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My granddaughter bought a Geni G910, a Korean cell phone, without a charger.

I've looked on the net without success to find a charger for sale.

I then decided to build this simple one call charger:

http://www.uoguelph.ca/~antoon/circ/lithium.html

But - when I examined the battery with a voltmeter there was no indication at all of any voltage between any of the terminals.

The battery has three terminals, two close to each other on the left, and one on the right.

Is there a way to determine which is positive and which is negative?

TIA,
Grant

Hi there,

100ma is too low for me, i prefer 300ma for the AA size
and 1 amp for the larger 18650 so they charge in about
2 hours.

I mark all the possibilities down on paper then give them a tiny polarized zap each way or possibility, and write down the results.

Two power, once sense.

Thanks, Chris.

How does the sense terminal work? On a fully charged 3.7 v li-ion battery what voltage would it be?

Grant

Uh, another question:

According to information here:

http://www.batteryuniversity.com/partone-12.htm

it is unsafe to recharge a Li-Ion battery which has been below 1.5V percall for more than 2 days. Anyone have experience to the contrary?

Grant

I don’t remember the actual numbers on the Li Ion battery but the sites [any of them] on the web should tell you that.

The small zap on each of the terminals will tell you which retains its power and which is pos and NEG, the left over is the sense circuit.

10 seconds worth of a few milli’s should do the trick.

You can also use a small load on the discharge to find out which is the Pos and NEG, as some batteries will negatively charge when empty, but always work better in one direction.

From memory the sense drops drastically right at charge while the nicad goes to a heat sensor, and other types all do their own thing.

Any Li Ion site should give you the idea and voltage for all the different devices based on the amount of cells.

Also the extra lead may be just a safety device, heat, pressure etc designed to ensure the battery cant explode?

grant fair wrote:My granddaughter bought a Geni G910, a Korean cell phone, without a charger.

The battery has three terminals, two close to each other on the left, and one on the right.

Is there a way to determine which is positive and which is negative?

TIA,
Grant

The Nicad batteries I've used of the same construction has 2 pins for (+) and one for (-). It may also be possible to see from where the treminals are connected in the electronics, (-) is usually GND.

TOK

Usually the outer pins are +/- and the middle one being the sense. + being the one closer to the sense pin.

I haven't verified this but it has been my understanding that the sense pin is connected to the +pos pin through a current limiting series resistance (since little or no current flows in this leg)

If you get 0V between all terminals than other than being dead, the thermal fuse may be blown open. In this case the meter should float like it was not connected while a connected but dead battery will show a stable voltage on all digits of the DMM.

There is a statment about dead Li ion batteries and it is said once it falls to zero, its history. The chemistry gets in the way.

Hi there,

I have read that if it falls to less than 2.5v you can restore it with a
reduced charge current, something like C/20, and i was going to
incorporate this functionality into my next charger design, but i have no
real proof that it is safe to do. I have read that you should never
discharge it to less than 2.5v also. Someone else had said that
once it reaches 3.0v you can go back to the normal charge current.

Luckily, i never discharge my cells below 3.0v anyway.

I did however have an old cell someone sent me and it was
discharged to 2v and i charged it back up with full current
(not knowing at the time to use less current) and it did work,
but the cell died rather quickly as it could not hold a charge
very well. I ended up throwing it out anyway and i would bet
this happens to all cells that are discharged too far.

I tried to zap various terminals, but never was able to deliver more than about 1/2 ma. I was using a current-limiting power supply set to 4.1 volts with the current limiting close to maximum.

Today I backed off on the current limiting and zapped another pair of terminals for a while. I wasn't monitoring the current as closely as I should have so may have delivered maybe 250 ma for a minute or so. But now those two terminals read 3.7 volts. I hope the heavy current did not damage the battery.

So, I will now go ahead and build my charger circuit, and see if the battery will take a full charge.

Thanks to everyone who provided information and encouragement on this topic. I appreciate the help.

Grant

You may have gotten lucky as some have a cut off switch should the voltage get dangerously low.

The problem with lithium is who made what and why.

The wiring configurations can be many.

If the cell returned I doubt you hurt the cell with the shunt, and probably woke it up.