SMX1500RM2U w/External Packs Strange Runtime

[jmiller31_apc]

This was originally posted on APC forums on 4/18/2020

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I have a number of these units but this one in particular is doing something really strange. It has 2 external packs and until yesterday had about an output load of about 38% and it was consistently reporting a run time in the 40-45 minute range. Yesterday I added a server to it which brought the load up to 55%, the runtime immediately went down to the 3 to 6 minute range.  That just doesn't any sense to me even if I had doubled the load the runtime should be around 20 minutes, it's acting like I'm close to 100% load.

I ran a calibration and after calibration I'm still down in the 3 to 6 minute range. The more I've looked into this even the 40-45 minute range doesn't make sense. According to APC's charts this unit with 2 external packs at half load should get a runtime of 2 hours. Now I realize that's in a perfect world so I wouldn't expect to get 2 hours but it should be off this much. BTW I'm looking at all this data using an NMC2.

Anyone have any thoughts? A bad UPS?

Thanks,

John

[older_apc]

This was originally posted on APC forums on 4/19/2020

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Hi John

I had similar symptoms a year ago - SMT1500RMI2U PCB: 640-3081J-Z-001 Tg = 170 SMT1500RMI.
Network equipment was connected to it with a load of about 50%. During automatic testing with a period of 14
days, UPS for some reason undelete the entire load without leaving NMC2 (AP6930) logs - no traces and no replicas
in the LAN.
By agreement with the personnel at the remote site, I gave the command through AP6930 to perform a test with the
transition to the battery and the load was disconnected. If you decide to do the same, then pay attention to
THIS!
I have been reading this forum for almost a year and you have now outlined what has been directly or indirectly
mentioned here more than once.
In short, I decommissioned the UPS in this series. Moreover, the platform or circuitry is the same for many UPSs
of this generation.
The only recommendation has always been Braindead or bring it to the service.
No one is even trying to explain the true cause or admit a mistake in the circuit.
Outrageous
and ashamed!

Vladimir.

[jmiller31_apc]

So what I ended up doing was replacing every battery pack in the UPS and the expansion units.. After doing that I ran a calibration and got something much closer to what I expected. Given this I'm assuming there was a weak pack somewhere in the string that was causing the aborted calibration. 

I reealize that given the way the expansion units are wired in it's not possible for the UPS to determine where the fauly pack is but it would sure be useful.

I have had a similar problem in the past with just one expansion battery and in that case the solution was the same as your's; retire the UPS. With that one even thought the calibration passed it would always return a ridiculously low run time given the load provided. 

These units seem to run great most of the time but when one starts giving problems it's failure mode seems to be all over the place.

[robmir_apc · Accepted solution]

On my own experience with this series and their external expansion units you just need 1 faulty battery in any of the battery packs  to mess with the estimated reserve time 😟