home router battery backup

Jordan Hazen jnh at vt11.net
Tue Jan 18 20:56:38 UTC 2022

On Thu, Jan 13, 2022 at 10:38:53AM -0500, Jay wrote:
> Greetings,
>     I am a home user.  Much of my home has been rewired to run off of 
> 12-volts D.C. from a large 1200 Amp/Hour LiFePO4 battery bank that is 
> recharged using Solar.  All my lighting, ceiling fans, water pump, Ham 
> radio gear, weather alert radio, USB charging stations, alarm system, 
> security cameras and DVR, my wife's CPAP machine, 40-inch flat screen TV, 
> ROKU streaming device, etc. all now run off 12 VDC.

What was required to run your 40" television on 12V?  Did you
replace its internal PSU, or just feed it a boosted DC voltage?

(For anyone unaware, most, but not all, switchmode supplies are
happy running from DC in the same general range as their marked AC
voltage.  Some are polarity-sensitive, and active PFC occasionally
causes trouble.  Also, small commodity MSW inverters can be easily
changed into 12V -> 160V or 12V -> 300V DC/DC boost converters by
disabling and bypassing their final chopper stage, at considerable
efficiency gain.  Just don't run the boosted DC through switches,
relays, or breakers meant for AC - these will quickly fail in such
use due to arcing and/or welded contacts! Fuse the DC-input side.)

I've gone down a similar path, standardizing on Anderson Powerpoles
for 12V distribution, but limited my scope to 24/7 loads, phones,
telecom/network/radio equipment, other low-wattage electronics, and
a small fraction of (LED) lighting, to avoid extending heavy-gauge
copper all over the house.  One motivation was to reduce the impact
if our main household inverter were to fail while operating off
grid.  Another was let that unit be turned off at night with little
inconvenience, or put into "search" mode where it switches on only
when detecting that an intermittent load wants to run, such as the
well pump or refrigerator.  Newer fridges with electronic controls
unfortunately don't like to operate in this mode, but have gained
enough efficiency to more than make up for standby inverter loss.

My 12V bank is still AGM lead-acid, but doesn't see frequent
discharge, usually floating from solar during the day and from a
central AC supply at night, providing the grid is up.  24V is
available too from the garage PV solar system batteries, though
only in two rooms.  This runs a 24V->12V DC/DC to power the 12V bus
(normally current-limited by PWM signal from the PV charge
controllers, based on available sun.  This makes better use of
limited PV power in morning & evening hours than the large Outback
Power hybrid inverter would, with its 40W standby loss.

To circle back somewhat to the original topic, Outback was acquired
by Alpha Power several years ago, but I haven't yet noticed much
integration between their traditional telco/MSO product line and
the Outback equipment.

> High consumption devices like stove, refrigerators, air
> conditioners, furnace, still run on AC but get *much* of their
> power from a 5kw Grid-Tied Solar array (Enphase IQ7
> microinverters) which I hope to soon add a battery backup to. 
> There is also a whole-house 4kw backup generator.  This is what
> is known as a "Hybrid" home :)

I installed a 120V-only protected loads subpanel next to our main
panel and moved most circuits over, to take advantage of the
Outback hybrid inverter's integral automatic transfer switch and
use it as an (almost) whole-house UPS.  240V circuits drop, but
little else does.  Most importantly, refrigeration and our
well-water pump (1hp, ~1200W draw, too large for practical DC
conversion) can remain powered indefinitely, whether anyone is home
or not.  Central HVAC is not backed up, but we can run a couple of
window units.

Due to its use of heavy 60A relays, the transfer time of this type
of inverter is a bit slow by UPS standards, roughly 30ms, but no
computers or other AC loads seem to mind.  Important gear is all on
12V anyway.  There is an alternate, zero-transfer-time mode of
operation where the inverter is kept constantly running in
phase-lock to incoming power, and steps in even before the
isolation relay fully opens.  This comes at the cost of 20+W of
additional 24/7 load, and may not entirely meet the letter of
UL1741 or IEEE1547 anti-backfeed requirements, so I opted against.

>     ALL of my servers, workstations, routers/hubs, WiFi, are also converted 
> to run on 12VDC from this battery/solar plant.  In many cases it is just a 
> matter of adding a DC-DC buck/booster regulator that can be purchased on 
> Amazon for ten bucks, or so.  These generally take 8-40 volts input and 
> will deliver whatever voltage output that you desire.  Both my DSL and 
> FTTH are powered this way.

My sister-in-law bought an off-grid home whose previous owner had
wired every room for both 12VDC and 120VAC.  Lighting, fans, etc. 
were nearly all 12V.  This was nice at first, especially the old
and noisy MSW inverter, but did complicate their eventual upgrade
to a larger system and its required 48V battery bank.  They
required a large DC/DC converter, losing out on some of the
efficiency gain, and elected not to extend 12V when building a new
addition onto the home.

>     It was mentioned that we need to address *reducing* our power 
> consumption in order to reduce our carbon footprint.  This ongoing project 
> has helped me to do just that and eliminate so many "power suckers" and 
> wall-warts from my home.

This was part of my motivation as well, but thanks to efficiency
mandates in the EU and elsewhere, most modern wall-warts and other
PSUs are not nearly so bad as they used to be.  A good switchmode
design with cycle-skipping, where the main oscillator only runs
intermittently at low or zero load, can be enough to reduce standby
loss to 0.2W or less.

>     We consume around 150 watts on DC and generally around 600 watts on AC 
> (unless a freezer or air conditioner cycles on).  When the power goes out, 
> sometimes we don't immediately notice it!  I think I am living inside a 
> giant UPS, and more independance from the Grid is refreshing.

With no HVAC, freezer/fridge or well pump running, we're usually in the
250-300W range, which includes the DC rectifier.

A neighbor was puzzled at calling to ask if our power was out, when I said
"let me go check...'

>     Enjoy!
>        --- Jay Nugent  WB8TKL
>            Ypsilanti, Michigan
>            jjn at nuge.com

Jordan - AK4PZ

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