What motor?

[Gammaboy]

So, finally got 15 minutes to mess with the switch unit and start cap on my Mars Thor - and it's knackered (Lathe hasn't run in 20 years at a guess). The motor that's there is a 19mm shaft 1hp single phase 1400rpm unit. Going straight for another 1hp/1400rpm unit seems the logical way to go, but part of me thinks "More power would probably be better"...
Of course, I'm keeping an eye out for cheap treadmills, but the only one I've spotted was a 600w unit - strikes me a a bit lacking in grunt...

[simonl]

Hi there,

Certainly a bit of extra power never goes astray (within reason) I think I have also read somewhere here that power for power, a 1 HP DC motor would produce more "useable" power than a 1 HP induction motor. HP is HP and it should not make any difference but a DC motor also can produce useable torque from 0 rpm whereas an induction motor torque drops away considerably once you deviate considerably from it's base frequency.

My lathe has a 2 HP single phase motor, I have a 3 HP 3 phase induction motor waiting to go in for a VFD conversion. I certainly don't need a 3 HP motor and indeed a 2 HP would have been fine but this motor was going very cheap and beggars can't be choosers! I have done a similar conversion with my mill and I have enjoyed the extra low frequency torque that the 3 HP motor delivers. I can use it down to 20 Hz with no trouble, creating a very flexible speed range with little changing of gears.

I guess it really depends on what work you are going to do on your machine and whether you think you will use/need every watt of power. I probably would not go smaller than original whether it be DC or AC motor.

Simon

[th62]

Don't three phase motors lose power when run on 240v?

[BobL]

Don't three phase motors lose power when run on 240v?

A 3 Phase motor wired up to specifically run on 415V will lose power when run on 240.
Some 3 phase motor come stock as easily convertible between 240V (∆) and 415V (Y) by switching around a set of jumpers at the motor junction box
A 3Phase 415V ¥ connected motor can usually be modified to run as a 240V ∆ but more work is required.

In this post you can see the HP output of a 3HP 380V Y motor converted to ∆ and run under 240V 3phase.
http://www.woodworkforums.com/showthread.php?t=182106&p=1800438#post1800438

[jhovel]

No they don't 'loose' any power - providing they can be configured for delta wiring. Most can.
Have a read of BobL's thread on VSD power tests here: http://www.woodworkforums.com/showthread.php?t=182106&p=1788271#post1788271
Lots of interesting info in that thread.

[th62]

I read most of that stuff a while back. With my interest piqued at the simple junction box switching,I thought of procuring a three phase for a belt sander I wanted to make. I do remember reading here that three phase motors lost power when converted, so lost interest.