APC ES 550 UPS diagnosis - Page 1
Forum section: electronics / repair

author: Peabody
author_rank: Super Contributor
timestamp: March 31, 2023, 09:38:17 pm
content: Having very high winds today, and the power is glitching. Unfortunately, my UPS takes over, beeps about twice per second, and 10 seconds later shuts down the output. However, the "replace battery" LED is not lit up, so I don't know whether it's just the battery, or something wrong with the charging or conversion. Is there any way to tell, short of replacing the battery to see if that fixes it? I'm a hobbyist, so don't have much gear. Would measuring the battery voltage when it's been "charging" overnight tell me anything? Or is it just time to replace the whole thing? It must be close to 10 years old. I know the batteries die over time, but do the innards die as well? The UPS almost never has to kick in for an extended period - maybe once a year. So it's usually just sitting there trickle charging. Anyway, is there any reasonable way to identify the problem?

author: floobydust
author_rank: Super Contributor
timestamp: March 31, 2023, 11:59:11 pm
content: I recently a similar problem with my UPS and it was due to a weak (cell) battery.You can check the SLA terminal voltage is typ. around 13.65V on float charge after the battery is charged.UPS smart battery check is to stop float charging, wait a minute and then measure battery voltage- it should not go below around 12.0V unless there is a problem. A battery with a weak cell can still pass that test though.It's under load the battery voltage quickly sags and the UPS thinks it's discharged and alarms then shuts down.You can load test the battery with a car light bulb/headlight etc and see how it does.With age, UPS float charging voltage will drift and can go too low. The innards do age. Failing electrolytic capacitors can also cause charging problems.

author: james_s
author_rank: Super Contributor
timestamp: April 01, 2023, 01:01:11 am
content: At least 90% of the time when a UPS is malfunctioning the problem is the battery. The next most common problem I've seen is bad capacitors, like any other gear.

author: Peabody
author_rank: Super Contributor
timestamp: April 01, 2023, 12:54:06 pm
content: This morning the battery is at 12.81V. So the charging system appears to be working. But if it fails under load, I still don't know if it's the battery or the conversion process that isn't working. I think I would have to load test the battery by itself. Not sure how I would do that.

author: SeanB
author_rank: Super Contributor
timestamp: April 01, 2023, 03:33:20 pm
content: 12.81V is a bad battery or charger, as the float voltage should be at 13.8V with a good battery being charged. Simplest test is to remove the battery, and use a car headlamp bulb of 55W to provide a load, and see if the battery is capable of providing over 11.6V under the roughly 5A load of the bulb after 5 minutes of use. Bulb will get hot, but a good battery should easily be able to maintain 5A of current for 5 minutes, assuming the standard 7/8Ah battery that is normally used in a UPS. 10 years old the battery is very likely dead, even if open circuit voltage is over 12V, and a simple test is to use the bulb, or to shake the battery, as it should not rattle.

author: Peabody
author_rank: Super Contributor
timestamp: April 01, 2023, 05:28:08 pm
content: I put the battery on my 1.5A car battery tender to make sure it was fully charged, and it ended up at 13.6V when the green light turned on. But an hour later, with no load, the battery had self-discharged to 12.28V. I think that tells me what I need to know. So I'm ordering a replacement battery. That doesn't mean the converter isn't also bad, but it seems more likely it's just the battery since the converter seemed to work fine while there's something left in the battery. I guess I could rig up a test of the converter with my car battery, but at this point I think I just need to get a new battery and see how that performs. Thanks very much for the comments and guidance.I think I'll order this one. It's 9Ah, but still fits.https://www.amazon.com/gp/product/B00A82A3QG/

author: floobydust
author_rank: Super Contributor
timestamp: April 01, 2023, 07:09:58 pm
content: Last check (with a new battery) would be to confirm the UPS is charging the battery.In APC UPS it's common for the electrolytic capacitors to go bad and the UPS to malfunction and/or not charge properly.

author: elecdonia
author_rank: Frequent Contributor
timestamp: April 02, 2023, 12:31:36 am
content: Quote from: james_s on April 01, 2023, 01:01:11 amI fully agree. SLA batteriesneverseem to last longer than 3-4 years.As for the electrolytic capacitors, it is the small ones which most often fail with age. 4.7uF, 10uF, up to 100uF. The big ones rarely fail. I always check the ESR of all electrolytics on the PC board.Another common failure is “box shaped” plastic film capacitors connected across the AC mains circuits.

author: Algoma
author_rank: Frequent Contributor
timestamp: April 02, 2023, 03:09:38 am
content: That ES 550 is only rated for 330W load, I've seen them often alarm an overload and shutdown when trying to go to battery, even when nowhere near that load level. Though its usually a continuous tone when I've encountered such behavior's. (Usually due to someone plugging in a laser printer to such a unit.)I find APC's quality really has gone downhill in their recent products, even their network and server class units have suffered compared to other brands. I've switched to recommending Eaton and Cyberpower over APC for home and small office locations.