The Tesla Powerwall 2 (PW2) is an excellent protection against grid power outages, yet its design does require an additional Uninterruptible Power Supply (UPS) for any devices that are sensitive to even extremely brief power breaks.
While your fridge, microwave, most lights and other devices will likely not notice the 300-2000 millisecond relay switch-over (I'll admit I really don't know the typical Gateway relay cycle-over time as I've never been able to find Tesla specs on it) in case of a power outage, your sensitive electronics certainly will. In fact, only a few Hertz cycles loss will cause anything CPU related to fail.
Thus the need for at least a -short term- UPS to get sensitive electronic devices 'over the hump' of the power outage to final relay 'snap' into the internal house power grid and PW2 power feed. So far, so good. Almost any UPS can fill that bill and, in fact, since it is only needed for a second or two, the battery power for most are severe overkill for the task they perform while supporting the PW2.
However, the PW2 has a specific issue with most UPSs in a specific setting. I'll explain. If the PW2 is at 100% charge while the sun is shining and the user ALSO has solar panels, the PW2 will attempt to 'turn off' the inverters for those solar panels once inside the internal house power grid (which the relay broke from the grid operator no longer providing power). In order to do this, the PW2 will raise the Hertz cycle (in the US) from 60 to 65.
Now, I believe most electronic devices can handle a range of Hertz cycles (I actually have a call into Tesla PW2 support to confirm electronics working at 65 Hertz), including computers, routers, modems and other devices. Thus, they should work just fine while the PW2 is inhibiting the solar inverters from producing power by going to 65 Hz.
The problem is that MOST UPSs will only see power coming from the outlet as 'good' when it is 60 Hertz plus or minus THREE Hertz (thus 57-63 Hertz). Thus, when the PW2 is 100% charged and in a Backup situation with no grid input and solar panels that need to be inhibited, the PW2 will raise the frequency to 65 Hertz to inhibit the solar inverters - this power will then be considered 'bad' power to those UPSs. The UPSs will then simply run on their own battery power until they run out and the devices behind them will die at that time. All because they see power at 65 Hertz as unacceptable.
In an outage event that occurred with my PW2 earlier this week, while my PW2 was 100% charged and it was actively inhibiting the solar inverters by raising the frequency to 65 Hertz, my UPSs only lasted for 5-15 minutes (depending on the load) at which time they failed. Howevver, the PW2 inhibited the solar inverters for 30 minutes while discharging into the house. Since all of the computers / routers / switches / NASs / etc. (which consumed most of the power at that time) were behind UPS's, they didn't use the offered PW2 power (now at 65 Hertz and incompatible for pass-thru by the UPSs) and simply used up the batteries on the UPSs.
Thus the PW2 discharge was just for fridges and other phantom loads that slowly got it to 97% in a half hour. At that time, the PW2 decided it was OK to allow the solar inverters to create power and lowered the frequency back to 60 Hertz. The UPSs reacted by immediately charging their now-dead batteries, but the devices behind them were long dead.
BUT a solution was found that is as inexpensive as the APC and Trip-Lite UPSs I was using. It turns out that Minuteman UPSs can handle an input of 60 Hertz plus / minus 6 Hertz. Thus, it will see the 65 Hertz that the PW2 creates during those specific timeframes as acceptable pass-thru power. Thus the Minuteman should provide the conditioning to get over the short relay switch-over loss of power AND allow the PW2 65 Hertz power to then pass-thru the unit on to the devices, which will then enjoy the huge (comparative to that UPS at least) battery backup capability of the PW2.
The only testing I must do for all my electronics is if they will function with the 65 Hertz power and also function across frequency changes from 60 Hertz to 65 Hertz and back again. If the power supplies for my devices can handle those small changes without causing a crash, I have solved that problem.
Here is the Minuteman UPS I am going to be testing out next week:
https://www.amazon.com/gp/product/B015QOEP0K/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
Here are the specs for the UPS that show it will see input at 60 Hertz - plus/minus 6 Hertz as acceptable power. Look at the Input Frequency Range:
Minuteman UPS - Entrust LCD Series
Although a grid loss at 100% PW2 power and during the day when solar inverters need to be inhibited by raising frequency to 65 Hertz is not a normal experience, this solution should provide the conditioning to get past the relay switch-over timeframe AND allow devices to use 65 Hertz power from the PW2.
I'll update this post when I know more about electronic devices working in a 65 Hertz environment. Testing will be occurring this weekend and next....
