question

phillih avatar image
phillih asked

BMV-712 and 3 House Batteries

I have 3 house batteries (and 1 starting battery) on my, new to me, boat. Two are physically located together while the third is about 15 feet away. I spent the better part of a day mapping all the connections to understand what the voltage and current readings are telling me. The attached drawing (apologize for the simplicity) is my rendering of the system (only shows positive connections). I want to add/install a BMV-712 to monitor voltage and current of just the 3 house batteries but I'm drawing a blank on how to do it. There must be an easy way but I'm stumped. Any advice? Also, if you have any other advice on this setup, I'm open to it. TIA.

boat-electrical-schematic-with-colors.jpg


BMV Battery Monitor
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3 Answers
kevgermany avatar image
kevgermany answered ·

Sorry, you're showing us the wrong bits. The 712's shunt goes in a common negative feed to all the batteries. Similarly the positive for voltage goes to a single common positive across the batteries.

So to install you may have a tricky rewire to do. Or multiple 712s.

Looks as if you have a common positive on the top pair. But the windlass battery looks like a standalone.

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kevgermany avatar image kevgermany ♦♦ commented ·
Maybe it would be better worded if I had said that we need to see the missing bits. Mainly the battery negatives.
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Kevin Windrem avatar image
Kevin Windrem answered ·

You would need three independent BMVs, one for each battery bank. All connected ahead of any switching. Some of the BMVs have a second voltage input but that won't give you state of charge for the alternate battery.

The shunts for each BMV would connect in line with negative terminal of each battery bank BEFORE any chargers or loads. That is the only thing that connects to the shunt negative is the battery (or batteries if two are in parallel).

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christern avatar image
christern answered ·

If I were you I would take the opportunity to make a cleaner installation.

Set one battery as a pure starter battery and make the others as pure house batteries. Have the solar panels charge the house batteries only as the starter battery will be charged while running the engine, and that quite fast if the engine is not too difficult to start.

Doing so will make it much easier to be in control of how much power you have left in your house bank.

In my boat I have set it up in that way using 6 house batteries and one for start with solar panels charging the house batteries only. I have a solution with a relay that connects the start battery with the house batteries when engine is running and by that also charges the house batteries. I also have a charger that charges both the house batteries as well as the start battery when connected to shore power.

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