all about wiring diagram

The goal of the circuit design was to make a charge controller with analog simplicity, high efficiency, and reliability. A medium power solar system can be built with a 12V solar panel up to 10 amps, the SCC2, and a rechargeable battery. The SCC2 works with lead acid, NiCD and NiMH batteries with ratings from less than one to several hundred amp-hours. With the appropriate parts selection, the SCC2 can be operated at 6V, 12V, 24V or other voltages.

The SCC2 acts as a medium power DC current switch between the + terminals of the PV and battery. Diode D1 prevents reverse night time current flow from the battery back to the PV panel.

When the PV voltage is high enough to charge the battery, zener diode D2 conducts and turns on transistor Q2. Q2 switches the power for the rest of the circuit on. The circuit is switched off at night. IC2 provides a 5 volt regulated voltage to power the comparator circuits, it also provides a reference voltage for comparator IC1a.

When the battery voltage is below the desired full voltage and needs charging, comparator IC1a turns on and activates Q1 and Q3, this allows the solar charging current to flow into the battery. Note that Q3 is a P-channel mosfet, this allows the circuit to be wired with a common ground for the solar panel and battery. The solar current loop is drawn in heavy lines on the schematic.

When the battery reaches the full charge point, IC1a operates as a comparator based schmidt trigger oscillator, it switches the solar current off and on. The switching causes the battery voltage to oscillate a few tens of millivolts above and below the desired set point. A rail-to-rail op-amp is required for proper operation, 741 style op-amps will not work in this circuit.

The red/green charging/full LED is driven between the output of IC1a and IC1b. IC1b has an inverted version of the IC1a signal. Pin 5 of IC1b only needs an approximate center point to work as an on-off comparator, it is connected to the varying IC1a pin 2 so that it does not require another reference divider circuit.

The resistors and thermistor on the input side of IC1a form a resistive bridge circuit that is used to compare the battery voltage to a reference voltage coming from IC2/R8/R9. The potentiometer adjusts the voltage point around which the circuit will oscillate on full charge. Resistor R7 adds positive feedback to IC1a for a schmidt trigger characteristic and C6 sets the maximum frequency of oscillation. The thermistor provides thermal compensation, as the temperature goes down, the float voltage setting goes up.

The equalize switch, S1a, forces the circuit on for intentional overcharging. Switch S1b and R1 can be used to select a different float voltage range, you can experiment with this by using different values of R1, typically R1 should be greater than 1M.

An unconventional, scalable high efficiency 12V solar power system and battery charge controller with low voltage cutout to protect the battery. (ideal for systems of 50W or less). The most common solar charger consists of a Schottky diode to prevent the battery from draining into the PV panel and a shunt regulator that effectively short circuits the panel once the battery is fully charged.

One problem with this approach is diode losses and the resulting heat. If a 50W 12V panel supplies 4A to the battery, the Schottky diode will drop about 0,4V across it dissipating about 1,6W of heat. This requires a heat sink and loses power to heat. The problem is that there is no way of reducing the volt drop, paralleling diodes may share current, but the 0,4V will still be there. The circuit uses a MOSFET in stead of the usual diode and the primary power loss is resistive. [Link]

Small-size AA cells and button cells used in electronic devices providing a terminal voltage of 1.5V are normally rated at 500 mAh. As the cells discharge, their internal impedance increases to form a potential divider along with the load and the battery terminal voltage reduces. This, in turn, reduces the performance of the gadget and we are forced to replace the battery with a new one. But the same battery can be used again in some other application that requires less current.

Here’s a simple tester for quick checking of discharged pencells and button cells before throwing them away. The tester detects the holding charge of the battery and the terminal voltage to indicate whether the battery is suitable for a particular gadget or not.

A 9V battery can power the circuit with sufficient voltage and current. When you close switch S1, it provides stable 6V DC to the circuit.

Simple Pencell Charge Indicator Circuit Diagram



The circuit uses op-amp CA3140 (IC1) as a voltage comparator. It can sense even a slight voltage variation between its inverting and non-inverting inputs. The non-inverting input (pin 3) of IC1 is supplied with a voltage obtained from the battery under test, while its inverting input pin 2 is provided with a reference voltage of 1.4V derived by resistor R4 and series combination of diodes D1 and D2. Resistors R1 and R2 provide a loading of 10 mA and 100 mA, respectively, for checking the charge capacity.

When a new battery is connected to the test terminals, the non-inverting input of IC1 gets 1.5V, which exceeds the voltage of the inverting input and the output of IC1 goes high. This high output provides forward bias to transistor T1 through resistor R4 and it conducts to light up the green half of the bicolour LED (LED1). Simultaneously, the base of transistor T2 is pulled down and it turns off and the red half of bicolour LED1 remains off.

When a partially discharged battery (with a terminal voltage of less than 1.4 V) is connected to the test terminals, the output of IC1 goes low to switch off transistor T1. This allows transistor T2 to forward bias by taking bias voltage through resistor R5 and the red LED within bicolour LED1 glows.

Slide switch S2 is used to check whether the battery is holding sufficient current to drive a load of 10 mA or 100 mA. If the discharged battery holds more than 100mA current, the green LED within bicolour LED1 glows, indicating that the battery can be used again in a low-drain circuit.

The circuit can be easily constructed on a perforated board using readily available components. Enclose it in a small case with probes or battery holder for testing.