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ade7276 avatar image
ade7276 asked

State of charge problem

We have a Victron 12/2000/80 multiplus compact inverter on our boat, linked to 2 220ah leisure batteries and a bmv 700 battery monitor which has been working fine for 12-18 months. We are connected to shore power when not in use, we took the boat out last weekend had an issue after 1 day where overnight the inverter stopped working and a low battery light was showing on the multi control panel. Once I started the engine the inverter sprang into life and all was fine until the early hours of that night when the same thing repeated and so on through the week. All the time the battery monitor said we had 92-97% soc. laptop connected to the inverter confirmed this was correct. Returning to shore power the panel shows only a float charge needed ?? Any ideas anyone, fridge and WiFi only 240 power on most of the week

battery charging
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2 Answers
billknny avatar image
billknny answered ·

You describe your batteries as "leisure batteries." I am not sure exactly what this category is, but I am going with the assumption that you are referring to standard deep-cycle, lead acid, batteries.

It is quite possible, even likley, that your batteries have died. Remember, your state of charge is not measured directly, but by computing the (power in) - (power out) and then dividing by the ASSUMED capacity of the battery bank. If you draw 100 Amp-hrs out of a battery bank that the instruments THINK is 440 Amp-hr capacity, they will report an SOC of (1-100/440)*100 = 88%. If the batteries have actually lost capacity and are now in reality 150 Amp-hr batteries, you are actually at (1-100/150)*100=33%. The instruments have no way of knowing what the capacity of the battery bank is other than what you tell them.

If we know what voltage you were seeing at the various point in the cycle, we'd have a better idea of the issues.

But, I'll bet your last dollar the problem is with the batteries and not the equipment.

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Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Do a full charge cycle and ignore the SOC at the BMV, charge until the charger stops.

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