question

jstorie avatar image

What should I set the BMV-712 charged voltage setting to?

According to the data sheet on my LiFe PO batteries (400ahs) the charge voltages and time are as follows:

LB12200-HCLT Data Sheet.pdf

Absorb Voltage (Uo) (CV) 14.1 to 14.6 Volts

Float Voltage (I) 13.6 to 13.8 Volts

Recommended CV or Absorb Time 15 minutes


What should the charge voltage setting in the 712 bmv be set to?

the manual states that it should be set 0.2-0.3 v below the float voltage which be 13.3 /13.4, but wont the SOC reset to 100% before it gets in to absorb stage?

Thanks

BMV Battery MonitorHelpsetup
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1 Answer
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @jstorie,

There are 4 relevant settings here and they all work together.

The charged voltage of {13.2V} is only the first trigger, that alone will not reset the SOC to 100%.

It must also simultaneously coincide with the charging (tail) current being {4%} or less of the battery capacity. So if the battery capacity is {400 Ah}, that is {16A}. This must also be sustained for {3 minutes}.

For such as sized battery, I would presume you have at least a 40A charger. It is very unlikely that it will be only outputting 16A at the absorption stage of the charge cycle. It's likely that it will be much more, so even though the voltage trigger threshold is met, the tail current will not, so the battery will not sync to 100% yet.

However, on the way back down after the absorption stage, you have a full battery and it does not require much current at all to maintain the float voltage. So output current is reduced by the charger to maintain that low voltage (and not go higher), that satisfies the tail current trigger threshold, and the SOC is reset.

Aside from the battery capacity, I always recommend using the default recommended settings out of the box. In nearly all cases they are the best place to start, and it is only worth tinkering once you are sure that they are not working correctly. That could occur in either direction, synching too early (reduce tail current), or not at all (increasing tail current).

Note, everything in the {curly brackets} is adjustable.

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I have the victron smart solar mppt 100/30 with 400w of panels, so my amp output could be anywhere from 0-30 amps depending on the sun. also have a blue smart ip67 12/25 version for my shore charger. What would you recommend for the tail current?

The default, until you are certain that it is not working correctly.

Then it depends on if it is syncing too early, or not at all.

It's intended to give you some indication of what is going on with the system at a glance. State of Charge is a best guess sort of thing, so usually it doesn't have to be really precise. Depends how much time you want to spend tweaking it. For me, not a lot :)