I did not on my previous boat but now I have 12v refrigeration and I think it is necessary to see a fairly accurate capacity.
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- Thread starter John
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Based on the responses here, and based on my experience with this unit, this is what I think it happening:
When I'm out sailing, including overnight, the monitor works as it should.
Same when I have the shore power turned off while the boat sits in the slip.
If the battery becomes completely charged up, and I leave the shore power turned on, then for some reason the monitor does not register the fact that a charge is continually flowing into the battery (actually, batteries); it only registers the parasitic draw coming out.
This is not such a great problem, as long as I know it's happening, and as long as there is not a problem with the shore power. Anyway, in general unless the batteries are down, I don't leave the shore power (i.e. the AC main switch) turned on for days on end when I'm away from the boat.
When I'm out sailing, including overnight, the monitor works as it should.
Same when I have the shore power turned off while the boat sits in the slip.
If the battery becomes completely charged up, and I leave the shore power turned on, then for some reason the monitor does not register the fact that a charge is continually flowing into the battery (actually, batteries); it only registers the parasitic draw coming out.
This is not such a great problem, as long as I know it's happening, and as long as there is not a problem with the shore power. Anyway, in general unless the batteries are down, I don't leave the shore power (i.e. the AC main switch) turned on for days on end when I'm away from the boat.
If anybody wants any further input on this issue, there is also an ongoing discussion on the C36ia forum. You can find it here: http://www.c36ia.com/forums/showthread.php?p=4165#post4165 It was suggested to me that some, Maine Sail in particular, might be interested and have comments.
Actually they are not just digital volt meters and the Victron 601 can be bought for under $200.00. Volt meters, as others have pointed out, really tell you little about state of charge unless you have allowed the batteries to come to a full resting voltage with no input or out put for many hours. This is difficult on a cruisng sailboat, to completely isolate the batteries from all sources in or out, and thus any voltage reading may be off by a considerable amount.
Battery monitors keep track of the amp hours (Ah) going into and out of the battery bank, can display amps in/out (A), net amps to the bank, Ah's remaining, % state of charge, charge capacity remaining, volts and more.. Some can even be connected to a computer to graph and chart non-constant loads like refrigeration to give you an average daily consumption. They also tend to give the owners a great education of what is really happening in terms of charging and discharging..
Batteries are very, very expensive, especially AGM's & gel cells, and it is well known that cycling your batteries too deeply can severely shorten their cycle life. Even in controlled experiments on my bench I have not yet been able to nail down battery SOC with a volt meter closer than within 10% without a full resting period of 12 hours or more. Battery monitors, even at $200.00, can actually save you money in the long run.
You are 100% right that no one "needs" one but then again no one "needs" a boat either..
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