It was posted “4 sold”. So this battery looks good.
Nope, I kept up with the thread. But I did get a pack cheap. Like I said before, most battery guys would have considered these batteries junk from their shipping voltages. It’s a learning experience, I just had to see this for myself. It will be interesting to see how they perform in a year or two, 4 to 5 years old.
That’s what it looks like to me too. It being a oem acer pack it very well could have the same 2900mah Panasonic cells. The oem pack would have only high quality cells. To much liability for acer to have used cheap cells.
“Ignorance is bliss”…. With that, I’m referring to ME :)!
I can!
I set up my board to do a constant current discharge of the battery. It does this by PWM’ing the battery voltage into a 2 ohm/200 watt power resistor and adjusting the PWM value until 2 amps is flowing into the resistor. There is an external filter to smooth the PWM’ed voltage pulses into a constant value. I put a current probe on one of the battery lines and am seeing 10 amp pulses! The inductor that I had in the PWM filter is not what it was thought to be… I need to replace it with a proper one.
I was using a 2S battery configuration on those discharges to speed up my cycling of the batteries to break them in. It takes a long time to do 10 charge/discharge cycles on 18 batteries… especially when it takes the I4 over 8 hours to charge 4 of them.
OH! 10 AMPS?? Are you saying that these NCR18650 batteries were able to source 10 amps (albeit in pulses)?
Thanks for the details (which you didn’t provide earlier)… I was assuming (yes, I know what A-S-S-U-M-E stands for) that you were just doing a “simple” series connection for the discharge.
And yes, I fully understand what you said in in the last paragraph… I spent many hours discharging/charging the batteries I got from 2 packs, and then, on top of that, I got two additional (used) packs. I did a really lousy job of scheduling, because all 4 packs showed up on my doorstep literally about the same time :(…
BTW, so are the batteries still ok, even with all of that?
Yes, the batteries are just fine. When asked to do a 2 amp constant current discharge, they were producing 10 amp (peak) pulses with around a 20–25 duty cycle. The actual current waveform into the filter was like 75% off followed by a sawtooth shaped ramp to 10 amps.
DIscharging a battery into a 2 ohm resistor down to 3.0V gives 2700 mAh (starts a 2A, tapers down to 1.5 amps). These cells are spec’d to discharge to 2.5V and should give the full 2900 mAh if you took them down to 2.5V
I was getting 2700 mAh out of them even with the 10A pulses…
That is pretty good, right :)?
In China these are 9000 mAh cells…
“Lost in Translation” :)?
Here is the data sheet for these cells: http://industrial.panasonic.com/www-data/pdf2/ACA4000/ACA4000CE240.pdf
They show a 5.5 amp discharge curve. It also shows they should do 2700 mAh at 2.75 amp discharge to 3.0V.
Finally got time to test one of these. I charged the battery at .8 amps until fully charged, then discharged at 3 amps. Then ran another cycle. On the second cycle I got 2740mah at a 3 amp discharge rate down to 2.7v. Ran logview with the accucel-8150 to give me this graph on the second cycle.
.
.
If anyone knows how to get the capacity on the bottom of the graph instead of the time, please let me know. I have spent hours trying to find out how to do that without any luck. :~
One of the 18 cells that I pulled from these packs has quite a bit more voltage drop after charging than the others. Most drop from 4.20 volts off the charger to around 4.18V after a few days. The outlier dropped to 4.12V It does measure OK capacity on the discharge tests. I’m gonna let it set for a couple of weeks and see what it looks like.
I had a bunch (like, all of them) that were dropping to 4.10-4.12v after resting overnight, after coming off the charger at dead nuts 4.20v. I'd been doing them 4 at a time in parallel, at 4A. Once I went back and topped them up individually at .5A rate, 4 days later they are every single one holding at 4.17-4.19v and staying there.
If these cells are headed to storage, the voltage should be reduced to about 3.75 volts before storing them, and keeping them in the fridge is a good idea as well, so they they do not lose capacity from sitting around fully charged.
Time and heat are enemies for li-on cells, but not charging to max voltage during use cycles will dramatically increase the life time of the cells, as well as not discharging to minimum levels.
The life span increases 3 times just from charging to 4.10 instead of 4.2, if I recall that correctly, and damage to the cells from voltage is eliminated at 3.92 peak volts.
You do lose a little run time, but don’t kill the cells off as fast.
Hi,
Some hobby chargers, like the one I use, an Accucel 6, actually has a function to charge a battery for “storage charge”.
Little update: This is the cell that I tested in post #152. I charged it up as soon as the test was done and has been setting ever since (A week ago). I have one cell resting at 4.18v (could be that I charged it a day or two later) but the rest measure around 4.17v.
.
What batteries are in the Fujitsu E8110 battery pack? It is 6 cells and 5200 mah and it says 10.8 volts
Should be 2600mah, 6 of them haven’t the clue as to brand maybe sanyo.