This was going to be a part of another post, but it has grown, as they tend to, into a post of it's own. Look out for the project itself in the coming weeks.
As part of an upcoming project, I needed a power source, and a good choice theses days are 18650 cells.
These are Lithium Ion cells 18mm diameter, 65.0mm long. 3.7V nominal, but up to 4.2V when fully charged. (did you know that is the same naming scheme as coin cells, 2032 is 20mm diameter, 3.2m thick)
They are being used in an increasing number of things, like solar lights, power banks and vaping devices. There are lots available online, and as usual with things like this, they often come with hugely optimistic capacity markings from far east sellers and local resellers. ("oh, 4000mAh is the part number")
You also find them in those cheap USB power banks, although those are often quite low capacity cells.
Another well known source of these is old laptop battery packs, and I have rather a lot of those. So when I need some more 18650 cells, I dig one of those out to scavenge.
A lot of old laptop batteries are composed of 18650s, you can usually tell by looking at the sizes and ratings.
In this case, the battery pack is just wide enough to contain an 18650. The voltage is 10.8V, so they are using 3.6V as the nominal voltage instead of 3.7V which is more commonly used these days. Three 3.6V cells in series is 10.8V.
Looking at the size of the pack, it is probably three sets of three cells in parallel (3s3p), 3.6V 1200mAh per cell giving 10.8V 3600mAh in total.
1200mAh isn't great. Modern cells are often three times that. Still could be useful for some applications (super long battery backup maybe?). But I'll leave that for another day.
Ah, this one looks more like it.
Looks like it is the right size to be six cells. 11.1V @ 4400mAh, would be three pairs of two cells (3s2p), 3.7V @ 2200mAh each. That sounds decent enough, and the laptop these were for is long gone.
Now, the warning. Lithium Ion cells are dangerous if mishandled. They can explode or catch fire if you short or pierce them. Be very careful, use plastic tools, separate the cells as soon as possible. If in doubt, don't.
This pack is probably 20 years old, so the plastic is quite brittle, and easy to start to snap bits off by hand.
Result! Samsung branded 18650 cells. (well, at least they have Samsung printed on them)
Six of them as predicted. You can see how they fill the pack. The only other thing in there is the battery management board.
But we don't need that anymore.
What we do need is the six cells. You can see here how the three pairs are connected in parallel then series. 3s2p, three series sets of 2 cells in parallel.
Those are joined by strips of nickel spot welded to the ends. Those break off quite easily and you end up with six individual 18650 cells.
Samsung ICR18650-22B would seem to confirm the 2200mAh calculated above. 615 may be a date code? 15th week 2006 sounds about right.
These differ slightly from standard cells in that they don't have the pip at the positive end, so they may not fit every application.
But you can still tell the difference from the negative end.
Note some cells have a small board at the end which is a protection circuit to prevent over voltage and over discharge. The ones in the packs do not usually have those.
It depends on your application, but these fit fine in 18650 battery holders. (I know one cell doesn't count as a battery, but they are still called battery holders)
It is not advisable to solder directly to the cells, you could try to leave some of the nickel strips attached and solder to those, but you have to be extra careful not to short things out if you leave those attached, so try to avoid that. You can buy the nickel strips and miniature spot welders from ebay or ali express if that's your sort of thing.
Time to test these out. First step is to measure the voltages and reject any dead cells. Anything above 2.5V seems to be salvageable, if the voltage is really low, the cell may have failed and you should probably reject it.
I use one of these cheap chargers from Amazon, seems to do a decent job. I am using the lowest charge rate this one supports, 500mA. These cells started out around 3V and quickly rose to about 3.5V and kept going.
Monitor them carefully to see if any are getting hot. I don't think this charger has any thermal cutout, so keep checking nothing is getting hot.
After an hour, they had all risen to about 3.9V, so were charging well.
And after 3 hours they were over 4V.
The charging cut off is 4.2V, which they reached after 4 and a bit hours.
Most of the cells had taken between 2100 and 2200mAh. They have been in a box for about 10 years, so would have been very flat. But that seems to confirm these are 2200mAh cells.
I repeated with the remaining two cells, which both performed perfectly as well.
These cells all behaved impeccably, but sometimes you get ones that appear to charge very quickly, but you put them in a torch and it goes dim after a few minutes. Again, you can reject those.
A powerful torch is a good test load. This one is optimistically rated 10W, but is probably more like 2. I ran one of those cells for half a day until it started to go dim, and then it took a full charge, so all looking good.
The next day, they are all still reading a bit under 4.2V. If any of them drop significantly in storage, then you should probably rule those out as well.
So far, so good. Six "free" 18650 cells, ready to use.
Find out what I have planned in an upcoming post, or subscribe to my Patreon (link below) to get an advance preview.
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I think I still have all the kits in stock, but I am down to only a few of each type of kit left, some are the last ones.
The SellMyRetro store is also on it's last days, everything is still listed there if you need more information, but best to use the contact me link about, tell me what you want and where you are and I will send a PayPal invoice. Sorry I have to keep saying that. I am working on an alternative.
All the links can be found here:
Patreon
You can support me via Patreon, and get access to advance previews of posts like this and behind the scenes updates. These are often in more detail than I can fit in here, and some of these posts contain bits from several Patreon posts. This also includes access to my Patreon only Discord server for even more regular updates.
