22 replies to this topic

[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

Edited by Wallowa, 28 September 2021 - 11:06 PM.

[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.vi...ge-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".