Hello,
I have a BMS NG connected to a 300Ah 12v NG litrhium battery, both brand new. There’s a 70mm wire between the two fused at 300A.
I noticed that eventhough the battery soc is 100%, the BMS keep on sending 100A (it’s been doing this for more than 30mn now!). Also, the battery positive terminal is very hot (80°c when I finally unplugged) ! For comparison, the negative terminal is at 24°c and the room temp is 19°c
Below screenshots of the BMS status. What’s going on here ? Thank you !
No worry, your battery is not fully charged yet. If this is a new battery your BMS probably doesn’t know the exact SOC yet.
Let it charge till about 14.2 ~ 14.4V after that the system will stop charging and is fully charged for the first time. If thats finished your SOC will be quite accurate!
If your battery is at 13.77v and still charging at 100a, it is not fully charged (100% soc) yet.
If you have a hot battery terminal, it is most likely a bad connection between the cable lug and battery, maybe a bad crimp, terminal bolt not torqued properly, or the cable lug is not flat.
Check that terminal and continue to charge the battery as per manual.
well this is not me saying it is fully charged, it is the BMS (see screnshot in previous post)
There’s a fuse holder connected to the battery terminal, and its base is flat (I checked). See attached picture.
The screw is torqued to specs.
I suspected the crimp also, but in that case the terminal screw wouldnt be the warmest spot, right? (see attached thermal screenshot)
Yes I saw that Victron Connect reported the battery as “balancing”
When the battery is fully charged Victron Connect will report the battery as “balanced”. #5 Initial Charging Procedure.
Pull it apart anyway and check.
Check the rubber boot is not between the batt terminal and fuse holder.
If it still runs hot, call your dealer for support.
So the charge current ended up going down to 0.5A so I removed that battery and plugged in another one. This time it says state 100% balanced, and it is charging at 110A anyway.. I guess the soc is just random when you plug in a new battery …(I assumed the internal eletronics inside the battery knew what the soc was…)
anyway this seems to be fixed…
and regarding the temperature, the culprit seems to be my fuse holder… it’s rated for 300A though, so I don’t know..
thank you for the help!
A new NG battery as with all lithium batteries is shipped at around 50% full. Knowing this, I set my SOC to 50% on my Lynx NG and they kept charging past 100%, they were closer to 40% SOC on delivery. I am not sure about the MRBF fuse on a 300Ah NG battery, the theoretical short circuit current is above the AIC rating of them, I installed Class T on my 300Ah NG batteries, much cost but better ratings, larger so better heat dissipation.
yes my mistake was to blindly trust the BMS soc on the new batteries. Anyway It’s all good now.
I’m going to follow your suggestion and install class T fuses ; not as convenient, but probably safer indeed. Thank you for the feedback!
