I have i battery pack 48V 33Ah with 13s and 16p, a charger with 250W and 5A power and a bms connected to it that sux. All it does is to cut off charging at 4,2v per cell and discharging at 2,8v..that's good, but it doesn't balance at all. The pack is very unbalanced right now. When fully charged the top cell charges to 4,18v and the lowest charged cell is at 3,88V. I have charged it up five times now but it's still at 3,88V when fully charged. It's there any good bms out there? I found one with app support at bmsbattery.com, sounds cool, is it good?
A bms that actually balances and is good!
- Thread starter apkungen
- Start date
Inwo
10 kW
Chargery bms has display and balances @ 1.2 amps.
I've used it on 100ah 24s packs. In a few days it fixes anything.
I've used it on 100ah 24s packs. In a few days it fixes anything.
That bad a problem would probably require at least days (possibly weeks) of leaving it on the charger constantly to fix. Have you tried that?apkungen said:
Or are you just charging it then unplugging it when the light goes green the first time?
If you don't let it sit there cycling the charger on and off as needed until it's really done, it isn't going to balance anything.
But if a cell group is that far down, it also means that the group is bad and should be replaced, because it doesn't have the same capacity or internal resistance as the other cell groups do, and it's always going to get unbalanced like that (no matter what BMS is on it).
Additionally, if you run the pack down to 2.8v/cell it's pretty hard on them. Doing it frequently is worse. I'd keep them well over 3V if possible, closer to 3.3-3.4v minimum. You don't get as much capacity out of the pack but it won't get unbalanced as easily and it will last longer before you have to replace it.
If you can get to the individual cell voltages (seems like you can, since you give an example) use an RC charger like the IMax B6. Start with the battery "fully charged" (as full as you can get it with your current charger), and then charge one parallel group at a time (using the balance leads if you have to) using the RC charger. Don't set it at too high an amperage if you're going through the balance leads and try to monitor it. The lowest voltage group is the one most likely to give you trouble, I would think.
You can even purchase a connector that mates with your balance connector to make this easy -- a two pin version of the same connector type that you can just move from position to position to get each cell group.
I find that adding to the lowest group is much faster than going through a "balance" that lowers the voltage in the highest cells so that charging of the whole battery can start again. And I suspect it's much friendlier to the healthy cells than a lengthy balance that bleeds their charge out through the bms. Seems to me that it's not great for them (the higher voltage cells) to be repeatedly charged up to the cut-off and then drained a bit so that the lower voltage cells can finally get topped-off.
You can even purchase a connector that mates with your balance connector to make this easy -- a two pin version of the same connector type that you can just move from position to position to get each cell group.
I find that adding to the lowest group is much faster than going through a "balance" that lowers the voltage in the highest cells so that charging of the whole battery can start again. And I suspect it's much friendlier to the healthy cells than a lengthy balance that bleeds their charge out through the bms. Seems to me that it's not great for them (the higher voltage cells) to be repeatedly charged up to the cut-off and then drained a bit so that the lower voltage cells can finally get topped-off.
RC chargers are relatively cheap -- that's why I use them. For an even cheaper route to the same solution, get one of the really cheap chargers that's meant to do a single cell and hook a group of cells up to it. I've resorted to using binder clips and hook-up wire before I had the IMax B6.
Thanks for the tip. I'll look into that bms.
The reason they are so unevenly balanced is because some of the soldering went loose after I fell with the bike. I went through the soldering and added some cells and now it is unbalanced. The cell is still good I am sure since it charges up to the same voltage every time even though the bms doesn't work.
I have tried leaving it on for maybe 15h, still exactly 3.88V in the cell so either the bms isn't getting any current at all from the charger after it has gone green or the bms it crap, probably the latter.
I could buy an rc charger but I still want a bms that can work in the future.
The reason they are so unevenly balanced is because some of the soldering went loose after I fell with the bike. I went through the soldering and added some cells and now it is unbalanced. The cell is still good I am sure since it charges up to the same voltage every time even though the bms doesn't work.
I have tried leaving it on for maybe 15h, still exactly 3.88V in the cell so either the bms isn't getting any current at all from the charger after it has gone green or the bms it crap, probably the latter.
I could buy an rc charger but I still want a bms that can work in the future.
Remember, the BMS does not charge the low cells.apkungen said:
The BMS drains the high cells.
Until the high cells drain quite a lot, you won't see much, if any, change in voltage of the low cell, because it is in the middle of the charge curve where it takes a lot of capacity change to make a little voltage change.
Are you measuring the high cells and watching them during the entire charging process? If not you are probably missing that they are charging up to just past full, then the BMS shuts off charging, then drains down that tiny bit of extra charge.
Then if the charger is designed to kick back on once the BMS re-allows charging (many are, but not all), then the current resumes and the process repeats.
As bad a problem as you have there, the process takes much more than 15 hours depending on the balancing current capabilities of the BMS.
BMS are only intended to keep small imbalances at bay, not the kind of problem you have there--those kinds of severe imbalances are meant to be fixed separately, by replacing problematic cells and manually ensuring they are at the same charge state as the other cells, and *then* letting the BMS fix any minor imbalance.
Also, the cell group itself may have at least one damaged cell that is discharging down to that voltage for some internal reason, and shorting all the other cells in parallel with it to the same voltage. You'd have to disconnect the cells in the group from each other to find which one is doing that.
You can also use a single cell charger to bring up the low group at least a little, then watch it with a meter and see if it goes back down again.
If you don't know, then you should measure it. Otherwise you don't know if you are wasting money on something that isn't needed, if the BMS is already doing it's job.
If you have a multimeter, it probably also has an Amps setting. If you put the meter in series with the charger's positive lead (or negative, doesn't matter, just one at a time), with it set to A, you can see how much current flows at any time. Series would be positive meter lead to positive charger lead, and negative meter lead to positive battery lead.
Or use a wattmeter.
Another problem you could have, since there was a physical impact involved, is wires and cells with damaged insulation you may not be able to see. If it's not a complete short, it could be draining that group of cells at a rate slow enough to not completely kill them, but to force them to unbalance.
Also, if you added cells to that group, the added cells could have problems either originally or from the work done to add them (overheating during soldering, for instance).
If you added cells because that group was low in voltage after the impact but not before, then the group probably shorted against something. The short could have damaged the existing cells, especially if they discharged at a high enough rate to internally heat them too much, but not enough to make them catch fire. That kind of internal damage has unpredictable results, and can include being unable to charge past a certain voltage, or being unable to hold a charge above that.
Until you thoroughly test the pack's cells and groups, and wiring (including balancing wires to the BMS) and get them charged evenly, you don't know what part of the pack is actually causing the problem.
Making the assumption that it's the BMS may cause you problems down the line up to and including a fire, if there are damaged cells or wires inside the pack.
I just read the last comment. Thanks for the info. I understand now how the charger works and the way it balances. I'm gonna leave it plugged in for two days and see. Thanks for the tip about the A metering from the multi meter. Gonna measure that as well.
I think the bms can balance 80mA (if it is working). The cells are 33000mAh each, so to bleed a cell from 4.2 down to 3.88V should be about 8800mAh if the curve would be linear (I know it's not but this will be a pessimistic calculation) meaning it will take 110h to balance!
I going to leave the charger in for 4 days and check back on it afterwards and see what has happened...
I have already checked all the cables, fuses and solderings after the crash. They should be fine. I won't go through every of the 208 batteries though to see if they are ok.I've done that once with a litokala battery discharger. It took forever.
I think the bms can balance 80mA (if it is working). The cells are 33000mAh each, so to bleed a cell from 4.2 down to 3.88V should be about 8800mAh if the curve would be linear (I know it's not but this will be a pessimistic calculation) meaning it will take 110h to balance!
I going to leave the charger in for 4 days and check back on it afterwards and see what has happened...
I have already checked all the cables, fuses and solderings after the crash. They should be fine. I won't go through every of the 208 batteries though to see if they are ok.I've done that once with a litokala battery discharger. It took forever.
