UPS and car battery, how to power up your emergency supply




UPDATE: there is a new article that expands and powers up this idea, you find it here.

For a while an old UPS of mine was abandoned in a corner because its battery was long dead and didn’t sustain the load of a PC for even a few seconds; and for a while I’ve been telling myself I needed to buy a spare battery off ebay or something, but never got around it because the prices were less than inviting; in the meantime, my little home server kept dying at each and every blackout or brownout.

The other day I noticed a car battery lying at home; we actually have a few car batteries here, unneeded but we keep them for the sake of it; none of them is new and they have been taken off old dismissed cars, they still work though.

car battery

When I saw this boulder I thought I may very well check if it was up and running, and hook it up to my abandoned UPS

Going by the theory, it’s still a 12V lead battery, so it should perfectly work with a normal computer UPS, yet I digged for information around several websites, and actually there weren’t any particular warnings (on the contrary, car batteries are made to sustain intense but short drains, followed by frequent charging, and that’s exactly the way an UPS is mostly used), but on the other hand, there could be, maybe, a little risk of production of toxic vapours, due to the acid contained in the battery; in other words, no problem whatsoever, but it’s recommended the setup be put inside an isolated, or well aired room; in the worst of cases you can keep the UPS by the PC, and use cables long enough to place the battery elsewhere; in this case the room I needed it into was quite isolated, so no problem at all.

After removing the old battery, I connected a couple of cables to the connectors (they should be thick enough), and I isolated everything with a hot melt glue gun (man's best friend)
ups battery cables outlet

I chose to make the cables come out of the front of the UPS, since the back was crammed with 220V outlets, so I made a little hole with a dremel and fixed everything with hot glue
car battery homemade contacts

I used a metal strip to fold into a couple of ring springs to connect to the end of the cables, isolated them with melt glue, and they fitted perfectly onto the battery poles
ups car battery setup

This is the final look of my own setup; the size of the UPS is roughly the same as the battery, so they fit together quite well; I could have found way longer cables (home AC cables are perfectly fine) to accomodate the battery farther away from the UPS, either in another room, or even outside

This setup has been tested to work perfectly, removing the plug activated the switch to battery power seamlessly, and I tested it for about one minute; I don’t know how long it could last, but probably could reach 30 or even 60 minutes, I didn’t test it thoroughly because I don’t really care, blackouts and brownouts last very short over here, and I don’t want to stress the battery for no particular reason, reducing its operative life.

A detail to note: when I wired the battery only, in a test setup, I couldn’t turn on the UPS, and I started thinking I failed somewhere, or even the UPS died for some reason, but it was just a coincidence, because my particular model of UPS is silly enough to refuse turning on if you try doing it without external power, in other words I needed to attach it to the mains plug as well, and I turned it on no problem.

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8 thoughts on “UPS and car battery, how to power up your emergency supply”

  1. ok nice but wery stupid
    1 very thin wires user thich ones more than the ups original ones
    2 make SOLID conexions not that crap whith glue
    3 you need to put bigger radiators on the moss-fet`s in the ups or they whill blow

    you need to understand that the ups, in your case a crap ups is made to work for a fiew minutes not an hour , it needs some modifications and never go abowe 60 % or so capacity
    TRUST ME Y DO THESE FOR A LIVING TONT PLAY WHITH THSE OR YOU WILL SEE SMOKE AND FIRE AND SOME DEATH TO
    DONT BE OFFENDED YM TRIING NOT TO SET YOU HOMLESS OR KILLED
    IF YOU REALLY WHANT THESE, BUY AN INVERTERA QUALITY ONE OR AN EBAY USED APC UPS(METAL CASE PREFERABLY AND SMART TIPE TO) AND GO WHITH THAT , ON THE BATTERY POSTS USE AUTOMOTIVE GRADE CONECTORS AND INSERT N FUSE IN LINE 10 TIMES THE AMPS OF THE UPS ORIGINAL BATTERY , YOU CAND PUTE FUSES IN PARALEL BUT BE THE SAME RATINGS EXAMPLE 7 AMP BATTERY YOU WILL USE 70 AMP FUSES SO YOU CAN USE 2 40 AMPS ONES , YOU WILL GET 80 AMP BUT WILL BE OK THE SHORT CURENT OF THE CARR BATERY WILL BLOW THESE UP IN THE CASE OF SOMETING IS RONG THE FUSES IS FOR PROTECTING THE BATTERY AND YOU FROM FIRE PUTT THEM ON THE + LINE OF THE BATTERY VERY NEAR TO THE BATTERY POST
    GOOD LUCK AND HAVE A NICE DAY

  2. Thank you for your very “passionate” comment 😀
    I respect your preparation in this matter, I am no expert myself, excluding the high school theoretics.
    Yes, that UPS is not an APC, still Liebert is not a crappy brand IMHO, but anyway, why do you say I would need to prepare for higher currents?
    The source is surely capable of higher power outputs than a simple UPS battery, but the voltage is still 12V, and the drain is the same it is requested from a UPS battery, because there’s still a PC on the receiving end; the car battery just gives more juice in terms of autonomy.
    So well, a lower rating fuse should be an even higher safety in case something goes wrong.
    By the way, the cables I used were taken from 220V appliances, so they are thinner than the UPS own ones, yet I don’t think it’s a safety hole…
    In any way readers:
    PLEASE DO ALL THESE MODIFICATIONS ON YOUR OWN RESPONSIBILITY, I CANNOT BE HELD RESPONSIBLE FOR ANY HARM THAT MAY COME FROM MODIFYING YOUR UPS

    Should have added this notice in the article 😉

    1. Woah, you definitely convinced me 😛
      I will need to reconsider the connections I made; the battery is already in a relatively safe place, nothing that can easily catch fire nearby, yet I will need to add a good deal of copper to the equation; I appreciated very much the sodium bicarbonate suggestion on that page you linked 😉
      Since I don’t own cables so large, I will resort to use several 220v cables in parallel, which should be good enough anyway.
      Too bad I don’t have proper car battery wrenches laying around.
      To my defense anyway, my system actually is a low power setup, 80W average, and plan to make it even lower since I am buying greener components, so the amps are not THAT many.

  3. hanno ragione , con quei cavi a malappena reggi 10 ampere , probabilmente non prende fuoco nulla perché la caduta di tensione sarà tale che l’ups pensa che è scarica la batteria , però è sempre rischioso e inutile oltretutto
    la batteria deve stare il più vicino possibile all’ups , se non vuoi avercela nella stanza , metti anche l’ups fuori della stanza e porta dentro solo i cavi a 220 volt e al max il pulsante di accensione

  4. ops sorry , i thought page was in italian 😀 , i mean : they are right , with these cable you won’t be able even to use 10 amps , it won’t catch on fire cause the voltage will drop so low that ups thinks battery is gone, intead put the ups near the battery and wire only power on button and 230 vac wires 🙂

    (drop my previous comment)

    1. Non ti preoccupare, la pagina è in entrambe le lingue, è il plugin bilingue di wordpress che dopo l’invio del commento ti rimanda automaticamente sempre alla pagina inglese.
      Comunque come vedi su entrambe le versioni compaiono sempre i commenti in entrambe le lingue 😀

      By the way, this goes to you and all the other readers/commenters… I have not done extensive tests on this, I just want to put in here a simple consideration: take into account the Pico-PSU products, those are rated to power up to 160Watts worth of PC, which means, with an efficiency of 95%, they draw at that power, and at 12V, 14 amperes from the 12V external power adapter. Now, it doesn’t seem to me PicoPSU’s power input cable is that thick…

      And by the way, in the case of my setup, which is a home server geared to have the least possible power consumption (~60W right now with all external stuff and a plain, super-unefficient 350W ATX PSU… I aim at ~40W for when I’ll finally get a switching 12V PSU and an 80W picopsu I’ve ordered), so the amperage we’re talking about here is 5 or less… quite safe for normal 220V appliances cables 🙂

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