12v Battery out of 18650 cells

[Peter Brigg]

I want to make a small battery out of 18650 cells with 3 groups of 6 cells joined in parallel then the 3 groups joined in series to give the amount of power and voltage that I want.

I have been charging individual 18650s with a TP4056 board and mobile phone charger for the power supply. Is this charging setup OK for 6 cells in parallel or would it take a long time to charge the 6 cells? And there would be 3 of them to charge,

Another thought is to use a 3s Li ion BMS and a car battery charger however I am doubtful if this will work-perhaps the car charger is too high a voltage.
Any ideas on this?

 

[Balmorhea]

Don't charge 3S lithium ion over 12.6V, ever.

4S lithium iron phosphate is a much better substitute for lead-acid 12V power.

 

[john61ct]

Better to go to 7S for 24V, buck converters down to 12V are common.

4S never fully charged could work, good for longevity, but sacrificing capacity.

As stated above 4S LFP is a good match

 

[john61ct]

also LTO at 2.3V nominal cell, 5S = 12.0V nominal, similar to lead GEL setpoints

 

[jonyjoe303]

If you have a 3s bms on your 3s6p battery, the best way to charge is to get a buck converter ( you can find them for less then 10 dollars) and then you can use any charger that at least puts out 14 volts or better yet a laptop charger. The buck converter you set it to the 12.6 volts and any power source that supplies the buck converter will be reduce to 12.6 volts, you can even adjust the max amps you want the buck converter to put out.

The buck converter is a CC/CV charger, it will safely charger any lithium. It will never put out voltage higher then what you set it , as the battery gets full the amps are automatically reduced. And then you have the bms on your battery to protect also against overcharge.

This picture is of a good buck converter I used before, you can adjust both volts and amps. You can charge at least 8 amps from these, just make sure you have a small fan on it at the higher amps. Mose laptop chargers put out about 4 to 5 amps, which is good enough for your small battery.



These are some buck converter chargers I built in a plastic box, I used a 5 dollar volt/amp LED meter so I can see the volts amps going into the battery. Buck converters are my preferred method to charge my small li-ion and lifepo4 battery packs. They are plug and play, just connect input/output and it starts charging.

 

[Peter Brigg]

Thanks for those replies-appreciated
However I have another question-I am making up a few simple projects and one of my concerns is that the Li ion cell becomes over discharged and damages a cell.
Have looked on eBay and not found anything suitable so far. Would you need under voltage protection on something as simple as a torch?
Or is waiting until the torch fades a sufficient warning to stop using it and recharge?

 

[john61ct]

That would best be determined by experimentation using a cheap wattmeter (Ah meter, coulomb counter)

Or just routinely recharge before it's needed.

Combined with a lower stop-charge setpoint, will result in 3x or 5x the lifespan compared to low avg DoD.

Cycling between SoC 30% and 70% every time might get as many cycles as LFP or even LTO!