Monday, February 27, 2012

The "5 Minute Warning" Alarm

The CellLog8s LVD is fine and works well at protecting the battery bank from over discharge but it doesn't give you any warning that the lights are about to go out.

So I started thinking about some kind of pre-alarm that would give me a few minutes warning (under heavy load) that the battery was nearly depleted.  I could then turn off some big loads and buy some time.
The old SmartGauge Voltmeter has a programmable relay in it too.  But it only works on pack Voltage.  I've been using it as an obvious visual reminder of pack Voltage (it's no good at reading SoC for non lead acid batteries).

Then I started looking around the house for something to use as a buzzer or alarm sounder that the relay could activate so that you'd get the message...
I found a small toy sound effect thingy that you press the top and it makes a cool police car sound.  I actually found another one that my wife had that made steam train noises and in fact a whole load of similar sound chip enabled things, like a Dr Who Darlek bottle opener that says "EXTERMINATE!" when you close a circuit (with the bottle top) and a Christmas card that plays George Michael's "Last Christmas"...

But I decided to go with the police car :D

Taking it to bits was very easy and then all I had to do was solder wires on to the existing switch contact and run these out to the alarm relay on the SmartGauge and program the chosen low Voltage alarm.
The toy still uses the same two 1.5V button cells to make the noise.  The SmartGauge does not provide any power to the relay contacts so external power for the alarm or whatever is needed.  If the batteries in the alarm go dead, it does not affect the safety of the battery bank as this alarm is just for information.

When the relay contacts close, the police siren only goes off once for a few seconds and then stops.  This is a good thing!  Saves the batteries in the alarm and prevents bricks being thrown at the thing for sounding too much once the message has gotten through to whoever is within ear-shot of it :D

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