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I have a treadmill incline motor that is blowing its circuits fuse every time it starts to run. This is the motor that lifts the treadmill up and down.

The motor is labeled: Output: 65W Input 36VDC Current: 3A Speed: 3700 RPM Torque: 1.7KG-CM

I tested the voltage off the board and it's correct per the manual. I have visually inspected the motor, taking the commutator out and it looks OK. I've performed the 3 tests (180 degree resistance, bar to bar resistance and bar to stack) here: http://www.groschopp.com/how-to-check-a-motor-armature/

Everything seems ok.

I did some other "cowboy" tests, which I doubt the validity:

  • I hooked the bell end (end with brushes, I think it's called bell end) to the board by itself. It's still an open circuit and sure enough the fuse stayed fine. No surprise. I left the bell end hooked up and I put the commutator in, alone without the housing.
  • With the brushes contacting the commutator the fuse immediately blew when voltage was applied.

The resistance across for the 180 degree test was 2.5 ohm. That resistance doesn't work with the watts and voltage.

Is this motor bad? Shorted out somewhere? Or am I missing something?

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  • \$\begingroup\$ What kind of fusese you have there? \$\endgroup\$ – Kamil Dec 10 '14 at 7:58
  • \$\begingroup\$ 180 degree resistance doesn't have to match with rated motor power. It will match power on blocked rotor. When rotor is rotating - current is smaller and it is alternating current (because of commutation) so simple Ohms law for DC is not only thing to consider if you want to calculate current at some voltage. \$\endgroup\$ – Kamil Dec 10 '14 at 8:04
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    \$\begingroup\$ 2.5 ohms sounds OK. I'm guessing the original fuse was a slow blow, if the replacements are fast blowing types that would explain it. Also look for any way to reduce the mechanical load on the motor - correct lubrication, is anything bent causing friction, etc. \$\endgroup\$ – Brian Drummond Dec 10 '14 at 10:01
  • \$\begingroup\$ Thank you for the responses: Kamil, 3A Fast blow fuses. Thank you for the responses. I originally found the motor bound up internally. I lubed it up and it spins much easier but still blows those fuses. I'll \$\endgroup\$ – Fitz Dec 10 '14 at 13:59
  • \$\begingroup\$ Sorry for the above, I started to edit and got interupted... Thank you for the responses: Kamil: 3A Fast blow fuses. I originally found the motor bound up internally. I lubed it up and it spins much easier but still blows those fuses. I'll try slow blow fuses to see if it is related to the start up of the motor. I'm just concerned about damaging something else. \$\endgroup\$ – Fitz Dec 10 '14 at 14:11
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DC motor current ratings are occasionally specified as their no-load current draw.

I would assume that the motor will draw considerably more power when it's starting, or if it's heavily loaded.

What kind of fuse is it blowing? If it's a fast-blow fuse, I would expect it to fail every time the motor starts.

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  • \$\begingroup\$ Yes, fast blow fuse. I haven't tried a slow blow fuse, I suppose I could try that. I was afraid of damaging the board if I did that and there was something wrong. \$\endgroup\$ – Fitz Dec 10 '14 at 13:55
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First, Do you have a Digital VOM? If you do, see if you get reading from the commutator (ring for the brushes) to the metal surface near the windings. If you do, you have a short in the windings to the shaft(direct short). The motor would be bad with this.

No reading on VOM means good.

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  • \$\begingroup\$ I think you are asking about the bar to stack test. I tried that and I got no reading for each of the bars. \$\endgroup\$ – Fitz Dec 10 '14 at 14:00

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