diy solar

diy solar

One cell charging faster, triggers voltage difference disconnect

kl3vr

New Member
Joined
Nov 14, 2020
Messages
26
Hello, looking for help with my 4s lishen 280ah battery pack with daly smart bms. Sometimes, but not always, when I'm charging the battery at 20ah I notice the charging gets into a loop of ramping up the amperage then disconnecting. It appears the "cell voltage difference disconnect" is triggering as I see the difference ramping up to 0.271v before disconnecting.

I did top balance the cells and I have an active balancer installed as well. It just appears one cell is taking up the voltage quicker than the others. is this normal ? Bad luck? or damaged cell? what are my options?
thanks!
1636780009816.png
 
Simple fact is your cells are not top balanced. That's the only way you would be hitting hvd on one cell during charging.

The active balancer is (likely) to blame. They will constantly try to balance the cells, which results in ruining your top balance as the pack discharges. The only way to alleviate this is to charge AND discharge slower than the balancer can operate.

Otherwise do a full charge, wait for the active balancer to fully top balance them, then take it off. This may take a few cycles of cutting off and turning back on to get a full charge into all the cells with the cutoff occurring.

Also you're not charging at "20ah", don't confuse amps and amp-hours with one another. That's an important distinction.
 
It just appears one cell is taking up the voltage quicker than the others. is this normal ?
What are the voltages of all the cells at disconnect? How high are you attempting to charge your battery? Are you sure it is cell voltage difference and not cell high voltage disconnect?
 
What are the voltages of all the cells at disconnect? How high are you attempting to charge your battery? Are you sure it is cell voltage difference and not cell high voltage disconnect?
If there's a disconnect based on cell difference in addition to hvd there is still a balance problem either way.
 
Hello, looking for help with my 4s lishen 280ah battery pack with daly smart bms. Sometimes, but not always, when I'm charging the battery at 20ah I notice the charging gets into a loop of ramping up the amperage then disconnecting. It appears the "cell voltage difference disconnect" is triggering as I see the difference ramping up to 0.271v before disconnecting.

I did top balance the cells and I have an active balancer installed as well. It just appears one cell is taking up the voltage quicker than the others. is this normal ? Bad luck? or damaged cell? what are my options?
thanks!
View attachment 72157
This is usually caused by a bad connection (if you've top balanced).
 
271 mV will take a long long time to balance with the balancer shown. I would bleed that cell down during the next charging cycle to get the cells closer. Possibly reduce your charging voltage to 13.80 if you are higher.
 
If there's a disconnect based on cell difference in addition to hvd there is still a balance problem either way.
Agreed, but I am not sure I have ever seen a disconnect based on cell difference. My Overkill’s do not have that disconnect condition. I would have to check whether my Chargerys do (I suspect they do).

It’s just an odd situation to me which is why I was inquiring if it was known which disconnect condition was really being hit. It would probably affect the solution I would try.
 
I take apart and individually test each cell frequently.
If the pack is top balanced correctly, it is ALMOST ALWAYS a bad connection. Clean/polish each busbar and cell terminal. Wipe each surface with IPA (isopropyl alcohol) and re-assemble.

If one cells spikes, and a proper top balance has been done, this will almost always solve the problem.
 
Back
Top