UPS runtime question

[TOOL_5150]

I read that when one questions the runtime of a UPS [for my specific model] You are to put a load on the UPS, and let it run with no line voltage till it shuts off. This is an APC Matrix 5000. I was wondering if it mattered what kind of load I apply to do this, can it be inductive, or does it have to be resistive - or does it matter at all?

I believe a load, is a load, so it shouldnt matter.

~Matt

 

[gar]

090622-0718 EST

It is self-evident and obvious that load matters.

A UPS has some maximum energy storage capacity. Suppose this is 400*10 watt-minutes. If the load is 100 W, then the approximate run time is 40 minutes. For 400 W it is about 10 minutes. Loads with a reactive component to the current may modify this to some extent. There also may be reactive loads that will prevent the UPS from working correctly.

You should test the UPS with the type of load that you expect it to supply, and operated as you might expect under loss of power conditions. Also under these conditions you would shed all unnecessary loads.

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[techntrek]

Actually the run-time graph is a curve and not a straight line, for lead-acid batteries (all types, including the gel-cells in most UPSs). A 5-minute run time at 100% load will give you closer to 15 minutes of run-time at 50%, and maybe 75 minutes at 10%. According to APC's web site, here are your run-times using the original included batteries for the Matrix 5000 (your system may have more if add-ons were purchased):

Typical Backup Time at Half Load 27.8 minutes (1875 Watts)
Typical Backup Time at Full Load 10.2 minutes (3750 Watts)

Like generators, UPSs need to be sized according to expected kva and kw. If you are running computers, their power supplies have an inductive component, thus the need to match their kva rating.

Edit: lead-acid batteries need 10-20 full charge/discharge cycles before they acquire their full capacity. If you have brand new batteries you'll get less than the expected run-time until you have exercised them 10-20 times.

 

[StephenSDH]

I believe if you connect to that model with a pc it would tell you without running it dry, but it would be so much quicker to just run it dry. I doubt the load type would matter much.

 

[catchtwentytwo]

Bear in mind those run-time figures are based on "fresh" Batteries.

Don't know if this model has communication capabilities but APC used to offer a free program called PowerChute to monitor a UPS and capture some data.

 

[brian john]

1. What we do is get the load specs for the battery.
2. Get the salesman promised run time for the battery at the specified load.
3. Perform a battery inspection (Volts per cell or jar, specific gravity if a flooded jar, inter-cell contact resistance, internal resistance and temperature0
4. Connect recording equipment.
5. Set the load at the determined level (resistive or resistive/inductive load bank)
6. Fail input and let it run to low voltage shutdown.

 

[Anthony Cox]

If the load is a computer, connected to the UPS via a communications port, it is usally accessable via the computer and will give you estimated run time. With the computers I work with, the UPS will do a graceful shutdown of the computer when there is an estimated 5 minutes of runtime left. It measures load dynamically and adjusts.

If you connect a laser printer to the UPS in addition to the computer, the load greatly increases when printing as it has to heat the fusing unit to melt the toner onto the paper.

In general, don't connect your display or printers to a UPS.

I wonder if it is foolish to connect a UPS to a GFCI...

I wonder if it is foolish to have a GFCI outlet connected to a UPS...

 

[techntrek]

I wonder if it is foolish to connect a UPS to a GFCI...

I wonder if it is foolish to have a GFCI outlet connected to a UPS...

Doesn't hurt to do both.

 

[Smart $]

...

In general, don't connect your display or printers to a UPS.

...

I disagree with not connecting the display.

While the PowerChute software slash communication will automatically shutdown the computer, without the display active, there is no way to know for sure that your computer is prompting you to save your work prior to shutting down. Thus even an attended shutdown may result in lost work.

 

[brian john]

If the load is a computer, connected to the UPS via a communications port, it is usally accessable via the computer and will give you estimated run time. With the computers I work with, the UPS will do a graceful shutdown of the computer when there is an estimated 5 minutes of runtime left. It measures load dynamically and adjusts.

I WOULD NEVER stake anything on these estimated run times.

 

[dereckbc]

There is no real answer to this question as it completely depends on the load, capacity of the batteries, State of Charge, temperature, etc?..

You can run all kind of calculations what it should be, but only a load test at a given load will tell, and 6 months the results will not apply as the batteries have aged.

As a very rough formula for design is:

T = (AH/L) x C

Where:

T = Time in hours
AH = AmpHour battery capacity.
L = Load current in amps
C = Correction factor. For example if the discharge rate is 1/10th of AH battery, then C = approx .75.

 

[dereckbc]

If the load is a computer, connected to the UPS via a communications port, it is usally accessable via the computer and will give you estimated run time. With the computers I work with, the UPS will do a graceful shutdown of the computer when there is an estimated 5 minutes of runtime left. It measures load dynamically and adjusts.

If you connect a laser printer to the UPS in addition to the computer, the load greatly increases when printing as it has to heat the fusing unit to melt the toner onto the paper.

In general, don't connect your display or printers to a UPS.

I wonder if it is foolish to connect a UPS to a GFCI...

I wonder if it is foolish to have a GFCI outlet connected to a UPS...

Well in the data and telecom world, you want every printer, control logic, and Video Display Units connected to the same UPS or battery plant. We call those items O&M (Operations and Maintenance). If the main frame, switch, or black box crashes we want a log of what happened, and be able to communicate without waiting for a reset and power restoration.

Folks get real unhappy when the phones, data, and internet don't talk: especially government communications, military, and banks/finance