Charge starting battery: BMV 712 relay vs MPPT SmartSolar Load Output

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xmd asked Feb 18, '21

Charge starting battery: BMV 712 relay vs MPPT SmartSolar Load Output

I have an older PWM charge controller which will charge both the House and Starting batteries. I am getting more solar panels and want to upgrade to MPPT, but MPPT charge controllers generally do not support 2 battery banks.

Assume I start with a single MPPT SmartSolar or BlueSolar controller

What would be the best solution?

I could use the Load Output and wire that directly to the starting battery, and set a rule for the Load output to turn on the load when the house battery is between X and Y volts. Pros: doesn't require more equipment. Cons: the bigger MPPT controllers don't have the Load output at all, so I'd have to stay with the lower capacity models.
I could get a BMV 712, and use its relay output to control a relay which connects the House and Starting batteries, and use a similar voltage-based rule (On between X and Y volts)
Some other Victron product - battery isolator or combiner or...?

Thoughts?

MPPT Controllers BMV Battery Monitor starter battery

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Answer 1 · 2021-04-28T21:57:40Z

xmd answered · Apr 28, 2021 at 09:57 PM

To follow up - this thread ( https://community.victronenergy.com/questions/53560/using-bmv-712-relay-to-trigger-the-mppt-10020-ve-d.html?sort=oldest ) seems to suggest that I can use the BMV's output relay to control the MPPT's Load output.

Am I reading that correctly?

In the VictronConnect app, the MPPT Rx Port function settings show this:

If I make that change, then what do I do with the actual Load Output settings?

In other words, does setting the MPPT's Rx Port function to Remote on/Off override the Load Output settings? Or do they interact somehow in an AND or OR fashion?

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Answer 2 · 2021-04-28T23:55:39Z

Matthias Lange - DE answered · Apr 28, 2021 at 11:55 PM

The load output is not designed to connect to another battery to charge it.

If all batteries are lead/Gel/AGM you can just use a cyrix-ct.

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xmd commented · May 06, 2021 at 10:05 PM

Thank you, and I understand that the load output may not be designed for charging another battery

Bt I'm still interested in figuring out how the load output controls work.

Can I set the load output on the MPPT 100/20 to only be on when the battery voltage is in a certain range AND there is solar input?
Or, can I use the relay output of the BMV-712 to control the load output of the MPPT 100/20?

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