I'm thinking of fitting a Smiths auto voltmeter to Anemone to give me an indication of battery state probably with a selector switch so that I can see either battery bank. These can be picked up off ebay for around a tenner against a ton for a battery monitor. Is there any reason why not - except accuracy?
Are these analogue devices? I had one years ago and found it consumed a surprising amount of current. I put a switch into the circuit so it was only on when wanted.
I bought a voltmeter/ammeter from http://www.dpmeters.co.uk/index.html I think it cost about £30 and performs extremely well. I rarely bother to monitor volts as amps tells me so much more. Seeing conditions on each battery bank ios simply a matter of changing via the 1-2-both-off switch.
It's just a voltmeter, so it will give a rough indication of which part of the charging process is active when the engine is running, and then show the decay as you use it all up.
If you're really interested in batt voltage, maybe consider a little digital one from Maplin (other suppliers are available....) and switch put neatly in the fuse panel, rather than cutting a 50mm hole in the dashboard and then regretting it. - cheaper as well.
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Last edited by Billjratt; 06-11-09 at 13:06.
Reason: spelling
You could use one of these from rs-online RS Stock No. 365-6252 (plus on/off switch) either tapped into the 1-both-2 switch or with a change over switch to select which battery to monitor.
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Last edited by LadyInBed; 06-11-09 at 13:24.
Reason: better item
A digital meter will give a more precise reading but many do not operate off the power supply they are monitoring so check on that if you go digital.
If you stay with an analogue meter then get one that is intended as a battery condition meter with an expanded scale to give a more precise reading. Scaled 8 to 16 volts or similar.
Battery voltage alone cannot tell you the state of charge of a battery. It does give an accurate indication if the battery is under no load and has had plenty of time to "rest".
Under working conditions the voltage is less useful. Say for example the battery voltage read 10.5 volts. What is the state of charge?.... Well if the load is small then it's nearly flat but if the load is high then it could be fully chaged.
That's why battery monitors cost a little more and have a shunt to measure the current as well as the voltage.
I've had several occasions when the domestic battery was flat but with no indication I could not tell without lifting cushions, locker tops and measuring with my multimeter. (Cause of flat battery - sticking bilge pump float BTW). I thought a switched voltmeter would save me groping around in the dark. I don't measure the charge with load connected. Maybe I'm talking rubbish.
This is the sort of thing I'm looking at
Last edited by ghostlymoron; 06-11-09 at 19:06.
Reason: picture added
Had a simple digital volt meter on my catamaran (similar to the one shown in an earlier post) - previous owner had installed it in place of the extinct decca receiver. Found it most useful once I took the load into account. I just left it turned on the house batts when on board. Have used analogue volt meters on other boats but prefered the digital read out as being more accurate.
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I have just recieved a battery test meter from Seamark-Nunn, along with other stuff and it seems just the job, panel mounted unit with three way rocker and a little dial. Cost under £20 and matches existing switch panel. Could be worth a look.
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Have used analogue volt meters on other boats but prefered the digital read out as being more accurate
Don't confuse accuracy and precision. Digital meters read to one or even two decimal places usually. But with an analogue meter you have to estimate the 1/10ths of a volt.
The greater precision of the digital scale does not necessarily mean that it is more accurate, ie closer to the correct value, than the analogue scale. It just seduces you into believing that it will be.
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Just a thought : I assume you don't have ST60 instruments aboard????
They will tell you voltage, as will some GPS (furuno) and possibly other things like garmin plotters
What I'm trying to say is, it may well already be there - but you haven't found it yet.
The greater precision of the digital scale does not necessarily mean that it is more accurate, ie closer to the correct value, than the analogue scale. It just seduces you into believing that it will be.
There are that many variables that a more generalisation is better, that is to say 1 decimal place. So called battery status meters have to big a scale, so tell very little.
One thing not mentioned is a bar-graph, allows monitoring all batteries and amps on one simple unit.
Brian
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