AW 18650 died, then came to life! Whaaa?

vio765

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Dec 24, 2007
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I ran a DBS 2x18650 on low with an MC-E emitter until failure. After 124 hours, I took the two AW18650 cells and put them into my Yoho-122 charger and one cell didnt charge! my voltmeter read 0.00V. OH MAN!!! $17 gone! but i put the cell in my WF-139 charger and it indiacated that is charging. I waited about a minute and took a volt reading. 2.17V. i put the cell back on the yoho and it appears to be charging ok. after about 15 minutes, my voltmeter read 2.20V. seems okay now. what is going on?
 

jasonck08

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Not sure exactly what's going on, but if the protection circuit kicks in on a protected cell, often times the voltage reading will be 0.00 until its charged.

But the fact that the battery read 2.17V's, indicates that the protection circuit did not kick in at the proper 2.5v, thus draining the cell beyond safe limits and maybe causing permeate damage to it.

If it went down to about 2v or so the cell may be bad. I would do some tests on it in single cell lights and stuff, before you mach it with another known good 18650. Because we all know that unbalanced Li-on's can be dangerous.
 

AW

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You may want to check the reading accuracy of your meter first ( may need to replace the battery ). If the reading is correct, you may have a bigger problem there because no charger is supposed to charge a LiIon battery with a voltage below 2.6V. As far as the voltage reading of 0.0V, it means the protection pcb is tripped ( open circuit ). If you have been running the pair of 18650s on low level with the DBS, it means they are running on under 50mA and there will be no voltage sag under such load - the pcb will kick in 2.45V.
 

vio765

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voltage sag? does that mean the the battery wasn't being ran hard enough for the PCB to trip?
 

AW

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In general, it will take a 0.2C load to reliably trip the low voltage cut off where the voltage will rebound to a safe 3.0V when the load is removed. The design is to maximize the use of the cell's capacity. If you have to use a smaller load, you must recharge the battery ASAP to bring the voltage up to prevent permanent damage.
 

Kestrel

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the pcb will kick in 2.45V
[...]
In general, it will take a 0.2C load to reliably trip the low voltage cut off where the voltage will rebound to a safe 3.0V when the load is removed. The design is to maximize the use of the cell's capacity. If you have to use a smaller load, you must recharge the battery ASAP to bring the voltage up to prevent permanent damage.
Thanks for this info, AW. There is some uncertainty on CPF as to what situation(s) are required for the low-voltage protection to kick in.
 
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vio765

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what would be an example of a 0.2C load? and i did place the cell on a charger within a couple of minutes after the light died. i didnt have a chance to fully recharge the cell because i had to go to bed and i take my li-ion batteries off the charger when i sleep, leave the house, etc. but i took a volate test at it read 3.17V. I put it back on and will wait until the yoho-122 charger gives me the solid green light indicating a fully charged cell.
 
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