Battery voltage circuit

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Subject: Battery voltage circuit
From: "Neville and Charlotte Brock" <>
Date: Fri, 4 Jan 2002 21:08:30 +1100
Hi all,
Brian - some details on that little circuit!
The circuit is a "LED Battery Voltage Indicator" circuit with Dick Smith's Kit Number: K3118.
The circuit board is 25mm square and incorporates a variable resistor (trimpot) that you use to set the voltage at which the LED changes from green to red (or vise versa - depending upon polarity and your needs).
For a container I used a 35mm film canister cut to approx 3/4 length (ie. discard the open end) so that the cap still fits in place (this can be later glued on).
I drilled a small hole in the middle of the solid end of the container and fitted a LED bezel (H1910) which holds the dual colour LED, epoxied in place from the inside. Attach you LED to the circuit board with hook up wire to allow for the above mounting.
A small hole drilled in the edge of the film canister cap can be used for the power leads. I wired this circuit in parallel with my spotlight from the rear of the cigarette lighter socket.
It is a bit finicky to set the resistor. I used a voltmeter and a partially discharged battery hooked up to my light dimmer control. You may have to slightly recharge your battery and try discharging again (with your light) a number of times if you miss your cut off voltage - Using 11.00 volts for cut off will give you approx. 30min on full power with a new fully charged 7.0Ah 12volt battery and a 100Watt globe.
Hope this helps, and doesn't sound too confusing.
Simon Brock.
ps. I have also used two of these circuits as a charging monitor. The first LED changes from green to red as the battery comes up to charge, the second LED changes from green to red when fully charged and activates a piezo alarm.
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