Mobility scooter turned into kids car burnt through trace on tiller PCB

Discussion in 'The Projects Forum' started by Graham Roberts, Jan 16, 2015.

  1. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Dear all

    New to forum and have a basic understanding of electron is but am no expert. Also typing from phone so apologies for errors:

    Bought a Freerider Knightsbridge mobility scooter, stripped-down and turned into ride on car for daughter. Didn't come with batteries so,I bought two 12v wet batteries and fitted these. Machine worked fine for a few runs over the course of a year then one day I noticed a burning smell and smoke coming from tiller circuit. Nothing too complicated on this, a diode, ports for speed pot and throttle controller and a relay. I thought initially that relay burnt out but on closer inspection the power rail trace had burnt through. Sent off to a friend who is an electronics engineer who replaced the trace with a wire and cleaned all contacts to avoid shorts that he reckons could have caused the problem. He checked the relay and said this was not the issue.

    Anyway wired it back up ran,it round the garden, back out in the street and the same thing happened again. Friend at school (I am a teacher) reckons it could be over-volting as not using correct batteries but I don't see how, its a 24v scooter and the batteries are each 12v.

    Any ideas

    Thanks

    Graham
     
  2. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Sounds like you may have an intermittent short someplace else down line of that circuit and thats the weak link that burns up first.
     
  3. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi:

    Thanks so you think the short is NOT on the board but somewhere in the loom?

    If the loom is insulated do you think this could have developed by itself or unlikely unless there is a break in the cable?

    Thanks

    Graham
     
  4. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Without a proper schematic I can only guess but yes its common to have splices or taps on wiring inside a main loom and have one of them develop a short or open connection to another point in the circuitry.
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    The other reason could be loading of the motor, particularly on the main power rail, excessive mechanical friction somewhere etc, another is the motor could be cooked? Have you taken any current readings on and off load?
    Max.
     
  6. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi:

    Not yet as it broke and then I decided to use the workshop at work to build the car body so I am going to tackle the electronics issue now the cabinet is broken. OK this is where my electronics knowledge peters out. I have a multimeter and can use it but how can i measure the current without the board that burns out being in place? Where would I need to probe?

    Thanks

    Graham
     
  7. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi:

    If I could find you a schematic (I have pictures of the board) would you be able to look for me please?

    On this picture, the burnt trace has subsequently been repaired with a wire and the second burn has moved to the trace above.

    Thanks

    Graham
     
  8. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi everyone:

    Herewith is the circuit diagram - my scooter is the three-wheeled variant.
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That board seems conspicuously component absent!
    The circuit diagrams seem to be based on very general physical layout, not the circuit diagram that would aid systematic trouble shooting, unfortunately.
    Max.
     
  10. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    If it is working for short periods and then over current damage to the board traces stops it, I say your MOTOR is highly suspect.
    (no no - look good, work fine, - last long time) :)

    seriously, examine the physical structure. Is the shaft easy to turn by hand when free from the drive coupling(bearings)? Is there any scraping or scratching noise heard when the shaft is turned(brushes). Do the rest of the transmission parts move freely when tried by hand?
     
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    hold on a minute!

    you are running a 24 volt dc motor large enough to drive a wheelchair with the MOTOR POWER WIRING in series with PCB circuit board traces?



    put power wiring directly to the solder points on the relay both from battery and to the motor. put the fuse in-line on one of the wires. get the main motor power off of any PCB trace.
     
  12. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi Kermit I understand the motor is probably no good from what you sag and replacements are cheap and easy enough to find. Hoverer would it be cheaper to repair or once a motor does that its dead?

    Would a repair just be a case of replacing brushes?
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,061
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    These mobility scooters were never intended to run in grass/dirt. They can barely get a make it up the handicap ramps at some stores without smelling hot. Especially moving a 225 lb operator.

    Now, your daughter may not be 225 lbs but a 60 lb operator and full speed for minutes at a time on bumps and rutting in the grass adds a great deal of extra drag vs the smooth pavement these were meant to drive on.

    Also, did you wire the batteries at 12 volts (in parallel) or at 24 volts (in series). How were the original batteries connected?
     
  14. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi:

    Thanks, I have never ran this this on grass as I didn't want to drag filth through the house primarily and secondly because I thought it would strain the motors. They are wired as they were on the scooter originally.

    Thanks

    Graham

    PS I am going to investigate the motor issue and get another if necessary. Could you tell me if brush replacement on the current motor would possibly resolve this issue.
     
  15. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi GopherT:

    I notice that at the start of the thread I said that I ran it round the garden...this does have grass. However, I literally made it go forward and reverse one or two times to see if it moved before taking it onto the sidewalk (I don't know if you have similar houses in the US. However, my house at the time was like a brownstone house with no entrance other than through the house to the rear garden/yard. Therefore I didn't want to drag it through the house just to see if it worked.

    In general, it was hardly ever/almost never ran on grass.

    Thanks

    Graham
     
  16. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Looking at the general specs on one of these at 110 pounds on its own plus a rider capacity of 250 more I would think that it would have a fairly robust motor and drive systems that could easily handle driving a 60 pound kid around especially if it had been stripped down.

    As far as brushes go no I don't think changing them would do much good if the motor has shorted windings from being overheated bad enough.
     
  17. ebeowulf17

    Active Member

    Aug 12, 2014
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    Was the scooter originally set up for two 12V batteries with wiring all set up for them, or was it set up for one 24V battery and you adapted accordingly? Your friend seemed to think you were using the wrong batteries, which may or may not be true depending on how they're wired.

    If wired in parallel, the batteries would deliver 12V to the load, not 24V. The problem is the motors could then draw far more amperage than they're rated for (depending on the type of motor; not sure if this applies to all motors) because of the low voltage situation, which would lead to overheating and breakdown of insulation.

    So, to reiterate the question, are they wired in series or parallel?
     
  18. Graham Roberts

    Thread Starter New Member

    Jan 16, 2015
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    Hi: I think my friend's was a wild guess - there is space (i.e. two connectors) for two separate batteries which both deliver 12v = 24v total. I may well have wired them in wrong but I haven't changed the wiring - I just put a 12v on each of the connectors and hoped for the best. So ultimately I do not know, I assume that I wired them in series or in short, I haven't tried to do anything other than do a like for like replacement.

    Thanks

    Graham
     
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