UPS vs Tiny Inverter - efficiencies?

Steven Lake
Steven Lake Solar Expert Posts: 402 ✭✭
in General Solar Power Topics #1
I'm back! :D Anyhow, I'm back and I've got another question for you guys. In the process of our family discussions the subject came up about the efficiencies of inverters, and one that nobody seemed able to agree upon was how efficient a standard APC UPS is VS an equivalently sized portable inverter (the kind you'd stick in the lighter socket on your car). I'm not thinking about the kind like we use for solar and wind power dc to ac conversion, as those are super super efficient. I'm thinking just an off the shelf office or personal use version of the two items I mentioned. In short, which is more efficient, and by how much? Many thanks on answering this as Google wasn't very helpful.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: UPS vs Tiny Inverter - efficiencies?

    Smaller UPSs are not, typically, very efficient (they assume "unlimited" utility power, and they only run 15-60 minutes during a power failure). But, you would really need measure them to prove it one way or another (using an old utility meter would be a good way--A Kill-a-Watt meter might do an OK job of estimating).

    However, by the time you throw in MSW (modified square wave) issues (less efficient for driving motor and some transformer coupled loads; can be very expensive to get accurate power meters to measure True RMS for MSW and non-sine wave power flow).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #3
    Re: UPS vs Tiny Inverter - efficiencies?

    Can you give us an idea of the intended use? I have a number of UPS units, and small inverters. I have found the $29 Vector 400W MSW inverters to be VERY efficient (>90%), and work well for CFL lighting, and other small loads. These also have a very low (parasitic) idle current. The UPS units I've measured, all have a fair amount of idle current. Not much of an issue as BB pointed out, it's feeding from the grid. The small internal battery (often a 7A 12V) doesn't have enough capacity to run much of anything for long.

    If you let us know what you're wanting to run, and how you plan on connecting the hardware, I can give you some actual numbers from a few different setups I have.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #4
    Re: UPS vs Tiny Inverter - efficiencies?

    My UPS is rated >92%, I assume that is the overall efficiency including the double conversion AC-DC-AC since it is an "online" UPS.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #5
    Re: UPS vs Tiny Inverter - efficiencies?

    you know you guys make me wonder how they figure efficiency for a modsine inverter because right off the bat the thd off of the waveform would ruin any hope of being in the 90 percentile area and maybe even in the 85 percentile area unless it's a purely resistive load.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #6
    Re: UPS vs Tiny Inverter - efficiencies?

    2manytoyz, we're not trying to power anything. It was just a friendly discussion about the efficiency difference between the two and which was the most efficient. That's all I was trying to figure out, and the answer was one of those "in general" type queries, and not device specific. Just overall mostly.

    TechnTrek, we were figuring this on a dc to ac conversion, and not with wall power. Especially since the normal inverter has no access to AC power, so the only apples to apples comparison one could rightly do is an inverter on internal battery vs a regular inverter running off battery.

    Niel, yeah, it was my assumption that UPS's were natively inefficient on battery. But that was best verified by looking at numbers, and we can't find any numbers. Again, it's not for a project. We're just trying to answer some curiosity questions that came up during a discussion. :)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: UPS vs Tiny Inverter - efficiencies?

    Since most of the small UPS units tend to be MSW inverters the same as the small inverters, it's a wash in generalized terms. Like Niel said, they aren't very efficient in DC to AC conversion. Considering the number of variations on the theme, 75% efficiency is probably more like the "low end" for MSW with 85% at the top. Not as good as a sine wave inverter, but the sine waves draw more for their own power.

    Now before anyone starts any arguments remember we're talking "in general", which is where we always have to start. Between "in general" and "specifically" there can be some pretty big changes.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #8
    Re: UPS vs Tiny Inverter - efficiencies?
    Between "in general" and "specifically" there can be some pretty big changes.
    Exactly! That's why I was saying "in general" as well. It was a general discussion, so general answers is all that's needed. :D
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #9
    Re: UPS vs Tiny Inverter - efficiencies?
    Steven Lake wrote: »
    TechnTrek, we were figuring this on a dc to ac conversion, and not with wall power. Especially since the normal inverter has no access to AC power, so the only apples to apples comparison one could rightly do is an inverter on internal battery vs a regular inverter running off battery.

    Logically mine must be higher than 92% on battery, but I've never done measurements to see.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #10
    Re: UPS vs Tiny Inverter - efficiencies?

    Ya know, another way to answer this question might be to simply take a generic UPS, and a generic inverter (off the shelf, use in car lighter style) and connect them to identical batteries. Then connect them both to the same load and time how long they last until they shut off, since both will have a 10.5v cutoff for the battery. Or at least they're "supposed to", given the standard for inverter operation. Anyhow, just throwing an idea into the meat grinder. :)
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #11
    Re: UPS vs Tiny Inverter - efficiencies?

    Mine cuts off above that.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #12
    Re: UPS vs Tiny Inverter - efficiencies?

    What does yours cut off at? The two portable inverters I have are rated to cut off at 10.5v. Not sure what the UPS would cut off at, but I figured it'd be close to that as well.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #13
    Re: UPS vs Tiny Inverter - efficiencies?

    I'll have to find the sheet I wrote my notes on when I was testing the big unit. I would have to do a full discharge test to find the number for the smaller one. I've only taken it down to the equivalent of 12.2 volts (195.2), not a full discharge.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • 2manytoyz
    2manytoyz Solar Expert Posts: 373 ✭✭✭
    #14
    Re: UPS vs Tiny Inverter - efficiencies?

    Here's why I used a Vector 400W MSW inverter for lighting at my last house:

    No load current: < 0.4 Amps
    Full load efficiency: 90%
    1/3 load efficiency: 95%

    A quick test setup:

    inverterwide.jpg

    dscn3318.jpg

    dscn3329.jpg

    dscn3310.jpg

    So a 12V battery, powering two 20W bulbs, took 3.4A. So somewhere around 88-92% efficient, depending on the actual battery voltage (probably between 12 and 12.5 at the time - wasn't fully charged). Granted, I didn't measure "actual" power output, but have measured these bulbs with a Kill-A-Watt when plugged into the grid, and pretty close to the rating once warmed up.
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  • Steven Lake
    Steven Lake Solar Expert Posts: 402 ✭✭
    #15
    Re: UPS vs Tiny Inverter - efficiencies?

    Just a quick side question. (sorry, been gone a while doing other stuff and just got back to this) Given your efficiency rating + the 7ah of the battery + your load, how long would your two lights run on battery before the inverter would kick out? Again, it's a dumb question, but one I figured to ask.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #16
    Re: UPS vs Tiny Inverter - efficiencies?

    i'll take a stab at this with a rough guess of about a half hour to 45 minutes to kill the battery.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #17
    Re: UPS vs Tiny Inverter - efficiencies?
    Steven Lake wrote: »
    What does yours cut off at?

    Turns out mine does cut out at 10.5 volts (or the equivalent of it, in my case 168 volts).
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #18
    Re: UPS vs Tiny Inverter - efficiencies?

    Charlii65,

    What kind of inverter do you have? MSW inverters can have about 1/2 the "wasted" power of a TSW inverter (simpler/fewer switching elements).

    However, many loads (like motors and some power supplies) can use upwards of 20% more power because of the issues of MSW (Modified Square Wave) form (AC power is a fundamental 60 Hz sine wave--and the higher frequencies that are components of the MSW waveform are not used for the work--i.e., a motor cannot use the higher frequencies, and many transformers will create "circulating current" in the metal frame of the transformer).



    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • bmet
    bmet Solar Expert Posts: 630 ✭✭
    #19
    Re: UPS vs Tiny Inverter - efficiencies?

    With the right type of MR16 lamp, your load would only be 0.4 mA (per lamp). I purchased a low-voltage 12VAC MR16 lamp used for garden lighting. It draws 4 watts, and is brighter than a 10W Halogen. I'm going to look at the box for the exact info. As an experiment I connected it to 12V battery, inline with a 2A fastblow fuse and standard AC light switch. Switched-on it only draws 345mA of DC current, and I use it to light my storage shed. Save my inverter for the box fan.

    ,
    2manytoyz wrote: »
    Here's why I used a Vector 400W MSW inverter for lighting at my last house:

    No load current: < 0.4 Amps
    Full load efficiency: 90%
    1/3 load efficiency: 95%

    A quick test setup:

    inverterwide.jpg

    dscn3318.jpg

    dscn3329.jpg

    dscn3310.jpg

    So a 12V battery, powering two 20W bulbs, took 3.4A. So somewhere around 88-92% efficient, depending on the actual battery voltage (probably between 12 and 12.5 at the time - wasn't fully charged). Granted, I didn't measure "actual" power output, but have measured these bulbs with a Kill-A-Watt when plugged into the grid, and pretty close to the rating once warmed up.
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