# BMS only charges until 90%

I’m not sure if my BMS is ok but, If I plug my 42V 2A charger the battery metter quickly raises to 100% if I unplug it, it goes down to 90%

The max voltage I can charge the pack is 40V instead of 42V . Any ideas?

Have you double checked with a volt meter?

Yes the 10S battery pack has only 40.5V at the end of the charge. Maybe I need to use a charger with more than 42V 2A

Is it going up to 42v while charging and then coming down or just stopping at 40.5?

It’s not necessarily a bad thing as stopping at 41V is good for battery health in exchange for a small loss in capacity.

Did you check the voltage of each parallel pack? Make sure there isn’t a dud or disconnected balancing connector.

If it’s just a simple voltmeter, then it will be skewed by the current from the charger.

The charger may still actually be charging when the battery meter hits 100% while plugged in. Mine does this.

Essentially, when you’re plugged in charging, your battery meter will show that the level of charge is higher than it actually is. My battery meter usually shows its at 100% when the charge gets up to around 90% but the charger will keep charging until the BMS cuts off the circuit when the battery is actually fully charged.

I agree with @smurf though, charging your board closer to 90% or less each time rather than fully charging it every time is a good idea as long as you don’t need the full range of your battery as it’ll help increase the life of the battery.

@Pantologist yes I check the charge if each pack.

There is a difference in one pack that holds a lower voltage than the other 9, for instance while all the packs have 3.794V the bad one only sees 3.685, there is a difference 0.11V, not sure if this has something to do with the fact it doesn’t reach 42V

Wel, it probably does not start balancing until it reaches 42v… How long did you leave it charging? Is it actually stopping the charge current at ~40V?

The charger I’m using is the Evolve one with 42V 2A, it has a led that turns green once it reaches 42V.

I’m not sure what the oroblem is buy the BMS might stop charging/balancing when it detects an unbalanced pack, maybe, maybe not.

I am pretty sure Evolve charger’s cut off at a lower voltage to improve battery charge cycles.

@whitepony might know.

I also have @barajbali charger it also goes up to 42V @ 2A, samething happens, stops charging at 40.5V

What BMS do you have? Some BMS cut off voltage at 4.25v and do not allow the other packs to reach full voltage.

I have the battery supports 10S 60A BMS, I couldn’t find the charging strategy of this particular BMS.

Tmorrow I’ll messure the voltage of each cable of the BMS disconnected from the battery to see if any wires are not giving me the correct voltage

I had a similar problem with my setup when I replaced one of my 5 Lipo packs. It had a storage charge and the rest of the packs where higher. My bms and charger would not fully charge the system but would stop short of a full charge. So I got my hobby charger out and balance charged each of the five packs separately matching them in voltage and then reconnected them to the bms. It worked fine after that.

I’ve been battling with this problem for weeks, but everyday it was charging more and more until 3 days it reached 100%.

I opened the battery cover and measured the voltage of each pack:

1. 3.74
2. 3.74
3. 3.74
4. 3.76
5. 3.77
6. 3.78
7. 3.66
8. 3.77
9. 3.67
10. 3.79

Cell 7 is always below average by 0.12V, it’d say that’s acceptable.

I wonder what’d happen if I discharge each pack, but the lowest one, individually until I get the same voltage, in other words, balance all packs?, I may have to do that sometime.

Try charging them indavidually to 100% to balance them and then reconnect the BMS.

do you have a little indicator light on your charger… if so follow it (wait until it is green, and then wait to see if it flashes in the balancing phase), but don’t believe you lcd.