DC UPS for Raspberry Pi 4 to run PiHole during power outage

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timmmay

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#319241 5-Apr-2025 21:35

TLDR: can anyone recommend a product to power a Raspberry Pi from a 12V SLA battery, so it continues to work during a power outage?

Background

I have a Raspberry Pi 4 running PiHole, including doing DHCP and DNS. My router and the fiber box are backed up by 12V SLA battery and a Sentry Lite, but if the power goes out we lose DNS so we can't use the WiFi easily.

I can have PiHole issue a secondary DNS address, but Windows uses primary and secondary DNS almost equally according to WireShark, rather than primary / secondary. I want Windows to use PiHole DNS unless it's unavailable, and I don't want to have to manually update DNS during an outage as if I'm not here my wife can't do that, and it's difficult on Android. There are a few possible workarounds to tweak how Windows does DNS, but I haven't spent the time to find an authoritative method to force Windows to use primary DNS. I'm interested if anyone has any thoughts there.

In the meantime, I'm looking for a way to run the R.Pi4 off the 12V SLA battery already right beside it. I could buy a generic 12V to USB-C converter like this one or a cheap AliExpress version, but I'd like something a little higher quality, ideally able to supply 5.1V @ 3A. There's plenty of options, like this and this but I'm wondering if someone has can recommend something they have experience with or have heard good things about.

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#3361246 6-Apr-2025 10:32

You did not specify how long an outage should be bridged.

In my case, the core system (ONT, router, DNS, switches, APs) is supplied by a UPS via mains voltage and PoE.

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timmmay

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#3361261 6-Apr-2025 11:41

I have a few 12V SLA batteries, so I can swap them out if I need to. I have a small 7AH battery on them as a UPS plus some 15AH batteries that are offline and charged.

I prefer to add to my existing 12V system than get a main UPS, but thanks for your thoughts Tinkerisk. I'm currently considering this DC-DC converter (cheapest and it's in Australia rather than the UK) and the Zero2Go Pi Hat.

Tinkerisk

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#3361289 6-Apr-2025 12:43

If you don't need the computing power of the RPi4 for other tasks, an RPi3B+ would be better suited to the task in terms of power consumption.

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timmmay

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#3361300 6-Apr-2025 13:20

I run about a dozen containers on the raspberry pi, including home assistant, website hosting using cloudflared with nginx and PHP, influx DB, grafana, and other things.

Anyone else found a good solution to keep their Pi running during a power cut?

richms

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#3361302 6-Apr-2025 13:44

I bought one of these https://vi.aliexpress.com/item/1005006578600241.html which a friend ended up using to run a pi and a few other things in their car.

It will only step down so no chance of getting 18v out of it when given 14.4, but for all the 5V stuff it works a treat and phones do charge pretty quickly on it. One of the things is a retropie and a screen for their kids, so it will at least power a pi 4 up without issue at all.

Richard rich.ms

timmmay

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#3361339 6-Apr-2025 16:07

richms:

I bought one of these https://vi.aliexpress.com/item/1005006578600241.html which a friend ended up using to run a pi and a few other things in their car.

It will only step down so no chance of getting 18v out of it when given 14.4, but for all the 5V stuff it works a treat and phones do charge pretty quickly on it. One of the things is a retropie and a screen for their kids, so it will at least power a pi 4 up without issue at all.

That looks interesting @richms! Much better for USB devices to have something designed for USB than a generic 5V power supply and me cutting up a cable to get at the positive and negative terminals 🙂

Any suggestions for a case? I was looking at the Jiffy UB3 at Core Electronics, it looks like it has some kind of system to mount PCBs in there easily but it doesn't say much about it.

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richms

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#3361355 6-Apr-2025 17:10

timmmay:

That looks interesting @richms! Much better for USB devices to have something designed for USB than a generic 5V power supply and me cutting up a cable to get at the positive and negative terminals 🙂

Any suggestions for a case? I was looking at the Jiffy UB3 at Core Electronics, it looks like it has some kind of system to mount PCBs in there easily but it doesn't say much about it.

He 3d printed something along with the pi and the HDMI switch and some media player box (chromecast? Not sure). This was all for use in the car to keep their spawn occupied so I didnt really care too much about what was happening other than giving it to them and saying try this.

Richard rich.ms

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#3361364 6-Apr-2025 17:45

timmmay:

I run about a dozen containers on the raspberry pi, including home assistant, website hosting using cloudflared with nginx and PHP, influx DB, grafana, and other things.

My physical pihole is an RPi3+ with pihole/unbound/nebula sync only. Two other piholes are virtual and run on VMs. So my approach is different than yours, but I also don't have to leave out any important constraints on questions I don't need to ask. 😎

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Mehrts

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#3361551 7-Apr-2025 10:19

I just run mine off a USB powerbank 🤷‍♂️

mdf

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#3361564 7-Apr-2025 10:45

Quite a different application, but I've used this style of car 12V --> USB socket: https://www.jaycar.co.nz/charger-12v-dc-with-fly-lead-to-usbc-3-0-and-pd-3-0/p/MP3623 (mine was a different brand but suspect they are all from the same factory). Works well. Plenty of other similar options with different styles and specifications (e.g., round ones to replace cigarette lighters). Not sure what your battery connectors are like, but you could just crimp ring or spade terminals straight on?

timmmay

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#3361583 7-Apr-2025 11:18

Mehrts:

I just run mine off a USB powerbank 🤷‍♂️

I considered that, but they're not really designed for it and I already have the 12V SLA battery, but thanks for the suggestion 🙂

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timmmay

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#3361584 7-Apr-2025 11:20

mdf:

Quite a different application, but I've used this style of car 12V --> USB socket: https://www.jaycar.co.nz/charger-12v-dc-with-fly-lead-to-usbc-3-0-and-pd-3-0/p/MP3623 (mine was a different brand but suspect they are all from the same factory). Works well. Plenty of other similar options with different styles and specifications (e.g., round ones to replace cigarette lighters). Not sure what your battery connectors are like, but you could just crimp ring or spade terminals straight on?

That kind of thing would probably work quite well. I can solder on some crocodile clips, it's already in a case so I don't have to muck around with it, and it can be purchased locally rather than from Ali. It's a touch more expensive, but I think it's worth it for the warranty and simplicty. I like Rich's idea as well, but I think this is probably the simplest option so far, thanks! 🙂

richms

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#3361617 7-Apr-2025 12:17

Mehrts:

I just run mine off a USB powerbank 🤷‍♂️

Do you have one that will change from charging and passing thru to powering the pi off the battery in it without a power glitch resetting the pi? I was not able to find one that would keep a pi running in a car when cranking or while away from the car for a bit without it glitching out making it pointless.

Richard rich.ms

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#3361749 7-Apr-2025 15:09

Mehrts:

I just run mine off a USB powerbank 🤷‍♂️

Do you run your pi off a powerbank and have the powerbank plugged into a wall charger? What capacity powerbank and how long does the pi survive on it?

timmmay

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#3362141 8-Apr-2025 20:20

I think I might go with a HAT, like this one or this one. That way it's sitting right there on the pi, though somewhat unprotected. The Jaycar option is ok, but those things go for $5 on AliExpress which makes me doubt the quality.

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