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APC Smart UPS USB to serial port workaround and guide
I have an APC Smart UPS 1000 that I obtained from work after they retired an old server several years ago.  After replacing the batteries, the UPS worked fine for about 4 years and then its USB port started intermittently dropping out.  This resulted in "USB Device Not Recognized" pop-ups and "UPS communication lost" errors within the PowerChute status page.  After a few weeks, the USB port ceased working altogether on the UPS.  I tried the brain dead reset procedure a few times, but without any luck getting the USB port to work again.

As this UPS also has a 9-pin serial port on the back, it made me wonder whether this port still works and whether I could use it with the serial port being obsolete on PCs.  Although the USB port did not work, the UPS was otherwise fully functional, transferring to battery during power cuts and able to perform a self-test.  It just lacked the ability to tell the PC to safely shutdown once its battery ran down during longer power cuts due to the defective USB port.

After plenty of searching, I found that APC uses a non-standard serial port on its Smart UPS range, requiring the original APC serial cable that I did not have.  Another problem is that my PC does not have a serial port to connect to.  So after checking through user reviews of USB to serial adapters, I found a specially made cable on AliExpress (search for APC 940-0024).  This one does not require APC's serial cable inline, unlike the other USB to serial adapters I came across.

As serial ports are not plug and play, this does require some setting up as shown below and reinstalling PowerChute, which wipes all its stored data.  What I can confirm is the UPS appears to be working fine with the serial port with PowerChute working (see updates below).  It shows the voltage readings, UPS load, temperature, etc just like it did previously with the USB port.

Setting up the serial cable:
  1. If you previously used a USB cable, remove this cable.  Take note of the settings in PowerChute, e.g. take screenshots of the various configuration screenshots.  Uninstall PowerChute from the PC.  This is required to change from USB to a serial port.
  2. Attach the new USB to serial cable to the PC.  Do not attach the serial end to the UPS yet (see Update #2 below).
  3. Shutdown the PC, turn off the UPS and and unplug the mains power to the UPS.
  4. Remove the battery connector at the back of the UPS.  If this is not present (e.g. USA model), disconnect the battery inside the UPS.
  5. Hold the power off button on the UPS for 10 seconds.  This performs a "Brain dead" reset, which lets it switch to the serial port. 
  6. Reattach the battery / connector.
  7. Hold the power on button on the UPS until it starts up on battery, then connect the mains power to the UPS.  By powering up the UPS on battery first, this prevents the cold start-up surge that can trip a ground fault / circuit breaker.
  8. Boot the PC back into Windows.
  9. At present, device manager will show the USB device as "ft231x usb uart driver" missing its driver.  This needs to be obtained through windows update in the following steps.
  10. Go into the Start menu -> Settings (cog wheel icon) -> Update & Security.
  11. Click "Check for updates".  Windows will search online for the USB driver as it searches for updates. 
  12. Once it finishes checking for updates, click "View optional updates".
  13. Tick the "FTDI - USB" option and click "Download and install".
  14. Once this completes, go back to Windows Update and click "Check for updates" again.
  15. Once it finishes checking for updates, click "View optional updates" again.
  16. Tick the "FTDI - Ports" option and click "Download and install".
  17. Once this finishes, right-click the Start button and click Device Manager.
  18. Go into Ports (COM & LPT).
  19. Double-click the "USB Serial Port" entry. Take note of the COM number.  E.g. it shows as COM5 on my PC.
  20. Go into the Port Settings tab, then click 'Advanced'.
  21. Clear the check box for "Serial Enumerator",  then click OK.  This prevents Windows detecting the UPS as a serial mouse, which can cause the mouse cursor to go erratic. 
  22. Attach the serial cable end of the USB adapter to the UPS.
  23. Download the APC PowerChute Business Edition and start the Installer.
  24. When it asks to search for the UPS, click 'No'.  Whenever I tried clicking 'Yes' here, the installer kept closing out without going any further.
  25. Choose the COM port noted above. 
  26. For the UPS type, check the model # on the back of the UPS.  With my Smart UPS 1000 from around 2004, it started with UAC. 
  27. You can now proceed with the rest of the installation just like when using its USB port.
  28. If you previously used the UPS with its USB port, you'll need to reconfigure its settings, i.e. check through the screenshots taken from step #1. 
  29. If PowerChute continues to show that communication is lost, try rebooting or performing another "Brain dead" procedure, i.e. steps #3-7.

Update 2nd June 2021: On the day I originally posted this guide, the serial port dropped out a few hours later that day which I'm not sure was caused by Windows falsely detecting it as a serial mouse or a more serious issue with its logic board.  I performed another "brain dead" procedure on my UPS (steps #3 to #8 above) and the Windows mouse went erratic during the following boot, randomly moving and clicking about the screen.  This is before I added steps #18 to #22 above. 

Since preventing Windows detecting the UPS as a mouse (i.e. steps #18-22), PowerChute continues to provide readings and has not reported any further drop outs from the serial port, so will see how long it lasts.

If the UPS drops out again, I will update this post.

PowerChute main screenshot, connected using the serial to USB cable:


Data page - I've mine set to record every 5 minutes.  Although there's no export option, this table can be easily copied into a spreadsheet such as LibreOffice Calc to produce graphs.

Just to update, there has not been a single communications lost record in the data log since the first of June, the day I disabled the serial enumerator setting (where I added steps 18-22 above).

Even before the USB port stopped working on my UPS, I don't recall it being this stable, at least not over the few years I owned it.

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