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DIY UPS project

Discussion in 'General Electronics Discussion' started by Mevuxatrox, Nov 1, 2015.

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  1. Mevuxatrox


    Nov 1, 2015
    Hello everyone!

    I have a problem that's been on my mind for a while now and i haven't been able to
    find a reliable solution to my needs so far. Thus, i have decided to ask for help on
    various forums to see if there is anyone with the skill and experience who could provide
    solid instructions or advice on how to achieve what needs to be achieved.
    (I apologize in advance for my limited english skills, I am not a native speaker.)

    To make things a bit easier, let's say hypothetically that i need to build a miniature
    bomb shelter (I'm not building a bomb shelter but we can all blissfully pretend i will).
    In this construction, i need to have a fan and 4 lightbulbs connected to some sort of
    UPS unit, battery bank, inverter or something which will be able to provide power
    for a minimum of 2 hours straight in case of a power shortage.
    People will be living in the bombshelter so risk of fire or release of harmful gases
    has to be minimized.

    The fan will be running at 40W, 220/230 Volt, 0.21A.
    The lights will be 4 x 8W CFL bulbs.

    My hopes are to be able to build an arrangement like this on a tight budget as possible
    while having it run safely with minimized risk of fire or release of hazardous gases etc.
    So i presume an offline setup would be the best?
    My plan was to get an old UPS unit and daisychaining external hobby/motorcycle batteries
    to lengthen the back-up runtime to a minimum of 2 hours.
    So far what i think i have figured out is that deep cycle discharge batteries (gelcells?)
    would be the best since they release no gases (unless i've misinterpreted this info).
    What worries me is how to get the right Voltage and amps to run both fan and lights
    without blowing eiher to smithereens.
    If i use an old UPS unit, what VA and W should i have to which batteries?
    How would this be built/assembled/connected?
    In total, power consumption in case of a power shortage will probably not exceed 100W.
    What kind of UPS could i get away with using which would be compatible with this
    output with a daisychained battery stack?
    Is there anything else which would be a better option?
    Since this isn't about computers, the switch to back-up power probably doesn't have to
    be immediate so ms's are probably of less importance unless it could fry the electronics
    in the fan or lights.
    Has anyone built something similar and what are your experiences?

    I would be very thankful if i could get any advice.
  2. AnalogKid


    Jun 10, 2015
    200 Wh is not a lot of energy, meaning that you do not need a large UPS. In terms of 12 V batteries, you need 17 Ah. Unless you have a lot of ups component parts laying around, you probably cannot build this UPS for less than you can buy one.

    If you have an old UPS unit, then you need whatever batteries that unit is designed for. Modifying it to suite available batteries will be much more work and expense than getting the right batteries or the controller. With the right batteries, the old UPS unit will make the right output voltage and not blow up your stuff. Increasing the battery size/count to give a small UPS a longer holdup time is not difficult.

  3. duke37


    Jan 9, 2011
    You will need considerable battery size and will probably want to run at low voltage.
    To minimise battery drain, run the fan and lights on low voltage also. This will not waste energy transforming back to a high voltage.
    You can get 12V fans and 12V leds.
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