Need solution to backup WiFi during power outage

Discussion in 'Networking' started by RAMhog, May 8, 2018.

  1. RAMhog

    RAMhog New Member

    May 4, 2018
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    Hi all,

    I bought this neat little mini battery-backup product, the APC Back-UPS Connect 50:
    APC Back-UPS Connect 50, 120V, Lithium Ion, Network Backup and Mobile Power Pack - APC - United States

    It is basically a USB battery pack charger like you see for phones/tablets, enclosed in a housing that plugs into the wall, and also has 2x standard power outlets for powering low-wattage devices via the battery when the power goes out.

    First, let me give you an overview of my network setup (the wireless-related portion at least):
    Internet -------> Netgear cable modem -----> Supermicro Atom-based server/router (running pfSense) -------> Black Box 24-port gigabit switch ---------> Ubiquity Unify wireless AP

    Now, I had hoped to be able to plug all of these devices in to the APC backup UPS, but the maximum power draw it supports is 50 watts. Using a kill-a-watt meter, I plugged in all 4 devices (modem, router, switch, AP) and measured the draw at an average of between 47 and 50 watts, with the draw sometimes going slightly above 50. The APC Backup-50 manual says that the UPS will automatically switch off if the draw goes over 50 watts, so I don't think plugging all those devices in will be a reliable solution in a power outage situation.

    I still have my old TP-Link wireless router (the usual consumer-grade router/switch/AP combo), which draws < 5 watts. The cable modem draws less than 10 watts, so both devices could comfortably operate via the UPS for a while, allowing my laptop to access the internet during a power outage. However, I am having trouble figuring out how to set things up so that the TP-Link AP takes over in an outage.

    I know I could place the TP-Link router in front of my pfSense router, but I want to avoid having a double-NAT setup.

    Secondly, is there a way to have the TP-Link router/AP have the same SSID as the Unify AP, but not be the "preferred" access point? The reason I bought the Unify AP is partly because the TP-Link wireless network will periodically go down, on average about once a month, for no discernible reason. I installed OpenWRT, but the problem persists; I can SSH into the router via a wired connection and the router is up, but the only solution is to reset the wireless interface. So, ideally the TP-Link AP would be a backup access point... is this possible?

  2. Rain

    Rain Active Member

    May 13, 2013
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    How frequently do you lose power? I would clone the MAC address of the WAN NIC in the pfSense machine to the TP-link router and only plug it in when the power goes out and its needed.

    If you're actively using the laptop when the power goes out, the switch likely wouldn't be seamless anyway. If you're not actively using the laptop when the power goes out, power on the UPS isn't being wasted in the meantime.

    You could DMZ pfSense to (mostly) avoid the double-nat issue, but putting the TP-Link in front of pfSense is like putting a lawn mower engine in a Ferrari.
  3. Occamsrazor

    Occamsrazor New Member

    Feb 23, 2018
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    Is the Netgear cable modem also doing NAT or just being used as a bridged modem? If the former, can it give out Wifi access itself? I guess I would be tempted to either get a proper UPS for the whole lot, or find some way to do "emergency" wifi access ahead of the pfSense.
  4. Blinky 42

    Blinky 42 Active Member

    Aug 6, 2015
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    It won't be a seamless switch because you can't clone the nat entries from pfSense over to the TPLink and bring up the TPLink and shut down the other wifi all at the same time. far easier to add another UPS into the equation or replace the small one with one that is properly sized for the load and the run time of that load for your power outage duration you want protected against.
    The run time you want will dictate how big a UPS you need. Do you want just 5 minutes to save work, or be able to continue for hours and hook up a generator manually if the outage extends beyond that.

    Most of the vendors have some sort of UPS calculator that lets you supply the power draw and desired run time
    UPS Selector
    Rain and K D like this.
  5. Tom5051

    Tom5051 Active Member

    Jan 18, 2017
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    Most of these devices run off 12v DC.
    From an electrical point of view, it's very inefficient to turn 120v into 12 or 24v and then turn 12 or 24v back into 120v.
    It would be more sensible to put the 12v devices onto a 12v SLA battery that is connected to a suitable charger.
    The server will need a larger UPS or look into 12v DC power supplies for PCs.
  6. Marsh

    Marsh Moderator

    May 12, 2013
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    Evan likes this.
  7. RAMhog

    RAMhog New Member

    May 4, 2018
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    I agree with those that are saying the best solution is to get a properly-sized UPS. That's the long-term plan, but for right now I don't have the capital to buy a nice rack-mountable UPS like I want.

    Not often, in fact I can't remember ever losing power in this apartment in the ~1.5 years that I have lived here. It's more about the challenge of setting it up, the cool-factor, piece of mind of having there, etc. Much like why most of us have servers at home, I'd guess... not because we really need them, but because we like to tinker and enjoy the process of setting them up and maintaining them.

    True, I didn't think of that factor. However, I only have the most basic-tier of broadband service, so I don't think that it would affect the bandwidth very much, if at all:
    Maybe there could be potential latency/congestion issues where the little router gets overwhelmed?

    It isn't doing NAT - the WAN IP of my router is the same as what my public IP appears to be on a site like It's only a modem, it doesn't have a WiFi radio.

    What if I were to install another NIC in my pfSense router machine, and then attach the TP-Link router (set up as an access point) to the 3rd ethernet port of the router? That would then cut down the number of devices I'd have to keep on the UPS to 3: the router machine (~25 watts), the modem ( < 10 watts), and the TP-Link router/AP (< 5 watts). With those 3 devices, I should be pretty comfortably under the 50 watt limit. I have no idea if or how this would work with pfSense, though, but it seems like it theoretically should be possible.
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