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My BlueNova BN13V-108-1.4K was n permanent sleep mode


rectangularBuilding
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I hope this might help someone some day.

I use this battery for my touring bakkie. But it's a new build and I was only in the testing phase.

When left alone, the battery had gone to sleep numerous times and I always woke it up, either by bridging the terminals with the included 6.8 Ohm resistor or by connecting a charger. Normal behavior of the BMS.

One day, after I think three months of inactivity, it didn't wake up. I thought I had disconnected everything but I believe a temperature sensor that I had forgotten drained the battery a little more each time it woke up.

Some emails later, BlueNova support concluded that the BMS was in "permanent sleep mode"  and that I should claim warranty. Then I learned that this would involve me paying for a courier no less than four times. From my town to the seller, from the seller to BlueNova, from BlueNova to the seller and from the seller to my town. I'm in Namibia.

Voltage on the terminals was 3.8 V at this point. I looked at the battery and removed the maintenance plug on the right side. There is a connector below the hole labeled PC2, with pins A and B. I measured the voltage between these pins and saw 0 Volts. I shorted the pins hoping to wake up the BMS.

I cut a rectangular hole into the battery enclosure (remember the 4 courier fees) to see more of the BMS. BMS uses two stacked PCBs. BMS is labeled XT4BA0971. You can't find this string on the internet search. I now had access to the internal cells voltage. Disappointingly, it was also only 3.8 V. LiFePo can be damaged below 2V per cell (8V) but 3.8 V should not totally kill it.

I applied 13 Volts to the internal negative wire on the BMS using a lab supply limited to 2.5A. After about 30 seconds, the voltage was 8 Volts and I guessed the BMS should be awake. I connected a Ctek 7A charger to the external terminals and charged the battery fully. After two full charge and discharge cycles, I got 1.2 kWh out of the battery and 96 Ah with a 180-140 Watt load. No idea what a new battery should deliver. Either my battery has degraded by the over-discharge to 3.8 V or the battery specs are too high.

Low-voltage disconnect by the battery was at 10.7 V.

I am guessing that BlueNova could wake up the BMS on the PC2 connector but I'm sure they wouldn't tell anyone how to do it. Also, "permanent sleep mode" seems to be a non-standard term and sometime I want to research if other BMSs have this feature.

Anyway, I plan to continue using the battery now. It's good enough for use.

Edited by rectangularBuilding
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I can tell you from experience on LiIon cells, you can store them longer term if you charge or discharge them to 50% state of charge. I just checked the ones I put away about a year ago... still alive and well, sitting at app. 3.8V or so.

The BMS should after no use/comms for a while go to sleep and not drain the cells. Important is, that the cells are at a SOC of 50%, then storing this lot for longer term of no use, should be no problem and things should wake up, once you reconnect power and charge the battery back up again.

I would imagine that LiFePO4's should behave similarly to LiIon's in this regard.

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1 hour ago, rectangularBuilding said:

Looks like this is just the voltage that the BMS uses for sensing the wake-up. Surely, internally the cells are above 12V (assuming it's a 12V block) or what do you think? 

These are actually individual cells, not connected to any BMS, its a mix of 4 different manufacturers and ages of cells as well, Samsung, LG, Sony etc. and all of them are around the 3.8V give or take 50mV  after about a year of being put in the cupboard...

As for your battery, yes, I think you did the right thing, I doubt BlueNova would have done much different than what you ended up doing and it would have cost you plenty.

My point was that if anyone has Lithium batteries that will be put away for a month or longer, it should be stored correctly, not to impact the batteries life negatively. Obviously though, the battery should be disconnected properly from everything else, in order for it not to be drained, whilst in storage and non-use.

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