Charging issues

[kl3vr]

Hello, I'm hoping this is the right area to post this. Ive been having trouble with charging my 280ah 4s battery pack. I have a Daly 200ah smartBMS and a kisae dmt1250 charger. using the DC charge setting and wired to my vehicle's alternator, the charger ramps up amperage then cuts off to zero, then tries again and again. I checked my voltages and the 4g cable running from the alternator is not causing a voltage loss that would trigger the charger to cut off. I noticed though in watching the BMS that my "cell diff voltage would climb to 0.339v during charging and suspect that is triggering a protection that is currently set to 0.25v. If this is triggering, it only interrupts connection and does not shut off the battery. very intermittently the charging will hold for a bit (I have it set to 30ah) but eventually resets. How can I diagnose this? are there BMS logs that would tell me for sure if a protection was triggered?

The other possibility is the charger's bulk voltage is triggering the voltage overload protection. From the manual, the dmt1250 will output 14.6v but my Juntek monitor is only seeing 13.8v when these issues are occuring.

I did top balance my cells when I got them, they've only been connected as a pack for about 3 months now. Its a pain to take them all apart and rebalance them so I'm looking at installing an active balancer like the cheap one Will showed that blew up on him lol. or replacing my BMS with one that doesnt have the bluetooth issues i'm having and can active balance?

 

[snoobler]

Your battery has gone out of balance. 0.339V is horrifying. If that's set at 0.25V, you've found the problem. BMS is cutting out. I don't know specifically about the DALY, but many BMS will only cut out the offending limit, i.e., still allow discharge if charging limits exceeded.

Set BMS to balance only during charge and only above 3.4V.

Start with 13.8V as your bulk and 13.6V as your float. Increment voltage 0.1V until it stops working, then back off. If it doesn't work at 13.8V, start at 13.6V. If it doesn't work at 13.6V, rebalance your cells. FWIW, you can get your battery to 95% SoC @ 3.4V/cell (13.6V).

Active balancers are fine, but they can cause problems. They may actively undo a top balance since they balance everywhere.

Per the manual, the charger restarts if the battery voltage drops to 13.3V

 

[Gazoo]

Its a pain to take them all apart and rebalance them so I'm looking at installing an active balancer like the cheap one Will showed that blew up on him lol.

The cells can be individually balanced without disassembling the battery. Since you claim you parallel top balanced I am assuming you used a 10 amp power supply? Set the power supply to whatever voltage you think will help before connecting it to the cell. Or you could top off all the cells to 3.6 volts or so. Just make sure balancing is turned off in the BMS app and there is no load. But you need to find out why the cells got out of balance. Possibly a bad cell connection.

 

[kl3vr]

good point on the individual balancing.

The cells can be individually balanced without disassembling the battery. Since you claim you parallel top balanced I am assuming you used a 10 amp power supply? Set the power supply to whatever voltage you think will help before connecting it to the cell. Or you could top off all the cells to 3.6 volts or so. Just make sure balancing is turned off in the BMS app and there is no load. But you need to find out why the cells got out of balance. Possibly a bad cell connection.

 

[kl3vr]

Your battery has gone out of balance. 0.339V is horrifying. If that's set at 0.25V, you've found the problem. BMS is cutting out. I don't know specifically about the DALY, but many BMS will only cut out the offending limit, i.e., still allow discharge if charging limits exceeded.

Set BMS to balance only during charge and only above 3.4V.

Start with 13.8V as your bulk and 13.6V as your float. Increment voltage 0.1V until it stops working, then back off. If it doesn't work at 13.8V, start at 13.6V. If it doesn't work at 13.6V, rebalance your cells. FWIW, you can get your battery to 95% SoC @ 3.4V/cell (13.6V).

Active balancers are fine, but they can cause problems. They may actively undo a top balance since they balance everywhere.

Per the manual, the charger restarts if the battery voltage drops to 13.3V

wonder why it fell out of balance? i'm not doing anything weird with them. Maybe the daly is pulling its power from one battery?

 

[snoobler]

wonder why it fell out of balance? i'm not doing anything weird with them. Maybe the daly is pulling its power from one battery?

Irregular use can cause it. These cells self-discharge, and they often do so at different rates, especially with these cheaper commodity cells.

IMHO, anyone who leaves a pack sitting for more than a week may suffer apparent imbalance. It will likely be easily corrected as @Gazoo mentioned with individual cell charging for < 60min each.

I recently helped a forum member with something similar. After sitting for 10 days, his cells drifted notably on voltage, and the series charge went haywire fast. No cell needed more than 6 minutes of 10A charging to reach 3.65V. Otherwise, they tested > 97% rated capacity.

 

[GSXR1000]

could be a loose connection... do a high discharge rate and see if it did it.
Also you can try bring the batteries down to 13.2-13.3v and then try... they won't deviate at that voltage due to the flat curve

 

[kl3vr]

Thanks everyone for the advice!

I singled out the low voltage cell and charge it up to match. its much more balanced now and the pack is resting at 14v when fully charged. I checked all the connections were tight. I also lowered my charging profile from 30amp to 20 amp which is a bit disappointing given its a 50amp charger from my alternator. i'll cycle it like this at 20amps a couple times and see if it falls out of balance again, and try ramping the amps up again if all goes well.

 

[GSXR1000]

Thanks everyone for the advice!

I singled out the low voltage cell and charge it up to match. its much more balanced now and the pack is resting at 14v when fully charged. I checked all the connections were tight. I also lowered my charging profile from 30amp to 20 amp which is a bit disappointing given its a 50amp charger from my alternator. i'll cycle it like this at 20amps a couple times and see if it falls out of balance again, and try ramping the amps up again if all goes well.

did you do an actual top balance? all cells in parallel and charge to 3.6v?

 

[kl3vr]

I had done one when I first got the cells. this time I just charged up the "out" cell.