12V Analogue Battery Volt Meter

Posted on May 8, 2012

This circuit is used to measure the voltage on a 12V (nominal) lead acid rechargeable battery system. It was specifically designed for use in solar powered systems, but is general enough that it can be used for automotive or other 12V systems. Lead acid batteries normally spend their working lifetime in the voltage range of 11-15 Volts. This meter circuit was designed to show the voltage range of 10-15V on an analog meter movement, it can be used to show the battery charge state from empty to full.

12V Analogue Battery Volt Meter - image 1
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Specifications Measured Volts: 10-15 Volts DC Circuit Current: 9.2mA at 15 Volts DC input Theory The input voltage is filtered from transient voltage spikes via the 10 ohm resistor and the 0.1uF capacitor on the input of the 78L08 regulator. The 1 Amp series fuse and Transzorb protect the circuitry from short circuits and over-voltage conditions. Construction An approximately 1³x3³ piece of perforated circuit board material was drilled with two holes so that the board could be mounted on the two terminals of the analog meter. The parts were assembled on the perforated board and connected together with point-to-point wiring. Teflon insulation was used over bare wires to make the cross-board connections. The two battery leads were twisted together, then secured to the edge of the circuit board with a loop of wire to prevent movement. The meter was mounted on a 4³x4³ metal plate that was cut and drilled to fit onto a standard electrical switch box. The box should be deep enough that the meter and accompanying circuit board do not touch the back of the box. Alignment The circuit should be wired in parallel with a digital Volt meter, both meters should be connected to a stable variable voltage power supply that is capable of operation in the 10-15V DC range. Set the input voltage to 12.5V, set the gain control to midway, and adjust the offset control until the meter reads in the center of its range. While...

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