serenity avatar image
serenity asked

Strange BMV-712 Readings w/ LiFePo Batteries, Solar, DC-DC, and Generator

We recently upgraded our two house banks on our sailboat to Lithium. All standard install processes were followed and a pair of 18V DC-DC chargers were added to replace the ACR's attached to the two engine batteries and associated alternators. The boat's generator is also attached to one of the start batteries as it is used to provide starting power for the device. We already had 2400W of solar onboard and the only changes made to that element and our inverter/charger were to reflect that the batteries were no longer AGM but Lithium (software changes). Final aspect of our configuration is that all of the solar controllers, DC-DC chargers, and shunts monitoring our system are Victron products. The inverter/charger is not Victron but was originally installed with the AGM setup and worked fine.

The issue/weird challenge we are seeing on the two BVM-712's monitoring the banks is that I would expect a draw (in amps), either individually or combined (they are connected to a switch allowing to combine or use independently) as a negative number when DC power demands are placed upon them. Conversely, I should see a positive number on the monitors when energy is being placed into them from solar, DC-DC, or generator power supplying voltage to the charger. Unless demand is higher than what is being put back in and I am not. I am seeing the opposite. We even ran a few tests by turning off all DC power draw sources and still had a negative draw being displayed on both 712's. I am seriously confused. Nothing was changed in our setup with the exception of the actual batteries, the addition of the DC-DC chargers, and the appropriate new gauged wiring, CB's, etc. for the new battery system configuration.

battery chargingMPPT SmartSolarEnergy Meterorion dc-dcmonitoring
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1 Answer
Justin Cook avatar image
Justin Cook answered ·

If you're seeing reverse current readings, then most likely the shunt has been installed backward - it is directional, as detailed in the user manual and quick install guide: the "Battery" side of the shunt must be the one and only thing connected to the battery bank negative, and all system loads, chargers, and chassis grounds must be moved to the "loads and chargers" side of the shunt.

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serenity avatar image serenity commented ·
Justin, thank you for the comment on our question. Our battery banks connect to a common bus bar that also has the PV connection and DC-DC charger connections. The shunt was installed 3 yrs ago with AGM batteries and the upgraded solar configuration and both, bank 1 and bank 2 shunts are on the negative side. We did not see this challenge after that install. Electrically/physically speaking should the PV and DC-DC negatives/positives be separated from the bus bars that the battery banks connect? I guess I am a bit confused.
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