Welcome!

By registering with us, you'll be able to discuss, share and private message with other members of our community.

SignUp Now!

12v UPS for my router and modem

andre

New member
Joined
Sep 28, 2024
Messages
13
In my area there's an energy crisis and we are having 4 hour power outages 2x a day… this of course is inconvenient for the most part, as I would usually be able to work on my laptop by tethering to my phone... except... Cell service collapses as everyone switches to mobile internet.

My ISP still works though. I put a step down converter on a 6S 21Ah battery (yes, it's big as a brick), but it’s difficult having to switch the cables on the router manually 4 times a day since the router and modem are not in my apartment.

I would like to build a UPS with more available 18650 batteries, I'm thinking in a 3S2P configuration.

Off the shelf UPS's are expensive and stupid for routers, especially because they convert 12v DC to 110v AC just to convert it back to 12v DC again...

Requirements are:
Fast switching (no brownouts of router/modem)
Stable output voltage of 12V @3A
Anywhere between 4-8 units of 18650 batteries.

Automatic charging when power available.
110v input with power outage sensing.

1729125956051.png
 
You did a great job of explaining the details of what you want to accomplish - Thank you! What are the project limitations? What parts do you have access to? Do you have a budget?
 
Well, I'd like to keep it "dumb" if possible - no programming. Cheap to make. I'm ok with using premade modules, but ending up with a custom pcb designed for it would be better! Budget is under $50 for a complete unit.
 
This is similar to what i want to achieve, but I need less features and complexity. 12v 1-3A barrel connector for output is plenty.

safety-of-cheap-12v-mini-ups-v0-ijzwttpokxlc1.webp
 

SOLUTION #1: Buy One

If you want a quick fix - Amazon has a highly-rated router UPS for just $49. It’s plug-and-play, designed specifically for your networking gear, and saves you time.
https://a.co/d/j0d5mvR
I realize it may not be available in your country so I'll give you two other options as well...


SOLUTION #2: DIY UPS

Create an advanced UPS that switches power automatically without missing a beat. Stack your 18650 batteries in a 3S2P setup, hook them up with a robust 3S BMS, and add a charger with load sharing. Toss in a buck-boost converter for steady 12V output and maybe some Schottky diodes for flawless switching. Pop everything into a neat enclosure, and enjoy uninterrupted internet even when the lights go out!


SOLUTION #3: STupid Simple Solution

I don't recommend this one... Buuuut you could just use two diodes.

How It Works:

Your DIY UPS utilizes two power sources: the 12V power supply and your 18650 battery pack. To manage the flow of electricity between these sources seamlessly, Schottky diodes could be used because of their low voltage drop. Each power source is connected through its own diode—Diode D1 is linked to the 12V power supply, and Diode D2 is connected to the battery pack. When mains power is available, Diode D1 allows electricity from the power supply to flow and power your router, while Diode D2 prevents the battery from discharging back into the power supply. If the power supply fails, Diode D1 stops conducting, and Diode D2 automatically permits the battery to take over, ensuring that your router remains powered without any interruption. This setup ensures a smooth and automatic transition between power sources, keeping your internet connection stable during outages.

In this version you'll have to manually recharge your batteries after they're depleted.



If you like any of these options and need more help. Let me know!
 
Well... The one from Amazon is essentially what I'd like to end up with, but I want to HackMakeMod it, not buyBuyBuy it!

If it works good, I might make a few for friends as well.

Anyway, the 3rd option is worth discussing... what are the downsides of such simple switching? And is it a BMS away from being the same as option #2?
 
It’s awesome that you want to hack, make and mod your own UPS instead of just buying one! :)

While tinkering can sometimes save money, in this case, building a reliable and safe UPS from scratch will likely exceed your initial budget of $50, potentially costing more than $200 once you account for trial and error and the need to test different components. Additionally, even though you can make parts yourself, you’ll still need to purchase essential assembled units like a BMS, buck converter, and power supply, making the project both costly and complex. Not to mention the possibility of destroying a router during testing! :oops:

Building Solution #3 with just two diodes is a great exercise and something you can probably try with materials you already have. However, it does come with significant downsides, such as voltage drops that can affect your router’s performance, lack of battery protection which poses safety risks, and the possibility of brief power interruptions that could reset your equipment. Adding a BMS improves safety by protecting against overcharging and discharging, but it still doesn’t provide the seamless and stable power management that Solution #2 offers.

I strongly advise caution when working with lithium-ion batteries and high-current setups to avoid potential hazards like overheating or short circuits. Starting with Solution #3 will give you valuable hands-on experience and a better understanding of the components involved, which will be beneficial if you decide to move on to the more robust Solution #2.

If you choose to go with the simple diode setup or decide to build the more advanced UPS, I’m here to help you through whichever route you take. Let me know how you’d like to proceed!
 
Why not both! In order of difficulty. I have a surplus router I can test on.
 
I was able to source a power pack with a solar controller and BMS. Not sure what the condition of the cells is, we'll find out - I'm charging them now.

It seems the solar controller handles the cycling of the battery. Stops charging at a set voltage and starts charging at another set voltage.

The output of the whole thing isn't regulated - it's pretty much battery out - however it should have low voltage cutoff.

It looks like I'll have to use a Boost Buck Converter to get stable 12v from this system anyway, no?

1729449917907.png
 
It looks like I'll have to use a Boost Buck Converter to get stable 12v from this system anyway, no?
That's a great find! Regarding the buck converter... I feel pretty confident you'll get clean enough power straight off of the batteries.

Please continue to share your progress!
 
I tested the batteries and they've got some great battery life. I tested with a LED bulb which I measured at 1.36 A at 11 volts, and it worked for more than 5 hours, and didn't even reach low voltage cutoff before I had to turn it off. Switching the AC power supply on and off didn't make the light flicker so that side of things does work fine.

Battery output voltage is stable enough however the bulb sometimes flickers a bit while charging. I think it's to do with the solar charging circuit being PWM based. Maybe a capacitor will smooth it out.

The other thing I'm worried about is the voltage drop from 12 to 9 volts as it discharges. I'm not sure how the network equipment will handle the undervolting. I wish I could take them apart to investigate their power stages but I'm not able to do this. I think I'll try it with the test router and see how long it lasts.
 
Back
Top