Charging Li-Ion cells below 0,1C?

[LightForce]

Hi everyone,

I have BIG Li-Ion 18650 4S4P pack with 10,4Ah, but the only 4S charger I have has max current of only 800 mA, what results in 0,08C charge rate and near 15 hr charging time. Isn't it bad for cells to charge it in this way? Cells are protected and balancer is applied.

Regards,
Damian

 

[Mr Happy]

I have no knowledge of Li-ion cells being harmed by low rate charging. If you have the patience to wait, I think it is OK.

 

[SilverFox]

Hello Damian,

I don't think there is a problem charging at low charge rates, but I don't think you get maximum performance from your cells if you do that. You may not be using your cells at near their maximum discharge rate, so this may not be an issue for you at all.

The main thing to monitor is the voltage at the end of the charge. Low charge rates may end up never terminating, and Li-Ion chemistry does not take well to continuing to charge after a full charge. If your charger is a true CC/CV charger, there should be no problem at all.

Tom

 

[SilverFox]

Oops, double...

 

[LightForce]

Thanks for input, Tom

Why I should bother with performance of my batterypack near its maximum discharge rate? It must withstand up to 16A discharging current, so it may be a concern for me.

I watch the voltage of each section in the pack and a comparator switch the battery off when charging current drops to 100mA.

 

[Turbo Guy]

OP

I have BIG Li-Ion 18650 4S4P pack with 10,4Ah,

Why I should bother with performance of my batterypack near its maximum discharge rate? It must withstand up to 16A discharging current, so it may be a concern for me.

16/10.4=1.54C discharge rate which IMO should not be a concern with decent cells.

If it were me I would be using A123 Systems(DeWalt) LiFePO4 2300 mAh cells. These cell can handle 60 amps. cont. and 100 amp. burst. They are 100 times more rugged,safer than LiIons, have a much higher shel life,number of cycles,etc. etc.Their only negatives are lower volatge and power density.

 

[Mr Happy]

A123 Systems(DeWalt) LiFePO4 2300 mAh cells: Their only negatives are lower volatge and power density.

...and cost?

 

[Turbo Guy]

If you are a careful / bidder around 10-11$ per cell on EBay in the form of DeWalt 36V (10 cell) cordless power tool pack. There are also 28V 8cell 2300 mAh and 18V 12 cell (6S2P) 1100 mAh DeWalt packs. Some have had better luch price wise on the 28V packs.

There are a lot of much cheaper LiFePO4 cells around but non that I have tested are nearly as good as the real A123 Systems ones.

Second best LiFePO4 cells are made by K2 EnergySolutions and they are close to A123 prices but they do have some higher capacity cells in the same sizes if you do not need more than around 10C discharge rate capabilities and do not mind limiting yourself to 2C charge rates. K2 also has protected cells available but protection is limited to extreem high discharge rates such as 20C. Handy if you happen to have a dead short.