UPS: The output power is turned off. Why??

[elsin_apc]

Hello,

we have Symmetra LX 16000 UPS. There are 2 power modules 8KVA, 2 intelligence modules and 2 battery modules.
The load is just about 10%.
As we wanted to check how long will it run on battery, we switched off the main power to the UPS.

After a few seconds, the output was switched off unexpectedly. We switched on the main power than.
There is a part of log and data below (unfortunately, the data are logged every 10mins only, there is nothing to check for the time of error).

Can anybody please explain what happened? Why was the output power turned off?

....

05.03.2018 14:51:45 UPS: Passed a self-test. 0x0105

05.03.2018 14:51:21 UPS: Started a self-test. 0x0137

05.03.2018 14:47:48 System: Configuration change. Event log web display time selection. 0x0033

05.03.2018 14:42:32 UPS: The output power is now turned on. 0x0113

05.03.2018 14:42:03 UPS: A redundancy alarm threshold violation no longer exists. 0x020E

05.03.2018 14:42:03 UPS: Redundancy returned. 0x020C

05.03.2018 14:41:49 UPS: The output power is turned off. 0x0114

05.03.2018 14:41:43 UPS: A redundancy alarm threshold violation exists. 0x020D

05.03.2018 14:41:43 UPS: Redundancy lost. 0x020B

05.03.2018 14:39:25 System: Configuration change. Event log web display time selection. 0x0033

05.03.2018 14:29:32 System: Web user 'apc' logged in from 192.168.10.102. 0x0015

....

Symmetra LX 16000                                                            Integrated EMU       

Date Time Vmin1 Vmin2 Vmin3 Vmax1 Vmax2 Vmax3 Vout Iout %Wout kVAout %VAout Freq %Cap Vbat TupsC TIambC %HumI

.....

05.03.2018 14:38:18 231.9 230.2 231.9 235.3 231.9 235.3 233.6 2.7 18 0.62 7 49.99 100.0 138.1 34.0 26.5    

05.03.2018 14:28:18 231.9 230.2 231.9 235.3 231.9 233.6 233.6 2.7 18 0.62 7 49.99 100.0 138.1 33.0 26.5    

.....

Thank you

[Anonymous user]

1. Check that the batteries are ok and well connected.

2. If 1 above if confirmed ok, then there's an internal fault

3. If under warranty take it to where you bought it but if not under warranty, snap the panel clearly showing the component label and send to me 

[elsin_apc · Accepted solution]

Thanks for your reply. UPS is out of warranty.

We opened the battery pack and checked each battery. In both packs, there was one battery that showed 13V without the load, but under the load it showed 0. All others were OK. After replacing those defective batteries everything runs ok.

How is it possible, that UPS did not recognize that during self tests?