Encore 2700mah Cell reversed?

[shobhitk]

Hi everyone,
am new to this forum and am happy to find such an informative discussion forum on electronics and all..especially batteries
am having an issue with my newly bought 4 Rechargeable Encore AA 2700mah batteries for my camera. for the 2-3 weeks they gave excellent performance. i could shoot 100s of snaps with them at a time and most of the time i recharged them even when they showed no sign of draining! but suddenly everything has toppled. now when i charge them and when i put them ito my camera say on the 2nd day of full charge, they wear out after just 2 or 3 snaps!! i thought this might have something to do with the charger so i tried charging them again and when i put them in my equipment after a day or 2, they again got completely drained after 1-2 shots :shakehead .
i then started to do some research and came to find about 'cell reversal' which usually happens in euipments which use a series of batteries connected and where the good cells reverse charge the completely discharged cell.
i remember that the last time they gave me excellent performance was on a trip where they helped me take around 250 snaps without a break! and when the camera showed me low battery i switched it off. but again after an hour or so i powered it using the same batteries WITHOUT charging them. after a few shots it again went off. i again switched it on and continued to shoot with the residual power left and again it got switched off and i continued this process for around 5-6 times....!!
i think this has caused 'cell reversal' of one or more of my cells

what do u guys have to say about this? if this is cell reversal, then is there a home remedy to resurrect them? i want to because they r brand new

Thanks

 

[SilverFox]

Hello Shobhitk,

Welcome to CPF.

You can take a volt meter and check the voltage of each cell. If you get one with a negative voltage, you have found your problem.

On the other hand, if they all show positive voltage, we then need to know what charger you are using, and if it charges each cell individually, or if you need to charge in pairs.

Tom

 

[shobhitk]

thanks TOM. i'll try to get a volt meter and conduct the foretold test.
i'll be back when i have the results.

 

[mdocod]

I've got 5 bucks on massive self discharge problems. 4 dollars on a junk charger, and 3 dollars on a "off" brand cell...


How much do I win?

Is anyone else playing?

 

[shobhitk]

hi Tom. sorry for the long delay...was busy. ok so i conducted the test on C9000 and it made startling revelations! 2 of my Uniross Encore 2700s showed HIGH immediately while the other 2 were around 1.9v on impedance...so i threw the 2 with the HIGH reading and kept the 2 for later resurrection.
now yesterday i again started with the revival process by doing a break-in...but too bad one of the cells now showed HIGH and the other one is showing around 2.09v on impedance. am still confused as to what happened so as to cripple them to this extent! (details in the first post above)

i know they have mostly become useless but nevertheless i want to give them one last try. i have read about impedance and dropping voltages as a result but i want to know if there is a way to revive the battery to atleast 50% of its capacity. Is there ANYTHING that can be done to reverse the process of high internal resistance?

Thanks

 

[SilverFox]

Hello Shobhitk,

Not really.

However, you can try running a few Break-In cycles and see if that helps.

Tom

 

[45/70]

shobhitk, just a quick comment. You shouldn't run NiMH cells down until the camera shuts down, and then try to use it again. Always charge your cells when the camera shuts down the first time (preferably when the warning starts, rather than going on until it actually shuts down), and all will be well. By trying to squeeze every bit of energy left in the cells, turning the camera on and off again several times, you most likely did reverse charge one or more of the cells.

Running a NiMH cell down to 0.9-1.0 Volt is the maximum you should ever discharge them, especially in series. Going beyond this is bad for the cells and can cause irreversible damage to the separator in the cell. Running cells down until a reverse charge occurs is much worse, and causes severe damage to the separator.

NiMH cells are really sensitive to over discharging, especially higher cap versions, and it's really easy to do when they are being used in a series application. NiCd's are much more forgiving in this regard. That's why a lot of power tools and some flashlights still use NiCd packs.

Dave

 

[shobhitk]

Tom: tried to do a break-in previously but it gave the HIGH warning...and the process couldn't take off.

45/70: thats correct but when i put the cell on the C9000 in discharge mode, it didnt even showed 1 mah, instantly it showed 'Available Capacity' as 0 mah and the voltage shown was around 1.23v which means it was not reverse charged...am i getting it right? because if it would have been reverse charged then the voltage reading should have been different.

 

[45/70]

Usually when a cell is subjected to reverse charging in series, when you take it out and measure the voltage, it will have reverted back to a positive voltage. The reverse voltage state only occurs when the cell is under load with the other cell(s). I have seen cells that actually read a negative voltage, but that's pretty rare. I think this only happens when the cell has been subjected to a long period in a reverse charge condition.

The reason your C-9000 is reporting 0 mAh, is because the cell is dead. As soon as any significant load is applied to it, as by the C-9000, it's empty. The 1.23 Volt you are reading is the actual voltage of the cell. The point being, the cell does still have voltage, but cannot supply any current at the discharge rate the C-9000 is set at. If you try to discharge the cell at a very low rate, it may be possible that the cell will supply a few mAh. It may also be that the cell is so low that you would need to discharge it at a slower rate than 100mA to get any measurable result.

I would speculate that your cell(s) more than likely was reverse charged, or at the very least, run down to a very low voltage. One of the signs of old, or damaged cells, is when they have voltage, but can't supply a reasonable amount of current. I would try a few Break-Ins, as Tom suggested. It's worth a try.

Dave

 

[shobhitk]

45/70 i think it was more likely reverse charged because in case of a low voltage condition i had read that the C9000 first trickle charges it to 1V and then carries on normally with the charge, so in that case the cell would have started charging normally after a few hours, whereas nothing of the sort happened in my case...:shakehead

thats the problem! how do i do a break-in? its constantly showing the HIGH message.

i know there are methods to bypass the impedance check of the C9000 but am not going in for them as they dont seem to be very safe.

kindly advice...

 

[bstrickler]

My dad told me about a method to bring back dead Nimhs/Nicad's, which has worked well for me in the past for most cells.

What he told me to do was get a 6/7 cell battery pack charger, thats capable of putting out several amps, and touch the positive/negative of the charger to the positive/negative of the battery for a few seconds (max of 10 second bursts, otherwise you risk blowing up the battery), and throwing it in the normal charger, then draining the battery again, and doing that a few times.

About 80%-85% of the time, it worked, and brought the cells back to life.

Mind you, the charger we do that with is an old charger that has an analog ammeter, with a pole switch for changing between 6 & 7 cell packs (not a smart charger by any means. Uses a 15 minute timer, and trickle charge), that charges up to 5 amps, so I don't know if that will work better than most chargers now, since most are smart chargers, and might not let you try to "shock" a battery back to life (putting the 7.2/8.4v @ X amps through the 1.2v battery).

~Brian

 

[MarioJP]

i know there are methods to bypass the impedance check of the C9000 but am not going in for them as they dont seem to be very safe.

kindly advice...

That's is one of the reasons why I chose the La crosse charger over the C9000 as it does not check for resistance.

 

[shobhitk]

hi brian, the 'shock' therapy looks promising ...but neither do i have that kinda charger nor does it look too safe....but appreciate ur advice :thumbsup:

MarioJP the C9000 impedance feature rocks and theres no doubting that fact. its a very good feature which lets u dispose of 'dead' cells safely...it protects ur devices from cell leakage, protects the charging device from bursting cells and the most important thing it saves u from some serious injuries.
now the problem here is due to some 'bad' batteries which are physically affected...so am just giving them one last try, if they revive then its good but if they dont then its due to the batteries and not due to the charger. the charger is simply reporting the fact-precisely!

other smart chargers which do not sport this safety feature are a bit dangerous to use because discretion is given to choose charging rates which can range from 100ma to ~2A, and if a person makes a wrong choice then the batts may go booom!

as correctly stated by a forum user: 'its the batteries that fail us, not the chargers'

 

[45/70]

shobhitk, koala's first method risks damaging your charger, as he said, so personally, I wouldn't try that one. Method 2 will work if you're quick enough.

bstrickler's method can work, however it's really a solution for NiCd cells, called "zapping". This is a way to deal with the short circuit effect of dendrites in NiCd cells. It really isn't a good idea for NiMH cells, as they don't develop dendrites. The biggest problem with this method, is it damages the separator, in either NiCd or especially, NiMH cells, as they have a relatively weak separator compared to NiCd's. It can temporarily revive a cell, however self discharge almost always is increased, due to separator damage.

There are a couple other methods you may try if the cell's impedance isn't too far off. First, try putting the cell into the C-9000, let it go until it reports "HIGH". Remove the cell, wait a few seconds until the charger returns to normal. Repeat this two or three times. The cell's reported impedance check voltage should be lower each time, and if it isn't too high, the cell will start charging. As I remember, this will work if the initial voltage during the impedance check, is no more than something like 2.30 Volts.

Another way, is to start charging the cell on another charger for a minute, then remove it, and put it into the C-9000. It may start to charge.

While some of these ideas may allow you to charge the cell on the C-9000, keep in mind that the cell is suspect. If you get the cell going, notice the voltage of the cell during a discharge cycle. If the cell is fully charged, and the voltage during most of the discharge is at or below 1.2 Volt at normal discharge rates, the cell is under performing, and susceptible to further problems, as well as performing poorly. Generally, high internal resistance = old, or damaged cell. :sigh:

Dave

 

[TakeTheActive]

...i want to know if there is a way to revive the battery to atleast 50% of its capacity. Is there ANYTHING that can be done to reverse the process of high internal resistance?

Maybe (a little bit at least).

Help: Correct strategy with C9000

 

[TakeTheActive]

...thats the problem! how do i do a break-in? its constantly showing the HIGH message.

• What other chargers besides the C9000 do you have available?
  .
• What's your cell's C9000 Impedance Check Voltages?
  • Measuring Maha MH-C9000 Impedance Check Voltage
  • Interpreting Maha MH-C9000 Impedance Check Voltage

 

[TakeTheActive]

That's is one of the reasons why I chose the La crosse charger over the C9000 as it does not check for resistance.

Yeah, but you've got the 'NULL' problem!

 

[TakeTheActive]

...There are a couple other methods you may try if the cell's impedance isn't too far off. First, try putting the cell into the C-9000, let it go until it reports "HIGH". Remove the cell, wait a few seconds until the charger returns to normal. Repeat this two or three times. The cell's reported impedance check voltage should be lower each time, and if it isn't too high, the cell will start charging. As I remember, this will work if the initial voltage during the impedance check, is no more than something like 2.30 Volts.

Another way, is to start charging the cell on another charger for a minute, then remove it, and put it into the C-9000. It may start to charge...

~2.10VDC is the go/no-go threshold.

IME, the closer you are to 2.10VDC, the less work required to get the C9000 to accept the cell. For a few hundredths, you can even hold the cell in a clenched fist to warm it up a bit. For the REALLY BAD ones, I'll hit them with either 1300mA from my Rayovac PS23-B or 1800mA from my BC-900, depending on which one is free - HIGH Internal Resistance + HIGH Charge Current = HEAT.

 

[shobhitk]

i have a 6-hours timer based charger which works @ 360ma for AAs.

the impedance check shows around 2.10v
i tried charging the cells in my other timer based charger and the C9000 accepted it. it now showed impedance @ 1.92v. but i think they are now at the end of their useable life because after a R&A both te cells capacities were as follows- 1s) 410mah, 2nd) 430mah

query: how does this charging in 'other' timer based charger work? i mean charging only encourages crystal growth, then how does the impedance goes down after a charge? Isn't breaking crystals the domain of discharging?

 

[J_C]

When you have a device like that camera that drains the cells pretty low, it is a good idea to start out with matched cells, meaning you stop and measure battery voltage periodically (if your charger can't compare them), pairing together cells with closer to the same true capacity. NiCd are pretty easily damaged by reverse charging too, can't tell you how many times I've seen people with those cheap ~18V cordless drills where the pack was shot after a year because they kept using the drill after the battery was obviously >90% drained.