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After a recent power outage I realized that while all our main computers are laptops with battery power, the WiFi and modem are not. Cable service to the area continued working fine, but without power to my modem I couldn't get online.

All the guides and ratings I've seen for UPSs are for powering a PC. A modem and WiFi base consume significantly less power, does that mean that a UPS rated at 20 minutes for a computer would power the network equipment much longer?

I would like to find out how to select a good UPS for my network hardware. How will I know which one fits my needs?

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Your two devices probably consume about 10 watts each, so your assumption that a UPS could keep the modem and wireless router powered longer than a PC is true. In one hour your two devices would consume about 20 Watt-hours. So a small 200 Watt UPS would optimistically backup these devices for a whole work day.

The problem with a low-wattage UPS is that they tend to be built cheaply. The electrical output is typically not a sine wave like the power from the utility company, but rather a square wave which may introduce electrical noise in some devices. The switch-over time from loss of main power to providing power from the battery can be another weak point. The best (and expensive) UPSes have zero switch-over lag by always supplying the power from the batteries.

UPS typically use one or more sealed lead-acid battery, which last for 3 to 5 years. I just had to replace a battery the other day after 4.5 years life.

BTW do not test the UPS by simply unplugging the UPS! That would also remove the (electrical) ground connection and create a shock hazard. If you want to test the backup capability of a UPS (after the internal battery has been fully charged up), have a power strip (with a switch) installed between the wall outlet and the UPS. Test the UPS by switching off at the power strip, which will maintain the electrical ground connection.

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You can pretty much stick to the same guides as you're already finding. Just total the wattage for the power supplies for the various bits, and work with that.

For runtime: yes, running at a fraction of the load will make a huge difference to the available runtime. It won't quite be "one tenth of the load means ten times the runtime", as there's some overhead to the inverter. But it won't be far off.

Feature wise, less is more in this case. It might be worth looking for one which provides surge protection for the cable, as well as the power (having surge protection on the power doesn't save you from strikes on the dsl/cable). Other than that, you don't really need any features. Software integration is moot point, 'green'/master socket switching is just a complication on always-on hardware, etc.

For a quick example, I have a rather old APC CS 500 on mine. It's old enough that it's beige, and I've exceeded their recommended lifetime on the battery. I still get roughly 90 minutes powering a cable modem, router, and two usb harddrives.

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You can't go wrong with anything from APC, I use them in the office and at home. They have a handy online calculator to figure out what size meets your needs. Your guess is correct in that a UPS rated for 20 minutes has been based on a desktop computer running windows, so just a cable modem will be very simple to keep powered with a cheaper model.

http://www.apc.com/tools/ups_selector/

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