Using mobile phone charger in place of RC car charger.

Discussion in 'General Electronics Chat' started by utilityhacker, Jan 1, 2015.

  1. utilityhacker

    Thread Starter Member

    May 1, 2014
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    So i have the RC car which runs on a rechargeable 3.6v, 500ma Ni-Cd battery. The car came with a charger that is rated 4.8v, 250ma output. The problem is the charger is not working anymore and i really don't want to lose the car. I have a mobilephone charger which is rated 5v, 500ma output. The question is can i use mobile phone charger in place of the RC car Charger...??
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Assuming that the charge-controller is actually built-into the car, then it should work, as long as you match the polarity on the plug...
     
  3. ian field

    Distinguished Member

    Oct 27, 2012
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    3.6 is the nominal voltage of 3 nickel cells, while 4.8 is the nominal voltage of 4 cells - if the packing dept put in the wrong charger, that might explain why it failed.

    It would be highly advisable to investigate what limits the charging current before raising the voltage even higher!
     
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  4. utilityhacker

    Thread Starter Member

    May 1, 2014
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    i actually opened up the car thinking its the car causing the problem to see but i was wrong and the fault was in the charger.
    Also i didn't see a charge controller.

    Yes it its a pack of 3 cells. The charger was working fine for a week or so before it died.
    but can i really use the mobile phone charger..???
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    No, as I said, not if there is no charge controller in the car.
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    Is there even the remotest chance of taking the cells out for charging? Various discount stores have NiMh chargers that have multiple bays and end of charge voltage change detection.

    You certainly need to have something to limit the charge current, and that's not specifically part of a mobile phone charger. The safest option for just a current limit resistor is to calculate for C/10 - it'll take about 14hrs to charge and can still damage the battery if left charging for weeks.

    Since this is an electronics forum, I can suggest something a bit more effective; Use temperature sensing to detect end of charge, about 45c should do it, you need a thermistor touching at least one of the cells, and wired in a potential divider with a normal resistor. Next you need a window comparator - 2 ordinary comparator referenced to 2 points on a string of 3 resistors. The window comparator outputs drive a S/R flip flop which in turn drives the series pass transistor or MOSFET switch.

    You still need the current limit resistor, read the current capability of the mobile charger and calculate the resistor accordingly.
     
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  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    How many pins are there in the charging plug on the car? I'm trying to figure out if it has a battery pack temperature sensor?
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    Since the old charger is dead anyway, it might be informative to break it open and see what's in there.
     
  9. utilityhacker

    Thread Starter Member

    May 1, 2014
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    Actually i found a charger that was rated 5v, 300ma which is 50ma more than the rc car charger but it works fine.
    The battery pack doesn't heat up and the cars is working good.
    THANKS FOR UR HELP GUYS.
    I consider this thread closed.
     
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