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    Can't get battery to charge

    I am new to all the battery stuff, so excuse my ignorance. I have done some research online. I have a 52V dolphin pack that will not charge. I have taken out the BMS and it still wont charge. I have a 52V advanced 300W Luna charger. Everything was fine until I came in from a snowy fat bike ride with a depleted battery. I got a flat and rode till the BMS cut out. The battery wouldn't charge. I took the case off and disconnected the BMS and tried to charge through the output port. The charger says 58.7V and my multimeter says 58.8V. 2 days ago when this happen the battery was approx. 48V. I have since cut out the BMS totally. Right now the battery 45.5 at the cells. When I put the charger on, the voltage is 58.8 or 9 at the cells, but the standing charge never goes up. I tried 2 days ago for hours during my Eagles loss to the Saints and the standing voltage never went up. The charger never comes on to show current and the fan doesn't kick on, but when I do the incandescent load thing, it works fine. Maybe the charger is good? So from what I read and can see, I have 4P-14S and 7 sets of wires that went to the BMS. All the sets show 3.7 or 3.8V except one which shows 2.5V. So it seems I have a bad group. I just don't understand why it won't charge. If there's a differential, there must be current flow, right? Why does the bad cells stop the charger from coming on. I'll do more testing, but I think the charger is good and I need to cut out some of the cells. Any direction would be appreciated?

    New info.. I plugged it all in to confirm my voltage before I sent this and the standing voltage rose to 48 and the bad group of cells is .4 now. I guess that settles it. I can have a 48V pack.

    #2
    Any chance you guys at Luna have any more dolphin packs? I know they're not on the website, but I got three builds with their brackets and I'd like to ride before I get this fixed.

    Comment


      #3
      It does sound like there is a shorted cell in that one parallel group. There has to be a short someplace for it to self-discharge that fast, I think.

      Was the pack still below freezing when you tried to charge it? If it was, and one cell shorted, others may not be far behind....
      Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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        #4
        I took out one of the Parallel groups and soldered two 12 wires in it's place and now I have a 48V battery that charges. Of course now I'm going down the rabbit hole of balanced charges and cell auditors. Now I know I need to split the bank in two cause there's no reasonably priced balanced charger for 13 or 14s. And all that jazz. I knew eventually I'd have to get into all that, but I was hoping later rather than sooner. It hasn't been that many charge cycles before this happened. I'd say less than 75. I was hoping for more.

        Comment


          #5
          Maybe the BMS can be configured for 13S? Don't know but would be perfect if so. Worth looking into.
          Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

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            #6
            Right now the bank is back in the case and I can ride and recharge. Although it is a bulk recharge as opposed to a balanced charge. So I'm going to have to do something soon or they may get out of wack quick. But they started no more than .1V difference between all the cells. I looked up how to change luna's 52V charger to a 48V. But now my questions are, first how do you know if a BMS except by checking series voltages and assuming because they are all the same they are balanced. And this bank has the 7s cells removed and shorted. So I have 2 24V balance wires. The polarities are going to be different from 8s up to 13 from the way they were. Does this matter? After all one sense wire is the neg to one and pos to another sense wire. Do they have to be progressive in voltage? If so I will hav4e to re solder or re-pin the end. In that case I should just buy 4 cells and get them back in. But is the BMS is bad?... what to do? Also three cells of the parallel group I took out are like .3V but one is 2.4V. Can one be revived?
            I'll keep working on it. I found an 8S charger on hobby king. So I was thinking of using the 30A automotive fuse that already exists in a dolphin case as not only the open point between the 6S and 7 or 8s, but then I remembered the BMS was 30A continuous and 50A intermittent. Should I get one of those resettable thermal fuses, so I don't get stranded if I happen to go over 30A? I really would like to go the way of cell auditors and occasional balance charges, but what do you set the overload to? I guess all fuses have a curve so I could find a slow blow fuse or something?
            Any advice?

            Comment


              #7
              How did you get a result of different voltages for paralleled cells? Something funny going on here, I think. If parallel, they would be at same voltage.

              Did you disassemble that group, wait a long time, then measure the cells? Or, what?
              Last edited by JPLabs; 01-22-2019, 02:23 PM.
              Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

              Comment


                #8
                Yes, when I cut the group out, I separated them. They have now been sitting on my desk for days. If I measure now they are about .6 for 2 of them and 2.5 for the other 2. Although the act of measuring seems to slightly drain them. They keep going down by .01 volts as you wait for the number to stabilize.

                Comment


                  #9
                  OK, some have self-discharged, over time, after you broke up the group. Now it makes sense. Thanks.

                  Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

                  Comment


                    #10
                    Now I'm stuck again. I rode with the newly configured 48V pack at 54V and now it is at 52V, but will not charge. I am going to take it apart and check for bad parallel group, but I am wondering what is going wrong. Last time I took out the bad cells, it started charging like normal. I don't think it's the charger. I guess the cells are getting damaged without the BMS?

                    Comment


                      #11
                      If the cells are damaged and some are weaker than others, running without BMS can let weak cells go too low and damage them. That causes unsafe condition.

                      I frankly think you should stop running that pack, it's very suspect and I'm worried you will have an accident. Don't take this the wrong way, but what you are doing is unsafe, and I suspect you don't have the understanding and experience to do so safely. Your actions so far back this up...
                      Fabrication is fun! Build something today. Show someone. Let them help. Inspire and share. Spread the desire.

                      Comment


                        #12
                        wow.. go for the jugular. I was just looking for some help troubleshooting, not a criticism of my actions. I guess I'll have to figure it out myself. Maybe my EE degree and PE license will help me from killing myself. I did have more data, but never mind.

                        Comment


                          #13
                          Oh, yeah... I guess I took it the wrong way. Sorry if I misunderstood.

                          Comment


                          • JPLabs
                            JPLabs commented
                            Editing a comment
                            Haha, it's hard not too, but you didn't mention you are a pro EE, either, how was I supposed to know that? I guess you are aware of unmatched cells/unbalance risks, and plating issues, and fire risks and all the rest, then. But please understand that as a fellow engineer, I need to be responsible in any advising, too, and part of that is trying to keep someone from thinking that just reading my comments is sufficient to do something, when they might not understand risks. So, I use what they have told me to try to judge if they have demonstrated that they DO have full understanding. If not, I try to openly say so, instead of just letting them go on....that's all I meant to do for you. No offense meant to your professional credentials, but to be fair, you hadn't said much to reassure me, at that point, either....


                            Thanks for the follow up comment. Carry on!
                            Last edited by JPLabs; 01-30-2019, 08:31 AM.
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