Hello, I have a Ultrafire Q5 CREE x3 LED 700 lumens flashlight model #WF700F. It takes two 18650 batteries and when I pull the discharged batteries out of the light, one of the batteries (tail battery) will not accept a charge on my Ultrafire WF-139. It appears that the flashlight discharges the battery too much. Will a different charger like the Pila IBC charge the dead batteries?
Help: 18650 cells wont charge
- Thread starter CPerry
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mudman cj
Flashlight Enthusiast
Some chargers will not charge a Li-ion battery that is discharged too low in order to avoid a charging current that would be too high. Charging or discharging at too great a rate can lead to overheating, which causes a thermal runaway reaction commonly referred to as 'venting with flame'. What you need to do is measure the voltage across the battery. If the voltage is below 3V, then the charger may be designed to not charge it.
You can bring the battery voltage slowly back to greater than 3V by connecting it to another Li-ion battery in parallel (+ to +, - to -) with a resistor to limit the current flow. If you select another battery that has a voltage within 0.5V of the over-discharged battery, then the current will be low enough without a resistor. Remember that the resistor needs to be capable of handling the current flowing or it too can overheat. If the battery voltage is less than 2.5V then it is sustaining damage the longer you wait to charge it. It shouldn't take long to bring it back to the point that the charger will begin a charge cycle.
In the future, try not to rely upon the over-discharge protection of the batteries. That is really intended as a last resort.
You can bring the battery voltage slowly back to greater than 3V by connecting it to another Li-ion battery in parallel (+ to +, - to -) with a resistor to limit the current flow. If you select another battery that has a voltage within 0.5V of the over-discharged battery, then the current will be low enough without a resistor. Remember that the resistor needs to be capable of handling the current flowing or it too can overheat. If the battery voltage is less than 2.5V then it is sustaining damage the longer you wait to charge it. It shouldn't take long to bring it back to the point that the charger will begin a charge cycle.
In the future, try not to rely upon the over-discharge protection of the batteries. That is really intended as a last resort.
Thanks for the reply mudman. I'm not quite sure how to connect two cells in parallel, is it something I can do at home?
As for my charger (Ultrafire WF-139) not being designed to charge a cell that is below 3V, is there a charger available that is designed to charge a li-ion battery that is discharged below 3V?
As for my charger (Ultrafire WF-139) not being designed to charge a cell that is below 3V, is there a charger available that is designed to charge a li-ion battery that is discharged below 3V?
mudman cj
Flashlight Enthusiast
To connect two cells in parallel, simply press them together with the + side of one touching the + side of the other and then connect the two - sides together using a wire. The cell with a higher voltage will discharge into the other cell. The use of a resistor is preferred to limit the current, but if the cell voltages are close enough this in not necessary. Also, you can connect them for only a second and then let them rest a few seconds before connecting again to help limit their heating for greater safety. The rule of thumb is to limit charging to 0.7-1.0C. In the case of 2200mAh 18650 cells, that means 1.5-2.2 Amps max.
The 3V is an approximation: there is certainly some variation among chargers and although I have used a WF-139, I have never given it a cell that was that low. The only chargers I know of that automatically charge at a slow rate until the cell voltage is brought up are ones that were designed and built by members.
The 3V is an approximation: there is certainly some variation among chargers and although I have used a WF-139, I have never given it a cell that was that low. The only chargers I know of that automatically charge at a slow rate until the cell voltage is brought up are ones that were designed and built by members.
Bullzeyebill
Flashaholic
CPerry, you already have a thread going concerning this problem, http://www.candlepowerforums.com/vb/showthread.php?t=241026
Ask a moderator to combine the two threads into one. Click on the triangle next to the post number of one of your posts.
Bill
Ask a moderator to combine the two threads into one. Click on the triangle next to the post number of one of your posts.
Bill
