Li-Ion 18650 Charging

[metrologist]

I have some good quality LG 2800 mAh cells from a laptop battery. If the cell is discharged to it's minimum spec (3V) and then applied 4.2V, how much current would you expect?

[darrellg]

[sleemanj]

I have some good quality LG 2800 mAh cells from a laptop battery. If the cell is discharged to it's minimum spec (3V) and then applied 4.2V, how much current would you expect?

That depends almost entirely on it's internal resistance, let's say 50mR:

  4.2 - 3 = 1.2 dropped over the internal resistance
  1.2 / 0.05 = 24A

followed closely by smoke, explosion, flame, running and screaming.

This is why you do not charge a lithium ion cell with a simple constant voltage, you need current limiting to do the bulk of the charge.

[metrologist]

I was asking because I got an Anself CMTD Li-Ion PWM solar charge controller and someone pointed that out. The device does seem to have proper voltage control for an 11.1V battery pack (3S, 9V low voltage cutoff, 11.1V resume charge up to 12.6V) and I guess you just need to have a battery that could take it's full output, limited only by the panel and its rating of 20A.

I was aware of the proper charging scheme, just expected the controller to be a little smarter. 20 amps is a lot of batteries.

[Audioguru]

A charge controller is designed to charge ONE battery so it can sense its current and voltage. Then 20A is not the charging current for a lot of batteries, it is the charging current for ONE very large Li-Ion battery. Most Li-Ion charger ICs allow the charging current to be programmed.

[ebclr]

Lipho Batterie  charge have 2 phases

1) Constant current

2) constant voltage

It's not a good idea to connect 4,2V before passing the constant current phase or getting approx 4.1V ( this is approx I didn't remember the acurate number )

[zoidiano0]

To be sure u should charge them at 500ma
If u need faster charging go for 750-900ma
Check in the data sheet what the charging voltage some are 4.1 and other 4.2

If the battery bits completely dead charge them at lower current if there's around 3.5 or 3.7 u can go for 700-900 with no problems
If u r in a rush go 1 amp
 And make sure your battery it's not getting hot

Hope this be useful

Sent from my Moto G (4) using Tapatalk

[amyk]

Limit the current to 0.5C or less, and limit voltage to 4.20V (officially +/- 0.05V --- better to err on the lower side). The cell will try to take as much current as it can until the voltage reaches 4.2V, at that point the current will gradually decrease and you can consider it charged once the current drops to ~0.01C or less.

Lion chemistry has no memory effect or other special needs, just keep the voltage and current within limits and it will work well.