Batteries only producing 97V when operating on battery

[Anonymous user]

Hi,

I checked my UPS and when i pull out the power cord in order for the UPS to operate on battery, the backup battery outlet behind the UPS are only producing 97V?

Is this an indication that my batteries are not good anymore? Or i just need to recharge them without anything plugged in?

How to make sure that the problem is the batteries (if it is the case) and not the circuit board in the UPS?

I have a Back-UPS RS 800VA

Thanks.

[EZ_Button_apc]

It could be that your power supply is sensitive to the step-approximated sine wave coming from the UPS.

Your voltmeter should measure 115 from the wall outlet since it is a pure sine wave coming from that source. When the UPS goes to battery it outputs a step-approximated sine wave that only a true RMS voltmeter will read properly. I would clarify that your voltmeter is or is not a true RMS meter.

You may also want to contact that OCZ and see if their supply is ok with a "Step-Approximated" sine wave for a power source. If it's not, then you may want to look into a smart-ups, which produces a Pure wave on while on battery.

[Anonymous user]

Because a Back-UPS puts out a step-approximated sine wave, it is common for some volt meters to misread the RMS voltage. A true RMS volt meter would be able to read the true RMS. In your case it would be about 115V when on battery power.

[Anonymous user]

dirtfoot,

So why when my UPS is on battery mode, my OCZ Power Supply is producing a buzzing noise but it is still working? Something must be wrong from the UPS.

So you are saying that the voltage out of the battery is not the same type as the one out of AC outlet?

When i use my voltmeter in AC outlet, it indicates 123v so why it would not read accurately the voltage out of the back outlet of the UPS while on battery?

Thanks.

[Anonymous user]

dirtfoot,

I just had a discussion with the tech support at OCZ and they told me that it is producing a noise because the voltage is too low. The PSU will operate fine wihout any sound when the voltage is between 100 and 240v.

So why the PSU produce a buzziung noise if the voltage is "supposed" to be 115v?

Is there something i am missing?

[Anonymous user]

Hello,
The power quality from that and many other consumer UPSs isn't anywhere near as good as the main line. The output on consumer grade UPSs are almost always modified square wave unless otherwise stated.

Smart-UPS is true RMS, however I understand APC's target market isn't consumers.

To measure the voltage on a modified squarewave inverters and UPSs, you'll need a True RMS meter. Not advocating for one brand, but an example is the Fluke 87 series. Multimeters are almost always "typical responding" or not true RMS. True RMS is a feature most meter manufacture would make sure to get printed on the front cover.

Tech support at OCZ was wrong. The buzzing is inherent to using modified squarewave (or modified sinewave as marketing folks like to call it).

Sinewave: 0 ramps to max, ramps to min, ramps down below, ramps back up.

Modified square wave: 0, jump to max, jump to zero, pause, throw in reverse jump to max, jump back to zero.

It's the sharp wave pattern that causes an acoustic noise. You're hearing the buzzing from power supply's filter choke, which prevents harmonics from getting into the powerline and since it contains parts that can vibrate slightly, you hear the noise. Even a light bulb will buzz slightly on modified squarewave.

Since I'm not aware of a long term study on affect of using modified squarewave with power supplies, but I wouldn't worry about it. You're only on modified square wave when the power is lost and in the US, that's usually less than an hour a year.

You need not worry about anything unless the PC malfunctions on battery.

KVAr - Not affiliated with APC-MGE.
My posts do not represent or reflect the opinion of APC-MGE.

[Anonymous user · Accepted solution]

It would be great if only one hour a year without power were the case everywhere in the world. In my country the organization the regulates the power companies says a maximum 19 hours a month without power is allowed. 19 hours! On summer we have a lot of power cuts and sometimes they last for hours...

I have recently bought a power supply with active PFC and the older one don't make the buzzing sound as the new one does when on battery. I think it has something to do with the PFC circuitry as well. So I'm really concerned with some possible damage or reduction of it's lifetime caused by this modified wave. I'm saving some money to buy a Smart-UPS unit and for now I set the powerchute software to run only one minute on battery.