28mV and 40mV Across 32650

Toaster · Jul 30, 2011

So, I have been using the crap out of my XMLT6 maglight while working on my car, but have run into a problem. Before I left for a vacation, I left the flashlight on the bench dead. Now today, about 2 weeks later they wont accept a charge.

They read 28 and 40 mV on my DMM.

Now, is there anyway to restart these batteries like jumping a car with the higher voltage from alternator? Or do I have to fork out a wad of cash for new ones? Thanks!

Jacob32123 · Jul 30, 2011

Apparently these Gens Ace i Mars-Charger-A will bring lithium batteries back from the dead. (not that it is cheaper then new batteries)

I cant vouch for that as I dont have one, but they claim it will

Jufran88 · Jul 30, 2011

Yikes, I would recommend you buy new batteries since over discharged batteries tend to suffer electrolytic damage and can be dangerous when you try to charge them - They get hot, hotter, explosion, fire..

You could try to charge them with very little current (under 100mA) until 3V and continue to charge at normal current, but to be safer, buy new batteries!

EDIT: Revived batteries also tend to lower capacity than normal because of the internal damage it takes.

Toaster · Jul 30, 2011

I not concerned about potential hazard or capacity, but usability. This economy is killing me, from gas food, etc. Earning ten an hour is hard. So low amperage at how many volts? Thanks.

benmwv · Jul 31, 2011

I would just set it up in parallel to another li-ion (a protected one) with a 100 ohm resistor between them. Check voltage every hour or two.

Toaster · Jul 31, 2011

In the charger correct?

benmwv · Jul 31, 2011

No not in the charger just connect the plus of one of the dead ones to the plus a a fully charged battery and connect the negatives through a 50-100 ohm resistor so one will charge the other with low current. Or if you have a variable bench psu just set it at 4.2v and about 50ma or so. After many hours of trickle charge you may bring it back to life.

Toaster · Jul 31, 2011

I will try, but I don't see how parallel would charge it. The current wouldn't be going anywhere. Series maybe?

benmwv · Jul 31, 2011

Trust me, in parallel is the way it will charge. Think of it like this, when charging a battery the charger positive goes to battery positive and the charger negative goes to battery negative. Same concept here. Imagine that the good battery and resistor are just a low current voltage source for charging the bad battery, so plus to plus and neg to neg.

Be sure that you recharge/change the good battery when it's voltage gets a bit low, and to check the progress of the charge on the bad battery you will have to remove it or else you'll just be measuring the good battery's voltage.

Toaster · Jul 31, 2011

Up from 28mV to 132mV!!!

Oh and I have an AW18650 hooked up directly to the 32650.

It is outside without a resistor. No heat so far. Most likely because of the protection circut. I was thinking though. Why couldn't I charge them in Parallel?

benmwv · Jul 31, 2011

No, don't do it without a resistor!

It will be like a direct short, so you get a short pulse of power then the protection circuit kicks in and it just sits there doing nothing until you disconnect and connect it again then it does the same thing. The resistor needs to be there or A. The protection circuit kicks in and/or B. You damage both batteries by exceeding discharge and charge rates.

That small change in voltage is just because of the few pulses of energy it gets before the protection circuit kicks in.

Edit: oh and charging them in parallel also makes a basically a direct short which will trigger the protection circuit.

Toaster · Jul 31, 2011

I was planning on the protection circut to save my ass, lol. I was thinking that maybe It would charge slow from the protection holding it back.

All I have are 2.7k and 1 ohm. Will the 1 ohm work?

It went up to 200mV with the direct short. hmm

Its going from a 3000 mAh to a 5000mAh battery. So say the 3000 had a 3c discharge and the 5000 had a 2c charge, I would still be within specs at WOT.

Jacob32123 · Jul 31, 2011

Toaster said:
I was planning on the protection circut to save my ass, lol. I was thinking that maybe It would charge slow from the protection holding it back.

All I have are 2.7k and 1 ohm. Will the 1 ohm work?

It went up to 200mV with the direct short. hmm

Its going from a 3000 mAh to a 5000mAh battery. So say the 3000 had a 3c discharge and the 5000 had a 2c charge, I would still be within specs at WOT.

The 1 ohm will give you a ~4.2 amp charging current. Do you a couple of those you could put in series?

i = v/r

v = 4.2 max so

i = 4.2/1
i = 4.2 giving you 4.2 amps of charging current.

If you hook 2 1 ohms in series,
4.2 / 2 = 2.1

Still a lot, but better

benmwv · Jul 31, 2011

How many 1 ohm do you have? Could you string together 10 of them? at least that would limit current to ~400ma.

Edit: lol he beat me to it

Toaster · Jul 31, 2011

Lol they were from test loads. I brought it to a friends house to use his bench psu.

benmwv · Jul 31, 2011

Good that's definitely the better option.

(I think) A lower charge rate will result in less capacity loss so I hope you are doing it around 50ma-100ma. It would be best to let it trickle charge until the voltage hits like 4.18-4.2 but if you are to impatient you could probably pop it in the regular charger once it's at 3-3.5 volts.

28mV and 40mV Across 32650

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