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Charging my power chair from a bench PSU?

Discussion in 'Power Electronics' started by Terry01, Jul 6, 2017.

  1. Terry01

    Terry01

    204
    48
    Jul 5, 2017
    I have wondered for a while now about doing this. Just because. I know my proper chair charger does this fine but I'd like to watch it happening. I'd like to see the process happening with one or both my meters hooked up measuring it and also watching it on the displays on my bench PSU.

    I'm also a member of another forum that's dedicated to power chair stuff. The guys there know their game and help the rest of us with problems. I've learned from them generic chargers will charge my chair,all be it badly because they are set up wrong. To high volts and go through the gears wrong. They are lithium daft if any of you fancy a natter with them on that subject.

    Anyways.....any thoughts one way or another on how this would go and how best to rig it up?
     
  2. dave9

    dave9

    773
    171
    Mar 5, 2017
    I would just get a ready made panel mount voltmeter/ammeter module on eBay, make an aluminum mounting bracket with a rectangular hole in it and put that wherever is most convenient (I don't know exactly what this power chair is), or put it in the charger housing if there's room for it, and continue to use the correct charger.

    You'd simply put wire them as expected, voltmeter portion wiring across +/- charger inputs, and ammeter portion you'd sever the positive charger input and reconnect it across the ammeter.

    Example:
    http://www.ebay.com/itm/DC-3-5-30V-...mmeter-Voltage-AMP-Power-New-FO-/301723533033 (This assumes 30VDC or lower charge voltage, which should be appropriate for a 12V or "just" within a typical 24V system peak charge voltage unless it's a rapid charger (bad for battery)).

    Perhaps we need more info, like what "go through the gears wrong" means as gears are not a common term to use in charging, or a link to the power chair and battery since what I am thinking of as a power chair is more conventionally powered by one or two 12V lead acid batteries instead of lithium.

    Regardless if you continue to use the correct charger for it then it should work so long as it has a single positive input rather than a higher voltage then reduced downstream for balanced charging.

    Could you use a bench PSU? Sure if you put a charge controller in series with the chair, but presuming it would work and you just want the visual feedback of charge state then the voltmeter/ammeter module I proposed above should kill two birds with one stone.
     
  3. Terry01

    Terry01

    204
    48
    Jul 5, 2017
    I was just thinking of doing it once or twice,I wouldn't want anything permanent in place. What your thinking of as a power chair is correct,two 12v lead acids powering it. Is it in series or parallel so it gets 24v?
    They guys on the other forum convert their chairs from lead to lithium. The benefits are awesome! I could get round to that once I learn some more and I'm more confident building things and stuff. I think its quite easy if you have some knowledge and confidence.
    By "through the gears" I ment charging cycle. Good thing there's always one willing to help ☺
    Thanks
     
  4. dave9

    dave9

    773
    171
    Mar 5, 2017
    What kind of mechanical connection does the charger use? You could just make an extension cable that has the voltmeter/ammeter module on it, that can be swapped in, or not used, depending on whether you want to see the state of charge. However I would think that it would be nice to have the module permanent on the vehicle so you can see what the battery voltage is. Relative to powering the chair motor, the display uses a trivially small amount of power.

    I would expect two lead acid batteries to be ran in series for 24V, but either way is possible. They could design for 12V then the 2nd battery would be an upgrade for extended runtime.

    Once you determine whether the batteries are in series or parallel, you could use a bench supply with adjustable voltage, and use its display or again a series volt/ammeter as I'd linked to monitor it.

    The optimal charge voltage depends on battery temperature but is around 13.8V for one, or 27.6V for two in series. Some chargers may go higher to charge faster, it's a personal choice what tradeoff to make, but you should stay below 14.7V/battery or 29.4V for two in series and that high a voltage needs more amps unless you have a quite beefy bench supply.

    In some cases an inexpensive bench supply may not even be able to supply enough current for 13.8V. You didn't mention what you have. If not then just let it run with a conservative margin and switch over to a constant float voltage of 13.5V per battery in series.

    Since I am not familiar with any possible charge termination circuitry that might be on the chair to safeguard against battery overcharge, it could be a bit more complicated trying to complete a charge with a bench supply without reverting to a lower float charge for a much longer period of time. It seems as though you already know of a better forum for details specific to your chair.
     
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