Using a 12.8v lifepo4 battery as a UPS for my network router

Thread Starter

zirconx

Joined Mar 10, 2010
171
Hi, I'm trying to make a DC backup power system for my networking equipment. Yes I could just buy a traditional UPS designed for this purpose, but 1) that is more expensive 2) they beep annoyingly when the power goes out, waking me up at night 3) I don't like powering my equipment with a modified sine wave 4) I can get longer run times by using a battery directly. And unlike the AGM batteries that come in a UPS, this lifepo4 battery will probably outlast this project.

I also like using a lifepo4 battery because the BMS will turn itself off when the battery is discharged. Where as if I used an AGM battery directly, if the power is out for more than a few hours the devices could drain the battery low enough to damage it.

I'm attaching a simple diagram of what I am thinking. I'll use an old laptop power supply to provide 19v to a CC/CV buck module set to 14.2v and probably 4-5amps.

That 14.2v line will charge the battery as well as directly power my cellular router/modem, which can run on 10-15v.

That 14.2v line will also power a boost module that will produce the 19v necessary for my Asus home router.

Do you see any major problems with this plan?

I did a bench test using a 12v light bulb as a load connected to a 6ah lifepo4 12.8v battery. In parallel I connected my bench power supply, which I had set to 14.2v and a max current of 4A. Everything seemed to work fine - I could disconnect the power supply and the battery would power the light until the battery's internal BMS turned off at 10v. Then I turned on my bench power supply. It provided 4A until the voltage started getting near 14v, at which point the current started to taper down, until the only current flowing was going to the lamp.

The only potential problem I see is depending on the size of the battery I use, I need to make sure to size the CC/CV module appropriately. So that when the battery is completely dead and being recharged, it doesn't cause too much of a voltage drop.

Thanks for your insight.
 

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