Most domestic UPS are not designed to operate for that long. Usually about 30 minutes is the limit, as they are only intended to provide power long enough for you to save your work.
The best option if you want a no-break system, which will run for longer, is to have a 12V-240V invertor which is connected to a leisure battery.
This battery in turn is kept charged via a constant voltage 13.6V power unit.
If you work out the total wattage used, or get on of those plug in power meters, you can then get some idea of what wattage the UPS needs to be, and also the amperage of the 13.6V DC power unit.
The other thing to consider, is that if any of the equipment has a power unit with a transformer in it, as opposed to being a modern switch mode power unit.
If that is the case, then your invertor will have to be a pure sime wave one, and not one of the cheaper simulated sinewave ones, which are damaged if you use them to feed an inductive load, like a transformer.
I use a combination of both. I have an APC BackUPS ES550 which copes with breaks of up to 20 minutes.
I also have a 300W pure sine wave invertor which is kept on standby, and is connected to a leisure battery.
All 12V devices are directly connected to this battery, so I do not use their supplied power units.
In the event of a longer mains failure, I simply turn on the 300W inverter, and plug the input to the APC UPS into it.
This can then supply power for up to 8 hours.
If you get regular power cuts, of varying duration, the I would recommend getting a pure sine wave invertor. One rated at 150W costs about £80 or less.
You would also need a 12V leisure battery, not a car battery. Car batteries are unsuitable for deep discharge cycles.
You would also need a 13.6V power unit. A typical one providing a maximum of 7 amps, costs about £40.
That works out at about 84 Watts to supply any equipment, and keep the battery topped up.
There is no simple solution to your problem. But you really need to measure the total power consumption used (in Watts), by everything you want to keep powered, and then you can work the rest out from there.
Here is a picture of my setup.
The leisure battery is on the left, the 300W invertor in the middle, and the APC UPS on the right.
Hello all, We occasionally get a power cut that lasts between a 30 second blip to a 4hour blackout, after having a short one last night (10min) I have thought about getting a UPS power pack just to keep things running my requirements are below: Home Hub 12V 1000mA Sure Signal 12V 1amp Modem 12V 1.25amp Sam Knows router bridge 9V 0.6MA Laptop charger if battery ran out - 19V 3.42amp What size pack would I need to run all this for around 3-4hours ? I'm guessing small any suggestions would be appreciated. Cameron
Just adding up your loads the total watts are around 75 Watts. That's if I understood your loads. Just add up all the volts x amps for the loads and that gives you watts. For 4 hours that is 300 Watt hours. But life is not quite as simple as that: Each device may have an inrush current, i.e. a surge current when starting up. So to be safe you should be looking at around 700 Watt hours. I'm only going on past work experience in the transport industry. I understood that some of the forum members are using UPS's. Don't forget that the UPS batteries must be discharged / charged periodically.
Maplin are showing a 1000 watt hour UPS on their site, as an example.
I added a picture to my last post.
Larger UPSs do not always mean a longer running time if only lightly loaded, as there are other losses which can exceed that used by the light load.
In theory, my APC one should run for a long time if it was only lightly loaded, but in fact, it makes very little difference, as according to their PowerChute software, 30 minutes is the upper limit.
As Ribblelancs has estimated yours at about 75W, then I would recommend a 150W pure sine wave invertor, or even a 300W one if you have the money, which gives you extra scope to power othe domestic gadgets, without worrying whether they present an inductive load.
Things like audio units will give a horrible buzzing noise if powered by a simulated sine wave invertor.
Then work out how big a battery you need. The invertor will consume about 8 amps at 12V, if you are loading at about 75W.
So if you wanted 4 hours usage, in theory, that would be 32Ah. But there are losses involved, so you really need a bigger battery. Mine is an 80Ah leisure battery.
To keep that topped up, and supply the load, you would need a 13.6V 10A supply.
You see its not that simple. You have to decide what really needs to be kept going, and what can be left without power.
Take a look at the ones that APC make. They have a very good reliability record.
I used to have a couple of Belkin ones, but they packed up after a very short time
The APC BackUPS range are very compact, and have mains sockets on the front, four of which are fed from the UPS, and the rest are just filtered.
They simply hang on the wall, as you can see in my picture.
Now that the electricity board have replaced most of the old aluminium distribution cables, the number of power cuts have reduced considerably over the 32 years I have lived here.
There is still a local overloaded substation which seems to blow a fuse occasionally.
Thanks for clearing up the details.
I was thinking along the lines of short term demands on the UPS system - start up loads etc.
Past experience has shown that you go for a large capacity supply, but, as you have said there are system losses in the inverter itself.
It was different in industry where there was a massive 110 V alkaline battery to be drawn upon - sufficient to keep ventilation and lighting going for some time, in the event of a supply failure.
If space is a problem then, perhaps a 10 minute rating should be considered, if 4 hour power cuts are infrequent. They are here - about once every 2 years.
That is slightly less capacity than the one I have.
I believe that you can download the user manual from the APC website, and there is a chart giving the typical running time at different loads.
APC give you a free software program called PowerChute, which monitors the state of the UPS, and gives the approximate run time with the current load.
A quarter of the loading does not actually equate to four times the run time, because of inverter losses.