable with speed of the AC motor? It's probably not very critical, as there is twice the power, and you can change the gearing on most lathes, but if the speed is very different then the DC motor might not have enough torque.

The DC motor speed is 2500 rpm and the current AC motor is 1400 rpm. I have calculated I will need to fit a 75mm pulley wheel to the DC motor so that when the motor is at full speed (2500rpm) the lathe chuck will turn at approx 1650rpm which is the max current speed quoted in the manual. The AC motor speed is currently changed via moving the drive belt on to stepped pulleys.

The DC motor is also available in 3500rpm and 4500rpm, but I figured the 2500rpm would be the closest and shouldn't require as much gearing down.

Please let me know if I have overlooked anything!

Many thanks
Stuart

 

[MaxHeadRoom78]

DC brushless or ECM (electronically commutated motors) are either 3phase or BLDC controlled, the 3 phase is a little smoother at low rpm, but the BLDC is generally higher torque.
Most HVAC blower systems or ECM motors now.
The ECM BLDC motor is more compact due to PM rotor.
Essentially they are identical in appearance, just the commutation is different.
Maax.