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UPS - a model with several hours battery life

I need to provide power for a PC, a LCD monitor and a fiscal printer. Printer is specified at 50W consumption. I believe PC and a monitor should have approx 200W consumption, but to sleep well, lets say that all three have 300W consumption (at full load). PC contains one HDD, one DVD-RW, integrated motherboard, 2 RAM sticks...

Now, I need a device that will provide power to these three devices for at least 2-3 hours after the power is gone. What are my options?

I am not clear about something. If there is a UPS that us declared at 1000W, what does determine how much battery will last when power is gone? It surely doesnt mean it can run 100W consumer for 10 hours. :)

Thanks,
Goran
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Priest04>>  It surely doesnt mean it can run 100W consumer for 10 hours. :)

nobus>   actually, that is exactly what it means

1000W is a power rating.  It is actually a 1000VA rating.  With APC's UPS unit, that equates approximately to 800 Watt rating.

You are thinking of Wh - Watt hour, which is 1 Watt load for a 1 hour duration.

In the case of the SUA750XL, specs are:

Typical Backup Time at Half Load with 2 additional batteries
372.8 minutes (300 Watts)

Typical Backup Time at Full Load with 2 additional batteries
179.5 minutes (600 Watts)


@300W, this would be 1864 Wh
@600W, this would be 1795 Wh

As the load increases, the UPS unit will become less efficient.
Also, theoretically, as the load decreases close to zero, it will become less efficient because of the loss of energy through conversion.  So, a 1W nightlight will not last 75 days.

Best to follow the mfr's chart and find the happy medium.  I try to stick to 50-60% load, giving me the option to add more load later, but also to keep the runtime long enough for a slow Windows server shutdown.  (Watch the timing on your SBS or Exchange server...buying 15 minutes runtime is not be enough!)
>aleqhart i used A/h, and said for Watts you have to take voltage into consideration - and there can be losses
if more info is needed i can provide it easily...but for a first understanding it is enough
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ASKER

Thanks guys for the info, it is of great value. I was reading informations about UPS on internet lately, to see what kinds exists, and what will be the best for my demands. The chart was very useful.

So, when I read this info about the UPS (ex APC Smart-UPS XL 750VA)

Output power: 600 Watts / 750 VA

there is no way I can tell how much backup time I can expect for the 200W device? Can it only be determined with manufatrurers runtime chart? And why devices with similar VA specs have different backup time at halp/full load?

>>  It surely doesnt mean it can run 100W consumer for 10 hours. :)   <<   actually, that is exactly what it means.

nobus, then on the above APC 600W should give 2h of backup time for 300W device, or at least 1.5h if we roughly take losses into reconsideration. But the specs show less.
yes that is what the battery can provide. in the chart, you have to divide the provided Watts thru the used Watt, giving 1 hr 24 minutes for 280 W user - fairly close
>there is no way I can tell how much backup time I can expect for the 200W device?

See chart below.  Came from link provided previously: http://www.apcc.com/products/runtime_for_extendedruntime.cfm?upsfamily=164


>Can it only be determined with manufatrurers runtime chart?

That is the best way.  You can try to extrapolate based on three or four data points...but you'd only get the data points by real-world load testing or by using the mfr's chart.

>And why devices with similar VA specs have different backup time at halp/full load?

I think there is confusion with the concepts.  VA (volt-amp) represents a load level, same as W (Watts).  Capacity is measured in Wh (watt-hours), which depends on the size of the battery and the conversion factor of the UPS unit.

Your run-time (the time you're seeking) is affected by the Load, Capacity, and efficiency.  Large loads reduce efficiency of UPS.  Small loads are less efficient because capacity is lost to conversion.

That's why the mfr's make runtime charts.  It's never a straight line or simple curve.
SUA750XL - 120V
Watts
50    5 hrs 1 mins
100   2 hrs 52 mins
200   1 hrs 24 mins
300   51 min  (HALF LOAD)
400   33 min
500   23 min
600   17 min  (FULL LOAD)

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Ok guys, thanks for all the help, I know have a better understand about UPS runtime.

Goran