A simple NiMH battery charger circuit can be designed using electronic diagram below. This NiMH battery charger circuit, do not use specialized electronic components, being built using operational amplifiers, CMOS component and LM317 voltage regulator.
CT13 output of IC2 goes to logical "1" after 2 hours 30 minutes, then stop charging. At the same time, IC1a's output goes to "1" when the battery voltage rises above 1.49 V / element (this also result in stop of charging).
Number of elements contained in the battery charged is determined from the value of R14: for an element, the resistor will be omitted, value is 100 K for 2 cells, 3 cells, 2 x 100 k in parallel (k = 50), four cells, 3 x 100 in parallel, so
Another way to stop the load is measured through IC5 temperature (when temperature rises above 40 ° C, IClb off loading control).
The voltage depends on the number of elements contained in the battery charged. Minimum value is 4 V battery plus the number of elements multiplied by 1.5 V.
IC4 is necessary to mount a small radiator cooling (10 ° K / W).
To connect the charger must be pressed two buttons: S1 reset timer IC2 and S2 blocks the thyristor Th1