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Voltage Sag Under Load

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    Voltage Sag Under Load

    Hello All,

    As the battery pack of my ebike is one of the most expensive items, I want to do all that I can to extend its life. I have a Luna Wolf 52V pack which is on a commuter bike. My commute is 13 miles of hilly terrain. I recharge at work and at home, to 80%. All of my reading in this forum says I should try to only charge to 80% and discharge to no less than 20%. I have noticed that as winter here in New Mexico progresses my range appears to be decreasing. Of course I can only use my 4 bar battery gauge as a guide but I'm starting to see a reduction in voltage, especially under load. My question is, is the 80%-20% capacity measured under load or a non-load situation? I don't have an actual voltmeter on the bike, but using the C961 display I consider 1 bar down to be 50% and 2 bars down to be time to recharge. Today on my commute I got two bars down, but as soon as i parked at work, the capacity gauge was showing full again. Does temperature play any factor in this? i am riding in 21 degree weather.

    Thanks in Advance


    #2
    You are charging to 100% at least every few times to balance - right? This is super-duper important...

    Comment


      #3
      Sure temperature play a role. See this link https://electricbike.com/forum/forum...li-ion-battery

      Comment


        #4
        AZguy

        I'm charging to 100% typically once overnight every 20 or so charge cycles (300ish miles). I have a Luna mini charger so i set the knob to 100% and let it run overnight. Is that how one would balance charge the pack? Or do I need to manually cycle the charger once its "done" to restart it?

        Comment


        • AZguy
          AZguy commented
          Editing a comment
          That's ok for balancing but I would do it more often than every "20 or so"... more like every fifth to no more than tenth and if I waited until every tenth I'd do two in a row or more. No need to leave it overnight, once the charge is complete it's pretty much finished balancing depending on the charger - some will indicate complete but still be trickling and for those you want to let them go for longer.

          When they are charged to 100% you should use them as soon as practical. Sitting around at 80-90+%, the more the worse, is not the healthiest for these batteries as is sitting around at 0-20%....

        • s205designs
          s205designs commented
          Editing a comment
          AZguy,

          Well that's good to know. Does it matter that i recharge at only 13 miles in? i don't typically see that much degredation but from my reading it seemed that it would be better to top it off to 80% than to drop below 20% on a ride.

        • AZguy
          AZguy commented
          Editing a comment
          There's no compelling reason I understand to run them down low... I will recharge at 50% plenty often and have recharged at 70% just to "top off".

          I just wouldn't go 20 cycles without a balance, especially with an older pack since in my experience they get out of balance more quickly... My old ones don't go more than about five cycles without a balance and I see them spending longer in the balance phase than my newer ones... but who knows?


          YMMV..

        #5
        Paxtana,

        Thanks for the link, my question on this statement from that link: Do's
        • You can use a frozen pack on your ebike (0C/32F), but be gentle as the voltage will drop a lot under high demand and you will hit the low voltage cutoff. As you use it the temperate will rise (see blow)
        Will hitting the LVC have the same effect of hitting the LVC with a truly depleted battery? Everyone says don't drain to cutoff, but in cold weather is hitting cutoff as detrimental to the battery as truly depleting the pack?

        Comment


        • paxtana
          paxtana commented
          Editing a comment
          Good question.

          The simple answer that anytime you hit lvc it's not great for the pack but you are going to see dendrite formation in the electrolyte affected not only by just taking the voltage outside of the recommended band of roughly 80% to 20% SOC but also a result of how long it is outside optimal voltage range.

          If you have a kit with programmable peak current like bbshd or bbs02 it makes a lot of sense to dial that back a bit in the winter. But you can also insulate the pack which will help with this a lot.. I know one guy just wraps his battery in fleece but you can get fancy with it..also storing at room temperature would help..
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