SMT1500 Stuck on Battery Operation

[rinconmike_apc]

I have both an SMT1500 and SMX1500.  Each are plugged into a dedicated outlet.  The load current on the SMT is 4.2A and on the SMX is 2.3A. 

Last night we had a power outage and my whole house generac 22KW generator kicked on.  All seemed fine.  I do not test the generator much (do not lose power often) so I decided to kick on one of the AC units.  In the past, when I did this, the the battery backups would go on battery for a few seconds when the generator RPMs increased and then back to wall power (I say wall instead of utility since the gen was running).

When I did it this time, the SMX1500 went on battery and then back to the wall power.  However, the SMT1500 stayed on battery.  

One difference is I had the sensitivity on the SMX at low and the SMT at reduced.  I have network cards on both and was logged in and switched the SMT to low, but it did not switch back to the wall power.

I tried unplugging the SMT from the wall and plugging back in, but it stayed on battery power.

I then went ahead and powered down the equipment connected to the SMT and powered off the SMT (pressed button on front).  I then powered on the SMT and it said on utility power.  However, around this time the utility power was coming back on so when I powered on the SMT, I am not sure if it was still on the generator or indeed the utility at this point.

Attached are clips of the logs.  In the logs, Power went out around 19:07.  Power restored around 19:53.  Around 19:40 is when I turned on the AC that caused the generator to rev up.  Looking at the log, the SMT was reporting a higher voltage than the SMX.  Both SMT and SMX are set to the same voltage settings with upper limit of 127 and lower 106.  

Any idea why this happened with the SMT?

thanks,

Mike

[BillP]

Hi Mike - 

When it comes to use with a generator, Sensitivity settings are frequently more important than the voltage transfer points. The sensitivity circuit looks at Frequency, THD (total harmonic distortion), and dV/dT (rapid changes in voltage). I would suggest setting both units to Low sensitivity. They should then behave in a similar fashion during a generator test. The reason the SMT didn't come back online when you changed the sensitivity mid-test was likely due to the hysteresis of the sensitivity circuit in the UPS. Effectively, if falling below a threshold causes the UPS to switch to battery, it will then have to come back up higher than that initial threshold before the change of state will happen. This is to keep the UPS from chattering back and forth when the input power is very close to the threshold.  

Thanks,

Liam

[rinconmike_apc · Accepted solution]

thanks.