can i use this to charge cells ?

Hi all

I want to charge a 3x 18650 cells in series and i have a 12 volt adapter with 500Ma can i just plug it to the cells and it charges it ?

i have tried it and it worked just fine the 3 cells after charging gives about 13 volts

my question is it safe or not for the battery ?

It's not a good idea. You'd have to watch it like a hawk - it could dangerously overcharge the cells and probably has. They'll discharge just fine but might be dangerous to recharge.

If any of the cells are above 4.3V after standing I'd treat them as single-use cells.

No, please don't do that. If you have a good grasp of how a battery charger controls the voltage/current during a charge cycle then you can pretty safely rig up something that more or less duplicates what a charger does, but just by asking this question that's a pretty good indication you don't understand it well enough yet.

Get it wrong and at best you'll damage the cells, at worst you'll start a fire and end up in the hospital.

ok can i use this then ? constant current and constant volt convertor i have used it as a constant current source for 5x XML in my Bicycle lights powered by 3s3p 18650 cells and it worked wonders

this is some of it’s Feature:

Output voltage: 12-35V (adjustable)
Output current range :0.5-5A (100W MAX) (continuously adjustable)

1. Step-up structure, Wide input voltage range (input less than output)
2. Constant current and voltage, Used to drive high power LEDs, and to charge the battery
3. Efficiency as high as 92%
4. Can be used for laptop power supply (voltage 16-20V)
5. Even the Step-up structure breakdown, Will not damage equipment, security design
6. With input reverse and undervoltage protection
7. Aluminum shell potting design, shockproof, Waterproof, Heat-Sink, harsh environments adaptable
8. Pluggable terminal design, easy assembly and disassembly, wiring more convenient
9. Can be Parallel work in power is not enough occasions

Don’t use that for charging either, li ion needs a charger with the correct algorithm to not overcharge a battery, you should look for a charger such as:

since you already used a bad method and overcharged your batteries you should seriously consider getting rid of them and replacing them because they are now an explosion hazard

At 500ma charging more than one battery at a time is a waste of the aforementioned…

If you have a DC supply, and can set it to a fixed open circuit voltage of 4.21-4.22v, and the current can be limited to a safe range, then it's pretty safe to use. But it'll take much longer than a proper charger that follows the correct algorithm.

In the CV phase, it should really be maintaining a fixed voltage across the cell of 4.21-4.22v, to do that will require a higher open circuit voltage. As the cell charges and its voltage rises, it'll require less voltage from the charger to maintain that target 4.21-4.22v. Unless you want to babysit the charger and 'drive' it manually, constantly monitoring volts/amps and adjusting it the whole time, just buy a charger that does it properly.

More like the same time.

With short and thick wires between the power supply and the batteries the voltage will be the same and you do not need any adjustment.

Longer and thinner wires will increase the charge time, but no do anything harmful to the batteries.

Note: Chargers are usual not capable of doing a perfect CC/CV, they have to much resistance in the connection.

Charge done with a power supply (Connection is optimized for low resistance):

Charge done with a good charger: