Circuit Schematic 12V, 4-AA Cell Differential Temperature Charger

Solar. - Here is electronic Circuit Schematic 12V, 4-AA Cell Differential Temperature Charger like in Figure 1 below. In this circuit schematic includes a number of improvements over my older Temperature Controlled NICD Charger circuit. This circuit runs on 12VDC, allowing it to be used in a car or from a 12V solar power system. Additionally, a current sensor LED verifies that the cells are receiving charging current. Note that the current sensor circuitry is not shown in the circuit board photo above, it was added to the side of the main board via a small perfboard.

Circuit Schematic

Component Part
  1. LM358 IC
  2. Resistors
  3. MOSFET IRFD110
  4. Capacitors
  5. LM317 IC
  6. 7809 IC
  7. See all component like in Figure 1 above

Description

Circuit schematic like in Figure 1 above is Circuit Schematic 12V, 4-AA Cell Differential Temperature Charger. According Solarb site that this circuit schematic includes a number of improvements over my older Temperature Controlled NICD Charger circuit. This circuit runs on 12VDC, allowing it to be used in a car or from a 12V solar power system. Additionally, a current sensor LED verifies that the cells are receiving charging current. Note that the current sensor circuitry is not shown in the circuit board photo above, it was added to the side of the main board via a small perfboard.

The current is adjustable in three steps from 100 to 300mA, allowing fast charging of AA, AAA or other small cells. Battery packs from 1 to 6 cells can be charged with this circuit. NiMH and older NiCD cells are supported. The circuit is protected from reverse input voltage and reversed cells.

Theory

12VDC power is supplied to the circuit from an external source such as a car battery system, a 12V solar power system or a regulated "wall wart" supply. If DC power is applied backwards, the 6A05 crowbar diode causes the 3A fuse to blow, protecting the circuit from reverse voltage. The power switch routes power to the 78L09 voltage regulator and the battery. The 78L09 regulator provides regulated power to the rest of the circuit.

The battery current loop starts with the +12V supply, then runs through the battery and through a 1N5819 reverse voltage protection diode. Current continues through the LM317 1 amp adjustable voltage regulator which is wired as a constant current source, through the IRFD110 power MOSFET transistor, which switches charging current on and off, through the 0.1 ohm current sensing resistor to ground (12VDC negative). The charge current is selected by jumpering one of three current-set resistors on the negative side of the LM317 regulator. The 120 ohm trickle charge resistor always allows 10mA of current to flow through the battery.


The temperature control part of the circuit starts with a matched pair of 10K NTC thermistors. One thermistor is epoxied to a small metal reference temperature plate. The other thermistor is epoxied to a metal battery holder. The temperature sensors are balanced by the calibrate potentiometer. The 100nF and 50nF capacitors across the thermistors cause different start-up time delays to insure that the following circuitry powers up in the off state.

See all information about Circuit Schematic 12V, 4-AA Cell Differential Temperature Charger using [link here].
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