UPS works in one office but not another.

By soatone ·
I'm having a weird problem with 2 brand new UPS's. When I install it in one particular office it does not function properly. The computer is correctly plugged into the UPS (battery backup vs. surge suppression only). But, when I pull the plug from the wall the computer instantly shuts off. If I take that same UPS, install it in a different office, and then pull the plug, the computer stays on.

Both computers are exactly the same; two Dell OptiPlex 960 mini-towers with exactly the same hardware configuration. Both computers also have the same bios power-management settings and the same Windows power settings. The UPS is a brand new APC Back-UPS ES 650.

To troubleshoot, I have removed all devices except the computer and monitor from the UPS and it still powers down. I have checked the power setting in the bios and Windows. All settings are configured for never shut off.

Has anyone ever seen this? Does anyone have ANY ideas? This is totally stumping me.


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Seen this on server...

by cmiller5400 In reply to UPS works in one office b ...

When the UPS did a self test, the server would power down hard. Other servers connected had no issue.

Try swapping out the computer's power supply... It may not like the modified sine wave that the UPS generates.

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Check the wiring

by Kenone In reply to Seen this on server...

I had a similar problem once with a faulty ground at the wall outlet, don't know why that would be but it was.

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Check the line voltage & polarity of outlet

by InstructorJWN In reply to UPS works in one office b ...


It is possible that the offices have different "sources" of power and as such, the line voltage may be below the "limit" of the UPS.

Anything below 100V is questionable, though some supplys work as low as 90V.

It is possible for some reason that the voltage is "too high".

Both of these conditions can occur when power is "generated" onsite, in other words, if there is a "sub station" particular to your location (mfg plant, large office building, etc).

Problems arise for example if the sub station also supplies power to a large energy consuming device.

In a plant environment, something like a punch press, or drop hammer which has a large power consumption followed by a low consumption phase.

another in an office buildign may be that you are on the same "sub" as the HVAC systems, and the Air or Heater is causing low voltage.

another thing you may want to check is the polarity of the outlet, it is possible that the common and hot wires were incorrectly hooked int he outlet you are pluging in to.

You can get small inexpensive electrical outlet testers at many home improvement centers which plug into the wall and can tell you whether the curcuit is working properly.

there are also dedicated data loggers which can monitor the voltage at the outlet over time.

Hope this helps.


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AC Ground

by TheChas In reply to UPS works in one office b ...

Actually, I find it hard to explain why the UPS works in the first office.

Most UPS systems will not switch over to battery if you simply pull the plug. As part of safety circuits, they require at least the AC ground if not the AC neutral connection on the input in order to turn on the output with battery power.

Instead of just pulling the plug to test the UPS, plug it into an outlet strip and then switch off the outlet strip.

Since most outlet strips only break the hot side connection when you turn them off, the ground and neutral connections are still present and the UPS should switch over to battery.

About the only thing that would explain why the UPS works as described in the one office is that you must have an extra ground connection to the PC chassis. Perhaps fully shielded Ethernet cable that is grounded back at the switch or server.


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I figured it out

by soatone In reply to UPS works in one office b ...

To those still following this post or to those who find it in the future, I have discovered what the issue is. While the hardware specs on the computers are exactly the same the power supplies were slightly different. Dell tells me this is because they contract with several different companies to manufacture power supplies for them. The power supply with the issue has a model number of H305P-02. During my testing (I tested several different machines all with different power supply model numbers) I found that ONLY those power supplies with the model number H305P-02 failed when switching to the UPS. All other power supplies work fine.

Dell maintains that the power supplies are not the issue; that they are in fact working as designed. Dell states that the power supplies are only rated to work with a UPS that outputs a true sine wave. Since the basic home/office UPS only emulates a sine wave the power supply will not transition properly and simply shuts off. As such technical support was not willing to replace any of the power supplies we had. I did inform them that I had limited the issue to only one specific model of the power supply, but they stated they could not replace it due to the UPS we were using. We did finally get them replaced by going through their sales department.

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by SPC_TCOL In reply to I figured it out

That's why we buy at a store that knows that we have some UPS and that there is a high chance that every computer we buy could hang on a UPS, in case that this would happen they would exchange the Power supply without a problem.

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