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ncomparini avatar image
ncomparini asked

Troubleshooting inconsistent SOC readings - is SOC based on V or Coulomb, or?

When looking at SOC and estimating how much a load has pulled from my battery vs how much charge has gone into the battery (for example, in my vehicle, drive time and charging amps), I'm seeing some inconsistencies.

For example, I fully charged my battery, let it rest, and synchronized it to 100%. It ran 12 hours on a load and then showed about 85% SOC. I drove for a bit and it then showed 92% SOC. I parked (note I do NOT have solar input connected so when parked there is no charging), then checked the system after about an hour and it read 100% SOC. Why is there about an 8 Ah difference? If the system is counting charge in and out, I would think that would be more accurate, or am I missing something?

My question is, when calculating the SOC, is the BMV-712 calculating based on the battery voltage or the coulomb counting of net current in and out, or some combination?

Thanks in advance!

BMV Battery Monitor
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3 Answers
Jason - UK avatar image
Jason - UK answered ·

@ncomparini What do you have the charge efficiency set to in VE.Configure? What equipment do you have? What is that actual charge efficiency of your batteries? What type of batteries are you using?

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ncomparini avatar image
ncomparini answered ·

Charge efficiency: 98%

Equipment: Charger is Redarc BCDC1225

Battery: LiTime 12V 100Ah (100A BMS).

Actual charge efficiency: unsure... I've reached out to the manufacturer

Screenshot_20240105_083521.jpg


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klim8skeptic avatar image klim8skeptic ♦ commented ·
@ncomparini The "charged voltage" has been set to low.

Your using the Li charge profile of the Redarc of 14.5v bulk/absorp?

Set the charged voltage to 14.2-14.3v, and the efficiency to 99%.


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ncomparini avatar image ncomparini klim8skeptic ♦ commented ·
Enlightening, and thank you!

Yes I am using the Redarc 14.5 charge profile.

Understood on the 99% efficiency.

I bench charged the battery to 100%, then let it rest for 4 hours, then took a voltage measurement of 13.3 V and used that for the charged voltage. Why is this not correct, isn't this what the monitor is looking for to set the top end?

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klim8skeptic avatar image klim8skeptic ♦ ncomparini commented ·

@ncomparini The BMV will reset the Soc to 100% when the following conditions have been met,

Battery voltage has reached the "charged voltage" and the current falls below 2% for a minimum time of 3 minutes.

I bench charged the battery to 100%, then let it rest for 4 hours, then took a voltage measurement of 13.3 V and used that for the charged voltage

To fully charge (and balance the cells) you have to charge the battery to 14.5v or so, until the charge current tapers of (2-4% is ok).

The resting voltage of about 13.3v (or so) is of marginal use. Just this morning my batt was at 13.29v with a small load @ 85% Soc.

v.png


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pwfarnell avatar image
pwfarnell answered ·

As nobody has specifically answered the basis question, the Victron shunts (BMV, Lynx, Smart etc) all use coulomb counting.

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