Anyone here ever mess with UPS's ( back up power supplies )

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dacflyer
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Anyone here ever mess with UPS's ( back up power supplies )

Post by dacflyer » Fri Oct 04, 2019 12:46 pm

I have 2 identical APC UPS Battery back up units ( APC BR800BLK )
Looks like this >--->> https://www.newegg.com/p/N82E16842101140
They both work, and function like they should, but the output on battery power is kinda low. I read 88VAC on one and 90VAC on the other.
I've looked on the boards for an adjustment, but there isn't any. And I don't see a way to adjust the output voltage.
anyone have any ideas ?
These units use 24VDC, 2x 12V batteries. And no the low battery led is not on..

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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by Engineer3104 » Fri Oct 04, 2019 1:17 pm

It may be working normally, but your measurement may be misleading. What type of meter did you use to measure the output? Most of these types of UPS's don't put out a pure sine wave. They put out a "modified sine wave" which is a lot more like a stepped square wave. A lot of simple DVM's can't measure this properly. Take a look at the output using an O'scope. If you have access to a true RMS reading meter, try using that.

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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by dacflyer » Tue Oct 08, 2019 12:16 pm

i was using a RMS meter, you can also see the test lamp dim a bit also.
when in Battery mode, the frequency is 120Hz.
the units are not really worth fussing over too much, i was just curious about them.
i have others that do well, altho the frequency on them ain't very accurate either.. its fun to watch my line dependent clocks go into warp speed while the unit is in battery mode..lol

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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by Janitor Tzap » Tue Oct 08, 2019 1:54 pm

How old are the batteries?

I was given an APC 280 by a friend, and I found out later that the battery was bad.
It checked out fine for voltage and charging, but when I "Load Tested" it.
The battery would fail.

This may be the case with your units.
Most batteries are rated for 3 to 5 years maximum use.

A lot of businesses just replace UPS's every 2-3 years, instead of the batteries in them.
Because the newer UPS's are rated to handle more power, and cost nearly the same,
or less than the replacement batteries for the older units.


Signed: Janitor Tzap

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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by dyarker » Wed Oct 09, 2019 6:47 am

Dac, was it a True RMS meter? Most meters report RMS voltage (when fed a sign wave) but are peak responding. ((they measure peak voltage, multiply by 0.707, display the result. 0.707 is the ratio of peak to RMS for a sine wave. Other wave forms have different ratios.))

The 120Hz probably means the steps of the output wave form are being counted (instead of the zero crossings in one direction like a sine wave count would).

I agree that replacing internal batteries is a waste of time (and effort).

Cheers,
Dale Y

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dacflyer
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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by dacflyer » Wed Oct 09, 2019 11:36 am

Janitor Tzap >> i am using new batteries for testing.

as for my true rms meter, i have a fluke meter model 114

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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by dyarker » Wed Oct 09, 2019 6:22 pm

Yeap, true RMS.

Cheers,
Dale Y

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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by dacflyer » Thu Oct 10, 2019 11:44 am

i like the older ones that you can adjust a little it. but the new digital units, are not adjustable.. unless there is a way that the factory can get into a file somewhere via the data port.

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Re: Anyone here ever mess with UPS's ( back up power supplies )

Post by jwax » Wed Oct 16, 2019 2:28 pm

Add an autotransformer (Variac) to get your 120 VAC.
Probably more trouble than the UPS's are worth.

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