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Is a 3.1 mA battery drain after charging a concern?

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    Is a 3.1 mA battery drain after charging a concern?


    My equipment...Luna, 52 volt-3 amp Mini charger with three position switch. 80,90, and 100% settings. With the two LED bulbs. Luna 52 volt 11.5 ah bottle battery with on/off switch.

    After reading a few threads stating that the battery will back-feed the charger after it shuts off, I verified that this does indeed occur for me at a rate of 3.1mA.


    Questions...? Is this why you have to remove the charger after charging to 100%, allowing the BMS to balance the cells. Then repeat a couple times. And after a 80 or 90% charge would this amount of loss be a concern? Say if you where to leave it to charge at a leisurely pace overnight.
    See my E-Bike build in progress HERE.

    #2
    Too small to matter, I think. Voltage won't fall fast enough to impede balancing. If the drain was continuous, you could leave it for 2000 hours and only use about 6 Ah. And the charger should cycle anyway to top off.

    no problem.
    Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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    • JPLabs
      JPLabs commented
      Editing a comment
      3 mA is probably just the LED.

    #3
    From the other thread:

    3mA is very small in the scheme of things. For 3mA to drain the battery even just 1% of a smallish 11.5Ah battery... 11.5Ah / 3mA = 38 hours - not much to worry about =]


    A very funny thing too... I'm very familiar with diodes in series. I've got several batteries so I like to keep them about 80% charged and I can either run them from 80% or throw them on a charger for an hour to bring them to 100% before using. I put two 5A Si diodes in series and then when the charger shows complete I unplug it and end up with about 80% charge. To bring it to 100% and balance I jump the diodes out with an alligator clip jumper. If I forget and leave them on the charger with the diodes in series, no harm, it will just charge it more than the 80% but very slowly. I guess eventually it would bring them all the way to 100% but I've never forgot for more than a day or two and it's not gotten more than about 90%. Poor man's approach to 80% charging... not perfect but plenty good enough for me!

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      #4
      Thanks for the replies, and doing the math! I feel better about it now. So why does the charger have to be removed to balance at 100%?
      See my E-Bike build in progress HERE.

      Comment


      • AZguy
        AZguy commented
        Editing a comment
        The charger needs to be connected at [near] 100% voltage for a while in order to balance

      • Tommycat
        Tommycat commented
        Editing a comment
        But why is it recommended to disconnect it (the charger) after hitting it (100% charge) for a few hours?

      #5
      I think you may be referring to an earlier post that suggested with new batteries (or a battery that is suspected to have cell balance issues) to charge them fully to 100% and then discharge them a bit with a light load and then charge them again to 100%. In that post the reason for doing this is that when a battery is not well balanced it can take several balancing cycles to get it well balanced.

      Just my guess... there is no other reason to disconnect once at 100% perhaps aside from it not being a good idea to leave a battery at 100% for a prolonged period (I avoid leaving them at 100% for more than a few hours and rarely more than a day) but that applies even if off the charger... That may be a bit more OCD than the derived benefit (longer life for the battery) but it's what I do.

      From my logs I'm comfortable that charging every time to 100% is harder on the batteries than charging to 80-85% typically and then after several cycles of this a couple to 100%. I have two nearly identical batteries with almost the same miles. One was charged to 100% every cycle for the first 6mo of its life and the other following my routine. The one that got charged to 100% does not hold quite as much charge (Ah) measured by batt-man and comparing to initial and final voltage and the voltage sags more under load (higher internal resistance).

      It's a sample size of one so not statistically significant (not a statistic at all =] ) but the theory is sound why it's an issue. How much? For me the cost of charging to 80% is almost nil as it is habit so even if the benefit isn't all that great - why not? As long as they get balanced enough...

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      • Tommycat
        Tommycat commented
        Editing a comment
        Excellent! Nothing beats experience and real time data! Thank you.

      #6
      My 52v Mini is appears to be intermittently draining the fully charged battery when left plugged in overnight. Charges to 58.3v then in the morning it has dropped to 54v. It doesn't always happen though. Have I got a faulty charger?

      Comment


        #7
        As you've read from this thread, even a good Luna Mini charger will allow some discharge to occur after charging stops. But not to the degree which you are experiencing. A couple things stand out...
        A 52 mini should charge to 58.8 volts. You should read this right when your charger shuts off, assuming that you have a good quality calibrated meter. This is when cell balancing may take place if required by unbalanced cells. Perhaps a volt or 2?
        Intermittent, again seems odd. Again assuming that nothing else is connected to the battery while charging, including controller or cradle. sounds like an intermittent internal battery parasitic drain or bad charger...
        I'd check the non-charging amp draw drain by the plugged in charger first... should be around 3 mA as per my experience. If that's O.K. Charge and immediately disconnect charger and see if problem persists. If so it must be internal to the battery.
        Last edited by Tommycat; 4 weeks ago. Reason: Added specificity of charger type...
        See my E-Bike build in progress HERE.

        Comment


        • AZguy
          AZguy commented
          Editing a comment
          A lot of the very basic inexpensive CC/CV chargers (all of mine) just hold the final voltage (CV) so no leakage _to_ the charger...

        • eCooker
          eCooker commented
          Editing a comment
          Yes I will test the drain with charger connected next. Battery is out of cradle. Charged over night, sometimes only drops buy 1 volt but others by 3 or 4 volts. I disconnect it now, when I remember, once charger stops so I don't get range anxiety on the way to work.
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