SMX2000RMLV2U, new batteries, low runtime, what gives?

[Anonymous user]

I recently installed 10 new 12V 5AH batteries in my UPS (SMX2000RMLV2U), at first it appears to work great. However when I let the UPS to do a runtime calibration, the estimate dropped to ~20min @~400W, which is about 1/3 of the spec. I then did a manual calibration (a heat gun drawing ~780W), it lasted 8min46s before battery run dry. I also measured the open end voltage of the battery pack with my multimeter, it was ~136V and ~126V before and after discharge. Though to my surprise the UPS reported ~43% charge after I plug back in the drained battery pack.

Searching on the Internet, some suggested to use a APC calibration key or APCfix.exe to resolve runtime issue. But my understanding is that they would let UPS get a better estimate, but actual runtime is not affected. Given that the runtime in my test is not far off, I suspect the problem lies somewhere else, no?

I would like to know your thoughts. Thank you

PS: I should mention that I got the UPS used so it's probably out of warranty

[voidstar_apc]

Yi-xiao,

The APC calibration key is only for older UPSes. Newer UPSes do not need it; the manual calibration you performed should be all that is necessary.

You are correct that this won't affect the actual runtime of the UPS. The UPS runs until the battery is drained or it is commanded to turn off. After discharge you measured 12.6V/battery which seems a bit high for a fully discharged battery so I'd be suspicious of a bad battery cell. If you bought the batteries from APC, then I'd recommend calling tech support and asking about the runtime.

[Anonymous user]

On 1/3/2019 1:41 PM, voidstar said:

Yi-xiao,

The APC calibration key is only for older UPSes. Newer UPSes do not need it; the manual calibration you performed should be all that is necessary.

You are correct that this won't affect the actual runtime of the UPS. The UPS runs until the battery is drained or it is commanded to turn off. After discharge you measured 12.6V/battery which seems a bit high for a fully discharged battery so I'd be suspicious of a bad battery cell. If you bought the batteries from APC, then I'd recommend calling tech support and asking about the runtime.

Thank you voidstar

You are right 12.6V for a discharged battery seems to be a bit high. OTOH the the battery pack was 110V (reported by the UPS) shortly before the load was dropped. I heard that drained lead acid battery may back-shoot the voltage once the load is dropped, but not sure if it's normal for it to be as high as 1.6V/battery. 

I am in touch with the battery vendor, but am also wondering if there is any other troubleshoot I can do to isolate the problem.

[voidstar_apc]

Make sure voltage reported by the UPS is similar to voltage reported by your voltmeter. You might try testing individual batteries rather than all 10 *edit: only makes sense for testing battery cartridges rather than individual batteries within the cartridge*. You could test batteries in a UPS system you trust for comparative purposes. You might also try looking for a manufacturing date code on the battery -- SLA batteries last roughly six months without being charged.

[Anonymous user]

The UPS reading on battery pack voltage, both before and after runtime calibration, seems to agree with my multimeter reading. I was not able to use my multimeter when the UPS was on battery though. And another UPS take the same RBC was not available.

Assuming the 110V and 126V reading before and after UPS drops the load are both accurate, that sounds like a internal resistance of 1-2 ohms right (to my limited electrical training). I believe good SLA batteries (even 10 in series) should only be a fraction of it?

Thanks for all your suggestions, I will find some time this weekend to open the cartridge.

[Anonymous user · Accepted solution]

I got some 100Ohm resistors today and tested the internal resistance of the batteries. It appears that each battery have a internal resistance of ~0.7Ohms when fully charged. A good battery should be only ~1/30 of that

It's most likely bad batteries, I am working on return/replace them