SUA 750 I

[Anonymous user]

Hi.

I have an older SUA750I that stood for a while. After having the batteries tested, only one was tested to be OK. So I replaced the dead one. The UPS works fine now and operates nicely, however when I switch the mains off, the battery level goes straight to 1 flashing LED and beeps constantly as if the battery level is critically low, even though it was fully charged before the mains was powered off.

Is this an indication that the second older battery is also due for replacement? Why doesnt the battery replacement light illuminate?

Thanks...

[voidstar_apc]

I don't think SUA has external battery packs so if I understand you correctly, you disassembled the UPS battery pack, tested each battery individually, and replaced one of the two in the pack?

That's a bit worrying for a few reasons: 1) it's hard to test a battery without load -- it can produce a "good" voltage yet be unable to support any load, 2) since both batteries in the pack are exposed to the same conditions, you'd expect them to be similar modulo manufacturing defects and 3) mixing good batteries and bad batteries damages good batteries because the good battery may end up taking the full charge or discharge current. APC only sells the full battery pack.

I suspect the replace battery light isn't flashing because the good battery is enough to pass that test for now.

[Anonymous user]

Thank you for the reply.

I had both batteries tested with load on it. But I suspect the load wasnt nearly as much as it would be in the UPS itself. I bought the new battery from an APC dealer and they were happy to sell me 1 battery although the 750 uses 2 x 7ah batteries side by side.

I appreciate your comments and will change the older battery asap.

Regards...

[Anonymous user]

Ok so I replaced both batteries and the same problem still persists. What can be the problem? Please help

[voidstar_apc]

Now that you've replaced the battery, the runtime estimationg might not be calibrated for the new batteries. This mostly affects reporting the state of the battery; the UPS itself will run for as long as possible. Details here which I'll summarize:

1. Make sure the battery is fully charged. Perhaps let it charge overnight for this.
2. Put 30% load or so on the UPS. For yours, that would be 150 watts. If there's not enough load, the UPS won't update it's calibration factors.
3. Pull the plug and let the UPS run until it turns off. Then plug it back in.

After this, your UPS' battery state of charge estimation will hopefully be accurate. Also, I recommend pulling the plug rather than using the software "battery calibration" command because some of the older units have an issue where they estimate the battery is too far gone to stay on battery. Pulling the plug forces the UPS to stay on battery as long as possible.

[Anonymous user]

Thank you for the reply.

I will let it charge overnight and will do exactly what you said, tomorrow. I will update you on what happens.

I have also not got the software on my computer, as I do not have the cable that joins the Mac and UPS.

Thank you yet again.

[Anonymous user]

Hi again.

So i drained the batteries, did everything you suggested, and it still does the same. Do you have any other suggestions?

Thank you

[voidstar_apc]

I'm out of suggestions, maybe someone else here has some idea?

I am curious about how much load you used and how long the UPS ran on batteries. At 150W, I'd expect the batteries to last at least 10 minutes. If the runtime is good, then it's just a problem with battery capacity estimation and while I'm not sure why the calibration procedure didn't work, there's another approach. If the runtime is not good, then it might be an issue with the batteries or the UPS.

[MarkC_apc]

I've had a similar issue (only one LED lights up on power failure) with a larger UPSs with multiple batteries in series.  The problem was that one of the batteries was bad even though it passed the battery test on startup.  As I have a way to externally load test each battery, it was possible to replace one and the unit worked fine.

With both batteries being new, this seems unlikely, but new batteries can be bad and can also be ruined by discharging into shorted batteries.

[Anonymous user]

I put roughly 180W load on the UPS which lights up 2-3 LED lights on the load meter. The runtime is good as it lasted for around 10 minutes, but the annoying thing is that the constant beeping is activated, as the UPS says the battery level is way down. I might have to take the batteries for independent testing, even though they are less than a week old.

Is there another battery calibration way? 

Thank you all for the help so far.

[voidstar_apc]

All APC UPSes beep when they are running on battery except when doing a self-test (see descriptions of beeps here). You can turn this off from the PowerChute software (see here). This seems to be your main concern and since you're not attaching the UPS to a computer, calibrating the battery capacity/runtime estimate isn't critical (it's mainly used to tell the computer when to start turning off). But if you're still interested in calibration, read on:

The SUA750I's tech specs doesn't show a load/runtime curve so I've been using the similar SMT750 load/runtime curve. At 180W, the SMT750 is advertised as getting about 20 minutes. The SUA750I is a bit less efficient than the SMT750 (comparing efficiency curves) and there's some variability due to age and batteries, so I'd say 10 minutes is borderline -- could be fine but I really don't know.

I don't know how easy it is for you to get batteries tested but it's not a bad idea. Another thing you can do is examine the battery for a date code (although depending on manufacture, this could be difficult to decipher). Batteries that aren't being charged will self-discharge and then die, so you want ones that haven't been sitting on a shelf for longer than 6 months without charging.

If you want to try an alternative way to update the battery constants, friend me on the forum and I'll send you more details in a private message.

[MarkC_apc]

Hopefully the alternative calibration method that Voidstar can provide will resolve your issue.  

There are a couple of easy things to try with the battery pack.  It appears your pack has two 12 volt,  7AH batteries in series with the fuse (blue w/ yellow wire) connected between the negative/positive of both batteries (24 volts to the UPS).  If you are familiar with charging batteries, You can disconnect the fuse and charge each 12 volt battery with a standard trickle type charger for several hours - independently of each other.  Don't overcharge these small AGMs as they can be damaged using a conventional car battery charger (flooded type batteries).  Connect up and install and see if that "equalizes" the two batteries and successfully brings the combined voltage up to the required 100% battery LED on you UPS.  

Another try is a simple load test on each battery by fully charging as above, then connecting a 12 volt automotive bulb across the +/- terminals (independently on each battery) and see if they both keep the light burning for similar times - could be for several hours!   DISCONNECT AT THE FIRST SIGN OF BULB DIMMING so that you do not over discharge the batteries - or better yet watch the voltage and stop at 11.9 volts.  If one quickly discharges - it's bad.  

No jewellery and use rubber gloves for safety!  A red hot ring will not be pleasant.  

Side note that APC battery packs are the top quality you can get, but most others will work if they are tested and conditioned as above.

[Anonymous user · Accepted solution]

Thanks guys for all your info. 

Its not so much the beep that annoys me, its the fact that the point of the Smart UPS is to see the remaining battery life remaining, but in my case, it goes from 100% to 20% in a matter of seconds, without even using half of the Wattage that I can draw on this UPS. And the batteries are less than 2 weeks old each. Both were bought in the past 10 days from an APC authorized dealer. These are Scott batteries. And yes, 2x 7ah batteries connected in the way you described. They charge to 100% indication, and as soon as I put load on it, it goes from 5 LED lights (100%) to 1 LED light (20%) flashing and constant beeping - indicating less than 5 minutes run time left. This happens in a matter of seconds (4 or so seconds)

I will send you a PM as well.

I will try the alternative methods this weekend and give you feedback on Monday.

Thanks again guys.