opins
Newbie level 4
Hi all,
I have a simple circuit for charging a 3.6V, 600mAh NIMH battery; I am using a simple diode-resistor circuit for charging the battery. In other to avoid overcharging, I have selected an input voltage of about 5.6V, and resistor value of 12Ω, if the diode forward voltage is 0.7V, then the charging voltage is 5.6-0.7 =4.9V
When the battery is low, each cell of the 3 cells of the battery is about 1.2V thus giving the battery 3.6V; while when it is fully charged, each cell is about 1.45V thus giving a full voltage of about 4.4V.
So when the battery is low the charging current is about (4.9 – 3.6V)/12Ω = 108mA
But when the battery is full, the charging current is about (4.9 – 4.4V)/12Ω = 42mA
Thus, when the battery is low, the circuit fast charge the battery at a charge current of 108mA. While as the battery is being charged, the battery voltage gradually increases thus reducing the voltage drop across the charge resistor and thus reducing the charge current, until when the battery is fully charged the current reduces to about 42mA which is (less than C/10) suitable for trickle charging, thereby avoiding overcharging.
Please I would like to know the suitability of this approach.
Thanks
I have a simple circuit for charging a 3.6V, 600mAh NIMH battery; I am using a simple diode-resistor circuit for charging the battery. In other to avoid overcharging, I have selected an input voltage of about 5.6V, and resistor value of 12Ω, if the diode forward voltage is 0.7V, then the charging voltage is 5.6-0.7 =4.9V
When the battery is low, each cell of the 3 cells of the battery is about 1.2V thus giving the battery 3.6V; while when it is fully charged, each cell is about 1.45V thus giving a full voltage of about 4.4V.
So when the battery is low the charging current is about (4.9 – 3.6V)/12Ω = 108mA
But when the battery is full, the charging current is about (4.9 – 4.4V)/12Ω = 42mA
Thus, when the battery is low, the circuit fast charge the battery at a charge current of 108mA. While as the battery is being charged, the battery voltage gradually increases thus reducing the voltage drop across the charge resistor and thus reducing the charge current, until when the battery is fully charged the current reduces to about 42mA which is (less than C/10) suitable for trickle charging, thereby avoiding overcharging.
Please I would like to know the suitability of this approach.
Thanks
