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this is my first posting.

I've searched the website tried the various recommended solutions for similar problems but with no success, so I've decided to post with a little more information.

Background: The motor is about 12 years old, an EMG 90 2-4 motor. Low speed 1440 rpm and 0.45 Kw (runs the circulation system and heating flow system) and high speed 2830 rpm 2.36Kw.

It stopped working and when I took it out, the junction box on top was 'burned out' and the two capacitors (16uF and 35uF) were burned out and almost unrecognisable, likewise the relay.

I purchased a new junction box, relay and capacitors from a well known Hot tub spare parts company and installed them.

It worked fine (on my work bench) for 3 or 4 times turning on and off and running for about a minute each time (without the wet end attached) then stopped working. I noticed the new relay was burned out. On closer inspection I realised I had been sent a 24V not a 240V specified relay !! There was an error on the Spare parts company website which I have made them aware of. They sent me without charge a replacement 240V relay.

Now when I switch it on to the high speed, it works instantly without problem. But on the low speed, it hesitates and one might say "wobbles / oscillates" about 10 degrees between clockwise and anti clockwise then does eventually spin in the right direction. Naturally it hums till it starts turning.

Once I refit the Waterway wet end (with new bearing and impeller also installed), it simply doesn't have enough "grunt" to overcome the slightly increased load of the wet end. It will though spin and continue to spin if I give it a manual spin to 'start it off'. Once spinning, I cannot slow the motor by applying a little resistance. The torque seems good.

I have checked for any earth loop / leakage from the armature wiring to the case and there is none.

I've checked the two capacitors and they both read accurately 16.2uF and 34.9uF respectively

On reflection a few weeks before the 'total failure' the slow speed pump setting was erratic.

I have also had an electrician check the RCD and MCB supply for the tub (its on its own circuit) as I was worried as to why the circuit breakers hadn't cut in. He can not find any faults.

I cannot identify any brushes for the motor, I suspect it is a 'brushless' motor. All the motor hearings are silent and smooth - no 'grittiness' and without the wet end on run smoothly and the motor rotates freely if given a twist by hand.

My questions: Have I failed to check anything ? Is it likely to be some of the windings on the motor which have begun to fail and hence I need a new motor ?

I don't want to potentially waste more money replacing the capacitors again if they are unlikely to be faulty, but a new motor is expensive if I may have missed something.

You advice and suggestion would be greatly appreciated.

Thanks in advance for your help and patience, Graham

Graham
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  • Sounds like a starting switch issue, given the "if I spin it by hand it runs" aspect. I have a fan with a similar problem (starts fine on high, no longer starts on low.) – Ecnerwal Mar 09 '22 at 14:30
  • I took it apart to see if there were any internal switches of smaller capacitors and there are none - back to square 1 – Graham Mar 09 '22 at 15:55
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    I would guess that the windings themselves are shorted , if things smoked they got hot and the motor windings only have a layer of varnish. If you used a megger at 500v to ground (at least) that will say there is no leakage to ground but several field windings shorted together sounds likely to me. Once the motor is rotating the fields are created and the motor makes it, to start it try’s to spin and reversed sounds like shorted windings, or winding to winding failure. – Ed Beal Mar 09 '22 at 20:28
  • I agree with @Ed Beal on the windings being shorted out. That's pretty common on hot tubs with motors that old. A little corrosion and that's it. Your supply company or an electric motor company should bee able to test the motor. – JACK Mar 09 '22 at 21:36
  • Thanks Ed and Jack, Your observations ae really helpful. Looking at the condition of the junction box when I took it out - it had melted and smelled 'very burned', I think you are right and some of the windings are probably shorted. So I'll get a new 2 speed motor. – Graham Mar 11 '22 at 07:39

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