Standby current draw of UPS

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telljf
telljf Registered Users Posts: 26 ✭✭
in Grid Tie and Grid Interactive Systems #1
My UPS (1000VA pure sine wave) draws 3.2A from battery in standby mode. That means it draws 3.2A just to keep it running even when no AC load is connected! At 3.2A over a 24hr period that would be about 75AH. That is about the generating capacity of my panels. So even if no load is supported, it will drain the battery back to its original state in 24hrs. Is such a current draw typical on other solar power inverters/UPS? I am interested in knowing what your system shows?

Thanks.
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  • Brianellul
    Brianellul Solar Expert Posts: 95 ✭✭
    #2
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    Re: Standby current draw of UPS
    telljf wrote: »
    My UPS (1000VA pure sine wave) draws 3.2A from battery in standby mode. That means it draws 3.2A just to keep it running even when no AC load is connected! At 3.2A over a 24hr period that would be about 75AH. That is about the generating capacity of my panels. So even if no load is supported, it will drain the battery back to its original state in 24hrs. Is such a current draw typical on other solar power inverters/UPS? I am interested in knowing what your system shows?

    Thanks.

    I'm currently using a BEST FORTRESS 600VA UPS. It draws slightly less than 1 amp at 24v when idle.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #3
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    Re: Standby current draw of UPS

    One possible problem with using UPSs is they aren't always the highest efficiency - or have the lowest idle draw. A few extra amps here and there isn't a big deal when they are operating from AC (for most UPS users, not people on this forum), and they are only expected to run between a few minutes to an hour or two when they operated from their DC source. So a few extra amps doesn't make much of a difference there, either.

    This isn't always true, you have to do a lot of extra investigation when you decide to use a UPS as an off-grid inverter. The first consideration is if it will do a "cold start" ("black start"), where it will start up from its DC source. Some don't, like my Liebert. APCs usually do IF you know exactly how to start it - you can't just push the "on" button. Many modern UPSs operate in the 92%-95% efficiency range, comparable to decent inverters, but some companies like APC won't hand out their efficiency curves so you may have to run your own tests to be sure. Another problem is most pure-sinewave UPSs require odd DC voltages like 96/192/384, with the standard 12/24/48 volts usually only used in small modified-sinewave units. It can be hard figuring out what they really need w/o testing one in person - I thought my latest purchase used 192 volts but really it uses 4 strings of 96 each to start and once running it needs 2 strings of 192 in series (384 total).
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • telljf
    telljf Registered Users Posts: 26 ✭✭
    #4
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    Re: Standby current draw of UPS

    I just found the specification of Magnum MS4024 24V inverter, and the no load current draw is given as 0.6A DC!

    Mine is also 24V system, has the cold start option and also has the option to charge from the mains. I think this last option adds some additional circuitry that eats up all this charge? I don't need charging from the mains.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #5
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    Re: Standby current draw of UPS

    You just touched on another possible problem when using UPSs. They are designed to charge gel-cell lead-acid batteries, which require a slightly lower charge voltage to prevent them from venting. If you convert to flooded lead-acid batteries (as I did), you often can't adjust the charge voltage of the built-in charger. Some APCs will let you do it via the serial cable connection and its PROG mode, some of them you must adjust a specific resistor value on the motherboard.

    The best way around it is to add a good external charger. Since it will want to charge to a higher voltage it will override the internal charger, but there is no way to completely kill the internal charger.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • System2
    System2 Posts: 6,290 admin
    #6
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    Re: Standby current draw of UPS

    Hi Gang! bussbar here AKA John W. Im not really too new to off grid solar, I started 20+ years ago using a Arco solar 16-2000 panel and a old car battery, this to power house lights at night. any way times got better and the arco was put away, till last month, we heat with wood and have to use a fan to keep the heat exchanger cool, last winter the power went out and we almost burned down the house! we have a gen but with all the wind and rain it would not start! so out comes the arco, and a APC 1000w UPS. we are using 2 100Ahr deep cycle batterys. as for the UPS, it charges the batterys just fine! and when the grid dies it covers the loss and at idal it draws less than a amp and a 100ahr battery that is a safe 24hrs. anyway I m on a mission to keep more Kwh's on the grid and out of my house! so far the basment is all LED 40W bulbs and the kitchen and living room. I now have 300Watts of panels (this includes my pet ARCO! i will be using a Coleman Air controler kit(mods installed) and a LOGO! PLC to keep things in order. a pc running vbasic to take care of the book keeping( amps,watts,time, and to snitch on the PLC!
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #7
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    Re: Standby current draw of UPS

    Sure, it will charge them but it will undercharge them. Thus the need for an external charger.
    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 ✭✭✭✭
    #8
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    Re: Standby current draw of UPS
    techntrek wrote: »
    You just touched on another possible problem when using UPSs. They are designed to charge gel-cell lead-acid batteries, which require a slightly lower charge voltage to prevent them from venting. If you convert to flooded lead-acid batteries (as I did), you often can't adjust the charge voltage of the built-in charger. Some APCs will let you do it via the serial cable connection and its PROG mode, some of them you must adjust a specific resistor value on the motherboard.

    The best way around it is to add a good external charger. Since it will want to charge to a higher voltage it will override the internal charger, but there is no way to completely kill the internal charger.

    actually none of mine are made for gel batteries as mine came with agm 7a batteries. i have quite a few of the internet office 500s and another off brand ups. i am facing the usual demise of these small batteries every 1.5yrs to 2yrs and these aren't cheap. i'm trying to tap onto my magnum to back up some of these circuits, but there are too many items needing backup with being remote of each other and of the magnum's circuits. efficiency wise it is true the magnum might see about a 20w or so draw if greater than the 5w for search mode, but that's far better than all of these little back ups added together.:roll: as with most of us, it's a work in progress and i fear i might outgrow my inverter's capacity, not to mention my batteries' capacity.:cry:;)
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #9
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    Re: Standby current draw of UPS

    As far as I know most UPS batteries are gel-cell and not AGM due to cost constraints, although both are valve-regulated so from the outside they will look the same.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • arghhh
    arghhh Registered Users Posts: 18 ✭
    #10
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    Re: Standby current draw of UPS
    techntrek wrote: »
    As far as I know most UPS batteries are gel-cell and not AGM due to cost constraints, although both are valve-regulated so from the outside they will look the same.

    They are all AGM. I can also tell you acid can come out of them if you stress the hard enough.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #11
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    Re: Standby current draw of UPS

    No, they are not all AGM. The 128 that I pulled out of my first large UPS when I bought it were gel-cell (looked up their model number when I was considering replacement options). Same for the ones in my 2nd large UPS. Search the net for "ups battery agm" and "ups battery gel" and you'll get lots of hits on both.

    There is no logical reason for manufacturers to use AGMs in UPSs all the time. They are more expensive and there is no physical advantage over gel-cell. Both are unspillable and maintenance-free.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • arghhh
    arghhh Registered Users Posts: 18 ✭
    #12
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    Re: Standby current draw of UPS

    As far as large UPS are you taking about 40+ kVA or 5-6kVA? All the C&D, Enersys, CSB, Powerware/Eaton, Power (before they tanked) are all the AGM type in the 200+ watt per cell. The issue is heat as well, gels heal up more during charge and discharge than an AGM. When you are discharging up to 2.5KW per battery at a 5 minute rate then immediately recharging at c/5 you can quickly overheat the batteries. AGM also have much higher charge rates, Enersys actually specs unlimited current for their UPS batteries.

    In the end expense is not really a factor of UPS batteries, run time and reliability are.

    http://www.enersysreservepower.com/documents/US-HX-RS-011_0309.pdf
    http://www.cdstandbypower.com/application/battery/ups/upshrm.html
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #13
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    Re: Standby current draw of UPS

    Yeah, the very large UPSs use full-sized batteries and I can see them being AGM. But you need to go back and read the OP's post to see what size UPS we are talking about here. He's talking 1 kva, I'm talking units below 20 kva. Gel-cell bricks, not full-sized batteries.
    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 ✭✭✭✭
    #14
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    Re: Standby current draw of UPS

    guys,
    i know there are some ups out there that have gel and some take agms, but nobody can say it is normally one or the other. a look at one battery replacement outfit shows that they have both types of batteries as shown on the left hand column under chemistry, all depending upon the ups model i would assume.
    http://www.apexbattery.com/ups-batteries-apc-ups-batteries-ups-batteries.html
    even a call to places that have replacement batteries like batteries plus could answer the question of the type you may require and maybe even elaborate on which is used most often.

    the argument of gel or agm is somewhat moot here. it is sidetracking the op with the argument if all are one way or another.
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