1762-OB16 — 1762 Series 16-Point 24V DC Transistor Output Module

The 1762-OB16 is a 16-point 24V DC sourcing transistor output module for the 1762 expansion bus. Sixteen solid-state outputs, each rated at 0.5A continuous, switch 24V DC loads without relay contacts or mechanical wear. For machines running dozens of solenoid valves, indicator lights, and 24V coil contactors that cycle frequently throughout the day, transistor outputs are the right call — contact wear and replacement cycles simply aren't a concern.

The outputs are organized into two groups of eight, each with its own output common terminal. This lets two different 24V DC supply circuits feed the two groups independently — useful when certain outputs need to be on a separate fused supply from the rest, or when supply redundancy for critical outputs is part of the design.

Specifications

Parameter	Value
Part Number	1762-OB16
Platform	1762 Series expansion
Output Points	16
Output Type	Sourcing (PNP) transistor
Output Voltage	24V DC (20.4–26.4V)
Output Current per Point	0.5 A continuous
Output Groups	2 × 8 points, separate output commons
Leakage Current (OFF state)	1 mA max
Voltage Drop (ON state)	1V DC max
Short-Circuit Protection	Yes (electronic, per group)
Operating Temperature	0°C to 60°C
Standards	IEC 61131-2, UL 508, CE

Load Types and Current Budget

Most 24V DC loads in a typical machine panel draw well under 0.5A per point. Typical figures to plan around:

LED pilot lights — 20–50 mA each. Sixteen of them simultaneously would draw under 1A total.
24V DC solenoid valves — 100–300 mA depending on valve size. At 300 mA per valve, six valves per group is comfortably within the 4A group limit.
24V coil contactors (small) — sealed power is typically 3–8W, so 125–330 mA. Inrush is higher for the first few milliseconds but the transistor output handles it without issue.
Relay coils (24V DC) — 50–150 mA per coil. Fit a flyback diode across each relay coil to suppress the inductive spike on turn-off.

Field Replacement Tips

When replacing a 1762-OB16 in a running system, a few steps prevent mistakes that take time to diagnose:

De-energize the I/O bus before removing the module. The 1762 expansion bus is not hot-swap capable.
Photograph or record the terminal wiring before disconnecting. The screw terminal positions on replacement modules are identical, but having a reference prevents transposition errors.
After re-energizing, verify all 16 outputs in the controller's I/O status display before running the machine. An output wired to the wrong terminal position causes the wrong field device to activate — catching this in monitor mode is much safer than finding it during a production run.

FAQ

Q: Can this module drive a 24V AC load?

No. The outputs are DC transistors and will not switch AC loads. For AC outputs, a relay output module is required.

Q: The module has short-circuit protection — does that mean I don't need output fusing?

The electronic short-circuit protection protects the module's output transistors. It does not protect field wiring from sustained overcurrent or replace branch circuit protection. External fusing on the output supply is still required for code compliance and wiring protection.

Q: Can sinking (NPN) sensors be used with these outputs?

The output type (sourcing vs. sinking) refers to the outputs, not inputs. The 1762-OB16 is sourcing outputs — it provides 24V to loads. Sensor input type is irrelevant to output module selection.

Q: Is a flyback diode needed on DC solenoid loads?

Strongly recommended. Inductive loads generate a voltage spike when the output turns off. The module has some internal transient suppression, but adding a diode directly across the solenoid coil keeps the spike from reaching the module at all and extends transistor life.

Q: How many 1762-OB16 modules can be added to one 1762 Series system?

The 1762 Series controller supports up to 6 expansion modules total. The specific combination of input and output modules depends on the controller variant — check the 1762 expansion I/O specifications for the exact I/O point and module count limits for the base unit in use.

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