Programmable DC Backup Power Supply

The uninterruptible power supply was once a standard fixture in the small office/home office as a hedge against losing work when the electrons stop flowing from your AC outlet. Somewhat in decline as computing hardware shifts away from dedicated PCs toward tablets, phones and laptops, the UPS still has a lot of SOHO utility, and off-the-shelf AC units are easy to find. But if your needs run more to keeping the electrons flowing in one direction, then you might want to look at [Kedar Nimbalkar]’s programmable DC backup power system.

Built inside a recycled ATX power supply case, [Kedar]’s project is heavy on off-the-shelf components, like a laptop power supply for juice, a buck converter to charge the 12 volt sealed lead acid battery, and a boost converter to raise the output to 19.6 volts. An Arduino and an optoisolator are in charge of controlling the charging cycle and switching the UPS from charging the battery to using it when mains voltage drops.

 If you need a DC UPS but would rather skip the battery, you could try running a Raspberry Pi with electrons stashed in a supercapacitor. Or if you’ve got an aging AC UPS, why not try beefing it up with marine batteries?

[Thanks for the tip, Morris]

8 thoughts on “Programmable DC Backup Power Supply

  1. On the thread on beefing up a UPS with a marine battery I commented (it’s from back in ’09) that no one pointed out that the battery in some UPS’s is at line potential. They are meant to exist inside of a sealed case for safety!
    Somehow the post doesn’t show up, (too old?), but this is very important. They will say so on a label (CYA), measure to ground to be sure.

    1. ??The lead acid batteries are 12v dc . Often ganged into 24v dc or possibly 96v dc. I could imagine a cap in the UPS at a high voltage but as for the batteries, they are often a far cry from the 120v ac line voltage.

    1. Basic Specs:

      UC3906 3 stage charger to safely and quickly charge the battery
      USB charging (with D+/D- iCharge resistors) – keep your USB devices juiced even when mains are off
      wide input voltage range (14-24v) – suitable for use with e-waste laptop bricks or input directly from a solar panel (20w)
      Relay to switch output between mains->lm2596-12 or directly from battery
      ATtiny85 monitoring battery and cuts the relay when voltage drops below 11.4v,.. The attiny also switches the relay between mains/battery

  2. Good one Dan! This is really informative. You are right about the fact that importance of UPS is on a decline with the introduction and success of laptops, tablets, and smartphones, but it was once almost unthinkable to use a PC without a UPS, especially where there was voltage fluctuations and frequent power outages. Things may have changed, but I still consider UPS as an essential equipment as I use my router and external speakers on my good old Staticon stativolt UPS. Well, beefing it up with marine batteries won’t be a bad idea.

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