question

kevingeerts avatar image
kevingeerts asked

battery dead/ monitoring

Hello,

Our setup on our second hand sailboat is the following:

We have a multiplus 3000 (see picture), 2 agm batteries in parallel (Dynac Accu agm semi tractie 12 volt 220 Ah) and an bmv 702 for monitoring.

We are currently in storage for working on the boat and recently we leave the fridge on overnight. When coming back the next day the battery monitor indicates we have about 94% battery left and used about 20 Ah.

Yesterday we came to the boat and the multiplus had the red light flashing of low battery. The bmv still indicated about 90% capacity left and a voltage of around 12.6.

I then measured on the battery itself with a volt meter and this showed 10.5 volts!!!


I assume the batteries are as good as dead but just trying to get around the differences we see on the battery measurement itself and the measurement the BMV shows.
Does the BMV measure the voltage directly on the battery or is this more a calculation derived from what it sees coming in and out, like for the percentage remaining?

AGM Battery
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2 Answers
klim8skeptic avatar image
klim8skeptic answered ·

@kevingeerts I assume the batteries are as good as dead but just trying to get around the differences we see on the battery measurement itself and the measurement the BMV shows.

Give your batteries a good charge, they might come good.

As to why there is a difference between the battery Soc and what the BMV shows comes down to 2 common user failures.

1. Failing to properly configure the BMV for your system. Have a look at this BMV video and check your settings.

2. Charge or load currents bypassing the shunt, having been connected directly to the battery. All loads, chargers and chassis earth has to be on the system side of the shunt. The only thing connected to the battery negative is the shunt. Check your cabling.

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JohnC avatar image
JohnC answered ·

@kevingeerts

The BMV measures V itself. A small, separate cable. You need to trace that to find out why it's not reading correctly.. https://www.victronenergy.com/media/pg/BMV-702/en/installation.html

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