UPS connected with Inverter: Safe?

Discussion in 'General Electronics Chat' started by Aamer7, Apr 23, 2012.

  1. Aamer7

    Thread Starter New Member

    Apr 23, 2012
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    Hello people,

    I was wondering, is it safe to connect a 650W UPS with a 2KV Inverter, would it have any side effects on the Inverter, its batteries or something else?

    The reason why I am trying to create such a connection is, that my PC either restarts or freezes every time the power from the grid goes out and the inverter goes on backup (running on two 12 volt, 120 amp deep cycle batteries connected in series). The inverter works brilliantly, apart from the PC issue.

    My PC is not a very heavy gaming rig, and I have a Cooler Master 460W power supply which comes with a 17ms holdup time. Seems like this hold time is not sufficient to accommodate the inverter switching to backup mode.

    The answers I am searching for are:

    1. is this set up safe:

    GRID-->INVERTER(2KV)-->UPS(650W)-->PC​

    2. Would the set up above have any side effects on the batteries? The darn things are bloody expensive!

    3. Would the set up have any side effects on the UPS or the computer?

    Apart from this, is there anything else I should be cautious about with the set up?

    This is my first post on a forum, so I do apologize if my formatting or wording is not up to standards :) I would really appreciate your guidance and kindness in helping me establish a safe long lasting set up. Please do treat this matter as urgent.

    Thank you, very much,
    Cheers!
     
  2. paulktreg

    Distinguished Member

    Jun 2, 2008
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    Can I ask why you have an inverter?

    GRID > UPS > PC Should be all you need?
     
  3. Aamer7

    Thread Starter New Member

    Apr 23, 2012
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    paulktreg: Well, because the backup time of the UPS (10~15 mins) is not enough for my requirements. Cant have the PC off you see :)
     
  4. paulktreg

    Distinguished Member

    Jun 2, 2008
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    I take it you're in a part of the world were power cuts are regular and prolonged?

    So your inverter automatically switches from grid to batteries when you have a power cut and provides the necessary AC voltage for your UPS?

    Is your inverter output a true sine wave or a stepped square wave?
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    If I understand your problem correctly, the time it takes for your inverter to start up creates the problem with your computer, but the UPS will allow power fail without interrupting the computer but has a short run time due to its own batteries draining. Have you thought about connecting the UPS to larger batteries? A higher amp-hour rated battery would give you longer run time without compounding the efficiency losses.
     
  6. Aamer7

    Thread Starter New Member

    Apr 23, 2012
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    paulktreg: Yes, I am in Pakistan and the state of affairs here is rather sad. I am sure you must have heard about the issues on the news from time to time. To wrap it in a nut shell, the power deficit is of about 6000MW expected to climb to 8000MW, so power cuts would be more frequent in a month or two. The output of my Inverter is Modified Sine Wave.


    BillB3857: You are right about my situation; but, I am not in a position of investing another dime on this set up. Either the UPS works along with the Inverter without causing any issues to anything, or I ignore the restarts when the Inverter goes to back up :)

    By the way, I connected the UPS with the Inverter to see what happens, the UPS seems to be running well, and so does the computer. Even during power cuts, the computer stays on. But, would this have any side effects in the long run, on the batteries, the inverter or the UPS?

    Thank you for your replies folks :)
     
  7. Aamer7

    Thread Starter New Member

    Apr 23, 2012
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    By the way, still waiting for some more suggestions....
     
  8. BillB3857

    Senior Member

    Feb 28, 2009
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    The down side of running the UPS off of the inverter will be shorter battery life for the inverter. If the inverter is 90% efficient and the UPS is 90% efficient, you are only geting 90% of 90% or 81% of your battery. If, on the other hand, the UPS were to be powered directly from the battery, you would get all 90%. Is there a way you can connect the UPS to the same battery powering the inverter?
     
  9. Wendy

    Moderator

    Mar 24, 2008
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    You would be much better off with a generator. Fuel is expensive, but a UPS will not last. UPSes have a very short lifespan overall, they are meant for emergencies only, while a generator is meant to last.
     
  10. Aamer7

    Thread Starter New Member

    Apr 23, 2012
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    Okay you lost me there BillB3857 :) Let me try to understand this. You are suggesting I remove the batteries from the UPS and connect the bigger batteries (the one inverter has) with it?

    If I do that, I think there is going to be an issue. Since both the UPS and the Inverter sense battery charge level, don't you suppose there is going to be some kind of conflict in the charging process? I mean, the Inverter might sense the batteries at 100% charge, and the UPS might sense them at 90% and might keep charging?

    By "battery life" do you mean back up time? See, what can go wrong if I connect the UPS with the inverter as is? I mean the Inverter is rated at 2000Va, and the UPS is 650W only; when I connected the UPS with the Inverter, with all the other equipment on (TV, 2 Fans, the PC and a couple of light bulbs) the Inverter showed a 50%~75% load.
     
  11. Aamer7

    Thread Starter New Member

    Apr 23, 2012
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    Bill_Marsden: I believe you missed the point, the question is not about alternatives. The question is:

    Is this safe? GRID-->INVERTER(2KV)-->UPS(650W)-->PC
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    2,536
    Oh, it is safe, just get used to the concept of replacing the battery every couple of months to possibly several years, depending on how frequently it is used. My UPS is much smaller, but the more you discharge batteries (especially to discharge) the less they will last.

    I bought my UPS to clean up the power. For a while there my power company was working on the lines, and the power would go up / down / up / down indefinitely, which will kill a computer.
     
  13. Aamer7

    Thread Starter New Member

    Apr 23, 2012
    7
    0
    Does a UPS continuously charge the batteries or does it stop once the batteries are at there 100%? Because if the UPS stops charging the batteries, I don't see any reason why there would be a discharge load on the Inverter's batteries.

    My theory (I might be wrong here, that is why I am asking your professionals for an opinion), is that the UPS will charge the batteries through the Inverter. Since the UPS batteries are used for only seconds a day (during the power cuts per day) the only load on the Inverter is going to be an additional 650w for running the UPS -right?

    Here is what I did:

    GRID--> INVERTER--> [2 Energy Savers, 2 Fans, 32" TV(CRT), 22" LCD, 460w PC, 650W UPS]

    The inverter shows a load between 50%~75% and functions well, no humming in the TV or fluctuations in the lights. The PC did not show any abnormal behaviour during the switch, the UPS did switch over to its own backup only for a split second and then went on normal mode.

    Also, the backup that I would normally need from the Inverter is roughly 1~2 hours for 3~4 times a day and the batteries charge up to full capacity within 2 hours.

    Sounds good my dear Electronic Gurus, or am I making an amateur's mistake?
     
  14. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,936
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    A professional UPS charges it's batteries through a rectifier. Batteries are being maintained at floating voltage once they are charged. Power to the load is supplied via the Bypass or the inverter, failure on one branch switches to the other.

    A typical setup is:

    [​IMG]

    If I understand your setup right, you have an inverter with batteries in series with a UPS (that also has batteries).
    There should be no problem in using it this way.

    Whenever possible describe your setup better, including a schematic, and model numbers of the devices you use.
     
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  15. BillB3857

    Senior Member

    Feb 28, 2009
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    I am making an assumption that he voltage for the inverter battery is the same as the voltage for the UPS battery. If one unit senses (with AC supplied) that the battery needs charged, it will charge it. If one senses that it needs charged before the other, it will start charging and that should keep the other one from trying to charge. Does your inverter really have charging capability?
     
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