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Keeping the broadband router alive during a power cut

Skimbleshanks
Investigator
Investigator

‎07-10-2026 02:43 PM

Because DV does not work in the event of a mains power cut, and following recent Government warnings, I need to make provision for an Uninterruptible Power Supply (UPS) to maintain broadband telephone service in the event of a power outage. 

To calculate a suitable capacity for the UPS, I need to know the power drain of the devices in order to maintain internet and DV services.  There are two devices that require power, the EE router and the fibre optic coupler at the wall box entering my house.  The power supply for the router has a stated output rating of 4 A at 12VDC, i.e. 48VA.  The power supply for the fibre optic coupler has a stated output rating of 0.5A at 12VDC, i.e. 6VA.  (NB. VA is the same as W (watts), but UPS capacity is traditionally quoted as VA.)

Due to the nature of solid-state converters, the input power of such devices, at 240VAC, will be greater than the output power at 12VDC.  This is because the conversion from mains voltage AC to low voltage DC is not 100% efficient and can be surprisingly much less than 100%. 

Does anybody know the input power requirement of the EE adapters?

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4 REPLIES 4
Denzel99
Established Contributor
Established Contributor

‎07-10-2026 09:28 PM

Yes, Watts is volts V x amps A, i.e. VA, but here it means something a little different.  VA is “apparent power” and attempts to measure the total theoretical power available, including any wasted as heat etc.  Basically, it’s the charge capacity of the battery, and manufacturers tend to quote runtime in VAh, (VA hours).

It’s one of those marketing things.  As the conversion from DC to AC is fairly inefficient, the actual useful wattage is only about 60% of the VA* – so manufacturers like to quote VA as it looks more impressive.  (*This figure is known as the “Power Factor” and varies with the design and battery type, age etc.)

You also need to remember that the PSU (power units) are rated for a bit more than the equipment requires.  (Or at least, should be if they’re designed well).  If you can specify the make and model of the box on the wall, (it’s called an ONT - Optical Network Terminal, by the way), and the router then we can give you a more precise figure for their power consumption.

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Skimbleshanks
Investigator
Investigator
In response to Denzel99

‎09-10-2026 03:06 PM

Thanks for your helpful response.  Silly of me not to describe the devices.  Before posting this, the Universal Law of Cussedness of Things meant I could not find any details for the devices.  18 hours after posting it, the same Law meant I found the specifications and the problem is solved!  

Thanks again.

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Skimbleshanks
Investigator
Investigator

‎09-10-2026 03:08 PM

Hello all.

As you might have seen from my response to Denzel99, the Universal Law of Cussedness of Things meant I could not find any details for the devices before posting here.  18 hours after posting it, the same Law meant I found the specifications and the problem is now solved!  

Thanks for such speedy and helpful responses.

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