What are some issues I may encounter when using an APC Back-UPS with a generator?

Issue:

ISSUE #1: The Back-UPS product stays on battery power while attached to a generator:

ISSUE #2: The Back-UPS product keep transferring on line to on battery power:


Product Line:

All APC Back-UPS product families.


Environment:

All APC Back-UPS product families.


Cause / Resolution:

ISSUE #1: The Back-UPS product stays on battery power while attached to a generator:

This is generally due to the generator being undersized. To prevent voltage distortion and complications with a UPS, the generator must be selected so that it will supply the peak current required by the computer load, not only the average current. It has been determined experimentally that this typically requires that the generator have a rating at least 3 to 5 times the rating of the entire load to be connected to the generator. However, due to wide differences in output impedance for generators, it is not possible to specify an oversizing factor that guarantees compatibility with all systems.

SOLUTION: The only solution would be to use a properly sized generator.



ISSUE #2: The Back-UPS product keep transferring on line to on battery power:

Using non-linear loads with a smaller generator will result in the output waveform of the generator to be very distorted. This distortion will most likely result in the Back-UPS product frequently transferring back and forth from On-Line to On-Battery.

SOLUTION: APC recommends that Back-UPS units be desensitized thru their respective software to allow the unit to be more tolerant of voltage distortion and, therefore, make less transfers to battery. All current Back-UPS UPS products support this functionality. Legacy model Back-UPS products (such as the BK series) may not support this functionality.

In most cases, to desensitize the UPS you will need to install the Powerchute software that is included with the UPS. Once the Powerchute software is installed, you can lower the sensitivity from the default setting of High, to either Medium or Low.


Note about Building-size generators - Generally, generators used to back up an entire building or facility, such as those used for hospitals, are sized large enough and are of good enough quality that any APC UPS will operate fine.