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Turn a small home UPS into a giant UPS (video)

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Having a UPS is fairly common these days. However, one gripe I’ve always had and that you might too is the limited capacity you get on them. Even nicer $200+ ones might only give you a few minutes on a powerful PC, and for large capacity you could easily spend $1000 or more. Neither option was good for me. So I decided to make a better one myself.

To start with, I purchased 3 “Ultra” brand UPSs about a year ago. They are completely silent, small, and functional. Cheap, yes, but functional. However, with my machine on one of them, it only lasts around 3 minutes before powering off. This might be enough to shut it down, but if the power is out for only 15 minutes I’d rather just ride it through. Inside the UPS were 2 small sealed lead acid batteries, like you find in most UPS units, 12V each, in series. They are the same type of battery you find in cars, trucks and boats – just smaller. Using that logic, I took some common hardware and rebuilt this UPS. I did a small bit of research to determine the proper wire size given the load. The UPS used is an Ultra 1000VA. (warning, a small bit of profanity is in the video)

The tools involved were simple. I had 20 feet of 10 Gauge wire, two ring terminals and several Male/Female disconnects. I needed wire strippers and wire crimpers for that. The UPS itself only required a screwdriver to take apart. I used a nice Dremel to bore a hole in the plastic, though realistically you could do that with a knife. For the batteries, I purchased battery boxes. It was a simple matter to remove the stock batteries, run and terminate the wire, then put the new batteries in place.

There are downsides to doing it with these batteries. Space, of course, and safety. These are standard lead-acid deep cycle batteries, meaning that they can and do release gas when discharging. For that reason, I have these batteries situated outside. To do this safely indoors, you need a well-ventilated room OR you need to use sealed batteries.

I am going to do this with the other two UPS units, too. Next time, however, several things will change. I am going to use sealed batteries, slightly more expensive but completely safe to use indoors. I will also use shorter cable lengths. I will remove the buzzer inside that makes that awful beep, and I will install a slow 80MM or perhaps 120MM fan inside, quiet but enough to bring some air over the unit in case sustained operation heats it up too much.

All in all, I spent about $300, including the tools, to make a UPS with an ~80AH capacity.

Written by Julio Franco

March 2nd, 2008 at 2:06 am

7 Comments so far

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  1. The UPS you mod _must_ have a fan
    The limited runtime is calculated so that the inverter does not
    overheat, if the inverters heatsinks are not cooled it will
    overheat and cause damage to the UPS

    Also the same is true for the carging circuit, it might not be able to properly charge 80 amp batteries without overloading itself

    It’s better to mod a UPS that it made with external battery packs in mind from the beginning, then you are 100% sure that it will be safe

    Oh, and a RAID-0 is never safe, not ever ever ever :D

    Per Hansson

    2 Mar 08 at 3:33 am

  2. How long does it take to recharge the batteries now using the small UPS? Can it really charge the battery to full potential? Just curious.


    5 Mar 08 at 9:56 am

  3. You should not charge non-sealed lead acid batteries indoors, as they can give off toxic fumes. This is something your girlfriend will be pissed about, let alone being woken up at 3am in the morning to a beeping UPS.

    You should be using sealed lead acid batteries, or AGM batteries, which are designed to be charged safely indoors and do not give off these fumes. These are available from marine stores as they are used for powering electric motors used for trolling.


    6 Mar 08 at 5:54 am

  4. This is really a cool trick. It’s a must for our types of countries where power outage is for hours, not minutes. I’ll try it out with my own UPS.


    19 May 08 at 1:56 am

  5. I’ve also some something similar before with sealed batteries. The problem is about about 30mins some components got so hot they de-soldered themsleves and the UPS died. You could add fans, but in reality I’d say dont mod the smallest ups u can buy. Go for something thats already near the 1kw range for safer prolonged use.

    The batteries will charge just fine, it just takes longer. Infact a charge at a lower amp rating is actually better than a fast charge with massive current.


    31 Jan 09 at 12:38 am

  6. ive also experienced de soldered diodes and a burst capacitor with modded ups,i used N40 electron lead acid cell…


    21 Feb 10 at 6:21 am

  7. hi i’ve same problem with my Belkin F6C1500TWRK 1500VA ups it also have 2 seald lead batteries each is 12 v 7.0 ah would u tell me what kind of battery i should use for a better backup cuz some one told me to use two 50amp battery for it if i can use it then what should i do what kind of fan i should use for my ups


    4 Jun 10 at 4:47 pm

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