Some people will not learn about the use of lithium batteries. I love them, but as you say they must be fused, and that should has close to the output as possible, but why do most lithium batteries explode (ebikes for example) not using a compatible charger, and gashing up a 'make and do'.
For you all, i am somewhat educated on this subject.
Li ions are very safe to use, second handed or new:
B U T :
RULES--->ALWAYS use a bms, and a dedicated charger.
When handling or wanting to use secondhand li ion cells there are some ground rules! for safe and longtime operation.
When you dont or cant follow the previous AND the next set of rules, DONT use li ion for your own safety and the insurance company will not help you.
RULES--->Second hand li ion cells MUST be tested for their remaining capacity; RULES---->this must be more than 80% of the new factory value.
For example, a 2500mah cell (fabric new) must hold more than 2000mah, if not ----> its done.
RULES---->For one-time period test charging you can go up to 4.2V and your discharge test down to 2.8v.(yearly)
RULES--->For in use keep them in between 3v and 4v.
RULES---->A MUST do is a BMS (battery management system) this will allow the cell or multiple cells to cut off at a to high voltage charge or a to low voltage discharge and balance the cells in between so that they all have the same state of charge.
RULES---->Also test for self discharging behaviour: charge the cell up to 4.2v and let them rest for a minimum of two weeks 4 if you can. if the volt drops to or below 4.00v they are considered
dangerous.
For hobby use those tests will do perfect, for a powerwall there is a lot more to it----> A LOT more.
For hobby use also, keep the c rate below 0.5, meaning per 1a no higher charge or discharge than 0.5a
For a 2500mah cell means no higher charge or discharge than 1250mah.(optimum is 1/4 of the new mah)
Rules--->Dont use them below 0 Celsius or above 45 Celsius.
RULES---->O yes cell level fusing: solder on every cell a max 1A fuse, a heater will start consuming power (self discharger) the more it can get the hotter it will become.
With a 1a fuse the fuse will blow before it gets dangerous.
What is the must to DO if you want to use them(second or new):
On ali express you can find enough cheap and very good 18650 testers
Search for zb2l3 and for tp4056.
Search also for 18650 bms and choose the one that fits your needs: 1s 2s 3s up to 36s
Also glass fuses..
I hope this will help someone to give their old laptop batts a second life.
Cous some new 18650's are up to 10 euro a piece.
My two cents, best Igor
PS:
why do some li ion self-combust:
1st: no adequate protection for over charging or over discharging, no auto cut off(or wrong non li ion charger!)
2d: lack of balancing,
3th internal resistance is going up(aka internal short)
4th: wrong temperature (full sun or charge below 0.)
5th: to high v and/or a charcge/discharge.
also some over spray (under spray really, snuck under the tape!) delt with and the first coat of cream applied, good job no one's coming to dinner!!
