Panelpwr-log

Purpose

panelpwr-log is a power logging script that is designed to measure how much power is provided to the XO via the external power jack. Its primary use is for logging and measuring the input power from a solar panel directly connected to the XO.

Data Column Descriptions

panelpwr-log data is 7 columns which are mostly for the scripts that process the output. The key for the columns is:

<date_in_seconds>, <battery SOC>, <bat voltage>, <bat current>, <bat temp>, <accumulated current><status>, <Net mAh>, <net time in minutes>, <Vin>, < W per sample>

In the panelpwr-log context there are only 3 key columns. Those columns are <date_in_seconds>, <bat voltage>, and <accumulated current> or ACR. Time and voltage should be self explanatory. ACR is a measurement of the battery current over a period of time. Its reported in microamp-hours (uAh). Using these 3 values and any 2 sample points the avg power between those 2 points can be computed. Assuming 2 points P1 and P1 the computation is as follows:

Compute the average current

(ACR P2 - ACR P1) / (date_in_seconds P2 - date_in_seconds P1) 

Compute the average voltage

(bat voltage P2 + bat voltage P1) / 2

Then compute the average wattage by ave current * average voltage.

The last 4 columns are human readable. They make it easy to look at the file to see to see what is happening. However, the values are calculated using integer math in the bash shell so they are only estimates. The last 4 columns are

<Net mAh>, <net time in minutes>, <Vin>, < W per sample>

Net mAh

This is the net sum of the mAh from the start of the log until the current reading. Its just the difference in ACR adjusted to mA rather than uA.

Net time in minutes

Time in minutes from the start of the log. Default sample time is 300 seconds so this usually bumps by 5 each sample. Pressing a key will make it wake up early so its not always a multiple of 5.

Vin

This can be ignored.

W per sample

This is the diff in ACR over the diff in time at the midpoint of the battery voltages between the current and previous sample. Its a rough approx of the average battery power for that sample period. Its in mW although its not accurate to a mW.