APC SMT1500IC - Incorrect Windows Critical Battery Level events (USB)

[ncr]

Hello everyone,

I have an APC SMT1500IC. I'm using Windows 11 and I've connected my UPS through USB. My UPS has the latest firmware. I am not using the APC software because I remember it had some battery monitoring bugs. It seems there's 1 bug in either the UPS's firmware or the Windows 11 driver. That bug causes Windows to get a critical battery level event ( <10% battery when the UPS is plugged in to the wall with power and the battery is at >98% ), causing Windows to either show a message / sleep / hibernate / shutdown.

I have this UPS for less than 6 months. This started happening this week, after a power outage. I had plenty of time to do a graceful shut down. I tried the old "turn everything off for a few minutes and back on", which didn't fix it.

Has anyone dealt with a similar situation with this specific model? Do I replace the USB cable? Do I wait for better Windows drivers or UPS firmware?

Thank you in advance!

[Teken]

You’ll need to cite the bugs / problems you stated for review. Regardless, connect the system to a computer running APC Power Chute (PCSS / PCBE) and report back the results.

Provide the following logs from the system: Event, Data, UPS. Show me the settings for this UPS as it relates to how it’s supposed to react during a grid down / lights out event.

Questions Ask . . . 👍

[ncr]

The first time I used APC Power Chute, I had this issue:

UPS-Communication-Lost - 339555 

This has not been fixed and it's been a problem for at least 4 years. For my case, it happens while using APC Power Chute (lose communication) or the default Windows driver (trigger critical power event when there's no actual event). It must be the UPS firmware mismanaging the USB connection somehow.

Settings:

Power quality	poor (otherwise I get a humming noise from the UPS)
Green mode	enabled
Sensitivity	low
Modbus Setting -> ser+usb	disabled

I tried uploading the logs.csv from smart connect here, but I get an error that "The file type (.csv) is not supported. Valid file types are: jpg, pbix, ...., .csv, .ktr, .kjb." 🤣

Here are the contents of the .csv:

Event Severity,Date,Device ID,Device Name,Event
"INFO","September 01 2025 at 11:41:51 AM","28298696B182","SMT1500IC","Communications Established"
"CRITICAL","September 01 2025 at 9:34:23 AM","28298696B182","SMT1500IC","Communications Lost"
"INFO","August 30 2025 at 11:48:21 AM","28298696B182","SMT1500IC","UPS Command (Self Test) Accepted"
"INFO","August 29 2025 at 7:25:31 PM","28298696B182","SMT1500IC","UPS Shutdown"
"INFO","August 29 2025 at 4:44:02 PM","28298696B182","SMT1500IC","UPS Shutdown"
"INFO","August 29 2025 at 1:46:49 PM","28298696B182","SMT1500IC","Communications Established"
"CRITICAL","August 29 2025 at 1:27:44 PM","28298696B182","SMT1500IC","Communications Lost"

I can try re-installing APC Power Chute if it provides better logs, but, as I mentioned above: there's a different issue with the USB.

Should I just go for the serial cable route too and we ignore this issue?

[Teken]

I would seriously consider using the supplied RJ50 - RS232 Serial cable with a USB Adapter as outlined in that APC Forum link.

Still waiting to see the three logs from this system along with the UPS ID / UPS Firmware installed.

You may also try disabling (Green Mode) to see if it changes the behaviour. I haven’t seen this next step yield any positive difference though.

Questions Ask . . . 👍