Long lasting UPS system for computer.

Discussion in 'The Projects Forum' started by Blacky11, Mar 2, 2015.

  1. Blacky11

    Thread Starter New Member

    May 27, 2010
    9
    0
    Hello everyone. I have a problem where the power goes out in my housing area once in a while. Its problems with the electric company so there is nothing I can do about it. I have a computer which I use to process information and it has to stay on sometimes for about a week or so processing. When the power goes out it turns off and I have to start the processing all over again. I would just buy a UPS except that the power sometimes stays out for hours (2-3) and the UPS that can last that long cost an arm and a leg. I also heard that if you buy a UPS and change the battery to a car battery or bus battery it still turns off at a specific time, it has a count down included. The charge left in the battery has nothing to do with when it turns off. So I designed this little setup and was hoping you all could go over it and let me know if its right. Someone told me that by the time the battery part kicked in the computer would have already turned off, is this true? Im also trying to spend as little as possible since its something I wont be using often. If I could make the battery charger and/or the inverter that would be something I would be interested in also to learn. I have a couple UPS that are bad which I haven't been able to figure out whats wrong with them. I could always take out the transformers since those seem to we working fine still. But the boards themselves have problems and I suspect one of them has multiple problems. I know how to solder and I have soldered boards before (with instructions). Thanks and hope to hear back.
     
  2. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    UPS units come in all sizes and flavors. I have no idea why you would say a UPS shuts down after a set period of time because that simply isn't true. A UPS will shut down when the battery voltage becomes low and how fast the battery voltage becomes low s a function of the load on the UPS. Years ago I used RV and Marine deep discharge batteries to supplement my UPS batteries and they would run for hours and hours. That said you choose a UPS that will support the load you have. Years ago I had several old APC XS1500 UPS units, the old style XS1500. They provided about 1500 VA and about 865 Watts of true power. With a deep discharge external battery they would run for 5 to 6 hours supporting PC, Monitor and a desk lamp as well as printer and scanner. I still use those old units but now have an emergency generator so during a mains power failure they only run for about 10 seconds.

    Something you need to consider in the drawing you provided is the switching time. A computer power supply has a "Hold Up" time. The power supply should maintain output regulation despite a loss of input power at the low-end nominal range—115 VAC / 47 Hz or 230 VAC / 47 Hz—at maximum continuous output load as applicable for a minimum of 17 ms. So whatever you do you need to consider it must switch over within about 17 mS or the computer shuts down or about 1 cycle of a 60Hz mains power. Failing that the PC will shutdown.

    Based on the above that would be true. You have about 17 mS to complete the transfer.

    Ron
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    Buying a low-cost UPS and adding extra external batteries is one way to get a longer holdup time without the higher cost of a larger UPS, but you are tampering with high power stuff. Will the charger in the small UPS be able to handle the larger batteries it was not designed for? Are you thinking of mixing sealed lead-acid (SLA) batteries with automotive (wet cell) batteries? If so, know that auto batteries give off hazardous gasses. I'm not trying to rain all over your idea, but know that it isn't as simple as a car battery and two wires.

    Try this: my USP will run my computer and monitor and printer for about 1 hour, or the computer alone for about 4 hours. Don't plug the peripherals into the UPS output.

    ak
     
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  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Try getting a battery for every u need.
    By the way you need to charge separately.
     
  5. Blacky11

    Thread Starter New Member

    May 27, 2010
    9
    0
    Hello. Thanks for all the replies. Seems I was wrong on the part about the UPS shutting down at a specific run time. I will have to look more into this before going out and buying one. If it doesnt shutdown then I can simply get a compatible bigger battery and done. I understand the part about wet batteries and sealed batterings. I had planned on teh setup being in the room next to mine which is open and has a lot of air flow.
    What wattage was your UPS?
    Did you have problems with the stock charger charging bigger batteries?

    Thanks again.
     
  6. Reloadron

    Active Member

    Jan 15, 2015
    963
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    No, while I knew the possibility existed I never had any problems. There are also a good number of UPS units which have external connections allowing an external battery supply. For what it is worth the APC UPS units I have are 24 volt using two WKA12-8F2 12 volt batteries in series. I just let the units internal battery charger maintain my external batteries. Something to consider is that today's newer UPS units are well packed with features older units never had. I recently got a new UPS for my wife's systems. I got her a APC Power Saving Back-UPS NS 1080VA unit. This unit overcomes a problem I have with my older units. When I lose mains power within about 7 seconds my generator comes online and does automatic transfer. While my older UPS units worked great and still do they have a problem with the generator power. My 120 VAC 60 Hz will vary between 122 and 124 VAC between 59 and 61 Hz. The problem is the variations so the old UPS units keep engaging and disengaging. Things work OK but the constant beeping is annoying. New units have a Generator Mode which can be selected where this problem is solved. Back to batteries for a moment and battery charging. Battery University is a wealth of information on batteries including their charging methods and characteristics. You may want to give them a read on charging specific batteries. Because I never had a problem does not mean you won't.

    When selecting a UPS just make sure you get enough UPS to fill your needs. My old CRT 21" monitors would require 250 Watts or more while my new flat panel monitors do not weigh 70 Lbs and consume around 20 Watts. Read the data sheets on UPS units.

    Ron
     
  7. Blacky11

    Thread Starter New Member

    May 27, 2010
    9
    0
    Got a hold of a UPS for testing. It works fine. I haven't tried to run everything on it and see how long it lasts before it turns off yet. I wanted to figure out how much my little computer server was using so I wiggled out the power cable a little and used a meter to see its amp usage. It says it uses .099 amps. This seems really low considering that i revved up the computer by running a number cruncher on it to see its max usage. I turned it off to see its peak usage when it turns on and noticed that even off it was using almost that same amount, .088 amps. Im starting to think something is wrong now with the psu in my computer, or are these normal numbers? Well after converting amps to watts I got 12 watts of use, revved up, seems off a bit. What do you think?

    I have a UPS that when connected keeps beeping. Maybe the voltage and/or frequency coming from the power company is whats making it beep.
     
  8. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Those numbers aren't correct. The only way to measure the current drawn by a computer is to place an amp meter in series with the AC line power and also measure the AC voltage. We won't even get into that. Years ago I helped out a computer hardware forum and did endless test on all of this sort of stuff. One little device which I did like was the Kill-A-Watt power measuring meters. Really a slick little tool. I would measure power with the PC doing nothing and power usage with pairs of dual core Xeons under full loads. Numbers like 200 and 250 watts come to mind but it has been a decade or so. Rest assured, I don't know how you got your numbers but they are incorrect, that I would bet on.

    If you have the manual check for beep codes. Some use different beep codes, rapid beeps, slow beeps, long and short beeps can all have different meanings.

    Ron
     
  9. A.D-J

    New Member

    Mar 5, 2015
    3
    2
    Hi All, first post ^^

    I'm just going to splat my brain out into this post so i appologise if it may be a bit scatty!

    Your best bet, as suggested above, would be modifying one of your existing UPS systems to fit your needs; BUT thats only viable in two cases

    • Only if you expect infrequent power cuts (not multiple times a day.) At most 1 per 24 hour period otherwise using an underpowered charger, you wouldnt be able to have the batteries to recover in time before the next outage - its fine if it happens infrequently but in the long term it would smash the longevity of the bank.
    • Your base UPS - a unit containing a 7ah bank would be totally inadequate for charging a stupidly bigger bank. The charger current limits would make it take days to recharge a bank which is not great for bank longevity - I wouldnt like to step over a factor of x5 really.

    So if thats not the case - my first port of call would be getting an idea of the battery capacity you'd require. I'd do this by getting inside the unmodified unit and place a high powered shunt in series between the +'ve of the battery and the +'ve input of the inverter; this will give you your most accurate figure on battery drain of the system. Just run your usual program on the PC, pull out the AC plug to trigger your UPS, then just measure the voltage drop accross the shunt and Ohm's law it to a current value.
    It should be the most accurate reading possible as you dont see any of the efficiency losses of the inverter ect - just gross Current. Then is just a case of Current * desired run hours = required Ah battery.
    I would suggest that if your needs are 3 hour run time, that you calculate it at 4 hours to account for the capacity losses you'd incur from higher current discharging.


    So you've got your desired bank size - I'd suggest a parallel arrangement - Get yourself some VRLA (preferably not gel) UPS/emergency lighting/golf cart batteries, definitley not car batteries(1) - Buy the whole lot from the same supplier at the same time - dont mix in any other batteries even if they are the same capacity - a pack must be as closely balanced as possible to perform well.
    When you've got them, its just a case of hooking them up in a parallel arrangement connected within or most likley, near the UPS and you should be hot to trot - give it a test and it should work without any major issues.


    (1)Automotive batteries are just not right for this application, they are specifically designed for starting/lighting/ignition of cars (massive peak currents, low depth of discharge.) They fail miserably quickly when exposed to regular cyclic behaviour and gas off quite alot of hydrogen during charge so you'd have to factor in some system of ventilation to address that; just more hassle than they are worth in this instance.

    Thats my two cents on it really, sorry if it seems a bit rushed and slapdash, its a stealth post from work ;D

    Arran.
     
  10. Reloadron

    Active Member

    Jan 15, 2015
    963
    232
    Welcome to the forums Arran and thank you for bringing more and important very good points to the table. Now get back to work before I tell your boss. :)

    Ron
     
  11. A.D-J

    New Member

    Mar 5, 2015
    3
    2
    nooooooooooooooo


    (thanks for the welcome ^^)
     
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