Testing and serial connection

Post date: Nov 9, 2019 6:37:24 PM

As I want to use the UPS with its RS232 interface, I looked for a cable to connect the UPS to a standard DB9 connector. Apparently, the jack on the UPS is an RJ50, a slightly wider variant of the well known RJ45 with 10 wires versus 8. As I could not find such a jack anywhere, I decided to open up the unit to see if I could solder wires on the board directly. It is not clear why APC decided to go with the RJ50, as only a few wires on the jack actually connect to anything.

However, when browsing for the pinout, it was mentioned that an RJ45 fits fine, albeit a bit loose. A page on the APC website confirms that the 'emulated' cable type should work.

For reference, I have summarized the information from pinoutguide.com in the image below.

After making this cable, I did not seem to get any response from the UPS when using the infromation from NUT's APC Smart protocol description. I rewired the cable, verified again and again but nothing appeared on the terminal.

I figured the best way to verify my cable was on a window box with the APC application, PowerChute. And lo and behold, PowerChute immediately recognized the UPS connected on my PL2303 USB-to-serial adapter...