When a UPS is used for extended time, is battery fully discharged?

[Anonymous user]

I have several APC UPS units.

The other day I came home and the power had been out for several hours.  The UPS units were out of power and shut down by that time (as expected). 

When the power came back on all the units recharged and work fine.

But now I'm wondering.  Were the batteries fully discharged or do the units automatically shut down with at 50% (or so) to avoid fully discharging and damaging the batteries?

I have an XS-1300 and several ES 500 units.

[Anonymous user]

Do you have any software installed to monitor the UPS or shutdown the PC when you loose power?

[Anonymous user]

I do now.  I have PowerChute installed. Wasn't at the time.

But I also have UPS units on my TVs, DVRs, Routers, SmartHub, Phones, Lamps, etc.

I'm mainly wondering if my batteries have lost some lifespan due to a complete discharge.

[BillP]

Hi S

If the unit is constantly discharging, there is a potential that the life expectancy of the battery will be significantly reduced. In the link below are other factors that can impact the battery life of your UPS.

http://www.apc.com/us/en/faqs/index?page=content&id=FA158934&actp=search&viewlocale=en_US&searchid=1...

Regards

[MarkC_apc]

So many variables, it is difficult to determine if any real damage was done to your battery packs.  After a "complete" discharge to shutdown, any weak cells in any of the batteries will be more subject to damage - and potential failure of that particular battery.  I would do a simple operational test of these UPSs (after they have fully recharged their batteries) by shutting off power with loads on and ensure you have at least half your expected run time with no power.  Try NOT to run them to shut off again.  This will tell you if any of the cells/batteries were actually damaged and close to failure.  My experience has been that failing SLA batteries (especially these small/cheap ones), will "die" very rapidly - and take any others in the same system with them.  

The "smart" UPSs will not restart with such a damaged battery - not sure about yours.

[Anonymous user]

Thank you for all the responses.

Yes, I understand that a full discharge will damage the life of the battery.

But I'm still not clear as to if the APC UPS units will shut down before the battery is fully discharged or if it automatically shuts down earlier to protect the battery.

[Anonymous user]

It's my understanding, that most of the APC units will turn off the UPS when only 2mins.

of battery life is left...

What is the model of the 500 unit.

Did the UPSes fully charge?

Can you see that from powerchute software?

How old are the units/batteries in the units?

[MarkC_apc]

I've done many load tests of used battery systems for Smart UPSs and it appears that, based on "settled voltages" of the battery pack after a load test to shutdown, that the state of charge (SOC) will generally bounce back at least to the 20-30% SOC range (but varies with loads).  This is still much too low for continuous use of a battery and does shorten life.  However, for infrequent use, as most UPSs systems are designed for, it's acceptable.  

If lithium based systems become economical, they would be a much better choice for such systems - kept in the 20-80% SOC range - plus keep the excessive size/weight down.  Just not cost effective yet?  You could argue that the reliability of Li battery systems would more than pay for their costs if they prevent one catastrophic failure of a valuable business server system!

I'll bet someone in Schneider knows the lower limit of SOC that their charging algorithms attempt to meet when the unit is shut down - likely under various load conditions. 

[Anonymous user]

Thanks.

I'm doing some tests also.

I took an older battery with and put a 100W load onto it.  It measured 13.4v at full charge and the UPS unit shut down at 20 minutes.  The battery then measured 12.2v.

I charged it back to 100% and it measured again at 13.4v.  This time it only lasted 16 minutes under a 100W load.

I'll keep repeating this test to see how fast the battery eventually dies out.

I wish that PowerChute had a setting that allowed the user to turn the UPS off after a battery capacity hits 80%.  I generally only need a UPS for a minute or two during power flickers that my area is prone to. If power is down for more than a minute or two then it's generally off for a while.

[MarkC_apc]

Your voltages indicate about 20-30% SOC at the end of test.  The voltage might go up by a .1V or so if you let it "settle" for 12 hours.  To get back to 100% SOC you would need to "float" charge for 12 hours or so - takes a while to get the last 5-10% of the charge back into the battery - that could explain your second test having less runtime.  

The older Smart UPSs (SU/SUA/SUM/SURT) do have a "writable variable" that sets the number of minutes that a low battery alarm will go off BEFORE the battery reaches shutoff conditions.  The manuals show from 2 to over 20 minutes (for SURTs).  This could be used to alert you ahead of time to manually shut down your systems.  I've not used PowerChute, but I'd be surprised if there is a variable that sets the UPS shutdown based on a % SOC mainly because there is no "Smart Protocol" command for such.  An APC tech could advise you on that.

[Anonymous user]

The APC software for you UPS units don't provide that setting for shutdown when battery is 80%.

This is another program that should do it, called  ApCUPSD not made by APC v3.14.14 is the current one.

See screen shot attached. Look at the fields below in the screen shot.

MBATTCHG            MAX% battery left will trigger a shutdown

or
MINTIMEL             MINTime runtime left in mins. will trigger a shutdown.

or       
MAXTIME              MAXTime on batteries in sec. will trigger a shutdown.

Which everyone happens 1st from the above will trigger a shutdown.

You can configure the software to only look at MBATTCHG % and set it to 80% if you want.

Mine are set to the following:

MBATTCHG=50%
MINTIMEL=40mins
MAXTIME=600sec.   (i.e. 10mins on battery)

I thinks that want your looking for.

[Anonymous user · Accepted solution]