1769-OB8 — Compact I/O 8-Point 24V DC Sourcing Transistor Output Module

The 1769-OB8 is an 8-point sourcing (PNP) 24V DC transistor output module for the 1769 Compact I/O platform. Each point switches up to 0.5A, with all eight outputs sharing a single output common terminal. It's the compact output module for CompactLogix systems — eight solid-state 24V DC switching points in one I/O slot, without the wear and noise of relay contacts.

The 0.5A per point rating covers the standard range of 24V DC field devices: solenoid valves, 24V coil contactors, LED indicator lamps, relay coils, and small actuator enables. For machines where the per-point current demand is consistently under 0.5A, the 1769-OB8 delivers eight outputs per slot without the current headroom concerns that arise with larger loads. When loads exceed 0.5A, the 1769-OB16 (which offers higher per-point current) or relay output modules are the right alternatives.

Specifications

Parameter	Value
Part Number	1769-OB8
Platform	Compact I/O (1769)
Output Points	8
Output Type	Sourcing (PNP) transistor
Output Voltage	24V DC (20.4–26.4V)
Output Current per Point	0.5 A continuous
Output Groups	1 group of 8, single common
Max Group Current	4 A (all outputs on simultaneously)
Short-Circuit Protection	Electronic, per group
Leakage Current (OFF state)	1 mA max
ON-State Voltage Drop	1V DC max
Backplane Current (5V)	100 mA
Field Supply Current	24V DC user-supplied via output common terminal
Operating Temperature	0°C to 60°C
Standards	UL 508, CE, IEC 61131-2

Practical Load Planning

Most machines don't run all eight outputs at full current simultaneously, but the worst-case analysis needs to account for what could happen, not just what typically happens. A few common loads and their approximate current draws at 24V DC:

Standard 1/4-inch solenoid valve: 150–250 mA per valve
24V DC coil small contactor (sealed power): 50–150 mA
LED panel indicator: 20–60 mA
24V relay coil: 50–120 mA
Small pneumatic cylinder solenoid (3/2 or 5/2): 200–350 mA

A realistic eight-output load of 4 × 250 mA solenoids plus 4 × 100 mA indicators totals 1.4A — well within the 4A group limit. The group current budget becomes relevant when several high-current devices (multiple large solenoids or small motor contactors) share the same module. Add up the worst-case simultaneous load before specifying the module.

Replacing a Module in a Running System

The 1769 Compact I/O bus does not support hot-swap — the bus must be de-energized before removing or inserting a module. In practice this means taking the controller to program mode and removing power from the I/O bus before the replacement. Steps worth following consistently:

Confirm the controller is in Program mode and all outputs are de-energized before removing the module.
Photograph the terminal wiring before disconnecting — the screw terminals on a replacement module are in the same positions, but a reference photo prevents transposition errors when rewiring under time pressure.
After re-energizing, go online in Studio 5000 and verify all eight outputs in the I/O diagnostics screen before running the machine. A single transposed wire causes the wrong field device to energize and is much safer to catch in diagnostic mode than during a production run.

The 1769-OB8 has group-level electronic short-circuit protection — a fault on any output in the group shuts down all eight outputs until the fault is cleared. For applications where a faulted output must not take down the other seven, the 1769-OB16P (with per-point protection) is the appropriate choice, at the cost of more module slots per output count.

FAQ

Q: Can NPN (sinking) sensors trigger these outputs via the controller logic?

Output type (sourcing vs. sinking) is independent of input sensor type. The 1769-OB8 is sourcing outputs — it has nothing to do with how sensors on the input modules are wired. What matters for the loads is that they accept 24V sourced from the output terminal.

Q: What happens to outputs when the controller loses its I/O connection?

Default behavior on a lost connection is to de-energize all outputs. This is configurable in Studio 5000 — outputs can be set to hold their last state or go to a defined value on connection loss. For most machine safety applications, de-energizing on connection loss is the correct fail-safe behavior.

Q: Is external fusing required even though the module has short-circuit protection?

Yes. The electronic protection protects the module's transistors, not the field wiring. A fuse or circuit breaker on the 24V supply to the module's output common terminal protects the wiring from sustained faults and is required for electrical code compliance.

Q: Can the 1769-OB8 be used in a remote chassis over EtherNet/IP?

Yes. The 1769 Compact I/O system supports remote chassis connected via 1769-L3xE or standalone communication modules. The OB8 module functions identically whether it's in a local or remote I/O bus — the controller program addresses the output tags the same way regardless of the module's physical location.

Q: How do I know if my loads are within the 0.5A per point limit?

Check the field device datasheet for operating current (not inrush) at 24V DC. Most 24V solenoids, contactors, and indicators list this in the electrical specifications as rated coil current or power consumption. Divide watts by 24V to get amps if only power consumption is listed. If the current is ambiguous, measure it with a clamp meter during operation before committing to the module selection.

1769-OB8 New In Box CompactLogix 8 Pt 24VDC D/O Module 1769OB8