Help with 12v

Discussion in 'The Projects Forum' started by yelnats69, Sep 23, 2013.

  1. yelnats69

    Thread Starter New Member

    Sep 22, 2013
    I am an absolute beginner,
    I want to be able to charge a 12v wheelchair battery while my car is running.

    The ideal use would be to simply plug the wheelchair battery into the 12v battery on the car or the 12v cigarette lighter.

    I think I would have to add some sort of Diode so that the current travels to and not from the wheelchair battery while plugged in.

    I do not want the car to use the wheelchair battery (if that makes sense)

    Once completed then I would like a second diagram to add some sort of led indicator. is their a led that will only light when battery needs charging or when battery is charged.

    I would like to have the whole thing run off the main car battery or 12v socket and not involve any ignition fed designs.

    main battery is 12 60amp second battery is 12v 20amp both are lead acid.

    I would like to use Anderson pole connectors what amps and wire size, I only want to charge the 12v 20 amp or keep it topped up.
  2. Efron

    Active Member

    Oct 10, 2010

    Usually batteries are charged through current source and not through voltage. I don't think you will get good results if you just plug your wheelchair battery into the 12v car battery or cigarette lighter.

    You should look for a current source circuit which will be connected to your car output on one side and to your battery on the other side.

    Usual charging capacity is 1/10 of full current, that is, 6A for your 60A battery.
  3. killivolt

    Distinguished Member

    Jan 10, 2010
    You would have to get above 12v supply to charge usually around 13.5v. Coming directly off the alternator, and going to a charger would be the only way I would do it.

    But, charging inside the vehicle is not a good idea. Gases will be venting into the vehicle and their could also be an explosive danger, not likely, but it's always possible. That's why they don't provide such things.

    If, you could isolate that part of the vehicle, providing air movement, then using the suggested method. I think would be the safe and practical way to approach this.

    FYI, just my opinion.

  4. wayneh


    Sep 9, 2010
    In my opinion, there is little risk to the simplest solution - just connecting directly through the accessory jack. With a running engine, reverse current will not be an issue. You could always add a blocking diode if it makes you feel better, but that will prevent charging to full voltage since the diode will drop ~0.4V or more depending on the type you choose.

    The jack is already fused, likely at 10A. If it was me, I'd add another inline fuse in my cable to limit the max current thru the battery under charge, if it cannot tolerate the full 10A.

    Venting is an issue, but I don't think it would be a problem unless the cabin ventilation is completely turned off. As long as there is fresh air, I don't see a problem.