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roamer105 avatar image
roamer105 asked

BMV-712, CCGX, Multi Plus & DVCC enabled, two separate battery banks

In this configuration (RV) with a main battery and a truck battery both connected and charged by one Multi Plus. BMV-712 monitors the main battery voltage and the truck battery voltage. DVCC enabled on the CCGX.. With all connected, it works as advertised. However if for some reason the main battery is disconnected from the camper DC system (BMS action), the Multi Plus gets confused seeing the main battery (now disconnected) voltage and trying to power/charge the rest of the system along with the truck battery. This of course causes the Multi to create significant voltage swings.

Is there a way of telling the BMV-712 to switch from sharing the main voltage to sharing the truck voltage instead as it is the one getting charged?

Any other suggestions?

The BMS could in effect via a relay swap the voltages sensed by the BMV-712. That appears to me the only alternative. I would rather not do that.

DVCC
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Saff avatar image
Saff answered ·

Hello, my understanding of DVCC is that it will only use the "main" voltage from the BMV or battery sense - that is the voltage of the B1+ input. In effect the "system" is the main battery bank in your case. The truck battery, its voltage being monitored and charge from the multi is simply an extra. If you don't have multiple MPPT charge controllers or are not worried about over current issues when charging then perhaps just disable DVCC?

To get things working in your example, perhaps the multi needs to be able to get charge into the battery even with the load disconnected by the BMS. I assume the BMS is in there to protect the batteries from DC loads other than the Quattro - if you don't have such loads, then do away with the BMS. If you do, then put the BMS only between the battery and the DC loads, leave the Quattro directly connected and let it manage its own shutdown on low voltage (then it can switch to charge only mode).

Hope this helps - apologies if I've missed the mark.

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roamer105 avatar image roamer105 commented ·

Thank you! I did consider just disabling DVCC but I like the benefits of having it especially sharing voltage sense. Connecting the Multi directly (of course fused) to the main battery worries me. I do like the idea of being able to completely isolate the main battery and let the system just use the truck battery as the "main" battery while in storage (garaged and plugged in).

I ended up installing a DPDT relay that is triggered by the remote Blue Sea battery disconnect switch state. The relay simply flips the two battery voltage sense wires based on the battery disconnect switch state. This appears to work exactly right for my setup.

I realize SOC will get "messed up" but upon connecting the main battery back, a full charge will take care of that.

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Related Resources

DVCC chapter in GX manual