Cell phone chargers

Anyone know is a cell phone charger can be used to charge 18650 Li Ion batteries?
Are the smarts in the phone or charger?

Usually in the phone, but if the charger says 4.2V you can use it directly.
I don't know which (if any) models would have that voltage.

thats a good question, ....

theoritically, it can be done.

have yr multimeter on standy and lots of diy work ... :sick2:

:twothumbs ironically, i too am thinking to get some solar cells at 4v +/- to charge the 18650.

its a blessing if it can be done ... great for outdoors usage.

I have a solar panel that is 4.2v. Only problem is that is the max voltage output. Usually you will only see 3.5v on a good day. Maybe if you use reflectors to direct more sun on the panel it can recharge a 18650 cell.

A "cell phone charger" in 99% of cases is nothing more than a power supply. There are no "built-in" smarts in the little wall-wart to speak of. Stripping the wires and connecting directly to an 18650 would over-charge it.

mdocod said:

A "cell phone charger" in 99% of cases is nothing more than a power supply. There are no "built-in" smarts in the little wall-wart to speak of. Stripping the wires and connecting directly to an 18650 would over-charge it.

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Hi, I agree, the charger is on the cell phone, if you search maxim-ic.com produce many very little ic that do the job with very few other componets.

Mirco

My car charger for Nokia fell apart the other day. Inside it is a Maxim chip so I guess it may work. I will test it before use.

It's probably a linear or step-down regulator, again making it effectively just a powersupply. There are no smarts in the car chargers either.

The wall-warts I've seen are voltage regulated (5V) with current limiting. The phones I've observed simply turns on & off the "connection" to the battery (no quicker than once/second), making for a kind of crude & slow PWM charging system.
If you're comfortable about breaking into a wall-wart or car-charger, identifying the IC, & soldering on SMD's, you could presumably adjust its output voltage to 4.1-4.2V, thus enabling it to charge a cell directly (but w/o soft-start check & end-of-charge indication).

Resqueline said:

Usually in the phone, but if the charger says 4.2V you can use it directly

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Never seen a phone charger (that plugs into the phone) that outputs 4.2V. Old ones tend to be 6-9V units, and newer modern ones are usually 5V (for USB compatibility, perhaps?).
In all phones I've seen, the smarts are always in the phone.

Packhorse said:

My car charger for Nokia fell apart the other day. Inside it is a Maxim chip so I guess it may work. I will test it before use.

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Some phone's have smart chargers this is due to companies wanting to have more features on the phone thus moving the charger off the phone.

How ever most are just constant current power supplies with some kind of step down.