For any mission-critical computer system, it’s a good idea to think about how the system will handle power outages. At the very least it’s a good idea to give the computer enough time to gracefully shut down if the power outage will last for an indefinite time. But for extremely critical infrastructure, like our home Wi-Fi, we might consider a more long-term battery backup that can let us get through the longest of power outages.
Part of why this project from [Next Builder] works so well is that most off-the-shelf routers don’t actually use that much energy. Keeping that and a modem online when the power is out only requires a few lithium batteries. To that end, three lithium ion cells are arranged in series to provide the router with between 9 and 12 volts, complete with a battery management system (BMS) to ensure they aren’t over- or under-charged and that they are balanced. The router plugs directly into a barrel jack, eliminating any switching losses from having to use an inverter during battery operation.
While [Next Builder] is a student who lives in an area with frequent interruptions to the electricity supply, this does a good job of keeping him online. If you’re planning for worse or longer outages, a design like this is easily adapted for more batteries provided the correct BMS is used to keep the cells safely charged and regulated. You can also adapt much larger UPS systems to power more of your home’s electrical system, provided you can find enough batteries.
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A sorta common internet methodology for delimiting user names, which may otherwise just look like random words thrown into a sentence, or otherwise introduce reading speed bumps (read bumps?).
Sorta common? I’ve never seen it anywhere else but here, and for me it does just the opposite of its intended use.
This is just a 3S lithium battery, not a UPS. There’s no voltage regulation, charger or circuitry to transfer between mains and battery power. Lithium ion batteries are also terrible for UPS use since they hate being kept at full charge.
I wonder how hard it would be to DIY a proper one.
Like plan in an…80% charge? ESP32 voltage monitoring?
What I don’t understand is how to have it swap over FAST except to have it supplying 12V or 24v or whatever all the time.
Just put a big enough capacitor on the output to supply power while the relay switches over and DC-DC converter starts up. An ESP32 is overkill for monitoring and fairly power hungry. I would probably use a CH32V003 since I have a bunch of them.
The hard part is keeping the lithium batteries at a specific partial charge level. I would just use an SLA battery on a float charge.
It’s not that hard. For charge look for the LM2596 DC-DC modules on AliExpress. You want the one with 3 trimpots – one for volts, one for current, and the last for voltage cutoff – very important! Add a 3S BMS. Use laptop power supply or USB-C with 20v PD trigger.
Add another module for power out regulation.
I converted some old 12v NiCad tools to LiOn with USB-C charge this way, the modules went into the pack. I wish all battery packs were USB-C charged, I have noticed some Chinese tools doing this but haven’t purchased any to see what they do.
“Lithium ion batteries are also terrible for UPS…”
Tripp-Lite (Eaton) would disagree with you on that. They make good bank on them.
Are they using Lithium ion (which generally means NMC) or LFP though? I agree in general that the effect of holding NMC cells at 100% SoC is greatly exagerated but LFP cells are still much happier sitting fully charged, not to mention generally lasting much longer with much higher cycle lives and much less calendar aging
Lfp cells are commonly used in Datacenter applications
That’s not really true, of course you should manager floating V but for this small applications It doesn’t matter at all
Couldn’t simply be kept charged with a small solar panel? That way it would self-charge during the day and get discharged overnight to stop it being constantly charged.
Is having a daily charge cycle really an improvement over sitting at 100%?
1) It supplies 9-12V to the router & modem?!?! While I’m not surprised that the router and modem can function off of 9V, this seems rather bold to design this “UPS” without regulating the output to the 12V the devices officially require. I think it would have been much better to add a couple cells to bump up the battery voltage range, then use a simple & efficient buck converter to step that down to a constant 12V output.
2) If it is determined that the router & modem are happy running off 9-12V, a much simpler design could simply be a small 12v lead acid battery in parallel between the devices and the 12V power supply. The 12V power supply would keep the battery charged to 12V, and supply 12V power to the devices. If a power outage occurs, the 12V power supply will no longer supply power but the battery will – no fancy switching circuitry required!
The ideal battery is a ubiquitous/universal SLA deep-cycle battery – they are cheap, available in tons of sizes, and there’s a reason why they are used in UPSs, building alarm system backup power, emergency lighting, etc.
One needs to remember that cost/benefit calculations must be biased with a user’s economic means, and that bias can be quite large. In this case one considers the economic resources of a /student/ who also lives in a /village/.
I can easily imagine they use a battery powered laptop; so the key device is that wifi router as mentioned. And as such a small, cheap, low-power, home-made battery-backed power-pack using a few dollars of components could well save the day despite the clear limitations we can all see.
There are certainly cycle limits there with lithium being the storage device as pointed out above, however those cells are a few dollars, and it would still be a cheap entry point when their village’s power fails.
While not a device for most people’s use it’s a nice case design and the components look to be easily obtained and quite cost reasonable.
It’s a great idea. I hope it keeps them online during an outage. I hope to see more projects or even products like this.
True inline UPS units with AC input, 5/9/12 V barrel out jacks, USB 5V and even POE have been available for a while; $36 for 20000 mAh claimed; mine cost $30 for 10000 mAh.
What this design does bring to the table is using an external battery.
All modems I’ve come across have a sizable brick to power them.
WiFi might be lower power but those modems are not in my experience.
That thing in the image above would power those very very shortly.
I was thinking about something similar recently. My router runs at about 10W average, each 18650 stores about 3500Mah at 3.7V or about 10Wh, so 3 of them would keep a router alive for 3 hours max, maybe long enough for electricity to return. I considered an old Android phone running as a hot-spot as alternative backup, but it only works as long as the local cell phone masts stay alive (typically 1-2 hours).
Buy an old APC ups. Drop in a 12v lifepo4 battery replacement. Done.
I’ve bought some similar solution off of Amazon, after the country-wide blackout last April in Spain. ISP had backup generators, surely, and my home internet connection is done via optic fibre, so in theory I should have been able to keep my Internet working. However, since I had no way of powering my router, I was screwed.
I love the DIY route showcased here, tough!