BATC Forum

Hello,

I have just purchased a LiFePo4 battery (12V, 50Ah) and on receiving it the terminal voltage was 2.7 - 2.9V - very low.

It was supplied with a 5A charger, and on connecting it the charging current was only a few mA. The battery has a Bluetooth battery monitor built it but this would not connect to the app - hardly surprising given the terminal voltage.

My initial thoughts were that it was faulty, but I left it connected to the charger and checked it every hour. After 9 hours the battery charging current was still only a few mA, and the battery terminal voltage (charger disconnected) had risen to around 3V.

On checking after 10 hours the charging current had risen to 4.9A, and the battery voltage (charger disconnected) was around 12.4V The Bluetooth app would now connect and reported that the battery was 11% charged, temperature 20C and charging current was 4.9A. I then left it disconnected over night.

I restarted charging this morning and after nearly 9 hours the app reports that the battery has reached 100% charge, the voltage is 13.95V, temperature is 26C and charging current has dropped to 1.08A. Shortly after this reading the charging current dropped to 0A.

The actual battery voltage now reads as 13.57V after a rest of around 1 hour.

Not tried a discharge test yet.

Considering the low initial voltage, and the reluctance to even start charging (over 9 hours), is this battery likely to be faulty ?

Any advice from LiFePO4 battery users would be appreciated.

The photos show the initial readings of the battery.

Nick - G4NKV.

That might have been the battery management circuit doing it's job. I would check the capacity. You should not let it go below 2.5V per call, so 10V in this case. The BMS should cut off the output at 10V but it might have a little leakage. Then it needs to be reset.

Mike

Thanks for the reply Mike,

I would have liked to check each cell, but unfortunately the battery is sealed - no way in. If I could have checked each cell and they were OK I would have assumed that the BMS had shut down. Don't know how to reset the BMS on this battery - no information was supplied with it, but can only assume that after some time (nearly 10 hours) it reset itself with having the charger attached.

Is there a general (quick) way to reset the BMS ?

Been looking at YouTube videos - they seem to suggest that you just supply a 14.4V supply to the battery to reset the BMS (which happens virtually instantly), but I had the charger connected supplying the 14.4V and the battery did not start charging for nearly 10 hours.

Interesting to note that with this particular charger there is a LED indication on it. It was green while the battery was not charging (for nearly 10 hours), which it states it indicates that the battery is full or disconnected. It was not full and it was not disconnected, so as you say it looks like it was something to do with the BMS.

It went red when it started charging which is correct, even if it took 10 hours to get there.

Nick - G4NKV

My battery (Fogstar brand) arrived 50% charged (as I understand they should be stored) and has since behaved as I would expect. I think you need to speak with the supplier and as Mike suggest, run a capacity test on it. The Portsdown 4 and a Lidl Multimeter will do that for you. My Lidl had loads of them late last week, but £12.99 now. Still a nice DMM to have especially with the added functionality.
Gareth