SOC Calibration

[webbbn]

How does one calibrate the SOC on a Victron shunt? I see a button to set 100% SOC, but I don't see an equivalent for 0% SOC.

I fully charged my battery, made a guess at capacity, discharged it, and now I'm charging it again, but my SOC is stuck at 0%, and my charge meters are all negative, and I don't see any way to zero anything out. If I manually track how much charge I put it it from full discharge to full charge, and then set the capacity and synchronize, will it reset everything and track properly?

I'm not as concerned about my BMS, but if someone has a method for calibrating a JK BMS, it would also help me straighten out the wild numbers that they have. I believe they have what look like voltage triggers for 0 and 100, but mine still show over 200% SOC and near 0%, so I'm not convinced they're working they way I assume they should.

 

[webbbn]

It does look like the total charge meter zeroed itself out, and the SOC percentage is climbing now, so maybe it just takes time to figure out that it was at 0% SOC. The SOC and total charge meter don't really agree, based on what I told it the capacity was, but hopefully that will normalize out with a synchronization at 100%. The total charge seems about right.

 

[Rocketman]

For the Victron shunt (mine is a BMV712),
Battery settings screen
There is a field call “battery SOC on reset” - set to 100%. So when the specs are met - the battery will reset to 100%.
Next line down is “State of Charge” you can set this to whatever you believe your battery is at.

I am not following you that your charge meters are negative while charging - is the shunt installed backwards? That would cause you to lose SOC while charging. Double check that the battery side of the shunt goes to the negative post of the battery (and there are no other negative items on the battery), and everything else is on the load side.

Good Luck

 

[sunshine_eggo]

For the Victron shunt (mine is a BMV712),
Battery settings screen
There is a field call “battery SOC on reset” - set to 100%. So when the specs are met - the battery will reset to 100%.

This setting controls the behavior when power is lost. It does not behave as you describe. Setting 100% SoC on reset usually results in a shunt that reads 100% when the battery is dead.

It resets to 100% when charged voltage and tail current are met.

The recommended setting is "Keep SoC" so that it reports the last SoC it knew before power was disconnected.

I am not following you that your charge meters are negative while charging - is the shunt installed backwards? That would cause you to lose SOC while charging.

I'm with you on this.

 

[webbbn]

I'm pretty sure it's hooked up the right way, and most of the numbers make sense on the app. Mostly what I'm seeing is in HA, which is another layer of filtering...

In the app, Consumed Ah is negative, but maybe that's because of the SOC when I connected it?

The history is helpful, and looks fairly accurate:

Deepest discharge -452Ah (assuming negative is correct here?)
Cumulative AH drawn: -491Ah
Discharged energy: 27.1 kWh
Charged energy: 10.5 kWh
SOC: 20%

The 491Ah, 27.1 kWh, and 10.5 kWh seem like like they could be accurate (17S battery with charge at 58.6V), but the SOC should be over 30%.

 

[sunshine_eggo]

I'm pretty sure it's hooked up the right way, and most of the numbers make sense on the app. Mostly what I'm seeing is in HA, which is another layer of filtering...

In the app, Consumed Ah is negative, but maybe that's because of the SOC when I connected it?

The history is helpful, and looks fairly accurate:

Deepest discharge -452Ah (assuming negative is correct here?)

That implies you have a 452Ah battery if you went to LVD from full.

Funnily enough, that's the exact same number my BMV-702 reports for my 450Ah battery.

Cumulative AH drawn: -491Ah

This is a sum of all discharges, full and partial. For me, it's -65,085Ah.

Discharged energy: 27.1 kWh

Again, this is a cumulative value for all discharges. Mine is 3.37MWh

Charged energy: 10.5 kWh

Again, cumulative. 4.2MWh for me.

SOC: 20%

The 491Ah, 27.1 kWh, and 10.5 kWh seem like like they could be accurate (17S battery with charge at 58.6V), but the SOC should be over 30%.

Set
Actual capacity
charged voltage to 0.2V below absorption
tail current to 2%
Peukert to 1.25
Charge efficiency 99%

It will synchronize every time you fully charge and it should track pretty accurately. Victron claims they need to be synched "about twice a month."

There is zero need to calibrate 0%. If it's not reading 0% when the battery hits LVD, then you don't have the capacity set correctly.

My battery is NMC, so I don't ever fully charge it, and there's a strong voltage to SoC ratio. I don't recall the last time I reset my BMV to match the BMS, but it's been a long time. They were 9% off.

 

[webbbn]

Thanks! I'll verify the 452Ah when it's fully charged by looking at the charts, but that's what I was trying to calculate.

 

[Rocketman]

This setting controls the behavior when power is lost. It does not behave as you describe. Setting 100% SoC on reset usually results in a shunt that reads 100% when the battery is dead.

It resets to 100% when charged voltage and tail current are met.

The recommended setting is "Keep SoC" so that it reports the last SoC it knew before power was disconnected.

Thanks for setting the record straight. Now I wonder how/when I changed that field from default… hummm..

 

[sunshine_eggo]

Thanks for setting the record straight. Now I wonder how/when I changed that field from default… hummm..

Keep SoC is a fairly new option (maybe the last year or so). Before, the only choice was 100% or "--" to indicate it had been reset and had no idea what the SoC was. I think "100%" was the original default and still may be.

Thanks! I'll verify the 452Ah when it's fully charged by looking at the charts, but that's what I was trying to calculate.

If you don't know, then your best option is to just set something notably higher than actual and then see what you get. That way, you'll never go "negative SoC"

 

[webbbn]

If you don't know, then your best option is to just set something notably higher than actual and then see what you get. That way, you'll never go "negative SoC"

I thought I did that, which is why I'm confused about the negative numbers. It's currently set at 500 Ah.

The SOC on reset setting was on Set to 100%, which must have been the default. I just changed it to Keep SOC.