Help repairing Mobility scooter throttle controller

Discussion in 'General Electronics Chat' started by theanurag, Nov 3, 2009.

  1. theanurag

    Thread Starter New Member

    Nov 3, 2009
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    Hi All,

    My mom's Mobility scooter ( Invacare zoom 220), has become immobile. I tried opening it and found that the throttle controller is not working. My problem is compounded by the fact that I Live in India and I cannot find any parts/repairing help here. So only option left to me is to troubleshoot myself and make arrangement for any parts needed. I need to understand how that works and how can I proceed to repair.

    I have no idea what that part is called, but I guess its called throttle Controller. because when you rotate it in one direction the vehicle moves forward and backward when rotated in other direction. I have opened the part and attaching the image of the cross section.

    Need help urgently!

    Thanks in advance guys.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    It is a potentiometer aka "pot".

    There should be markings on it somewhere as to the resistance value. There also may be manufacturer's markings.

    You may still be able to measure the resistance value of the potentiometer by using a multimeter set to Ohms across the upper and lower wires. Make certain that you check for voltage first; if you measure any voltage then you must disconnect the pot from the electronic controller.
     
  3. theanurag

    Thread Starter New Member

    Nov 3, 2009
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    Thanks Sgt, this is really a big step for me to move forward. The marking says RV024YN03-8A 21S B502. Can you please decode that value for me?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Hmm. The part number "RV024YN03" portion actually sounds vaguely familiar, but I'm not at home and thus don't have my reference materials handy.

    I think that's an Allen-Bradley part number. [eta] Allen-Bradley no longer makes potentiometers (or any other electronics for that matter); they sold the rheostat/potentiometer business to Clarostat, now a division of Honeywell.

    The B502 indicates a resistance of 5k Ohms.

    It would help a great deal to know what the diameter and length of the shaft is, so a replacement might be found.
     
    Last edited: Nov 3, 2009
  5. theanurag

    Thread Starter New Member

    Nov 3, 2009
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  6. SgtWookie

    Expert

    Jul 17, 2007
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    It depends on how you were measuring it.
    The two outer terminals are connected to the "ends" of a 5k resistor.
    The center terminal is the "wiper" that runs on the surface of that resistor.
    When you turn the pot, measuring from one "end" of the resistor to the wiper, that resistance will vary from nearly 0 Ohms to nearly 5k Ohms.


    OK, that's good to know.

    RV024YN03-8A
    RV = Carbon Film
    24 = 24mm diameter
    Y = Operating temperature, -10°C to +85°C
    N = Panel Mount, Single Unit, Single Shaft, Right Angle Ear-Lug Terminals
    03 = shaft length 3mm (yours is some kind of customized part)

    If you want to make certain that the pot is bad, try turning the power on and measure the voltage across the "ends" of the pot. Then measure from the grounded (more negative) end to the wiper, and see if the voltage changes from nearly 0v to nearly what you measured across the ends of the pot.
     
  7. theanurag

    Thread Starter New Member

    Nov 3, 2009
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    Thanks Sgt, that was again very helpful.
    Opps.. I think was measuring it wrong. I was measuring resistance between two ends of the resistor. I should have measured it between wiper and one end.

    RV024YN03-8A 21S B502
    RV = Carbon Film
    0 = Long Life Type (I guess it must b reading as 0, due to printing falut)
    24 = 24mm diameter
    Y = Operating temperature, -10°C to +85°C
    N = Normal Type (Panel Mount, Single Unit, Single Shaft, Right Angle Ear-Lug Terminals)
    03 = Type Name
    21 = Shaft Length ( 21mm)
    S = Shaft Type (Slot)
    B502 = Linear 5 Ohm..

    btw, I think I found nearly the exact part:
    http://www.tocos.com/products/?ProductName=RVQ24YN03
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    Yep, that's it.

    It's easy to mistake a Q for an O or 0. Frequently the "tails" on the Q's don't print.
    I don't know where you are, but click here:
    http://www.tocos.com/sales-locations/

    You should then be able to find a distributor near you. If you can't find a distributor, you may be able to order one from the manufacturer.
     
  9. theanurag

    Thread Starter New Member

    Nov 3, 2009
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    I checked that link, they don't have a distributor in India, but I have written a mail to them if they can ship it to India. Meanwhile I have checked the pot with proper method, and still looks faulty.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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    OK, I have no idea what part suppliers you may have in India.
    You should put your approximate location in your profile; that helps people help you.

    In the meantime, you could try to find a 5k Ohm pot locally that has the same diameter shaft, and as least as long, with the same threads. The diameter of the pot body may or may not be critical in your application; I do not know as you have not supplied any information on that.

    You might temporarily use a carbon pot, but it will have a very short life compared to the original pot.
     
  11. theanurag

    Thread Starter New Member

    Nov 3, 2009
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    I am also trying to find suppliers in India, who can give me similar pot. I will go to a part market this weekend. Moreover I have found one more problem with the scooter. The servo motor has a locking mechanism, that is also not functioning properly. I dismantled the scooter and tried to run the motor by giving direct supply from the battery. The motor has a engagement/disengagement lever which is i guess not functioning properly.
     
  12. theanurag

    Thread Starter New Member

    Nov 3, 2009
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    Hi Sgt, I have managed to get a pot, but its is unfortunately 1K less its 4.7k ohm (the earlier one was 5.7k). So I am not getting desired result, can I add 1K resistance in series with pot?
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    I do not know anything about your circuit other than it's using a potentiometer for a speed control; the original pot was supposed to have a resistance of 5k Ohms.

    I do not know if the pot was being used as a potentiometer or as a rheostat.
    If it were used as a potentiometer, a low voltage or ground would be on one end of the pot, and a more positive voltage would be on the other end of the pot, and the wiper (middle terminal) would have a voltage on it that was somewhere between the two "end" voltage levels.

    If it were wired as a rheostat, usually just one end and the wiper is used. Optionally, the unused end can also be connected to the wiper.
     
  14. theanurag

    Thread Starter New Member

    Nov 3, 2009
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    I have converted the problem to a mechanical problem now... and I can solve it now.. I will have to change the pot rotation mechanism. I will use a gear train so that I can convert a 25 degree handle lever rotation to 150 rotation of pot. Thanks a lot for your help

    By the way I found a potentiometer in India.
    http://www.pankaj.com/prd_singleturnpanel_RW1.html
     
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