Treadmill Motor Overload

Discussion in 'General Electronics Chat' started by Travis1, Feb 27, 2014.

  1. Travis1

    Thread Starter New Member

    Feb 25, 2014
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    Good morning,

    I have a treadmill motor that I think is drawing too much current. It burned out the resistors on the control board and shuts down after about 60 seconds. When I bypass the control board and apply power directly to the motor itself it again shuts down after about 60 seconds.

    I believe there is a thermal sensor in these motors that will shut the motor down. The motor itself doesn't feel warm but the burnt resistors mean that too much heat was being generated at some point.

    Can someone lend advice on where to go from here? Are there any tutorials that could be recommended? More fundamentally though I want to know why an electric motor would draw too much current.
     
  2. strantor

    AAC Fanatic!

    Oct 3, 2010
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    uncouple the motor from the treadmill and see if it still trips. Check that the belt is free and easy to move. check the brushes and commutator in the motor.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    When you say 'bypass the control board' where are you taking power from?
    If you place the motor directly across the TM supply you apply full voltage without the advantage of acceleration needed.
    Try the motor on an automotive battery and see if it comes up to speed and turn equally in both directions.
    Test for continuity to ground or case of the motor from the power leads.
    Max.
     
  4. Travis1

    Thread Starter New Member

    Feb 25, 2014
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    Yep, this is exactly what I've done so far to the letter. Checked continuity, bypassed with a car battery, turned in both directions.

    I checked the brushes - they may be worn (it's hard to tell visually though) but let's say they were completely worn - how would that cause overheating exactly?

    As far as the commutator - that looks fine upon a visual inspection. What should I be looking for?
     
  5. strantor

    AAC Fanatic!

    Oct 3, 2010
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    badly worn/broken brushes will not make good contact with the commutator and will cause arcing at the commutator. The arcing is the source of the heat. The commutator will become scorched and pitted, causing even worse transfer of power and even more arcing/heat.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    When you say the motor shuts down after 60 seconds, is this also when checking with the auto battery?
    Normally for a temp sensor to come into effect on a DC motor takes more than 60 seconds.
    The T.S. is usually on the stator, and for it to sense heat, this has to be radiated from the armature, so this would take time, the armature at this point would be exceedingly hot.
    If and when it does shut off, immediately check the continuity of the motor leads, or on the voltage scale, turn the armature and see if voltage registers..
    Max.
     
  7. Travis1

    Thread Starter New Member

    Feb 25, 2014
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    Max,

    Yes it shuts down with the auto battery as well. It may take less than 60 seconds actually - I'm just estimating here. The point is that it shuts off fast. I agree that it's curious how so much heat is being generated in just a few seconds but clearly the resistors on the control board were scorched. I just don't know what else it could be.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Did you do the open circuit test?
    How long does it take to reset and be able to run again?
    It may be worth opening it up, rear end bell etc, to check the internal condition and location of any sensor.
    Max.
     
  9. Travis1

    Thread Starter New Member

    Feb 25, 2014
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    It can run again after a second or two of being disconnected from the power source...but then it will **** down almost immediately once reconnected.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Is the motor shaft feel hot at all? This would be a sign of armature heating.
    Did you check continuity (resistance) when it cuts out?
    Max.
     
    Last edited: Feb 27, 2014
  11. strantor

    AAC Fanatic!

    Oct 3, 2010
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    Have you verified that the belt and motor are both free and easy to move as I said in the first reply? You never confirmed if you checked that. That's the first thing to check.
     
  12. Travis1

    Thread Starter New Member

    Feb 25, 2014
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    Yes, the bearings and belts are all fine.

    I opened it up and it looks fine. The brushes aren't worn, the commutator shows no signs of heat, the stator is fine.

    I'm guessing there must be a short between where the windings attach to the commutator. Is this correct? How can you test for continuity between windings and commutator?
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Ohm meter (slowly rotate the motor while connected to meter - but you will need a good ohm meter with low resistance capabilities).
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If you test it on the bench or with the belt off using a 12v auto battery, the current should drop to a couple of amps at the most once it is up to speed.
    A armature short can usually only be done with a unit called a Growler, it is similar to a transformer with one side missing, the armature is placed across the missing side and a voltage taken across each coil/comm segment.
    You may not detect one shorted turn on a coil by resistance test, T.M. motors are wound with fairly large gauge conductors.
    Max.
     
    Last edited: Mar 2, 2014
    GopherT likes this.
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