UPS Configuration

jumpered

barely

diesel

cut

Or these days power the electronics in the phone. At a rough guess there is about 250 mW available, off hook voltage = 12 V, loop current 20 mA.

--
Cheers 
Dave.

And a suitable charger can easily be built round a Unitrode UC3906

--
Stuart Winsor 

Tools With A Mission 
sending tools across the world 
http://www.twam.co.uk/

It's a very nice chip and even includes temperature compensation but there is one potentially dangerous condition that can arise (and I've actually seen it).

If the external drive transistor goes into thermal runaway the battery will get the full uncontrolled supply voltage. This happened in a commercially produced unit. The retaining bolt had worked loose from the transistor and a 6V battery was being charged. The incoming supply was a simple transformer/rectifier/cap that was pumping out about 14V. With no effective heatsink the transistor went S/C and the battery got *very* hot and swollen. Fortunately this was spotted before it exploded.

Because of the way this transistor is driven in the reference design, there is no way to turn it off once internal leakage becomes significant. A more conventional emitter-follower arrangement would be more stable, and the transistor would have to get much hotter before leakage became severe enough to 'self-bias'.

--
W J G

Choose a cheap UPS which uses a 12v battery (e.g. APC ES550 which uses a single 12v 7Ah) - tap the battery directly to feed an efficient +5v regulator (via a 3A fuse), then initially feed the router wall wart from the mains output.

For an encore, you can then look at feeding the router from the battery.

Note that the battery voltage when on charge could be high as 14v.

If you choose a UPS with any kind of management interface you can plug this into the Pi and then use Network UPS tools to manage a shutdown.

This method means that the hardware task is reduced to sourcing a DC-DC converter, rather than sussing out how to float charge a battery

Indeed. I have 4 pi's, 6 odroid's (hardkernel.org, very good alternative to a pi), one screen, a wifi router and the fiber modem and the isp supplied firewall all on battery power. Plus two small gigabit ethernet switches. This takes all of ~55 to ~105 watts depending on the load, with the fiber modem and wifi router taking a base of ~32, and each pi around 1.5 idle and around 3 fully loaded, the odroids alightly more, around 2,2 idle.

It all runs on 12V, regulated 12V and regulated 5V power, directly from the "car"battery (it is a slow-discharge model). It is charged from a CTEK 8A charger, and the supply also has a halogen supply that I have tuned up to 14.9V and it supplies through a diode bridge so it takes the load when there is house electricity; but the batteries will take the load initially at 13.2V and falling gradually to 11.8 where I have set alarms on the firewall, and have written a small program to broadcast UDP shutdown messages on the network. It will also trigger a relay for full shutdown of everything at 11 volts on the battery.

Cost? (* are estimates, this was parts I had lying around)

Battery : 110Ah gelcell lead-acid battery $140 Charger : CTEK 8A unit $90 Marine distribution fuse block, 12 fuses $80 (3 fuses of 30A, 9 of 6A) Diode bridge $15 (audio use, dual 30A) Protection relay $20 * (camping van style) Cabling and connectors, 12V $30 * (car style)

5 and 12V regulators, 11 and 2 respectively $90 Halogen supply $40 * Plugs and fuses for the various devices, $60 *

Total $565 or ~$50 per unit.

For a simple setup with two pi2, firewall, wifi and modem I would estimate something like

Battery : 60Ah car battery $60 (this is how big you get cheap ones) Charger : simple car battery float charger $40 (3A CTEK, e.g.)

6 fuse block for a car $25 Protection relay, 10.2V $15 Cabling, regulators and plugs $35 $175 .. pure estimate

Lately I have added two more batteries for a total of 330Ah and have used another 10-80W for some house lighting, a small inverter for the TV screen and some essential equipment that doesn't use a lot of power.

On a normal use schedule we can handle a 24 hour outage quite well.

We live in an area with two ~200unit development projects both about

1.5 km away, and they do a lot of work on the electricty grid here. This is not too stable in the outset, and 2 hour outages happen quite regularly. There has also been two announced 10hour night outages the last year. We have made it through all of this very nicely.

But we do have FTTH; a very good gigabit WDM-link right into our attic. We do get 50/50 megabit that we pay for (but if use is lower than 1mbit for a prolonged time we do get ~800 mbit for around 8 seonds, which make morning downloads very pleasant indeed.)

It holds out for all the power cuts we have had. This was our experience with the previous ADSL links too, they lasted longer than most mobile towers near us (but there was still mobile coverage, although 3G delivered a lot less bandwith after around 30min without power).

Cable however barely lasts 10 minuts.

The last year with this connection we have had two all-night annouced cuts, announced for 10 hours but in reality they were 6.5 and 8 hours. There has also been ~15 blinks of ~2-3 seconds (as they flip the

21kV relays) and 4 unplanned ones of from 10 to 40 minutes as well as one 3hour one. We had ininterrupted internet connectivity and wifi links through all of them.

Before that we had cable, which was useless in power cut situations. It had so much separate interruptions that I ordered a minimum ADSL backup, 1.5M down / 256k up; and this stayed up.

Booting a large docsis network often requires manual intervention (docsis is the usual standard for internet over cable). It is a nightmare operationally.

ADSL and FTTH are dead simple in comparison. The routers DSLAMS and fiber switches usually boot from cold in less than a minute all by themselves.

-- mrr

ADSL was made to coexist with a normal phone line on the same copper pair. This could draw ~30mA, or around 1.5W, to power a phone. They kept the 48V because it made life a lot easier for the linemen when the ADSL was left alone on the pair.

And because the standard says so.

-- mrr

In some of the metro areas, the copper lines were changed to pole mounted carrier terminal equipment. The old the phone line works when the power is down went out the door.

My neighborhood has an occasional power outage, usually due to wild life incinerating themselves. But, when this happens, usually on a Sunday morning, it may take several hours before a lineman comes along and replaces the fuse at the end of street disconnect.

Occasionally we've had outages that extended for several days, usually when the power companies crews were sent elsewhere to deal with major outages. This sort of encouraged me to obtain a gen set that is large enough to carry heating and cooling along with reasonable other loads.

I ended up having to do things a certain way, because the main breaker panel splits the load into four groups. Extensive rewiring would be needed if I were to just power essential circuits from a generator via a transfer switch. Instead, the transfer switch allows a 15Kw generator to carry the whole load when needed. (And can be used to totally isolate the home breaker panel etc. from any power. This avoids getting the power company involved if work inside the breaker panel is needed.

I also have smaller 3Kw and 2Kw 125vac inverter generators. They are used to support a heat pump and electronics in a trailer. (Electric RC model plane hobby)