About 6 months ago I installed a solar power system with 2 Tesla Powerwalls for backup. Today, we got to test out the system with a power outage from an ice storm in the southeast. (We are still on battery power as I write this.)
My kids came downstairs to tell me that it was time for bed (9PM), but when I looked at my phone, it was only 8:17PM. They were reading the time off the microwave. I checked the alarm clock in my room and it also read 9PM
I know that the way power is "pushed" around between solar, utility, and the Powerwall is by modifying the frequency of the ac signal. I also know that many digital clocks keep time via utility frequency.
So, my question is this: if our power went out at roughly 10AM, and by 9PM our digital clocks were off by almost 45 minutes, what frequency is the powerwall delivering backup power at? That large of a shift in time seems excessive (purely speculative).
Best Answer
Units such as APC and Tripp-Lite UPS detect 60+/-3 Hz as a power good and either reduce AC load outside this frequency or switch off AC charge to rely on battery backup. They also use voltage thresholds.
However, these UPS units have a relatively short backup time compared to the PowerWall2 (PW2). There are UPS's with +/-6Hz tolerance for input power detection such as the Minuteman.
Therefore to reduce non-essential loads that have short-term backup such as UPS, the PW2 runs > 65 HZ intentionally (or > 7.7% fast).
Your clocks were reading (21:00-10:00) * 60min/h = 660 minutes when you were expecting (20:17-10:00) * 60min/h = 617 min or 43 minutes fast = 43/617*100% = 7.0% fast which was the actual increase on the PW2 or 64.2 Hz.
The PW2 was 10% within the 65 Hz that I expected, but I do not have their actual specifications.
I am aware of this but cannot prove it.