18650 battery capacity range.

Maybe it's like with Nickel metal hydride cells where they have slowly leaned to make higher and higher capacity cells of the same size?

Also I believe 18650 sometimes include protection ICs, sometimes not.

One of the packs I stripped for cells said "5.2Ah" in the info label - a quick search didn't find any 18650 cells higher than about 3.4Ah.

One of the packs had parallel pairs, the 5.2Ah pack had an odd number of cells, so parallel pairs isn't likely. The pack with parallel pairs was marked "4.2Ah", so I assume the individual cells are 2.1Ah.

I have seen laptop batteries with three cells in parallel. I think it was 3x3, or 3S3P.

Is there a derating curve for parallels, or do you actually get the sum of all the capacities?

On Tue, 23 Dec 2014 17:26:11 +0100, Robert Roland wrote as underneath :

Yes Ive seen 3S3P as well, each 3P set of cells having separated control and monitoring circuitry. C+

You do get the sum of the capacity of all the cells.

Also, since the internal remittances are also paralleled, you get a battery that has less internal resistance and therefore is capable of delivering more current.

The disadvantage of paralleling versus a single, bigger cell is size and weight. You will hardly ever see a model airplane with a parallel setup, since weight is so important in a plane.

Lithium cells are well suited for parallel operation, since they are charged to a specific voltage.

There was an article on paralleling lithium in a past issue of Elektor, they focussed on the equalising current of joining 2 cells with dissimilar charge and making sure charge/discharge ratings weren't exceeded.

The article didn't answer any of my questions - some of the packs I harvested contained parallel cells that were like that since manufacture.

Claimed and actual aren't the same.

Odd. Either outrageous claim or some awesome electronic trickery going on.

That's a reasonable capacity for an 18650.

IME 18650 capacity varies from abpout 1.2Ah to 3.2Ah depending on age of cell (newer ones are improved), price of cell and source. Also often claimed capacity and actual are very different. Again IME Japanese cells have a much higher capacity than most Chinese cells. I've found that laptop cells in the last couple of years average around 2.6Ah whilst (DIY-level) powertool battery packs from the same period tend to average 1.5Ah. The difference is likely down to the cost of the devices they're powering.

Trade powertools often have 2.5 - 3.0Ah cells fitted but cost 3x what the DIY versions cost. Likely a goodly chunk of that increased cost is down to the price of the cells.

I wish I could find (and access) recycling bins such as you mention. The only time I found one it had a slot to drop the battery pack in - I couldn't get anything out. When I asked the store manager if I could have a look with the view of re-using a pack or two I was told it wasn't possible as they take over responsibilty for proper recycling of the batteries when their customers put them in there and he has no control over what I would then go on to do with them. In short it was a legal thing. Damn red tape!

Question for you;

I've pulled a couple of laptop battery packs apart for the cells. I have an LED headlamp that I use quite a bit which takes two 18650s in parallel (but will of course run off one). I have no elegant way of checking the remaining capacity of the cells I'm using. Just today I decided to charge the two (Sony) cells that I have in it and, in my 'dumb' charger that switches off at 4.2v for each cell one only charged for 30 minutes while the other is still charging three hours later. (It charges at 500mA.)

What can I deduce from this? Is the cell that took little charge better than the one that took a lot or vice-versa? Is it fine to continue using this pair together? Is using 18650s in parallel like (the ideal of) communism - 'from each according to it's ability and to each according to it's needs'? Oh, the headlamp wasn't dimming so the pack wasn't 'flat'. It's just it'd been used for a few hours so I wanted to top it up.

Cheers,

The current tails off as charging progresses, I'd assume the one that doesn't take much current for long has lost a chunk of its capacity.

There are hazards in recharging an over discharged cell - some datasheets and appnotes show a constant power charging phase on the control chip for this situation.

In any event; you should avoid exceeding the 4.2V on the terminals - they tend to vent with flaming gas if overcharged!!!

In a certain supermarket; the battery recycling is a bit smaller than an oil drum and has a sort of plastic chimney with a slot to drop the cells in.

On one occasion it seemed fixed on so I couldn't figure how to shift it - I thought they'd got wise to me.

More recently it was just dropped in place - but it had recently been emptied, so I wouldn't have been able to reach anything interesting.

Also the security guard usually lurks within yards of the recycling - so I have to pick my moment when he wanders off.

Building supplies/DIY/tool shops is a potential resource I keep meaning to check out - it would probably help if I went in there to spend some money and asked on the offchance.

Or the other ones internal resistance has gone high? It took six hours to charge and was fairly warm by the end. 2.5w going in to charge them and I'd say from halfway through it was radiating 2w of that as heat. For now I've just put the one that was charged in 30 minutes into the headlamp and will see how long it lasts. However it's been wet here for a while so in a day or two....

I know nothing about this charger other than

Indeed. This charger stops charging at 4.2v (apparently).

Cheers,

Thanks for the reply. I'm an invalid with limited mobility so 'shopping' for a battery recycle drop-off isn't really an option.

Last year I had a rare windfall just as my cordless drill and (corded) jigsaw both started playing up terminally. I used the money to buy myself some new tools, Bosch DIY range. "Power4ALL" 18v Li-Ion;

The first two came with two battery packs each and, as I don't use three tools at once I sorted out the two with the newest date stamp, charged them fully then discharged about half-way (the first two tools have 'battery gauges'). Then I put them in zip-lock bags and in the fridge. From using the tools quite a bit in the first couple of months I think the 1.2Ah battery claim is *very* conservative. Maybe so tradesmen don't use these for light / medium duty rather than trade tools?

They charge *so* much for replacement batteries that if I'd just bought the four batteries it would have cost me nearly 70% of what the three tools, two chargers and four batteries cost. So I'm going to get every last bit of use out of the batteries I have - On my income I'll really need to baby these puppies as I doubt I'll ever be able to replace them again. That said they're excellent tools. I used to work as a cabinetmaker and used trade-quaility Makita tools and, after having these ~9 months and using them a lot as they were 'new toys' they feel better made than the Makitas ever did.

LOL. The drill has something like 5x the torque of my old cheapie cordless and, when I was testing it out after I bought it I sprained my wrist driving huge screws into and out of some waste pine! Heh, I even removed the galvanising off the screws. :)

Technically I could get done for stealing - you'd probably have a card or two in your favour to just ask.

If they're not very helpful - shop somewhere else.

Once upon a time on usenet ~misfit~ wrote: [snipped]

Ehhh! I just bit the bullet and ordered a Nitecore D2 charger for not much more than I paid for the charger above - I have some body fat, I don't need to eat this week. They weren't this cheap when I was looking last year dammit or I would have bought one then. Oh well, with the LCD and available data when charging I should be able to get a better idea of which of my cells are best.