Can a bad battery cause a motor to draw more Amps?

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by MTMAUS, Nov 5, 2022.

  1. MTMAUS

    MTMAUS Light Load Member

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    I have a freightliner argosy with the electric steps. The steps won't fully come out as the motor is pulling too many amps at the end of the push.

    Basically I have been told that the step motor should draw 2 amps, as the motor starts to push the steps out it starts to draw at 2 amps but as it keeps going it is eventually getting up to 6amps. At which point the safety systems cut power to the step motor to stop it burning out

    The step motor is brand new.

    Could a bad battery cause this? I thought I smelled a bad battery the other day.

    Freightliner want to just keeping changing parts until they work it out, but I am not convinced any of the parts need changing.
     
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  3. MAMservices

    MAMservices Medium Load Member

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    Is it a possibility the step is binding in some way to cause the motor to overload at the end of stroke?
     
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  4. baha

    baha Road Train Member

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    If it's binding at the end of the steps travel it was probably bumped in a Truck Stop when it was left out and is bent a bit, if you haven't had batteries ck do that before spending more at the dealership?
     
    Last edited: Nov 6, 2022
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  5. roundhouse

    roundhouse Road Train Member

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    I’d disconnect the linkage swing the steps open and closed by hand and make sure it’s not binding up

    My guess is that it’s bent or something and is binding up and overloading the electric motor
    I’ve repaired a few busses that had the electric steps and electric doors and I always Unhooked the linkage and moved it through its entire travel by hand so I could feel where the scrubbing started and usually you could see where it’s rubbing because it’s all shiny
    Sometimes you could hear where it was rubbing


    that’s what most repair shops do now , they can’t properly diagnose problems , and instead just throw parts at it until the issue goes away . After all, it’s your money they are throwing at it .
    and a stealership is the most expensive place to get anything worked on.
    If it’s out of warranty , avoid the stealership and find a private independent shop .
     
    Last edited: Nov 5, 2022
  6. MTMAUS

    MTMAUS Light Load Member

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    The motor pushes the steps from the front and the rear slides along a bar. The bar is smooth as and shows no signs of damage. But I can't tell if it's bent or not, I would need to take it out.

    I spoke to the technician and what has me worried is he said, the amps start off at 2 and build up to 6 as it slides along.

    Surely if the end of the bar was bent or damaged it would stay at 2 amps and spike at 6 at the end, it wouldn't gradually build up.
     
  7. baha

    baha Road Train Member

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    It seems to be a bent part at the inside of the slide bar? Where it gets tighter and tighter at the end of its travel, Like MAM pointed out?
     
  8. AModelCat

    AModelCat Road Train Member

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    Yes, weak batteries will cause more amperage to be drawn. Motors consume power based on watts. If voltage is lacking, there will a proportional increase in amperage draw.

    That said, I have my doubts its a weak battery. You'd have noticed issues with the starter long before having an issue with the stairs since the starter draws over 100x the juice the stair motor draws.
     
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  9. roundhouse

    roundhouse Road Train Member

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    Only way to find out is disconnect the linkage and slide the steps by hand .
     
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  10. tscottme

    tscottme Road Train Member

    Your theory is valid if the resistance to pushing the steps stays constant from start to full travel. If the path has resistance to movement starting early in the travel path it would produce the increase in amps you describe.
     
  11. baha

    baha Road Train Member

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    Does it have a brace at the end of its travel that can be adjusted out to make it slide easier down the slide bar?
     
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