Back-UPS ES 500 - low voltage during blackout

[rickapc1_apc]

This was originally posted on APC forums on 3/28/2009

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I have a Back-UPS ES 500. During a blackout, the output voltage drops from 120 volts to 90 volts, and stays at 90 volts until the external power is restored a few minutes later. Shouldn't the battery outpout voltage stay constant at approx. 120 volts?
The test load is only one 60W light bulb.

[BillP]

This reply was originally posted by Angela on APC forums on 3/30/2009

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this UPS outputs 115v while on battery.

[Cap1_apc]

This was originally posted on APC forums on 3/29/2009

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Hi,

How are you validating 90v output? Are you using a voltmeter?

Because this unit outputs a step approximated sine wave on battery, only a true RMS voltmeter will read the correct voltage while the unit is on battery. True RMS voltmeters tend to cost more $, so perhaps yours isn't?

More info here:
http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=1493

[rickapc1_apc · Accepted solution]

This was originally posted on APC forums on 3/29/2009

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Hi. I am using a simple voltmeter, which is most probably not a true rms-voltmeter.
I will try to get one from Radio Shack if available.
And thanks for the article included in your link. It was very useful.

The only doubt that remains for me is that the 60W light bulb gives a dimmer light when on battery power,
compared to the bright light given when the battery is connected to an electric wall outlet.
How much drop in voltage would be normal to observe when on battery power?

Thanks.