Treadmill tripping GFI (RCD)

[Jontyc]

I had my treadmill trip the ground fault indicator last night during use, and continues to do so when flicking on the treadmill's power switch.

The treadmill's 15A circuit breaker is not being tripped.

The treadmill does not trip the GFI when the motor is disconnected from the motor controller board (PWM).

The motor is a DC brushed permanent magnet (2 wire), but with no markings beyond 4000RPM/10A I can not track down datasheets to see what its winding resistance should be. It measures (via multimeter) 2Ω.

The motor spins without problem by hand, but becomes harder to spin when the terminals are shorted.

So I feel the motor itself is ok. It was not hot to touch upon failing.

With the motor disconnected, neither of its terminals are shorted to the earthed chassis.

Although the controller board attaches to the chassis via its heatsink, ithe board appears to be electrically isolated from its heatsink.

So I'm at a bit of loss here. If the ground fault indicator is immediately being tripped, before the motor is even being told to spin, something is shorting to earth. I just can't imagine what?

 

[debe]

The only way to check for leakage from windings to frame, is use a Megger Ohm meter(Device that measures resistance with a high voltage aplied) An ordinary Ohm meter will not do the job. You have a leak from active to earth triping the earth leakage CB, which may only show up with high voltage.

 

[Jontyc]

Hmmm, haven't got one of those

The ELCB is however tripping as soon as power to the treadmill is supplied, i.e. the treadmill hasn't even been told to start moving yet. I would have thought the motor isn't being powered at that stage. But I don't know PWM too well--maybe it's still pumping out a high voltage, just with a small enough duty cycle to not spin the motor, yet still enough to cause a short. Does that sound ridiculous?

 

[Nigel Goodwin]

Hmmm, haven't got one of those

The ELCB is however tripping as soon as power to the treadmill is supplied, i.e. the treadmill hasn't even been told to start moving yet. I would have thought the motor isn't being powered at that stage. But I don't know PWM too well--maybe it's still pumping out a high voltage, just with a small enough duty cycle to not spin the motor, yet still enough to cause a short. Does that sound ridiculous?

The motor doesn't need to be powered, the ELCB is tripped by current leaking to earth, as disconnecting the motor stops it doing this it's reasonable to assume the motor has a leak to earth.

As suggested it needs testing with something like a meggar, or (even better) a PAT tester - to measure the leakage current to earth.

It could even be that the treadmill is fine, and that your ELCB is faulty - I've had a number of items in for repair which tested perfectly fine, so obviously the ELCB's involved were overly sensitive. A great many items are designed to have leakage to earth, but this is only a small amount, and too little to trip a correctly operating ELCB.

 

[Jontyc]

Ah ok, I thought dede was suggesting the leak might only occur when the motor is powered with high voltage, but if I read you right, the motor will have the leak regardless of it being powered or not, it's just only detectable by instrumentation if the motor is powered?

I guess the ELCB could have developed a fault, although I have run the treadmill for about 2000 hours on the same ELCB over the last year without issue. I can't recall any new appliance put on the same circuit either that could be take the ELCB close to tripping with the treadmill taking it over the top.

If I take the motor to a winding, this is the sort of thing they should be able to test for, correct?

 

[Nigel Goodwin]

If I take the motor to a winding, this is the sort of thing they should be able to test for, correct?

Presumably, but it's probably something any electrician could test.

 

[tunedwolf]

I used to repair them for the local authority in their sports center cardio suites. Several of them began to trip the RCBO and usually turned out to be a dodgy mains input filter. Look for a big shiney box on the supply input from the mains, it's usually right after the mains switch and fuse/ breaker and before the supply goes to the driver board. I wouldn't recommend that you remove it, but a quick test by connecting the in to out wiring should be ok. Only replace it with the correct part from the manufacturer if it is faulty
Oh, and a tip for ya, take a photo before disturbing the wiring...old age plays tricks on yer mind

 

[Jontyc]

That's interesting what you say. I had enormous trouble with this treadmill when I first got it, completely contaminating the mains line and even radiating into the phone lines, taking out my ADSL connection when the treadmill was under load. That PWM is nasty stuff.

I had to plug it in to one of **broken link removed** just so I could use the internet.

So before checking the switchbox, I might just reassemble everything and try without the power filter board in place.

Thanks for bringing it up.

 

[tunedwolf]

I never did rate the DC motor idea as being a good one in these types of machine. The radiated EM and RF contaminates everything around it. Fortunately most of the machines I used to work on were using multiphase motors and inverters for control. Much cleaner, much better control and an order of magnitude more reliable. I probably had more problems with rollers, bearings and dry decks than I ever did with the motors or inverters

 

[Jontyc]

Removing the line filter from between treadmill and GPO did not solve the problem.

The mains filter in the switchboard - there is none, unless it's encased inside the metering. Reading around we don't seem to have them in Australia.

I took the motor to a motor repair place today and his megger immediately showed one of the lines was shorting out to the casing. So the motor guy's going to have a look inside and see if it's anything simple.

 

[tunedwolf]

I'm glad you have identified the problem. I was referring to the mains input filter on the machine itself, usually fitted right after the IEC input socket. I don't think I have ever seen EMI filters fitted to domestic distribution boards anywhere, either here in the UK, or when I worked in Canada or in the USA. I would guess that's also the case in Australia