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SOC keeps decreasing when on shore power

Hello,


We are using a setup with 2 batteries 12V parallel, total of 210 Ah. It is fed by the alternator of course and via a Multiplus 800/35 when on shore power. On the system is a BMV-702 and it works very, very good when not using shore power. SOC is very accurate etc. But when in the harbour and switching on the Multiplus, SOC keeps decreasing. Load current of the Multiplus is much higher than the users (only a fridge) so it is not possible that batteries get empty.


I’ve checked the battery-settings in the BMV and also the Shunt and everything seems ok. Software BMV is also up to date.


Anyone got an idea?


Kind regards,


Pim

BMV Battery MonitorSOC
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2 Answers
Mark avatar image
Mark answered ·

I think that the negative cable from the multiplus may be connected to the wrong side of the shunt or directly to the batteries. Check this wiring and if in doubt post some photos.

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pim answered ·

Hello Mark,


Thanks for your answer! I discovered the same today :-). Indeed, the negative side of the multiplus is connected directly to the battery! It should be on the load-side of the shunt isn’t it?


Kind regards,


Pim

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No problem.

Yes the Multi should be connected to the 'load & charger' side of the shunt so that it's current draw or charge current can be measured by the shunt.

Correct the wiring & it should work fine.

Hi Pim,

I have the same problem, with a similar set-up. Everything works great when not using shore-power, can see AH consumed and +AH when the alternator kicks in. But it continues to show -aH when on shore power and the SOC continues to go down (whilst the voltage goes up.)

I've connected the shunt between the negative battery and the engine ground BUT the shore power comes in via a Mutli-plus to the other negative side of my battery bank.

How did you wire up to solve the problem?


Thanks

Damian

There is one simple rule. The Battery - side of the shunt must be the ONLY connection to the - side of the battery,
Anything which is not connected to the Load / Charger side of the shunt cannot be measured.