Re: home router battery backup

[Mark Tinka <mark@tinka.africa>]

On 1/13/22 17:56, Aaron C. de Bruyn via NANOG wrote:

> I bought one of those power monitors and tossed it on the circuit that 
> goes into my house.  At *night* when everything is off, I might get 
> down as far as ~800 watts.
> During the day it's more like 2,000-3,500.

Almost the same here... down to about 700W between 11PM - 4:30AM, and 
mostly 1,500W - 2,000W during the day, unless the Mrs. wants to grill 
some chicken or do some baking in the oven that day.

Fair point, it's a family of 4 + 1, so...

> If I get the hat-trick (water heater, central air, and well pump) 
> running at the same time, I can get up to ~24,000 watts.

Ouch!

For our traditional water heater, we're using a system that can power 
the tank elements either via its own independent PV array or via the 
grid (where the grid is either the main house's PV array or the utility):

https://www.geyserworx.co.za/

I, then, added tankless, on-demand gas heaters into the mix, and piped 
that into the house:

https://gasgeysers.co.za/qr/20lt-room-sealed-fan-forced-gas-geyser/

I use a solenoid valve attached to a little IoT thingie to switch 
between the tankless gas heater and the traditional tank, depending on 
time-of-day. Tankless heater on at 8PM - 10:30AM, and traditional tank 
on at 10:31AM - 7:59PM (unless we had poor solar yield that day and it 
didn't heat up enough).

In all, we haven't had to use the utility to heat water since we went 
this route. Saved tons of cash, and guarantees a hot shower any day, any 
weather.


> I definitely notice it when the power goes out.  The sound of UPS 
> relays and alarms is enough to wake the dead.

For my setup, even if we generally can transfer from utility grid to 
battery backup between 0ms - 20ms, I attached UPS's to all sensitive 
appliances in the house as an additional backup anyway (small ones, 1kVA 
- 2kVA, type-thing). The reason for that is if we have an outage while 
the battery inverter is forming its grid from the utility, there are 
instances where the power outage is not a clean one (like a brownout, or 
slow low voltage event), and this would trip the battery as the inverter 
tries to quickly re-form the grid from the battery (230V/50Hz).

In such cases, the battery would protect itself from a possible short 
circuit, and shutdown for about 50ms, but that's long enough to power 
down the inverter, and it would take 60 seconds for it to restart. 
During that time, the UPS's will keep appliances running (Internet, TV, 
computers, consoles, a/v, e.t.c.).

Of course, if a utility outage occurred when the inverter was forming 
its grid from the battery, then we won't notice anything.

I've added voltage sensors to the grid supply to cut the power before 
the voltage gets too low, too quickly (cut at 219V), but that only 
improved the situation slightly. There are other inverters that have 
their own internal voltage sensors that could handle this far better, 
but I preferred the model I went with for its data management capabilities.

Mark.