Low output voltage on battery mode.

[Anonymous user]

Hi, guys.

I'm from Brazil e I have an APC BR1200N-BR (input: bivolt / output: 120V). Some days ago I've tested the output voltage using an eletronic multimeter and, for my surprise, I've noticed that, when on battery mode, the device provides a strange too low output voltage: around 90V.

When working with input power, the reading of the output voltage is around 115V. That is to say, completely normal. However, on battery mode the too low voltage has scared me, as, I think, 90~92V doesn't seem to be a reasonable margin for devices that require 120V, although, up to now, I haven't faced any problem.

Besides that, another fact has called my attention. A friend of mine has the same unity model and he, indeed, has been having troubles. His pc reboots all the time and the motherboard, when the pc loads Windows, has stability problems and fan reading issues. In his case, the output voltage measured with the multimeter, on battery mode, is: 70~75V.

Having that said, I'd like to know what would be the accurate and safe output voltage range when on battery mode, so that the devices connected to the UPS work without risk of problems.

Thanks in advance and sorry for my bad english.

[BillP · Accepted solution]

Alexandre,

Are you using a non True RMS or a True RMS voltmeter? If you are using a non True RMS, that is the usual voltage that you'll get on our UPS. If you could find a true RMS voltmeters you could use that and it would give you a reading of ~115V AC.

With regards to your friends problem, it can be caused by a lot of things such as: power supply is too sensitive with the UPS transfer time, power supply doesn't read or like the step approximated sine wave that BackUPS supplies.

Below are APC Knowledgebase articles that would give you ideas with your problems:

[True RMS Voltmeter Required to Read Stepped Approximated Sine Wave|http://nam-en.apc.com/app/answers/detail/a_id/1493/kw/true%20rms%20voltmeter/session/L3RpbWUvMTMxMDk...]
[Different Types of Voltmeters|http://nam-en.apc.com/app/answers/detail/a_id/4119/kw/true%20rms%20voltmeter/session/L3RpbWUvMTMxMDk...]
[Equipment connected to a Back-UPS product turns off unexpectedly and/or reboots.|http://nam-en.apc.com/app/answers/detail/a_id/20/kw/equipment%20reboots/session/L3RpbWUvMTMxMDk2MTk4...]

[Anonymous user · Accepted solution]

Well. If there's something I can add is that, when reading the voltage in the wall socket, the multimeter reports about 222V. That is to say, the electrical source for the UPS is completely normal.

Then, my concerns come exactly from the fact that, although I have a normal reading from the wall socket, the reading from the UPS, when on battery mode, is far too low (90V).

Thanks again.

[BillP · Accepted solution]

Like what I have said on my previous post. You will need to use a True RMS voltmeter to read the proper voltage of the UPS when it is running on battery. When our BackUPS are online, it provides whatever is being fed into it unless it is trimming or boosting the voltage. When it goes to battery mode, it switches to a step approximated/ square wave. This is where the problem happen, if you are using a non True RMS voltmeter it cannot read the voltage properly. But if it is a True RMS voltmeter, it will read all the voltage points and would tell you that the voltage is ~115V AC.

[Anonymous user · Accepted solution]

Old post but I'm having the same issue. Question if my voltmeter is reading 89V and my equipment is not working on a fully juiced battery then my equipment is faulty as well? I can't believe there was no response from the other user or they probably lost patience because of lack of attention to their issue

[BillP · Accepted solution]

You probably are not using a True RMS meter, as mentioned. More detail is here -> http://www.apc.com/support/index?page=content&country=ITB〈=en&locale=en_US&id=FA157483 

The UPS outputs a step approximation to a sinewave so if you aren't using a true RMS meter, it will show as 88-90V for 120V. You will likely see 120V from the wall outlet correctly using a non-True RMS meter because it is a pure sinewave and not a step approximation to a sinewave..

[wayne_i_apc · Accepted solution]

Lacking a "True RMS" Voltmeter, a very effective test is to plug an incandescent (filament) light bulb (NOT LED or flourescent) into the UPS output. The brightness of the light should change very little (dimmer or brighter) when you go from utility (mains) to battery by pulling the wall plug. Not only does this tell you that the UPS is providing something close to the proper voltage, like you could read with a "True RMS" voltmeter, but it also demonstrates that the UPS can support (at least) the load created by the light bulb (100W?) which a voltmeter cannot.

You would know if you have a "True RMS" voltmeter, because they cost significantly more than your typical multimeter!

[wayne_i_apc · Accepted solution]

Sorry, just noticed the second part of your question about your equipment not working!

Some equipment does NOT respond well to a stepped approximation UPS output. I won't try to suggest all the possible ways that something could react if it can only work correctly on a "clean" sinewave input, but if your equipment operates correctly when the UPS is running from utility (mains) power, but doesn't function correctly (or at all) when the UPS is on battery, I would suspect it needs a better (True Sinewave Output) UPS. I am only a home user of APC products, so I can't tell you what the best choice of replacement APC brand (or other) UPS is for your needs, but I'm sure there are many options available!

[rhjt · Accepted solution]

may be true, but voltage is LOW.  Lamps are dim and fans runs slower.  devices which require full voltage may not operate or even fail.

[Deoraj]

What if the display on the UPS is showing an output of 60v with no loads connected after battery replacement? I did not even want to plug anything in when I saw that 60v. Input is 117v and frequency is 60Hz.