Ni-MH Ni-Cd Adjustable Constant Current Charger


Ni Cd Ni MH Adjustable Constant Current Battery Charger

Ni-Cd Ni-MH Adjustable Constant Current Battery Charger Circuit

This is a Adjustable Constant Current Ni-MH or Ni-Cd battery charger circuit. It can be used to get a constant current power supply. Here is the schematic diagram of the circuit:

Ni MH Ni Cd Adjustable Constant Current Battery Charger circuit

PARTS LIST

R1
100Ω

VR1
500Ω Preset

C1
0.1µF

C2
0.01µF

D1
1N4001

Q1
BC140

IC1
LM317

This circuit can be adjusted to any value from a few milliamp to about 500mA. The max current is 500mA because it is the limit of the BC140 transistor in the current-limiting part of the circuit.

The input voltage has to be 5.25v above the required output voltage, because of 1.25v across the current-limiting section and Approximately 4v is dropped across the regulator.  The LM317 3-terminal regulator will need to be heatsinked.

LM317 pin configuration

the LM series of regulator is suitable for this circuit because they have a voltage differential of 1.25v between “adj” and “out” terminals.

BC140 transistor pin Configuration pinout

For example, to charge 4 Ni-Cad cells, just connect them to the output and adjust the 500Ω preset until the required charge-current is obtained. The charger will charge 4 Ni-Cad cells at the same current. But, don’t forget to turn off the charger before the cells are fully charged or the battery will be over-charged.

LM317 Adjustable Constant Current Charger
Ni Cd Ni MH Adjustable Constant Current Battery Charger


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