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Daisy-chaining UPS'

Discussion in 'Electronics & Electrics' started by AEKaBeer, Oct 27, 2006.

  1. AEKaBeer

    AEKaBeer Member

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    I need to get some high power UPS units but looking at the price's I was just wonderring if I could get away with hooking up 2-4 1400VA units in a daisy chain configuration rather than forking out ~$3k for a single 5000VA unit?
     
  2. dakiller

    dakiller (Oscillating & Impeding)

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    You will increase the time that they will last (due to losses, I'd say each would add about 1/2 more time) but not the VA rating
     
  3. Sadow

    Sadow Member

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    i doubt they would even do that

    as soon as power is gone they will all switch over to battery.

    The first one loses power swiutches to battery, starts putting out a modified sine wave. Second one detects modified sine wave and switches to battery mode, etc.

    UPS's dont just protect from power failure, they protect from bad power too. THis usually includes the sort of voltage a UPS provides, as the UPS cannot differentiate between a UPS modified sine wave, and a very dodgy AC signal which could kill equipment.
     
  4. cvidler

    cvidler Member

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    APC recommend you DON'T daisy chain them.

    If you have multiple pieces of equipment to run, run them each from a sepeate UPS, you'll gain time, as each UPS is working less. If it's one piece of equipment you're going to have to buy a bigger UPS* if you want extended run time.

    *or hack in some extra batteries, but that may not work depending on the UPS.
     
  5. grimwood

    grimwood Member

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    What do you want to use it for? If it's for a single computer then get a redundant PSU and stick each input on a separate UPS. Then if one UPS goes it's not the end of the world. Daisy chaining sounds like asking for trouble to me.

    Daniel.
     
  6. OP
    OP
    AEKaBeer

    AEKaBeer Member

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    It's for a server room with 3 servers, the current UPS is on the way out and doesn't provide enough time for 2 of the servers to shut down before all power is gone.

    One UPS for each looks like the way to go.

    In regards to the clean power statement, one of my mates says that is no longer the case. He says many UPS units are active units and not passive which send the stored charge, I've never heard this before can anyone verify?
     
  7. Sadow

    Sadow Member

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    Active UPS's mean the source is always supplied from battery, and the batteries are just constantly charged when 240v supply is available.

    Passive UPS means the source is supplied from the 240V supply, when the 240v supply dies or goes crappy, the UPS quickly (milliseconds) switches to battery power.

    Most cheaper UPS's are passive. If a UPS is an active UPS, it will say explicitly that it is. Active PSU's will wear the battery out quicker.


    What your mate might have been getting at is a Pure Sine Way UPS. Which generates a voltage cleaner and more reliable than the 240v supply. These are generally much dearer and generally only higher spec models. If you daisy chained these i see no reason why they wouldnt run as dakiller suggests.
     
  8. Lespom

    Lespom Member

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    Sorry for the NOOB question, but if you connect two or more independant AC sources, like UPS's, how do you synchronise the sine waves of the output?
     
  9. Sadow

    Sadow Member

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    you dont

    If you plug a UPS into a pure sine wave UPS, which is plugged into your walsocket.

    None of the UPS's are generating AC voltages until they lose power at thier input.

    Thus, when wall socket voltage is good, all points are simply connected to this supply.

    If the wallsocket was to lose power (or the UPS detects the power is crap) the first UPS will disconnect from the wallsocket supply, and begin generating its own AC voltage from its battery. The second UPS is still simply passing through the AC voltage it is supplied. If the First UPS goes down the second one disconnects from its supply and begins generating its own AC voltage.

    In the case of an active UPS.

    The AC voltage supplied from the wall socket is used only to charge the UPS batteries.(converted to DC and charges the batteries) The voltage on the output of the UPS is generated from the UPS batteries and thus is totally seperate from the wall socket, and does not need synchronisation.
     
  10. Lespom

    Lespom Member

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    Fanxalot Sadow,

    Now I get it, they're connected in series not parallel, hence "daisy chained"

    Cheers
     
  11. maddhatter

    maddhatter Member

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    You would probably find it's just the batteries that are on the way out, and not the UPS.

    Also, if your running exchange on a DC (not saying you are, but it's notorious for long shutdowns) see if you can configure your UPS software to shutdown the exchange services first, before commencing the system shutdown - as what happens is AD shuts down before exchange does and exchange times out waiting to talk to AD - and that causes the slowness...)
     
  12. banshee

    banshee Member

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    I second the dead batteries theory. I picked up a couple of UPS's for $20, one a passive 1 active. Both worked ok when power was supplied but shut down immediately when the 240 was switched off. $200 worth of batteries later, and both work perfectly. :)

    Or you can send me the old one and buy yourself a few new ones. The power here is always dropping out and I could use another! :p I only have 4 at the moment... :rolleyes:
     
  13. Symon

    Symon Castigat ridendo mores

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    Slightly OT, but I could never understand why people get so hung up on pure sine wave inverters when they are only supplying switch mode power supplies, which really don't care what they are fed - you can run them on DC if you really wanted to.
     
  14. digamma

    digamma Member

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    Maybe I read the original post wrong, but if theya re connected in series ie ]wall-ups1-ups2-ups3-ups4-Computer, then it won't matter what the ratings of the cheaper upses are, the only one that matters is the one connected to the computer (or whatever). If the computer tries to pull more than what that ups is capable of giving, then it will trip its own littel circuit breaker and then the show is all over. Had it happen to my own ups.

    If you need a ups for multiple items, then you can get away with smaller upses, just connect the different items to the different upses. But if you need 1 big one and try to daisy chain several smaller ones, it ain't gonna do what you want. They won't boost the power, they will only output 240v at 1400va.The last ups in line will still only put that out, even if it is connected to 3 or more 1400va upses behind it.
     
  15. Oosh

    Oosh Member

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  16. OP
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    AEKaBeer

    AEKaBeer Member

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    Thanks for all your help guys.

    I still haven't found any ups' that mention anything at all about passive or active, but right now I guess I'll just go with a couple of less expensive units for each server untill we can figure everything else out.

    Again thanks.


    -Fred.
     
  17. cvidler

    cvidler Member

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    Some other terms to look for regarding 'active', are 'online' or 'dual conversion'. They are also more expensive then 'passive' UPSs.
     
  18. maddhatter

    maddhatter Member

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    Anything under $600 will generally be line interactive.

    Anything over will generally be online.
     

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