Is my 48V LiFePO4 battery with problem?

[louispower]

I have just read another post from this forum that it is okay to charge a LiFePo4 battery without a BMS so long as you monitor the voltage of each cell closely that it won't be higher than a certain value. I am planning to try it on my battery. If the result is my battery voltage can go up to 58V and stay there for a certain period of time, then can I say that my current battery system (the charger and/or the BMS) is with problem (because it cannot go up to 58V)? Your comment on this is highly appreciated.

Hello Tmho, with a lifepo4 battery if you leave it there and use it seldom, its capacity will drop after 3-6 months quickly. The best for a new lifepo4 is to charge it immediately after you use it on ebikes, most importrant is not to have the new battery discharge fully before you charge it. After 20--30 cycles the battery will be in bst condition and could use it normally.

When charging the cell without BMS you have to be very careful with the operation, the BMS protect the cells to be over-charged otherwise the cells might be killed when over-charged.

 

[tmho]

I have just read another post from this forum that it is okay to charge a LiFePo4 battery without a BMS so long as you monitor the voltage of each cell closely that it won't be higher than a certain value. I am planning to try it on my battery. If the result is my battery voltage can go up to 58V and stay there for a certain period of time, then can I say that my current battery system (the charger and/or the BMS) is with problem (because it cannot go up to 58V)? Your comment on this is highly appreciated.

Hello Tmho, with a lifepo4 battery if you leave it there and use it seldom, its capacity will drop after 3-6 months quickly. The best for a new lifepo4 is to charge it immediately after you use it on ebikes, most importrant is not to have the new battery discharge fully before you charge it. After 20--30 cycles the battery will be in bst condition and could use it normally.

When charging the cell without BMS you have to be very careful with the operation, the BMS protect the cells to be over-charged otherwise the cells might be killed when over-charged.

Hi louispower, thanks for reminding me to be very careful when charging without BMS and I sure will do so. Do you agree that if the battery can be charged manually without BMS up to 58V and stay there, then the charger and/or the BMS should be with problem?

 

[louispower]

Tmho,

The BMS is setup 3.9V protected for charging, that is when BMS detects any cell voltage is 3.9V it will cutoff the charging.

Without the BMS you could charge a single cell above 3.9V or even higher, but after you cutoff the charger this voltage will drop quickly to the voltages you have given in this post, impossible to stay there.

Wish I have made this clear, thanks.

 

[tmho]

Tmho,

The BMS is setup 3.9V protected for charging, that is when BMS detects any cell voltage is 3.9V it will cutoff the charging.

Without the BMS you could charge a single cell above 3.9V or even higher, but after you cutoff the charger this voltage will drop quickly to the voltages you have given in this post, impossible to stay there.

Wish I have made this clear, thanks.

Hi louispower, you have made yourself clear. But you have not answer my question. Do you agree that if the battery can be charged manually without BMS up to 58V and stay there, then the charger and/or the BMS should be with problem? Your reply on this question is appreciated.

 

[dnmun]

nonsense. you don't know what you are doing so how could you be careful about overcharging without a BMS?

you have not yet listed the cell voltages during charging. all of this legalese entrapment stuff you are setting out for louis doesn't mean crap.

there doesn't appear to be anything wrong with your pack so now you wanna remove the BMS and charge it. !!????????????????

why can't you just follow a reasonable analytic procedure and measure the cell voltages during charging.

that shoulda been the only thing you needed to do. still haven't done it and listed the cell voltages for us to see.

 

[tmho]

I have tried charging the battery without the BMS. I used a regulated power supply to do the charging. Since the maximum voltage of my power supply is just 23V, I have to charge 4 cells each time. I adjusted the output of my power supply to 14.5V and then connected it to the first 4 cells which were originally 3.35-3.36V. I monitored the voltages and current carefully while charging. I could see the voltages increased gradually to 3.6V and the charging current started from about 2A and ended up to 0.1A. Charging time was about 2 hours. After disconnecting the power supply, the cell voltages gradually came down back to 3.35-3.36V in about 8 hours. Then I charged it again for 30 minutes and this time the cell voltages just dropped to 3.41-3.42V and hold there even after 3 days. I followed the same method and charged the second set of 4 cells and got the same results (voltages are higher than before and cannot held there).
Since the other cells (no. 9 to no. 16 except no. 13) are already at a higher voltage, I only charged cell no. 13 to increase its voltage to match with the others.
After that, I plugged back the BMS and plugged back the original charger. It charged (red light on) for about 2 minutes and then stop charging (green light on). After 2 hours, then I unplugged the charger and have the voltages are as follows:
3.64, 3.65, 3.69, 3.60, 3.52, 3.52, 3.73, 3.66, 3.71, 3.74, 3.72, 3.71, 3.66, 3.70, 3.72, 3.65.
After 10 hours, the voltages are as follows:
3.54, 3.54, 3.57, 3.52, 3.47, 3.47, 3.61, 3.53, 3.62, 3.66, 3.63, 3.62, 3.55, 3.61, 3.62, 3.57

From the above figures, it seems that I could get the voltage higher as it should be. But for the balancing, it is still not that good. I understand I may need to hook up the charger for longer time to do the balancing. But since some of the cells are above 3.7V which may be too high (Is 3.7V too high?), therefore, I dare not keep the charger connected for too long.