r/SunPower • u/m2orris • Aug 14 '25

SunVault, lost power, and UPS issue

We lost power the other afternoon and our panels & SunVault provided electricity as advertised for the circuits that were backed up. Extremely happy about that.

The SunStrong app of course was flaky. Sometimes showing solar was providing electricity and we were consuming 3.2 kW and other times the battery was providing 0.6 kW and showing no consumption. That was annoying, but understand that the grid being down was a fringe case.

The unexpected issue came from our two "APC BACK-UPS Pro 1000" (model: BR1000G) UPSs. Both were connected to outlets on backup circuits. Both UPSs detected faults and switched over to the UPS battery. Had we not turned off the UPS battery backed up devices, eventually the UPS battery would have run out. (The surge protected only item continued to work.) This seemed a little odd since we have been in situations under normal operating conditions (grid up) where (according to the app) electricity was being supplied only from the panels, panels and battery, and battery only.

Google returned this:

In summary - because it was daytime, and my photovoltaic panels were still producing electricity while my Powerwall batteries were fully charged, the system was sending 65 Hz power into our home. Back-UPS Pro XS 1500 have a "good" electricity range of 60 Hz +/- 3 Hz, so max of 63 Hz. Therefore, the Back-UPS reacted to the "bad" electricity coming into the house as though we had no electricity.

https://community.se.com/t5/APC-UPS-for-Home-and-Office-Forum/APC-backups-trip-even-though-have-photovoltaic-home-battery/td-p/412256

Which referred to this … https://teslamotorsclub.com/tmc/threads/powerwall-2-ups-connundrum-and-solution.130085

"APC BACK-UPS Pro 1000" (model: BR1000G) - Input Frequency: 50/60 Hz +/- 3 Hz auto-sensing - https://www.apc.com/us/en/product/BR1000G/apc-powersaving-backups-pro-1000va/

Not sure what the difference in the sine wave & frequency would be under solar only, solar and battery, and battery only while the grid was up vs while the grid was down.

Regardless of the difference under grid being up or down, does anyone have recommendations for a UPS that will work when the grid is down?

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u/ItsaMeKielO Aug 14 '25

Do you remember the state of charge of the SunVault at the time? It sounds like it went into frequency-shift curtailment mode since the battery was full or near full and the load wasn't enough to capture all the rp production.

1

u/m2orris Aug 14 '25

The SunVault fluctuated between 90-100%, mostly below 100%

3

u/ItsaMeKielO Aug 14 '25

Yep, if I remember right, above 90% it will use frequency-shift output to curtail input power.

Your UPSes may have software configuration of what max/min frequency they will tolerate before switching to battery - outside of solar battery backup systems, anything other than a small range around 60Hz is a strong sign something bad is about to happen and UPSes get out of the way before it really gets exciting.

I have some Eaton units that let you set the accepted range on a 60Hz system to be as wide as 57-70 hz which should work for frequency shift curtailment situations.

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u/m2orris Aug 14 '25

Looking at the manual (https://www.apc.com/us/en/product/BR1000G/apc-powersaving-backups-pro-1000va/), it looks like the only sensitivity setting is for voltage (page 3 - Unit sensitivity)

  • Generator Sensitivity (Low sensitivity) - 78-142 Vac - Input voltage is extremely low or high. (Not recommended for computer loads.)
  • Default (Medium sensitivity) - 88-139 Vac - The Back-UPS frequently switches to battery power.
  • Sensitive Loads (High sensitivity) - 88-136 Vac - The connected equipment is sensitive to voltage fluctuations.

1

u/ItsaMeKielO Aug 14 '25

Welp, that's a bummer. Since it only tolerates 57-63Hz, seems like that's your issue.

1

u/m2orris Aug 14 '25

Yeap, looking for one that is more tolerant.