[time-nuts] Li-ion Battreries
cfharris at erols.com
Sun Jan 22 10:44:27 EST 2017
Just a quiet message that needs to be said:
18650 style LiIon cells are indeed one of the most common
styles of LiIon cells, but with their popularity comes a
great deal of fraudulent sales activity.
The 18650 cells are used in all sorts of trendy gadgets, like
the vape appliences for niccotine addicts, over powered green
laser pointers, and vibrators for... well... urhmm...ahhh, I can't
I went on a quest to try to buy 18650 cells for cheap prices,
and then tested them on my Christie CASP battery charger/tester,
and I found that I could buy the things wrapped with the labels
of Samsung, Sanyo, UltraFire, PowerSonic, and probably a dozen
other brands, labeled with 3000 through 9800mAH capacities.
In testing, I found two things. If the batteries came from
eBay, or Amazon, they would weigh between 1/3 and 1/2 as much
as the manufacturer's spec sheets said they would, and they
would test at between 400 and 500mAH. And that was with allowing
them to discharge until their internal protection circuitry
shut them down... in other words to an unsafe level.
So, the moral of my story is know your sources, and do test
every one... a twist on the old saying: Don't trust but verify.
I quit the project, as I feared that the high number of items
I was declaring as counterfeit for refund, would soon catch up
with me and render me unfit for ebay and Amazon purchases.
The safest, surest supply I have found is discarded laptop
batteries for Dell computers. Bust them apart, and you will
find that all but one of the cells is in good condition. The
one bad cell can almost always be resurrected by charging it
manually to 4.2V at less than 1C current.
Note, they won't have the protection circuitry installed as part
of the cell, but you can buy that part on eBay with pretty good
Attila Kinali wrote:
> Hoi Bert,
> Some small remarks: 18650 is by far the most common form factor
> of Li-Ion batteries on the market. This is IMHO the better choice
> than the 26650 if you want to be able to replace them in 10-20 years.
> If you stack Li-* batteries, you will need to have a controller that
> monitors each cell individually while charging or has some other means
> of ensuring that none of the cells are overcharged (or rather that they
> are charged the same amount). This kind of circuit is called balancer.
> A protection circuit does _not_ replace a balancer. The protection circuit
> is only to protect against catastrophic failure. Ie it is still possible
> to overcharge a battery even if it has a protection circuit. You also do
> not know what the protection circuit does to protect the cell. There are
> a lot of chips out there, that simply open a switch and thus disconnect
> the cell. In this case, the protection circuit of one cell will disconnect
> the whole stack and break charging.
> A lot of the multi-cell Li-Ion charger chips have integrated cell protection
> circuitry. Ie if you use one of them, you will not need an additional
> protection circuit. But be aware, the regulation for battery protection
> circuit states that the circuit has to be wired fix onto the battery
> in a way that this connection cannot be broken (without breaking the
> housing of the battery pack). The reason for this is, i think, pretty
> obvious. I would recommend that you solder each cell indidividually
> into your circuit instead of using some kind of holder. Or if you are
> using a holder, make it such that there is no chance any of the cells
> can be accidentally short circuited.
> Attila Kinali
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