question

sam-strider avatar image
sam-strider asked

BMV 712 Smart showing 100% when batteries are not

My Setup:

  • 200Ah ReLion LiFePO4 battery (recommended charged voltage 14.2-14.6V)
  • BMV 712 Smart
  • REDARC 50A DCDC Charger (Absorbsion: 14.5V; Float: 13.6V)
  • Victron 50/100 MPPT Smart (Absorbsion 14.5V, Float 13.6V)
  • Portable Power Tech 30A AC Battery Charger (Absorbsion 14.1V; Float 13.5V)


BMV Settings (as of now):

  • Battery Capacity: 200Ah
  • Charged Voltage: 14.4V
  • Discharge Floor: 20%
  • Tail Current: 1%
  • Charge detection time: 3 mins
  • Peukert Exponent: 1.05
  • Charge Efficiency Factor: 99%
  • Current Threshold: 0.1A
  • Time-to-go averaging Period: 3 mins


My Problem

I am not using much power, so my batteries rarely drop below around 70% SOC at the moment, but when recharging them the SOC never reaches 100%, and over time it drifts more out of sync to the point where after a month or so, it is showing ~95% as my maximum (it won't charge when the BMV shows SOC being 95%).

I know that you do have to calibrate the BMV every now and then, but with low power usage, a month to lose 5% SOC accuracy seems high.


My question

Do I need to adjust my BMV to any other settings? I cannot adjust my REDARC DC-DC or my AC Charger Float and Absorbsion Voltages (as far as I can tell). Any advice would be beneficial - TIA.

BMV Battery MonitorSOC
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2 Answers
Erik Sporns avatar image
Erik Sporns answered ·

This means that, if the voltage is >=14.4v the tailcurrent is more than 2a or the Charger is not holding the voltage for at least 3 minutes. I’m not familiar with the other chargers, but on the mppt you can set a tail current for absorb (which should be a bit lower than the bmvs setting).


if you can check what happens beyond 14.3v, e.g. with a multimeter and some patience, it’ll give you an idea what to adjust.



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seb71 avatar image
seb71 answered · 
I know that you do have to calibrate the BMV every now and then

Synchronize, not calibrate.


Not related to your SOC question:

Your 14.5V Absorption voltage, although in the manufacturer limits you listed) is quite high for LiFePO4.

Decrease the Absorption voltage in the SmartSolar MPPT to 14.1V (same as Power Tech) or 14.2V.

Set Float voltage to about 13.4V.


Now back to your SOC question:

Which one is the main charger of your battery (which is usually doing most of the charging)?


Have you made a VE.Smart network between the Victron SmartSolar and the BMV?


For a starting point, in BMV set the "charged voltage" 0.2V lower than the lowest Absorption voltage from all your chargers. Set the tail current to 3%. You can also perform a Manual Synchronization of SOC to 100% (by pushing that "Synchronize" button when you are sure that the battery is fully charged).

Observe (for 1-2 weeks) how the system behaves and adjust if necessary.

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sam-strider avatar image sam-strider commented ·
Thanks Seb, yes I did mean synchronise*


I'll do more digging to see if I can find out more about the DCDC 14.5V Absorption.


My main charger will be the DCDC, and then the MPPT, with the AC Charger rarely being used.

I just set up a VE Smart network for the two now.


I've followed your advice and will see what happens in a few week's time, cheers!

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