SOC jumping over night

[Peter WA]

Has anyone (mostly OVMS users I guess) noticed that SOC jumps up and down a fair bit over night?

The screenshots below are all from the same chart, just highlighting values for different points of it.

On August 20th I came home after a 120km round trip. Since I prefer to charge from solar and got home too late I did not plug in the car that day.
When I arrived home SOC was 48.63%.
Next afternoon, when the sun finally came through the heavy clouds, I plugged in to charge: SOC was shown as 45.9%, a drop of 2.73% over night.

When I stopped charging after a few hours SOC was 60.55%.
Just now I plugged back in to charge and SOC had over night changed to 62.95%, a jump up of 2.4%.

I have observed the same a few times now. While the SOC jumps around like this, the Estimated Range (GOM) does not change at all at these points. The Ideal Range (calculated by OVMS) changes with the SOC, as expected, making the same jumps.

What does that mean for the SOC value? Quite obviously it is not an accurate reflection of actual battery state of charge. There might be a little self-discharge over night, but nowhere near 2.7%, and it never should go up all by itself.

GOM distance, while it must be somewhat correlated, is clearly not calculated directly based on SOC. What other information would the car have?

 

[Cocijo]

My experience is that both the soc and predicted range can change after the car has been standing. Battery packs can gain a little or reduce depending on temperature and chemical structure. Most algorithms will build in a buffer to take this into account and not change predicted range for example in real-time. An old trick was to warm up a battery to get a little more charge out of it. I’m sure that there is a very technical explanation for this behaviour.

 

[Lovemyev]

My experience is that both the soc and predicted range can change after the car has been standing. Battery packs can gain a little or reduce depending on temperature and chemical structure. Most algorithms will build in a buffer to take this into account and not change predicted range for example in real-time. An old trick was to warm up a battery to get a little more charge out of it. I’m sure that there is a very technical explanation for this behaviour.

I have witnessed this strange phenomenon in my previous car that was a PHEV with only a small pack.
Go out to the car early in the morning after an overnight charge, open the door and the GOM displays 27 miles of range.
Close the door and lock the car.
Return mid afternoon ( car has not moved all day ) the weather has improved at this point, unlock and open the door to find that the GOM has increased its prediction too 28 miles now !.
Ambient temperature ? plays a part in this story I am convinced.

 

[Peter WA]

Ambient temperature ? plays a part in this story I am convinced.

Good thought, in this case unlikely though: the temperature range in the garage in the last 2 days days was very narrow, between a low of 15 and a high of 19.