Li-Ion battery/charger help (non-flashlight)

[greg_in_canada]

My daughter won a pair of Freetalker radios (**** Tracy type
wrist walkie-talkies) a few months ago. Now the batteries
appear to be dead. One is 0 volts and the other 0.9 volts.
The charging indicator doesn't come on when plugged
into the wall adapter so it may be the charging circuitry
rather than the batteries.

I checked the wall adapters and they are putting out about
14 volts open circuit. About what I'd expect for an
an unregulated 12 volt adapter.

This web page says not to plug in the charger without the battery being
in place. So it is possible the charging circuits in both
have been blown by her fooling around. Though why they
stopped taking a charge in the first place would still be
a mystery.

I don't own any other Li-Ion equipment or chargers so I
don't have any other way to charge the battery.

Can I charge it a C/10 or C/4 with just a resisitor if I
keep an eye on the voltage? I just want to get an idea
if the batteries are dead or just the chargers before I
spend any time or money on them.

The cells say "Part No. NTA2176, Voltage 3.7V, Capacity 570mAh, Date Code G3, Plant Code T".

Thanks for any help - Greg

 

[VidPro]

i am just working with this right now.
if they have some voltage like 2.5v , then you would just charge them to 4.25v MAX.

if they dont, from what i can tell a low current might even damage it.
its hard to explain, but when i set a voltage on the voltage rugulator,
if at that voltage,
the voltage of the battery does not go UP,
and the current go down,
then the battery is not taking it. and it seems to make things worse.

how better to explain, when charging a battery if i give it a specific voltage, the voltage DIFFERENTIAL would usually decrease as the battery accepts that , and as the differential decreases, so to does the current.

in the really bad ones, putting in the power just has the power going nowhere, probably messing things up.

a PULSE, seems to be accepted for at least 1/10th of a second , long pulses like 2 seconds the break occurs and it goes nowhere.

once you get it to the 2.5v or about there somewhere, they seem to take off flying again.

sorry if i am no help, but i came here to read about it more myself.

 

[SilverFox]

Hello Greg,

It is generally accepted that when a Li-Ion cell is deeply discharged the chemistry changes inside the cell. Over discharging to a low voltage (below 2.3-2.7 volts under load, 3.0-3.5 volts resting) results in the copper current collector dissolving in the electrolyte. This dissolved copper is plated onto the anode on subsequent charges. This inhibits the utilization of the active material and results in reduced performance and life. If this is repeated several times, copper dendrites can form and can produce a short circuit in the cell. A short circuit will produce a localized hot spot in the cell. Several hot spots can lead to "rapid venting with flame."

Since you seem to have not had repeated excursions to low voltages, it would appear that your cells just died. At any rate, your cells are in the process of "polluting" the electrolyte because of the time spent in a low voltage state. I know of no way to change the electrolyte in these cells, so they are best removed from service and disposed of.

VidPro is trying several methods that are more suitable to Nickel chemistry. He should not be able to bring the voltage back in his cells, but if he does, the capacity will be extremely reduced, the self discharge rate will be very high, and the risk of shorting the cell(s) out during subsequent charging will increase with every charge cycle. I am following his efforts with interest. I never thought of singing to my dead cells, but the BatMax device was trying to shake some ions loose, so why not try some vibrations... If he happens to revive a pack to the point that it is good for service, I will try to get him to send it to me for testing. I have had no luck in reviving Li-Ion cells, but I remain open to new ideas.

Tom

 

[greg_in_canada]

Thanks Tom,

I've zapped shorts out of Nicad cells many years ago
using a big capacitor. I was hoping (but didn't really
expect) that I could do it with these Li-Ion cells too.

Any idea why they went bad so quickly? Bad design that
lets then get over discharged maybe.

Greg

 

[andrewwynn]

no undervolt protection is the surest way i know to kill a LiON bat... that would be my guess to whta killed them.. however.. i have had several LiON bats that read like zero v and put them on the LTC4054 charger and it brought them back to life.

-awr

 

[SilverFox]

Hello Greg,

There is the small chance that your batteries have a low voltage cut off circuit. When that trips, you often read voltages of 0 volts. I have found that every so often they can be difficult to trip back.

If you have access to an adjustable power supply, set the voltage for 4.0 volts and see if that will reset the circuit. If you can adjust current, set it to 0.5 amps. In effect you are zapping them with 4 volts to try to reset the low voltage cut off circuit.

If you don't have access to an adjustable power supply you might be able to do it with a 123 battery or a couple of AA's.

If all else fails, PM me and I'll give you my address. You can send them to me and I'll give them a test.

Tom

 

[greg_in_canada]

Hi everyone,

I finally got a chance to "zap" the batteries.

I used a 12V regulated supply (because I have one)
and first used a 100 ohm resistor. After a second or two
the voltage was up to 1.6 volts and the resistor was
getting hot. So I switched to 200 ohms and held it on
until I was over 2.8 volts (a minute or two).

Then I stuck them in the watch/radio and used their
chargers. The display came on dimly and I could see that
they were charging (the battery icon was blinking).

So I charged them overnight and the next day one was
3.9-something volts and the other 4.07 volts. I let them
sit around for a whole day (no charging) and the voltage
remainded the same. So the self-discharge isn't too
terrible. Hopefully she can use them again.

FYI: with the 100 ohm resisitor the current was about
110ma (=C/5) and with the 200 ohm about 50 mA (C/10). So
not really a high current zap at all. I'm guessing the
charger in the watch wasn't doing anything when the batteries
were really dead. So this just got them high enough so
the watch charger could do its job.

Thanks for the help guys.

Greg

 

[junglemike]

Hello everyone. Very interesting topic.
I also had some experience with reviving completely dead shortended li-ions.
I have a couple of li-ions. They are 18650 and 1400mah each (2 of them in parallel) They were sitting shortened many months. and were discarted as totally dead.
After unshortening them, they both read, of course 0.00v.
Well, i started to charge them - and mentioned they started to heat up - something wich never heppends with liions (becasue of almost 100% efficiency in transferring electrical energy into chemical, unlike NImhs, which are only 71% efficient at C/10 charge).
Anyway, they were heating up only from 0.0v till 2.5v.
Rest of the charge they were cool.

I also need to say thta i charge ALL my lithium batteries with super-simple circuit made by myself. I don't trust any commertial liion chargers, as i don't know what they actually do.
The interesting thing, that the dead battery showed almost 70% of initial capacity (don't forget that it's 4 years old) when discharging at C/5 current !!!
The only bad effect was that initial voltage was very low - due to damaged chemistry. So usual hardware would not power at all off such battery, but i have a dc-dc step up converter that can use it up to 3.0v , or lower , if needed.
This is discharge graph:

 

[andrewwynn]

I had an old cell phone battery that refused to charge with the built-in circut.. i put it on the LTC 4054 ckt i built and it brought it up to a full charge of like 4.1V... it took a while.. it charges at like C/10 or maybe even less until it figures out that it will take a charge.. that part of the process took hours and hours. once it started charging took like 4hrs and i've recharged the batt several times afterwards. the battery had laid in wait for over a year.. can't remember what the voltage read but i believe it was below a volt.

-awr