trailstoride
Newly Enlightened
My UltraFire WF-138 charger was terminating the charge on my 10440 (AAA) batteries at 4.3V. From what SilverFox has said, this dramatically shortens the life of the batteries. I spent some time examining the circuit board and came up with a simple fix to adjust the charger termination voltage.
The positive battery terminals are conected via R25 and R26 (10K ohm) resistors to the LM393 (?) voltage comparator IC. The power supply of the charger is 5V (measured 5.14V.) By adding a small forward bias to the IC at R25 and R26 , I was able to lower the termination voltage. I found a 51K ohm resistor dropped the termination voltage to 4.17V. I suggest tack soldering the resistor in place to test the termination voltage before installing the two additional resistors.
The 5V passes thru J2, down a wide copper trace to Q4 and Q5. There was room to drill two small holes on the 5V trace, and one next to R26. Be careful not to allow the resistor leads to touch any other leads or jumpers. Below is a picture - sorry for the poor image quality.
The positive battery terminals are conected via R25 and R26 (10K ohm) resistors to the LM393 (?) voltage comparator IC. The power supply of the charger is 5V (measured 5.14V.) By adding a small forward bias to the IC at R25 and R26 , I was able to lower the termination voltage. I found a 51K ohm resistor dropped the termination voltage to 4.17V. I suggest tack soldering the resistor in place to test the termination voltage before installing the two additional resistors.
The 5V passes thru J2, down a wide copper trace to Q4 and Q5. There was room to drill two small holes on the 5V trace, and one next to R26. Be careful not to allow the resistor leads to touch any other leads or jumpers. Below is a picture - sorry for the poor image quality.
