Battery voltage alarms help please!

peteandthira

peteandthira

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Afternoon all

Does anyone know of a cheap way of warning of battery voltage variations outside pre-set parameters?

I would like an alarm to go off whenever my battery voltage drops below 12.2 or so, or rises above 14.4. I might be able to self-build given the right advice but would rather buy an off-the-shelf doodah.

Any good advice appreciated!

Thanks

Pops
 
quite a few fridges are supplied with such an alarm for low voltage, but actually designed to shut the fridge down. I am sure that they must be available as a spare.
 
Talbot

Thank you for your reply, but although it would probably look after the low voltage warning, I doubt it would alarm at overvoltage. Unless you know differently!

Pops
 
Problem is if you take out a a decent current (definately engine, possibly fridge, heater etc.) will reduce the voltage even if the battery is fully charged, and your alarm will sound. So perhaps you set it at a lower voltage when it goes off? If you do this you can flatten the battery by taken a little out at a time.
 
Stoopid question: why should I worry if the voltage(s) go outside these parameters. What will be damaged? What won't work?

I can actually suss when lights are dim or the engine won't start! Actually it's the stereo which goes off first, then the chart-plotter, my fault for wiring the bow-thruster (wash-yer-mouth) into the domestic circuit.

C'mon Talbot, high-tech comment please.
 
The circuit is very easy and you can get the parts from Maplins or Truro. There is a friendly radio amateur local to you who would no doubt sketch out a circuit in less time than it takes to drink a coffee! You'd need to be able to solder but the cost would be less than £10 in parts.

Better still, why not invest in a proper battery monitor? e.g. link? I have the BEP and it is an essential piece of liveaboard kit. I'd go for the Link next time, tho'. Not over-impressed with BEP though it does incorporate a bilge pump monitor, which is a vital piece of kit.
 
The circuit given here is an adjustable voltage monitor and 2 of there one for high voltage and one for low voltage si all you need. Replace the leds with relays will allow you to drive a sound alarms or switch off circuits. If a capacitor is included into the input line to ground and a resistor in series with the input this will smooth out engine start volt drops
 
No, that's not suitable. No voltage reference. There is a much easier way to get hysteresis than building two of those circuits. Definitely not a good circuit for what he wants to do.
 
I though you might ask that /forums/images/graemlins/smile.gif It isn't that difficult but from past experience if I do that then I am going to have to support the design with all sorts of questions and debugging help. It's one thing to help people on an ad-hoc basis and quite another to take on the responsibility of seeing folks through a project especially as we will be getting out and about quite a bit soon, what with the Barcelona boat show, etc.

So reluctantly, I decline, but am happy to answer any specific Qs if I am around. For instance, in 'your' design, you need to add a zener reference and a feedback circuit to give some hysteresis. Try googling on "op amp circuits/projects/etc"

Such as bags of smashing op amp projects here
and Lots more here as well as voltage comparators
and Loads more here, all good stuff from National Semiconductor
 
Know the feeling I run a software development company and the number of little !! programs I get asked for. Have also done digitial micro processer design and the same.

Yes circuit is the basic but as you say needs more development to make a proper job.

I don't need one my self but tried to show a sompler circuit than the one from the user Transcur.
 
Sounds like an excellent project for a PIC. You should be able to pick up a PIC prototypying board/kit for about £20 which you could use for that - and a lot more.

I did seriously consider doing something like this a couple of years ago - create a boat control system using a PIC to monitor things like the batteries, engine (temp, oil, running hours) and so on - but never quite got round to it!
 
THIS looks like it may do the job. if you click on the image once you are on the site it gives more details. It says it can be set for both high and low voltage warning withing a pre set range.

"The CBC High or Low Battery Alarm is a solid state device that measures the dc supply from which it is powered and energises a sounder if the potential rises above, or falls below a pre-set level, depending upon the model selected. The standard unit consists of a printed circuit board, adjustment potentiometer and sounder housed inside a plastic enclosure. A Relay driver option is also available as an alternative to the sounder if required."
 
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