3.6V NiCad battery charger with auto cut off

Thread Starter

sanjubluerock3

Joined Mar 22, 2011
2
Hello, I made this charger circuit for 3.6V NiCad Battery with auto cut off just wanted to check if this works or3.7V NiCad battery charger with auto cut off.png any modification required?
 

Dodgydave

Joined Jun 22, 2012
8,680
Looks ok, but as the Nicad should be charging at a Constant Current rate, your circuit will drop current as it charges upto 4.3V, then the op amp will shut off and may keep pulsing on/off as there is no Hysteresis levels . I would put a 470K resistor on pins 3,5 to prevent pulsing.
 
Last edited:

ian field

Joined Oct 27, 2012
6,539
Hello, I made this charger circuit for 3.6V NiCad Battery with auto cut off just wanted to check if this works orView attachment 160505 any modification required?
Worth having commercial chargers sense the very small drop in terminal voltage when it reaches full charge. (much smaller drop with Ni-Mh).

Temperature sensing has worked for me.

Cheapo commercial chargers just use a timer - the end result is pretty much dumb luck.
 

crutschow

Joined Mar 14, 2008
24,115
Your circuit will not correctly charge your battery.
You cannot reliably determine the charge status of a NiCd battery by its end voltage.
That's why good chargers sense the small change in end voltage to terminate the charge, often along with temperature sensing, to properly charge NiCd batteries, as Ian noted.
 

Thread Starter

sanjubluerock3

Joined Mar 22, 2011
2
Looks ok, but as the Nicad should be charging at a Constant Current rate, your circuit will drop current as it charges upto 4.3V, then the op amp will shut off and may keep pulsing on/off as there is no Hysteresis levels . I would put a 470K resistor on pins 3,5 to prevent pulsing.
Thanks a lot! I will try to build this circuit next week and post the results.
 
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