DC UPS Keeps The Internet Up

We occasionally get annoyed that so much gear takes the ubiquitous “wall wart” these days. But one advantage is that the devices operate on DC voltage. [TechRally] takes advantage of this to create an automatic DC UPS with dual outputs to power a router and modem in the event of a power outage. You can see two videos about the project below.

Some may say it would be better to use conventional UPS, but think about it. That UPS has a battery in it that gets converted to AC so the wall wart can convert it back to DC. Each conversion loses some energy, of course, and in the case of a cheap wall wart, you may even lose quite a bit.

The project contains eight 18650 batteries, an off-the-shelf charge controller, and power converters. Could you do a more efficient custom design? Maybe, but the use of these inexpensive and commonly available modules makes it quick and easy to pull something like this together.

No one would mistake this UPS for a commercial unit, but it does have a certain hacker aesthetic. We wouldn’t carry it through an airport, though. With those digital displays and all the wiring, it looks like a bad TV show’s bomb prop.

If you don’t care about the automatic switchover, we hear that 5V will power a lot of equipment these days and that makes battery operation as simple as stripping a USB cable. This could probably drive some other gear like a connected Raspberry Pi. Or, you could do that job with some supercaps.

31 thoughts on “DC UPS Keeps The Internet Up

  1. Where I am (rural UK) if my power goes off, so does the telco’s (BT’s) connection box up the road, and it takes *ages* to come back to life once power is restored. Often the 4G transmitter a few miles away stays up and I can keep going by tethering my mobile phone, with its 1 bar of signal, at least until more people catch on…

      1. My ADSL goes back to the exchange a hundred yards away, so I’m hoping it’s in a rack powered off the 48V DC (which is a big rack of batteries as you say). Haven’t had a power cut long enough to test this out.

      2. Most FTTH providers are using passive last mile equipment so much like old school POTS, as long as the CO retains power, your fiber line is active all the way to your house.

        Similarly, DSL based services will often have better luck in power outages due to the simple fact that copper POTS lines are still mandated to have some level of service uptime for phone service.

        Cable tends to be where things become sketchy or in many cases completely unreliable in an outage due to all the active last mile equipment and lack of maintenance on their own battery backups.

    1. I was looking into either a traditional UPS or a simple (no switchover) battery back-up for my router and modem until I learned that a lot of broadband internet systems have these connection boxes that go down when the grid is out. So there’s not really much point if you’re on e.g. cable broadband.

  2. Nice, but too complicated for my taste. Most networking gear that comes with a 12V wall wart can be directly connected to a cheap 12V SLA brick or even a car battery, these devices usually have their own step-down converters built in and do not need an exact input voltage. Just take an old laptop PSU and a simple charger circuit built around a LM317. No converters and relays needed, all that extra stuff can and will fail anyway.

    1. That reminds me of an episode of Knight Rider.
      Something happened to K.I.T.T. that made it forget the people it interacted with, among other (bad) things.
      The climax of the show happened when “David” refused to move while K.I.T.T. was threatening to run him over.
      As K.I.T.T. slowly approached, “David” reached under the front bumper and replaced a circuit board, and made everything better.
      As an RCA TV repairman at the time, I recognized the circuit board to be an RCA TV IF board of an older model line.

      I now keep one of those boards in my car, just in case a Tesla goes rogue. And I know right where to put it! j/k

  3. I considered doing this then went for a second hand ups as it had more capacity. It did have the problem of an always on fan but I put it in another room. I just have to upgrade the battery now.

  4. My T-mobile home internet router is up on the roof because it doesn’t work inside a trailer. And the damn thing has a battery, but no method to reboot it from the web interface. So I have to climb on the roof to reboot the thing, which includes removing the battery. Trying to get the 5g trashcan that has external antenna provisions, but the chip shortage limits these to new customers only. So a battery can be a pain sometimes.

  5. 12 volts makes a handy DC power system. Look around and see what low power stuff you can run off a low voltage wire run instead of a bunch of wall warts. VOIP adapter, router, modem, TV amplifier, wall phones, night lights, cellphone chargers, smart speakers, Pi Hole … and for backup all you need is a car battery and diode, or supercap bank.

      1. Deep cycle batteries are a good candidate, they’re sealed and better suited for continuous draw than standard starter batteries. Motorcycle batteries are also suitable, also sealed, and have been used in commercial emergency lighting, etc. for years.

    1. Yeah… just watch out for ground differences returing through signal cables… I lost a USB hub and an HDMI port that way, I think. Lucky I didn’t fry the hard drive. Went back to AC, even though that requires an inverter and wallwarts, which isolates each system’s ground…

  6. I have ATTuverse. My router has a spot for an internal battery but it only powers telephone service through the router. Because I don’t have landline phone service the router did not come with its internal battery. When the wife started working from home we became concerned about power outages. I found a Belkin UPS at a garage sale for free. The battery in it would not hold a charge. I replaced the battery and now have a working UPS. The belkin UPS was made for backup of an older ATT router so it’s power cord plugs directly into the router I have. Real simple, no mods, keeps internet up until battery dies. (3-4 hrs.)

  7. One of my favorite topologies is one of the “MINI USB 5V 1A 18650 TP4056 Lithium Battery Charger Charging Board” with one to ten 18650’s in parallel feeding a “Step Up Power Apply Booster Module DC-DC 2V-24V 2A”. I power this from a good quality microusb power supply. This works well but there is room for some improvement.

    Ideally given this is on line all the time, I would like the “MINI USB 5V 1A 18650 TP4056 Lithium Battery Charger Charging Board” to stop charging at more like 4V than 4.2V, and now, if I run the thing down, I am counting on the current limiting on the USB power supply to be working. It also takes a long time to recover from a serious outage.

    On the plus side, it has proper charging for the cell(s), over discharge protection, over current protection, and is small and neat, and very inexpensive, with the modules running about 60 cents a pop in 10 packs. And it can power anything, the boost converter can go from about 4.5V up to about 24.

  8. I have several UPSes. All are discards from work. When the internal lead acid gel cells die, they tend to replace the UPS rather than get inside and change the batteries. Ask around, nobody wants a UPS with dead batteries, you can often get them for free.

    I order (name brand) replacement batteries from Amazon (Lead is heavy, and the free shipping pays off) and replace the worn out ones. I get about 4-5 years out of a cell before I have to replace it again. Old ones are recycled at Lowe’s.

  9. This is of limited use if you’re in Australia on a 4G service, and absolutely useless if you’re on HFC NBN unless your power problems are strictly limited to your own house.

    Cell towers, including those operated by Telstra, only have 4 hours of battery back-up, running on batteries that often are only being replaced when they fail completely (so quite possibly do not have the original stated capacity).

    HFC NBN (not sure about other types, but suspect this is applies to all but satellite NBN) while you certainly _can_ power the NTD via back-up power (and I do; HFC NTD just needs an LM1085IT-12 to keep it happy), it’ll just blink and boot-loop uselessly in a black-out since the amplifiers in the street run on mains power with no back-up supply.

    I’m glad I have a radio license!

  10. My current solution is a commercial (Sherlotronics) DC UPS, using an 18Ah SLA battery. Not terribly exciting for Hackaday, but it works pretty well for me. It is a 6.4A unit, split over 6 1A outputs. Unfortunately, my “ideal topology” for my router and Access Point is to power the router via passive PoE (24V), which then feeds the AP with the same voltage.
    So I included a 12V-24V step up converter connected to a passive PoE injector, having bridged two of the UPS outputs to get 12V@2A stepped up to 24V@1A.

    Potential useful hacks include rewriting/reimplementing the firmware on the STM8 uC that controls the charging circuitry, so that it switches off automatically at a slightly higher than normal voltage (it powers my setup for around 12 hours, but at that point the battery voltage is lower than I would like for longevity), as well as adding an ESP32 with a couple of INA3221 power monitoring boards for realtime monitoring. The stock board also has a 12V signal when it is running on battery, so that could be used to instruct the ESP32 to engage deep sleep power saving mode when on battery, so as to not drain the battery more than necessary. Obviously, when running on mains, such a strategy may not be required.

  11. Great build – for me though, all my internet “devices” such as router, modem, access points etc are all using PoE injectors and my Procurve switch is then plugged into a UPS. That way all my devices will be online during an outage.

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