Sizing a UPS for cable modem and router; market opportunity for a long duration low power UPS?

Things that our neighbors hate more than Donald Trump:

  • cell towers
  • underground power lines

Power failures are routine and, when they happen, we lose all communications capability (since a mobile phone won’t work inside the house and only barely works out in the yard).

I’m thinking it might be nice to back up our Verizon FiOS service, including the Internet. Then, in theory, we can at least use our landline and our smartphones or laptops that are charged.

A friend in town says that this is a fool’s errand: “when we had power failures, it turned out that the fiber switch on the street would go down.” On the other hand, this FiOS customer had 72 power outages with Internet in a 6-year period (great advertisement for U.S. infrastructure!).

I’m wondering how to size the UPS to run the latest ONT (corresponding to a cable modem) and VZ’s WiFi router. Verizon sells a ghetto backup battery system, just for the ONT (to run the landline for 24 hours), based on 12 D cell disposable batteries. Wikipedia says a D battery has 18 amp-hours of capacity at 1.5V, so the total of 12 would have 324 watt-hours?

If we assume that the WiFi router draws a similar amount, and will have both boxes plugged into a UPS, we therefore need a UPS with 650 watt-hours of battery? Add another 20 percent for the efficiency losses in converting from DC up to 120V AC down to DC, so now we need 800 watt-hours of battery inside the UPS to run for 24 hours?

It seems to be tough to find this information. UPS vendors spec them in volt-amps or watts and then bury the battery details. Also, maybe Verizon is selling its own thing because the appropriate product does not exist in the market? To get a beefy battery one needs to invest in crazy high max VA, which is irrelevant in this application. A $200 UPS rated at 1500 VA is backed by only two feeble $20 8.5 Ah 12V batteries (204 watt-hours; less than Verizon’s 12 D cells). We bought one to try out and it supplies the ONT and router for 2.5 hours, less than half as long as expected. The higher-capacity machines seem to be marketed as “generators” (without the generator!), e.g., this 412 Wh 11 lb. box for $550.

APC makes a box with a replaceable lithium ion battery for only about $71, which they say is intended to power routers, but it stores a pathetic 41 Wh. Lithium-ion is just not a sensible way to buy watt-hours, apparently.

Readers: Is there a market opportunity here? Apparently providing even the power of 12 D cells on a trickle-out basis is crazy expensive right now. How about a device that holds 24(!) D cell batteries and, in the event of a power failure, will supply power from those batteries to a router and ONT or cable modem? A brief interruption in the power supply is acceptable. Amazon sells D cell Energizer alkaline batteries for about $1 each, delivered. Instead of buying a $500 lith-ion battery that will be garbage after 3 years, just buy $24 of D cells every year or two.

12 thoughts on “Sizing a UPS for cable modem and router; market opportunity for a long duration low power UPS?

  1. As you say, using a typical UPS for this will spend a lot of energy in the DC – AC – DC conversion. Have you considered a DIY approach with a lead acid battery and a DC – DC converter? The idea is that you would replace the power supply that came with the device. You have a battery charger, battery, and DC – DC converter that provides DC to the device. I have not priced it out, but bet you could get ~500 watt-hours for ~$200. You would want a “deep cycle” battery for this. You would not need a large battery charger.

    I guess you have rejected the idea of just getting a generator? I live out in the woods and suffer from prolonged power outages relatively frequently. If I had natural gas or propane already I would install one of the widely available residential standby generators that come on automatically when the power goes out. When travelling, it would be comforting to know that the house was heated and the fridge was running even if the power goes out.

  2. I bought whatever UPS at Costco to power cable modem and wifi router. Turns out that after power outage local Xfinity CO’S UPS runs out in couple hours and internet dies anyway. My UPS outlasts it with the large margin.

  3. In 2017, after Hurricane Irma, I lost power for 7 days and the FL heat was brutal w/o air conditioning. Estimates for installation of a a whole-house 16KW Generac generator were $10,000 -$11,000. I ended up buying a Chinese-made 7500 watt tri-fuel portable generator for $1500 delivered. I run it on my natural gas service and have an inlet wired to my electric panel. It starts on the first pull and runs the whole house including the 4-ton central AC.

  4. The interesting thing about cellphone towers is they tend to be opposed by people who worry that cellphone RF fields cause cancer. Whether true or not, modern cellphones raise transmit power when they are further from the tower (lower recieve power) so having towers further away actually raises the cellphone RF exposure, since the inverse square low pretty much ensures that RF exposure is dominated by what’s in your pocket rather than what’s on the tower. A nice example of unintended consequences.

  5. So your fancy neighborhood has ugly power lines strung over houses and power poles? So every wind storm causes outages? I will never own a home again without total neighborhood underground power. We never loose power due to storms etc.. We go months to years with no outages even in our mountain home.

  6. Boats and off-grid solar and wind powered house face this same problem. Instead of thinking of it as a UPS you might want to treat it as a nighttime solar power solution. These can likely be speced appropriately for your needs.

  7. I’m late to the party but the constraining factor is the batteries in the off the shelf UPS’s, which tend to be too small as you say. Fortunately, lead acid batteries are cheap and you can get big ones to replace whatever is in the UPS. Of course they won’t all fit inside the case – you can just have them sitting external to the UPS. You just need to make up some extension cables with wire and spade connectors.

    If marine batteries are too big, you can just get the biggest SLA (sealed lead acid) batteries you can find.

    As far as off the shelf UPS’s go, just look at the shipping weight and buy the heaviest one you can find – it will have the biggest batteries. This is not necessarily correlated with their VA output. There are some high VA UPS’ s that come with undersized batteries.

    The UPS won’t put out more watts than it is designed for but any UPS will take pretty much any sized battery and keep running indefinitely at up to around 75% of the rated wattage as long as the batteries hold up.

    Doing DC-DC conversion would be even better but it’s not as easy a solution – you would need to combine a trickle charger for the batteries with a 12V to 5V (or whatever the router takes) car adapter, find the right connector plugs, etc. Just adding bigger batteries to the UPS is a trivial 10 minute project.

  8. For an off the shelf solution,

    comes with four 9AH batteries, which would more than double what you bought, for around the same price. But still this would only get you 5 hrs it seems.

    This: is 30 AH. 4 of them, hooked up to the above UPS would get you 120AH. Since you will be discarding the included batteries anyway, you could buy a used UPS off of ebay sans batteries for cheap.

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