Earth fault - motorised treadmill (long) ...

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DIL-to-be? (son's current squeeze) presented a "yumcha" motorised
treadmill for me to check/repair.  Badged Vibelife V815.  History is
that it was ordered on the web, and was faulty out of the box.
Supplier sent a replacement motor which was installed by a local
sparky as a warranty repair, but that also didn't go.  Sparky
apparently then muttered "(expletive) house wiring" and left - either
his payment or expertise had run out.  Attempts to chase up the
supplier failed as they had folded their tent and disappeared.
(Warranty has expired before owner qualified as a potential DIL.)

As soon as power to the machine was enabled, it tripped the earth
leakage (30mA).  Opened up the machine and found no signs of damage or
escaped smoke, etc.  It has two motors, one for platform incline and
one for belt drive.  Both have explicit earth leads bolted to the
frame, as is the incoming earth lead.  Transformer provides low
voltage for electronics board in the base frame, which also houses the
control relays and diode bridge for the motors (DC drive).  Console
contains all display and UI controls. All good in terms of
configuration.

Test 1:  With power leads for both motors disconnected, the fault is
still present. That's not a surprise, as I'm sure the earth leads are
directly connected to the motor frames, which are directly connected
to the machine frame.

Test 2:  After checking other considerations, I lifted the incoming
earth lead - leaving both the motor leads connected to frame and all
other connections as original,  and the machine operates OK.

Test 3:  With transformer secondaries isolated from electronics module
- no fault. For a moment I figured this eliminates a frame-fault in
the transformer, pointing to the electronic module having earth fault,
BUT of course it doesn't.  Either leg of either secondary could have a
path to frame.  Nevertheless, the resence of the eltronics module is
required to complete the path to earth, so where is it?

Electronics is a pcb mounted via insulated standoffs to a large
earthed heatsink.  Three components use the heatsink - a 3-terminal
?volt-reg (bigger than TO-220), a TO-220-sized diode (both these use
insulating washers), and the diode bridge.  Apart from these, only
outgoing cables:

.  power to belt motor.
.  power to jack screw motor (incline adjust).
.  UI connection to all-plastic unearthed console.
.  speed sensor on frame adjacent belt roller.

offer the potential for that path.  Motor cables had already been
disconnected (test 1).  Speed sensor isolation made no difference.
Without UI connected, nothing at all happens.  So the focus is back on
those three heat-sunk devices next time I look at it.

Yes, I DO know what I am doing around mains power, thanks for your
concern, or I wouldn't be working on an unearthed machine with a
demonstrated earth leakage issue even with upstream ELCB/RCD
protection.

Any comments on the fault-finding process so far?  Anyone had to work
on one of these?

Re: Earth fault - motorised treadmill (long) ...

"who where"

( snip piles of drivel )


** Have you checked to see if safety earth and neutral are connected ?

 I mean a simple ohm meter test on the AC plug.

 Also check if any suppression caps go from active to ground.

 Always start with the basics.



...  Phil



Re: Earth fault - motorised treadmill (long) ...

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8<  -    - --------------------

That thing is rated at 6.5 hp. What have you got it plugged into?



Re: Earth fault - motorised treadmill (long) ...

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Heh, that was one of my first observations since it comes with a 10A
plug-top.  The belt motor is labelled 220V (DC) at 11.4A, but on
tong-test the whole machine shows a tad over 1A AC input at 12kph with
a victim up a 10% slope, so I suspect that's an out-of-someone's-arse
number to make the sales pitch more impressive.  Clearly the "Leeson
USA" motor is still loafing if the input is ~ 300W.

All fixed now.  Silpad under the motor drive IGBT had a perfectly
circular ~0.8mm dia hole so instead of providing ~ 4kV isolation the
motor drive on the IGBT tab was arcing straight through the hole
(about 4cm from the "QC" sticker on the heatsink).  Cleanup, new
silpad and compound and it's running better than new ....

Re: Earth fault - motorised treadmill (long) ...

"who where"

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**  Nice one  -  that is a " result " .




...  Phil



Re: Earth fault - motorised treadmill (long) ...

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After an "event"



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