Single phase electric motor ?Faulty

Today I thought I'd try out a 1/4 HP, 240v single phase motor of senior years. New supply wiring after checking winding to earth seems ok. It is a cap start Hoover motor rated for continuous use and it is resilent mounted.The bearings seem fine when spun manually, bothe directions and the motor started fine and runs quietly, but, there's always a but, there is a regular groaning noise about once every second when the motor is under power. The centrifugal switch can be clearly heard disengaging on swich off and run down. Does anyone have any suggestions as to what may be causing this, I have been spoilt by using lovely smooth three phase motors, is the resilent mounting there to cope with the single banger design?Thanks in advance for any suggestions.

regards Paul

Could be anything really. First step might be to strip it down and inspect for loose windings, swarf etc inside the working area. Clean it up. Fit new bearings and seals and give it another try. Bearings and seals are cheap so not worth putting the old ones back together. They could be the source of your noise. Or not. Only one way to find out.

Yes!

Single phase motors are much more likely to vibrate than other types. As an AC motor that works on a domestic supply they're a compromise and more than adequate for many purposes. However, now that electronics can deliver affordable DC, 3-phase and Brushless power from a domestic supply, there are few good reasons for putting a single phase motor on a machine tool.

It's not that single-phase motors are awful - they're just not as good as the alternatives, particularly where smoothness matters.

Dave

Paul,

There may be nothing wrong with your motor,I have one the same type/make,fitted with a sanding disc,operating for the past 25 years or more. It aint broke,so I,m not going to fix it .

It does sound like an effect from the bearings. Have you tried applying an axial load (in line with spindle) to alter the bias on the bearings.

Thank you all for your responses.I am reassured! I have feasted on three phase nectar, now for some single phase stodge, "You can eat it, but it tastes like cr*p" to quote Hogan.

Thanks again Paul

If it spins up, the switch clicks and it slows down that suggests it might be a dual capacitor arrangement and the run capacitor may be damaged.

Neil

Edited By Neil Wyatt on 20/08/2018 21:15:53

Thanks Neil, for your clear diagram.This motor only has one cap for starting and noobvious run cap, the centrifugal switch is normally on and the start cap and start windings are isolated when the motor spins up.The switch can be heard closing when power is cut and the revs drop ready for the next start. However Bazyles comments made me think again and rolling the motor around its long axis whilst under power changed the vibration from zero to very bad. I hope this old lady has ball races and not oilite bushes! Although there apears to be no axial play even when powered up, the bearings are clearly sensitive to the orientation of the motor about its longitudinal axis, ergo excessive clearances

I will be opening her up to see very soon.

Thanks again Paul

Edited By Paul Barter on 20/08/2018 21:34:58

Hello againI Have been inside and it has plain bearings, albeit with oil grooves and thrust washers but not much oil. There did not seem to be too much damage so a blow out with compressed air, smear of moly grease and a paper and wd40 polish on the spindle bearing surfaces and now it purrs. The weird noises must have been bearing related but not excessive clearances. This motor is probably almost as old as meand is now going to drive a picador linishing attacment, once I can get a small enough pulley.

Thanks to all of you who were kind enough to suggest solutions

regards Paul

Don't go too small on pulleys for your Picador. Mine came with an M section one a little smaller in overall diameter than the drums. Bought a similar size one for the motor but drive was never satisfactory. Lots of belt slip-stick and stall tendency if more than light pressure was used. Changed pulleys for largest I could get in. Want to say 3 1/2 inches OD but sold the finisher many years ago so can't be sure.  Nowadays I use multi-groove so a small pulley would do fine.

 Made a new post for the table so I could lift it bit getting more belt clearance which helped. Think I also made longer bottom rails to use a readily available belt length too. Think getting Picador ones was hard in my neck of the woods. Even with the larger pulleys I had minor drive issues. Sorted those by turning things round and putting the drive pulley on the front drum rather than the more logical rear one. I imagine the longer belt put some shock absorbing into the drive as it could be seen jumping up and down in use.

Cast iron bearings on mine had worn a bit oval so it got some T section oilite bushes with integrated thrust face, courtesy of a mystery box from friend Whistons Cat-a-log, and put proper flip top oilers on. Which meant new axles for the drums. Worth the effort as it was a freebie. Sold it after 15 or 20 years to get a modern Draper branded belt'n disk sander. Which was not an improvement!  Interestingly that has a tooth belt drive to the drum.

Clive.

Edited By Clive Foster on 21/08/2018 12:18:51

Edited By Clive Foster on 21/08/2018 12:21:02