Typical last mile battery runtime (protecting against power cuts)

Mark Tinka mark at tinka.africa
Sat Feb 4 05:05:04 UTC 2023

On 2/3/23 21:11, Sabri Berisha wrote:

> Living in an area served by PG&E, I've had my share of power cuts. At home
> I have a 600va UPS that protects my cable modem, RPI router, and POE switch
> which serves 2 APs. That lasts about 30 minutes, which gives me enough time
> to fire up my generator.

I'd assume it doesn't take you that long to fire up the genie, if you 
are home when the power goes out :-).

Out of interest, depending on how long you've had the UPS, how many 
times have you changed the battery?

> Tip of the day: I also have a 1000va UPS that protects my garage door opener.
> This makes it a lot easier to a. get a car out if needed, and b. get my
> generator out of the garage.

In South Africa, garage door motors historically come standard with a 
12V 7Ah Lead Acid battery. What most people don't realize is that within 
1.5 to 2 years, those batteries are dead, and since there was power most 
of the time, they never noticed, until the power went out and the 
battery did not have sufficient energy to drive the motor.

It is not uncommon to see folk here moving to Li-Ion batteries with the 
same capacity to drive garage and gate motors. Personally, I try to only 
use Li-Ion packs in well ventilated, not-too-tight spaces, that come 
with a BMS and a charger that is predictable :-). So I avoid these 
little ones, and feel safer with Lead Acid batteries for garage and gate 

> Lastly, in the spirit of happy wife, happy life, I have another 600va UPS
> that covers my tankless water heater. It heats using natural gas, but the
> control panel still needs power. That thing lasts pretty long.

There are tankless water heaters that can take standard AA batteries to 
spark the igniter as well, but yes, if yours is electric, makes sense to 
put a UPS on it. At my place, I use both a PV-based controller to heat 
traditional water tanks, and also have just as many tankless water 
heaters. The former is for end-of-day showers and dish washing once the 
sun has done its thing, the latter is for the morning jobs for the same 
things, or if it's cloudy/rainy outside.

Even though I have whole-home backup, I did place a UPS on the PV-based 
controller, because even if it is connected to solar panels, it is 
still, in essence, an inverter, meaning it requires a grid before it can 
generate solar power. That is what the UPS does for it. It was my first 
deployment of renewable energy, so I needed the UPS before I backed up 
the entire home.

> YMMV, of course, but I went through numerous outages recently. And by
> numerous, I mean enough for our City leadership to get pissed off at PG&E
> and demand explanations.

Judging by our situation, I'd take the city leadership demanding 
explanations any day :-). We are way past that, down here. It's so bad, 
folk are deploying self-generation and self-storage by the truck loads. 
It's the gold rush for solar and battery installers right now. People 
have all but given up on the power company (Eskom) ever going back to 
its glory days.

> So far, my current ISP (Spectrum cable) has had 0 outages as a result of
> power loss. Which is pretty impressive, given the instability of the grid
> in this area.

Not bad.


More information about the NANOG mailing list