Emco Unimat motor tripping RCD

[David TParticipant @davidt96864]

Hi everyone,

SWMBO has just bought herself an Emco Unimat SL1000. The trouble is, the motor is tripping the RCD. It is not tripping instantly, so it’s not the in-rush, but it trips after 2-3 minutes of running. By the time the RCD trips the motor is warm to the touch, even running no-load. The trip is bypassing the circuit MCB and hitting the master RCD, so it’s a leakage not an overload.

The motor is a 70W, 240v single phase brushed motor. I’ve dismantled the motor and cannot see any obvious faults in the wiring. Using a multimeter I’ve found there is good continuity between the Earth pin and the casing, and open-circuit between Earth and live / neutral (I have no means of doing a proper insulation test of the windings). I’ve tested the motor in two different sheds (so two different RCDs), and with everything else unplugged to rule out the combined effect of a secondary leakage.

Can anyone offer any advice please?

Thanks

[David TParticipant @davidt96864]

[John RuddParticipant @johnrudd16576]

Does the lathe have a speed controller fitted to it?

If so, disconnect the motor from the controller, then check see if the rcd trips…that will rule out the motor…

report back your findings, we’ll go from there..

[Dave WoottonParticipant @davewootton]

As these are all quite a few years old there is a known problem with the suppression capacitor deteriorating, if you look on the Lathes.co.uk website there is a page devoted to the motor capacitor change with diagrams. I had a look ast one of these for someone a while ago and it was doing a similar thing, tripping after about thirty seconds,although the motor did not seem unduly warm after that short time, got a new capacitor as mentioned in the article from Maplins. I know Maplins have gone now but someone must sell an equivalent, the lathe is still working now I believe.

Dave

The replacement capacitor is larger and will not fit in the motor casing, it was put in a small plastic box with a toggle switch to replace the original inline switch.

Edited By Dave Wootton on 18/07/2022 06:17:12

[John HaineParticipant @johnhaine32865]

Easy thing to try, just remove the capacitor. If it runs ok you have found the problem. New cap available from eg RS or Darnell, cheap as chips. No problem to run briefly without.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by David T on 17/07/2022 17:57:59:

[…] but it trips after 2-3 minutes of running. By the time the RCD trips the motor is warm to the touch, even running no-load. […]

.

It doesn’t really make it any easier, but that would seem to suggest that the leakage only occurs when the motor is warm. … Ergo, you have a fault which causes the motor to heat-up, and an effect of leakage to Earth

So … simple bench-tests on a cold motor are unlikely to identify the fault

MichaelG.

.

Edit: __ as John suggests, the culprit might very well be the capacitor.

Edited By Michael Gilligan on 18/07/2022 06:36:13

[Brian GParticipant @briang]

Mine did the same thing, I followed the instructions on lathes.co.uk and fitted a capacitor (and a switch) in an external box.

Link to lathes.co,uk

Brian G

[David TParticipant @davidt96864]

Posted by John Rudd on 17/07/2022 22:47:53:

Does the lathe have a speed controller fitted to it?

If so, disconnect the motor from the controller, then check see if the rcd trips…that will rule out the motor…

report back your findings, we’ll go from there..

There is no speed controller fitted.

Thanks all for the replies, I will try the capacitor as suggested and go from there

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