A short while ago I voted "over three volts" in the "how low do you go" forum poll. The idea was to give the standard low voltage recommendation of the major manufacturers a fairly wide berth. Having ripped my fair share of laptop packs and tested my fair share of cells I am well aware that initial voltage is no indicator of the potential health of the cells. A BLF member (EAS?) has opined that the danger of internal shorts occurs in cells that have been discharged past the manufacturers recommended safety limits under load and that cells that fall into this danger zone due to self discharge may not be vulnerable to the development of internal shorts and spontaneous thermal runaway. I did some reading and I believe battery university agrees. I am not entirely sure where the low voltage limits may lie as protected laptop packs should never over discharge under load.
Some folks who presumably know more than I, have use two volts as their lower limit and found well behaving cells. I decided to go back through my buckets of rejected cells and pull out those between 2 and 3 volts that I had previously discarded as being too low a voltage and test them for general health and capacity. I ended up with 44 cells between 2 and 3 volts for further testing.
I then ran the cells through my standard testing procedure which consists of:
-Charging a subset of each pack's worth of cells.
-Checking for high cell temperature while charging. Hotties get tossed.
-Test for amp draw capability in a standard light. I test on a triple XP-G2 convoy S2 with BLF17DD and separate cells into three groups based on performance. Less than 4 amps gets tossed. 4-5 amps gets put in a box of marginal cells cause they're too good to toss and too crappy to use. Over 5 amps get set aside for use or storage. Now that I have an OPUS I add a discharge test. Of the cells kept so far:
-Cells registering over 2000 mah get kept
-Cells between 1400 and 2000mah get put in the "meh" box.
-Cells under 1400mah get chucked.
Here's what I ended up with.
The 9 cells on the top were keepers plus six more I didn't photograph for no particular reason. The two lime panasonics turned out so well I dug back through the bucket and pulled out the pair at 1.86v to test. They were great too. 15 good cells total.
The middle batch of 18 were in the marginal group including the two peach LGs that tested over 2000mah but gave less than 4 amps on the draw test. Weird.
The last batch of 13 went back in the buckets.
I'm not sure this post can help anyone but I have decided to use 2v as my new cutoff and can't decide whether to recycle my buckets of duds or start an Ultrafire business.
Those cells would and could be sold as “premium” UF cells. They test out better than ANY of the ones I have ever seen!
For them is all about quantity and there is where everything stops, so the 2000mAh cells from the bucket would be rated as 8000mAh cells on their wraps, considering the 600mAh cells are rated 3000mAh.
For this test:
“-Test for amp draw capability in a standard light. I test on a triple XP-G2 convoy S2 with BLF17DD and separate cells into three groups based on performance. Less than 4 amps gets tossed. 4-5 amps gets put in a box of marginal cells cause they’re too good to toss and too crappy to use. Over 5 amps get set aside for use or storage.”
I am assuming that you are doing tail cap amp readings with a multimeter, right?
Thanks, kyfishguy, for doing this testing. This will help us all to be more educated with our decisions to keep or to toss old cells, rather than going by gut feelings, urban legends, and superstitious paranoia! H)
You mentioned cells with less than 1400ml capacity get recycled. Is that based on safety reasons?
I’ve been using a couple laptop pulls with less than 1200ma capacity (my best guess). Now I’m wondering if I should recycle them. They don’t get hot while charging.
Good work and given the tools you had at hand, have very methodical. But it seems like an Internal Resistance (iR) test is really what is needed as a first cut, then maybe capasity so you can choose how much to carry.
If you pick up a charger with iR or Mean Resistance (mR) it would be great to see how “all” the cells test.
Those cells get recycled because not only do they not have as much capacity as the cells I keep but they just do not perform as well in terms of amp draw. I think you know I'm always looking for top performance from my builds, I'm also looking for top performance from my cells so I don't cripple my builds. I'm sure your cells are perfectly safe as long as you have followed the basic rules of cell harvesting.
You mentioned cells with less than 1400ml capacity get recycled. Is that based on safety reasons? I've been using a couple laptop pulls with less than 1200ma capacity (my best guess). Now I'm wondering if I should recycle them. They don't get hot while charging.
The OPUS does have an IR test but it doesn't appear to be repeatable or particularly accurate across a sample. The amp draw test I do uses a single light as a repeatable standard to essentially get at the same parameter. I have not done any actual math on this but I suspect that the performance in the amp draw test would demonstrate a strong positive correlation to percentage of original capacity. Bet I could even get a significant p-value! There are outliers of course and sanyo cells are always relatively strong performers even at low capacity.
Good work and given the tools you had at hand, have very methodical. But it seems like an Internal Resistance (iR) test is really what is needed as a first cut, then maybe capasity so you can choose how much to carry. If you pick up a charger with iR or Mean Resistance (mR) it would be great to see how "all" the cells test.
I did similar testing with a bunch of my batteries, I kept and use all the batteries that read over 8A (most 9+)in my mtn17dd/triple xpg2 s6 or triple xpl s5, meh box holds 5-7.9A batteries and anything less was tossed or given to friends. None have been "bad" from the battery packs I got from Haag.
resistance readings seem sketchy on my liitokala charger too, a good battery might read 90mR at 3.8V and fully charged it will be 40-60, but a battery that only draws ~5-6A will say the same thing, yet sometimes they say 40-60mR at 3.8V and 150mR at 4.2, so I can't base anything on the resistance readings with my charger.
No expert here. Long time ago I read that NASA was the group that discovered the issue and that it was created by repeated (I think it was like 50) discharges below some voltage. Please don't rely on this statement. Just something to base a search on for those interested.