The AP9584 serial-to-USB conversion kit for older APC UPS models with a serial host interface is the manufacturer-endorsed solution for interfacing such older UPS units with a USB-based host computer. However, it is specified on the label for “use with APC Back-UPS and Back-UPS Pro only”. Will it work with a Smart-UPS unit?
Initially, it would seem so – all the variables are read properly. However, after a period of 30 days or so, and generally unnoticed to the operator, the “LB” (Low Battery”) status flag is flipped on, while nothing is actually wrong with the battery. This does not cause an immediate problem. However, the next time the UPS does a periodic self-test, the “OB” (“On Battery”) status flag will be temporarily set as is expected during a self-test cycle. However, from the perspective of UPS monitoring software, the combination of LB and OB means “The UPS is nearly dead, so shut down the system cleanly”. As a result, every system listening to the UPS monitoring software would immediately (and cleanly) shut down, and then dutifully wait for a UPS power-cycle that never came!
- I thought at first this was an anomaly with the particular UPS (Smart-UPS 1500), so I switched to a Smart-UPS 1000. Same result.
- I thought then that I had just gotten a defective cable, and bought another AP9584 to test. Same result.
- I then replaced the AP9584 with a good old APC 940-0024C and a Kawamall USB to DB9 (male) serial converter. After months, the problem never happened again!
The Kawamall USB to serial converter has USB vendor:device 1a86:7523 corresponding to a QinHeng Electronics HL-340. Others have noted that Prolific converters also seem to work.
In any case, don’t bother trying to use the APC AP9584 on a Smart-UPS – there seems to be a bug that will cause your systems to be powered off unexpectedly. Just use a normal USB-to-serial converter with the APC 940-0024C or similar smart monitoring cable.