22 replies to this topic

[Wallowa]

 

 

BB 100ah with Victron 712....voltage shows 13.25-13.24V when "stored", no charging and FWC master switch off...here is the question: Why does 712 show "100% SOC" while Prowse chart shows closer to 85% SOC? Is 712 accurate or is the voltage closer to actual SOC?

 

Edited by Wallowa, 27 September 2021 - 05:37 PM.

[pvstoy]

Sitting batteries slowly drop voltage over time. By having the master switch to off the battery sees no usage drain and the meter does not either, so it stays at 100%.

I watch my agm batteries over the course of months drop voltage. When it gets low enough I plug it in to be charged. Meanwhile the meter always show 100 percent while the master switch is off.

[Wallowa]

Sitting batteries slowly drop voltage over time. By having the master switch to off the battery sees no usage drain and the meter does not either, so it stays at 100%.

I watch my agm batteries over the course of months drop voltage. When it gets low enough I plug it in to be charged. Meanwhile the meter always show 100 percent while the master switch is off.

 

 

So you are saying the Victron 712 does not see any current/voltage drop with Master Switch off?  Hawk Master Power switch does not turn the 712 on or off; 712 and shunt are direct wired to BB battery...can't wrap my mind around that...I expected the 712 to reflect not only the voltage drop [it does] but the attendant SOC drop [which it has not].

 

Thanks...Phil

Edited by Wallowa, 27 September 2021 - 06:53 PM.

[Ruck_and_Roll]

What are your float settings at? BB has specific recommending settings for charging.

[Wallowa]

What are your float settings at? BB has specific recommending settings for charging.

 

 

Bulk, Absorp, Float and the many other settings are all specifically set for the BB....this includes all 4 Victron devices:  DC/DC, MPPT solar, 110 charger and 712.....charging the battery is not an issue; getting the 712 and BB voltage to reflect the same SOC is...the 712 is home plate and the go to source for battery status...knowing that it is accurate is #1 priority.

 

Ps...FYI:  I believe BB sezs that there is no need for a 'float' charge on their batteries...

Edited by Wallowa, 27 September 2021 - 07:26 PM.

[pvstoy]

With master switch off there are no Amp draw coming out of the battery to supply the camper for the 712 to record.

Edited by pvstoy, 27 September 2021 - 08:08 PM.

[Wallowa]

With master switch off there are no Amp draw coming out of the battery to supply the camper for the 712 to record.

 

 

Understood...nothing coming across the shunt...then how does the 712 "catch-up" with the correct state of charge as the BB slowly loses the SOC?  

[pvstoy]

Understood...nothing coming across the shunt...then how does the 712 "catch-up" with the correct state of charge as the BB slowly loses the SOC?  

 

Charge the battery up to full and good to go.  You can synchronize the 712 to force it to 100% after you charge up the battery if you want.

Edited by pvstoy, 27 September 2021 - 09:39 PM.

[Vic Harder]

First off, Patrick is right, with the master switch off, there should be no current flow in/out of the battery.  And AGM batteries drop voltage in a well known way.  Li battery voltage to SOC tracking is trickier, as they are so flat in their discharge voltage.  That said, Phil's batteries are a voltage that would indicate 90% SOC.  

 

Over what time period did they get to that point?  Li batteries have a very low self-discharge rate (not sure what that is right now) so if they really are discharging (is the voltage dropping?) then there might be a load on the batteries that is NOT going through the shunt.  Testing that would require fully recharging the batteries again and then disconnecting them from everything except the BMV and seeing if the voltage continues to drop.

 

As for how the BMV "catches up" - I believe your settings have "AutoSync" turned on (I do not on mine) which means that when charging again and when the battery reaches full, it resync's to 100% at that point.  Resync = catch up

 

In the meantime, the BMV SOC and actual SOC are not in sync.

[rando]

Open circuit voltage is NOT a good way to estimate the SOC for an LiFePO4 battery.    The discharge curve for an LiFePO4 cell is almost dead flat - ie the voltage only changes a very small amount, around 0.2V for a 60% change in battery SOC.   If your Victron 712 is correctly set up, it is a far more accurate way of determining battery SOC than the battery voltage.