Thread: Electric motor info please, please

Originally Posted by Calm

Looking at buying a 3 phase motor to put on a lathe as EVS.

What is the difference between 4, 6 or 8 pole motors? the speed

What determines if they are 720, 1440 or 2880 RPM? 8 pole, 4 pole , 2pole

What is the best motor for this job in your opinion?

If i can find a 720 rpm motor, use a 2 or 3 step pulleys system to give 3:1 step down/up i would get 240 rpm then less with the variable speed and 3:1 up would give 2160 plus the EVS to hopefully end up with a speed range of 150 to 3000 rpm.

Am i on the right thought train?

Any more info appreciated

Thanks in advance.

.

Thanks Bob

i now am in the market for a 8 pole 3 phase motor. That should be 720 rpm to give me the speed range i want

Thanks again

david

Hi Calm,

on industrial lathes for metal work, dual winding motors are often used. These can be switched between 8 and 4 poles, making possible 720 as well as 1430 rpm. I've seen similar switchable motors with 4 and 2 poles on wood lathes, making possible 1430 and 2850 rpm. Together with the usual belt pulley combinations (or a gear box on metal lathes), this results in very versatile machines.

But single rpm motors are possible as well, of course. 4 pole motors are used most often, 1430 rpm is a range most often used in all sorts of industrial applications. At 1430 rpm, the motors have long bearing life and good efficiency and because there are so many around in all shapes and sizes, they are affordable. 2 pole motors are easier and cheaper to make (less coils to wind and mount) and their output efficiency is also higher. Their price is comparable. 8 pole motors are used less often than 4 pole or 2 pole and so are harder to come by. Whereas 4 and 2 pole motors are often ready on the shelf, 8 pole versions have to be ordered unless there is a specialist with a large product range nearby. 8 pole motors have more coils and have slightly lower efficiency. Their price will also be higher.

But it's not half as bad as i make it seem. Don't let my story stop you. If you would like an explanation of induction motors (poles, speed, single and three phase, etc.) let me know, i won't dare bore you to death with it beforehand.

regards

gerhard

David, I am going through a similar exercise at present.

I have narrowed it down to a VSD like this, available to handle a range of horsepower. These devices work from a 240V power point and drive a 3phase motor. They vary the speed by varying the frequency. You therefore don't need the pulleys to get your speed range, as the frequency variation does this.

I was going to bid on this motor, but like a fool I forgot!

Basically, you need a 240/415V 3phase motor that can be set up as star or delta.

If you download this book and this book, it will explain this in a lot more detail than I can (I am only a simple chemist)

Thanks Gerhard & BS i have a mate and cousin that are talking the same system, thay both use them at their work so i dont need the research just ask them. It is just how i purchase the EVS system that i am wondering about.

As with the gearing i am led to beleive you lose torque and the motor runs hot if you run them too slow - that is why i hope to get a 720 motor to start with. That way gear it 3 to 1 step down is 240 then the evs should easily give me 100rpm with reasonable torque. 720 with 3 to 1 step up is 2160 and run the evs at 200% gives me the top speed i will ever require.

Thanks again for the tips but the 720 motor could be more expensive than i was hoping, but even at $300 it wouldn't be too bad.

Cheers