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Data Gurus...Any ideas why battery charge not changing?

Damclarkd

Member
Aug 2, 2020
19
3
Tucson, AZ
7.4kW System w/ 2 PW's

I've been up and running for a couple of months now and have been getting data from the API every 5 minutes. I export this data via Raspberry Pi to InfluxDb/Grafana locally and PVOutput for data analysis. I am running the PW's in Self-Powered with a reserve. I have recently noticed a sharp knee in the PW charge % as the solar day ends and the batteries take over. I have attached a screenshot of the data from Excel showing the battery flow, home load and charge % as an example.
It appears that there seems to be a lag in PW charge reporting about the time they take over the house load. Wondering if anyone sees this or might have an idea what is actually happening.

Cheers
 

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wjgjr

Active Member
May 11, 2020
1,299
1,034
Silver Spring, MD
I suspect what you are seeing here is that 100% is not the actual capacity of the PWs, but a nominal capacity based on some calculations from Tesla. Because you are in self-powered mode, I believe the PWs do fully charge, and are likely exceeding 100% of nominal. However, it appears the API may be designed to not report values over 100%. So, my guess is what you are seeing is due to that and not to a delay in the SOC number reporting. However, you could look at what happens at sunrise to see if there is a delay there.

I am also aware Tesla does report the current capacity of the PWs, but only on the remote API. You could potentially check that to see what it is reporting - perhaps it is low or takes some time to settle in.

Looking back at the data I have over about 7 months, I only logged numbers of 100% in September (and, though the percentage normally falls slightly over time in backup-only before re-charging every day or two, it was pegged at exactly 100 for a few days.) This supports the idea that 100% SOC is a nominal amount and that the API does not report values in excess of 100%. I have not seen it since - I do not know if that indicates degradation in the batteries (since I have not been logging data from the remote API,) adjustments in the calculation from Tesla, or a change with a software release (or something else.)
 

Damclarkd

Member
Aug 2, 2020
19
3
Tucson, AZ
I suspect what you are seeing here is that 100% is not the actual capacity of the PWs, but a nominal capacity based on some calculations from Tesla. Because you are in self-powered mode, I believe the PWs do fully charge, and are likely exceeding 100% of nominal. However, it appears the API may be designed to not report values over 100%. So, my guess is what you are seeing is due to that and not to a delay in the SOC number reporting. However, you could look at what happens at sunrise to see if there is a delay there.

I am also aware Tesla does report the current capacity of the PWs, but only on the remote API. You could potentially check that to see what it is reporting - perhaps it is low or takes some time to settle in.

Looking back at the data I have over about 7 months, I only logged numbers of 100% in September (and, though the percentage normally falls slightly over time in backup-only before re-charging every day or two, it was pegged at exactly 100 for a few days.) This supports the idea that 100% SOC is a nominal amount and that the API does not report values in excess of 100%. I have not seen it since - I do not know if that indicates degradation in the batteries (since I have not been logging data from the remote API,) adjustments in the calculation from Tesla, or a change with a software release (or something else.)

Couple of great ideas here, wjgjr. I think the nominal reporting of 100% is worth checking out further by crunching some of the values just before and after the event. As far as sunrise goes, I am not seeing the same thing there. Also as battery rises to 100%, nothing there either.
I have not looked at the remote API at all. So that bears looking at as I was not aware the current capacity could be shown.

Thanks and cheers.
 

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