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Thread: Question about SF750 hold up time and using a UPS

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    Quote Originally Posted by ashiekh View Post
    Did you have a sine-wave UPS in mind? there are also zero switch over time (on-line) UPS units.

    For me the problem is the recurring cost of batteries every few years; one thing I tried was to run a UPS on super capacitors
    https://www.instructables.com/id/Con...er-Capacitors/

    As well as an attempt to extend the life of lead acid batteries
    https://www.instructables.com/id/Rev...cid-Batteries/

    One might consider using lithium batteries instead of lead acid

    In the end I just invested in a lot of premium surge protectors.
    Sorry for my late reply. Crazy working weeks these ones after we have come out from the lock-down here.


    Interesting...specially the capacitor batteries. But aren't they risky? A capacitor, if damaged for some reason, can explode...and if they are big, they can make a hell of a BAM!

    The lithium batteries..would they be worth the expense? And what about efficiency?

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    Not sure efficiency is really an issue given that they are rarely used; I'd get them just for the longer life.

    The capacitors I used are really big (2600F each) but the pack can only hold up a computer for a few minutes; more than enough for power glitches.
    Last edited by ashiekh; 05-24-2020 at 08:58 PM.

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    Quote Originally Posted by ashiekh View Post
    Not sure efficiency is really an issue given that they are rarely used; I'd get them just for the longer life.

    The capacitors I used are really big (2600F each) but the pack can only hold up a computer for a few minutes; more than enough for power glitches.
    Ah yes, capacitors are good for filter power glitches, so using a big pack of them does filler for sure a power glitch from the source.

    Is it possible for them (or a circuit applied to them) to deliver the source power (110V or 230V) at constant voltage, and then turn off/drop current all together, so not to decrease voltage and maybe deliver insufficient power to a computer, for example?

    And also, is there a way to calculate the dimension/number of capacitor to adopt if knowing the seconds needed to keep it up at constant voltage and wattage needed?

    Thanks.

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    Quote Originally Posted by PIRATA! View Post
    Is it possible for them (or a circuit applied to them) to deliver the source power (110V or 230V) at constant voltage, and then turn off/drop current all together, so not to decrease voltage and maybe deliver insufficient power to a computer, for example?

    And also, is there a way to calculate the dimension/number of capacitor to adopt if knowing the seconds needed to keep it up at constant voltage and wattage needed?

    Thanks.
    One puts them in a UPS in place of the battery and the UPS takes care of everything.

    The calculation is easy as the energy is 0.5 C V^2 and one can assume the UPS has access to about half of this. In my case I have 6 2600F capacitors in series, so the pack is about 433F, so

    P x T = 0.25 C V^2

    V ~ 14V so 100W can be delivered for 212 seconds (about 3 and 1/2 minutes)

    After UPS and power supply losses this might be 2 minutes; since I only need a few seconds to cover power glitches it would cover most any power consumption.

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    Quote Originally Posted by ashiekh View Post
    One puts them in a UPS in place of the battery and the UPS takes care of everything.

    The calculation is easy as the energy is 0.5 C V^2 and one can assume the UPS has access to about half of this. In my case I have 6 2600F capacitors in series, so the pack is about 433F, so

    P x T = 0.25 C V^2

    V ~ 14V so 100W can be delivered for 212 seconds (about 3 and 1/2 minutes)

    After UPS and power supply losses this might be 2 minutes; since I only need a few seconds to cover power glitches it would cover most any power consumption.
    Regarding your calculus, I think I might be too beginner in electrical laws

    First of all, lets say I have an UPS that has:

    Nominal power (VA) 1500
    Active power (W) 900
    Input/Output voltage 230 V
    Battery range type/voltage 12 V, 9 Ah

    Considering that 3 minutes are quite ok for me as well, could you use these parameters so to go through your exposed formula?


    EDIT: Just added batteries info.

    Thanks!

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    Well if 100W is sustained for 2 mins; 400W will be a quarter of the time or half a minute; 800W for a quarter of a minute; enough for glitches but maybe not enough time to shut down.

    Lets compare this to your 12V 9Ah battery

    P = I V

    so your battery could hold about 50W for an hour (assuming half losses) or 800W for about 4 mins; so about 16 times longer than the capacitor bank. then again I think your battery would be unhappy at such a load, while the super capacitors would have no problem.
    Last edited by ashiekh; 05-24-2020 at 10:07 PM.

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    Quote Originally Posted by ashiekh View Post
    One puts them in a UPS in place of the battery and the UPS takes care of everything.

    The calculation is easy as the energy is 0.5 C V^2 and one can assume the UPS has access to about half of this. In my case I have 6 2600F capacitors in series, so the pack is about 433F, so

    P x T = 0.25 C V^2

    V ~ 14V so 100W can be delivered for 212 seconds (about 3 and 1/2 minutes)

    After UPS and power supply losses this might be 2 minutes; since I only need a few seconds to cover power glitches it would cover most any power consumption.
    Here in NJ the power outages are measured in hours.
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    Quote Originally Posted by ashiekh View Post
    Well if 100W is sustained for 2 mins; 400W will be a quarter of the time or half a minute; 800W for a quarter of a minute; enough for glitches but maybe not enough time to shut down.

    Lets compare this to your 12V 9Ah battery

    P = I V

    so your battery could hold about 50W for an hour (assuming half losses) or 800W for about 4 mins; so about 16 times longer than the capacitor bank. then again I think your battery would be unhappy at such a load, while the super capacitors would have no problem.
    The capacitors you say would have no problem, but would last too less..right?

    Anyway to place different capacitors or a higher number of them so to have a decent time available, like if I was using batteries?

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    Back when I used my computers more I had a separate UPS for each machine and the router. It's been years, now; time enough for all but the router batteries to age out. The last hours-long power outage we had, my daughters' phones had nary a glitch. So, from this, I conclude that lead-acid batteries can power a low-power device a long time, and do it for a long time. Of course, if all you want to do is have a comfortable margin for an orderly shutdown, you can go with a lithium battery; but years ago I had a telework setup where it would have been bad to close a session before it was finished. A UPS with lead-acid batteries allowed me to get through uninterruptible sessions.
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    Quote Originally Posted by PIRATA! View Post
    The capacitors you say would have no problem, but would last too less..right?

    Anyway to place different capacitors or a higher number of them so to have a decent time available, like if I was using batteries?

    The super-capacitors should have no problem with the high load, although I don't know how long they last. One needs to know what one is doing as an over-voltage would destroy them; pictured is a 6 bank than can take the UPS charging voltage (they are in series). In theory they need balancing, although I found that not necessary.

    This is not just a plug and play project and best not done if one is not comfortable with electronics.

    Just designing and making the wooden carrier was a long task (I was foolish enough to make it of oak); it is glued and cannot be disassembled, but the design is such that the capacitors can still be removed.


    A lithium (12V 10AH) might be 20A max (continuous) and so only good for say 200W
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    Last edited by ashiekh; 05-25-2020 at 09:40 AM.

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