Small BMS (ng) does not respond to temperature dropping below 5degr

Q&A and troubleshooting
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1

Hi there,

I’m struggling a bit with my new small BMS ng that doesn’t respond to the battery temperature dropping below 5 degrees.

I have a 24V 200ah lithium battery bank NG that powers my boat systems, there are two battery protects installed, one for loads and one for charges.

With the lower temperatures right now in N Europe the BMS should shut off the charger port. However, doest not respond to the battery cell temperature currently being 3.9degr. Meaning, it allows the battery protect to charge.

To make things more complicated; I did have a problem with my previous small BMS being faulty (unit did not respond properly to manual shut down command, and it ALSO did not shut off the charge port when the temperature dropped), so I replaced it.

Right now I installed the new small bms ng. While installing the battery was below 5degr and hasn’t been above since (so I decided no charging), but like I mentioned, the BMS disagrees and would let current pass via the battery protect. One theory could be that the BMS would need a full cycle before being able to control the charge/load ports. For that I would need to wait until the battery gets warmer, charge it, then let it cool down again to see if then it responds as it should when the temperatures drop. However I find this unlikely,

Any idea’s or similar problems with small BMS NG in colder climates?

‘ will update as soon as issue is solved

2

Can you clarify if you only have the minimum cell temperature of 3.9°C but the maximum cell temperature is 5°C or above and the displayed battery temperature is also 5°C or above. I am also showing min cell temp of 3.9degC but max cell temperature and battery temperature are 5°C or above. I have the Lynx NG BMS and this is still allowing charge. I have Node-RED flow which limits the charge current to 0.03C (18A max charge on 600Ah) if the minimum cell temperature drops below 5°C. My conclusion is the charge control works off the battery temperature which is an average of all the cells rather than the minimum. The manual quotes battery temperature as controlling the charging rather than minimum/maximum cell temperatures.

3

Max cell temp was 4.1degrC in my system, its relatively close to 5. Still I would expect the system to have a hard setpoint at 5.

4

My max is 5.2degC so I am keeping an eye on this but I am less worried with the low rate of charge from my Node-RED flow but I am keeping a close eye on this. In your case, as long as the battery temperature was below 5degC I would have expected it to have stopped charging. I will pass on to Victron.

5

Mine went below 5degC overnight and allow to charge is still saying Yes with a 600A CCL. Will definitely raise with Victron.

6

I have been told that the NG BMSs stop charging at 2degC and restart charging at 3degC. I can confirm this, mine dropped to 2degC and ATC went to No and CCL to 0. The battery manual will be updated to remove reference to 5degC. The NG batteries are better than the Smart Lithium and the 5degC is a hangover from them.

8

That would make a lot of sense. I’m happy to hear this as it would mean my system is OK. By now my battery is properly warmed up, so It’s hard to test this scenario right now. But perhaps in the coming month it will drop below 2 at some stage and I will see the result.

Thanks for investigating this Pwfarnell, very helpful

Ciao, Roman