The Tripp Lite part number 73-0724 is a proprietary contact-closure serial cable used to connect OmniPro 450, OmniPro 675, OmniPro 280, and OmniSmart series UPS units to a PC serial port for monitoring with PowerAlert software. The UPS presents a DB-9 female port on its rear panel that carries contact-closure signals indicating line-fail and low-battery status; no serial data protocol is used. The cable cross-connects UPS relay outputs to the PC handshake inputs, with resistors biasing the DTR line to drive CTS and DCD inputs. Standard straight-through or null-modem cables are not suitable for this interface.
9 pin D-SUB male connector to the UPS
9 pin D-SUB female connector to the computer
| UPS Signal Name | DB-9 Male (UPS end) | DB-9 Female (PC end) | PC Signal Name |
|---|---|---|---|
| Ground | 1 | 3 | |
| AC Fail | 5 | 8 | CTS |
| LOW BATT | 6 | 1 | DCD |
| Inverter shutoff- | 4 | 5 | GND |
| Inverter shutoff+ | 2 | 7 | this wire includes one 1N4148 or 1N4149 diode |
Notes
- Pin 4 at the PC end (DTR) connected by R1 10kOhm to pin 8 (CTS) and by R2 10kOhm to pin 1(DCD)
- The DB-9 port on the UPS rear panel uses contact-closure signalling; the UPS closes relay contacts to signal AC failure or low battery rather than transmitting serial data.
- The 1N4148 or 1N4149 diode on the inverter shutoff+ wire provides reverse-polarity protection on the RTS line.
- Tripp Lite’s own owner’s manual for the OmniPro 675 confirms the DB-9 interface and PowerAlert software compatibility but does not publish the cable’s pin-level wiring; part number 73-0724 is required.
Signals
- Ground — UPS chassis ground, wired to PC pin 3 (TxD) to provide a common reference.
- AC Fail — Contact-closure output; UPS closes this contact when mains power fails, pulling PC CTS (pin 8) low.
- LOW BATT — Contact-closure output; UPS closes this contact when the battery is low, pulling PC DCD (pin 1) low.
- Inverter shutoff- — Negative side of the inverter shutdown relay contact; wired to PC GND (pin 5).
- Inverter shutoff+ — Positive side of the inverter shutdown relay; wired via a diode to PC RTS (pin 7), allowing the PC to command a UPS shutdown.