Victron 712 Shows 100% SOC at 13.24Vs..Accurate?

[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?

 

[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

 

[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...

 

[pvstoy]

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

 

[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.

 

[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.

 

[Vic Harder]

rando, assuming his BMV is set up correctly, and that he has had no known loads on the batteries, it does seem odd that the voltage is that low and still showing 100% SOC, no?

 

[rando]

I don't think it is too far off from what it should be. With my battery (which is of a similar construction to a BB with lots of cylindrical cells) I see about 13.4V at the end of a charge cycle, which drops to about 13.3 after a few hours of rest. So 13.25 seems reasonable for 100% SOC or at least close to it. It maybe that the BB did some cell balancing (which will eat up a little power that the BMV can't see) or that the BMV settings are a little off, but it is not something I would worry about.

The SOC vs voltage charts that are floating around for LiFePO4 don't make much sense and seem to be yet another attempt to make Lithium conform to hold over lead acid ideas.

 

[Wallowa]

Hey folks...many thanks...this appears to be Phil yet again fretting over nothing..odd, you think I would stop trying to worry things into place!

Time will tell if the BB and 712 sync up and in the mean time I have plenty of juice....solar [330W] and that huge DC/DC [30A] charge are really slick.

Thanks...Phil

 

[Wallowa]

FYI...just got this back from BB;I assume they mean screen shot of 712.

Hello Phillip,

Yes the chart that appears in the video is accurate.
I've attached the chart below. Our lithium bbattery isn't at 100% SOC at 13.24 volts, at this voltage its going to be at 80% SOC. Can you provide me a screen shot of the battery settings that were programmed into the unit.




-----Original Message-----
From: 23350 Anonymous Customer
Sent: 9/27/2021
Subject: SOC Question
Hi,

I have your BB 100ah battery with heater in my FWC Hawk. My question is on the voltage vs SOC. The YouTube below lists the voltages of the BB with corresponding SOCs; is the chart in the video accurate? Do you produce such a chart?

Appreciate your help; I am trying to reconcile a Victron 712 showing a 100% SOC at a voltage of 13.24V.

Thanks,

 

[Wallowa]

I don't think it is too far off from what it should be. With my battery (which is of a similar construction to a BB with lots of cylindrical cells) I see about 13.4V at the end of a charge cycle, which drops to about 13.3 after a few hours of rest. So 13.25 seems reasonable for 100% SOC or at least close to it. It maybe that the BB did some cell balancing (which will eat up a little power that the BMV can't see) or that the BMV settings are a little off, but it is not something I would worry about.

The SOC vs voltage charts that are floating around for LiFePO4 don't make much sense and seem to be yet another attempt to make Lithium conform to hold over lead acid ideas.

Rando...at your readings of 13.4V and then dropping to 13.3V....what are the SOC readings? "End of charge cycle" at what voltage is that?

Thanks..Phil

 

[rando]

This is all at or near 100% SOC.

I have my Victron MPPT set to charge my battery to 14.0V*, and I also have my BMV-712 set to sync to full at 14.0V. Once the sun goes down the battery drops to about 13.4V almost immediately, then over the next few hours it slowly drops to 13.3V even if I haven't used any substantial energy. The BMS, BMV-712, propane/co alarm, monitor panel, MPPT 100/20 are all always on, so there is a small load, but it will be at 13.3V even at 98 - 100% SOC.

 

[Wallowa]

This is all at or near 100% SOC.

I have my Victron MPPT set to charge my battery to 14.0V*, and I also have my BMV-712 set to sync to full at 14.0V. Once the sun goes down the battery drops to about 13.4V almost immediately, then over the next few hours it slowly drops to 13.3V even if I haven't used any substantial energy. The BMS, BMV-712, propane/co alarm, monitor panel, MPPT 100/20 are all always on, so there is a small load, but it will be at 13.3V even at 98 - 100% SOC.

Thanks this helps a lot...so when at 13.3V what SOC does the 712 show?

Ps...my "small load" is a constant -.11A @ 2w

 

[rando]

Around 95 - 100%. Remember that the BMV-712 does not use voltage to calculate SOC and there isn't a 1:1 relationship between voltage and SOC.

 

[Wallowa]

Around 95 - 100%. Remember that the BMV-712 does not use voltage to calculate SOC and there isn't a 1:1 relationship between voltage and SOC.

You may have mentioned it...but what is your tail current set at? Appreciate you sharing your experiences...

Phil

Saw this article: https://community.victronenergy.com/questions/51110/712-bmv-charged-voltage-setting.html

 

[Wallowa]

Succinct...



seb71 answered ·

Jan 25 2021 at 2:31 AM



There are 3 BMV (or SmartShunt) settings which control when the SOC is synchronized to 100%:
- Charged voltage
- Tail current (which is not set directly in Amps, but set as a percentage of battery capacity)
- Charged detection time

The SOC gets synchronized to 100% when these 2 conditions are met at the same time:
- the battery voltage is higher than "charged voltage"
- the current into the battery is lower than "tail current"
for the duration set at "charged detection time".

"Synchronizing to 100%" means the SOC jumps to 100% when the above conditions are met.

So if it happens too early, you have to do one, two or all three of these:
- increase "charged voltage" value;
- decrease the "tail current" percentage;
- increase the "charged detection time".