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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Catalog Number | 1746-OB32 |
| Module Type | 32-Point DC Sourcing Output |
| Number of Outputs | 32 |
| Points per Common | 16 (two isolated groups) |
| Voltage Category | 24 V DC |
| Operating Voltage Range | 5–50 V DC (source) |
| Continuous Current per Point | 0.50 A @ 30 °C (86 °F); 0.25 A @ 60 °C (140 °F) |
| Continuous Current per Module | 8.0 A @ 0–60 °C |
| Continuous Current per Common | 4.0 A @ 0–60 °C |
| Continuous Current per Common Pin | 2.0 A @ 0–60 °C |
| On-State Voltage Drop | 1.2 V max @ 0.5 A |
| Off-State Leakage Current | 1 mA max |
| Minimum Load Current | 1 mA |
| Surge Current per Point | 1.0 A for 10 ms |
| Signal Delay (Resistive Load) | On = 0.1 ms; Off = 1.0 ms |
| Backplane Current | 190 mA @ 5 V DC; 0 mA @ 24 V DC |
| Isolation | 1500 V AC for 1 minute (field to backplane) |
| Operating Temperature | 0 °C to 60 °C (32 °F to 140 °F) |
| Storage Temperature | −40 °C to 85 °C (−40 °F to 185 °F) |
| Chassis Location | Any I/O slot except slot 0 |
| Connector | 40-pin keyed female connector (crimp pins or 1492 prewired cables) |
| Weight | Approx. 0.37 kg (0.81 lb) |
4. Product Introduction
The Allen-Bradley 1746-OB32 is a high-density 32-point DC sourcing discrete output module for the SLC 500 platform. It switches loads across a 5–50 V DC range and is organized into two groups of 16 points, each with its own VDC and common connections. Continuous current is limited to 0.5 A per point at 30 °C (0.25 A at 60 °C) and 8 A total per module.
This module is used where chassis space is limited and a large number of low-to-moderate current DC outputs are required. Series D units removed the internal fuses found on earlier series and support the full published current ratings when both VDC pins of a group are connected. Optical isolation protects the backplane, and individual LED indicators show the state of each output.
1746-OB32
1746-OB32
5. Installation & Configuration Guide
Stage 1: Pre-Installation Preparation (5–10 minutes) ⚠️ Safety First: Notify operations of planned downtime. Place the process in a safe state. Lock out/tag out all power sources to the chassis and field devices. Wait at least 5 minutes for capacitors to discharge. Tools Required: Grounded ESD wrist strap, PH1 screwdriver, digital multimeter, wire labels, smartphone or camera for reference photos, appropriate crimp tool if using discrete pins. Data Backup: Export the current RSLogix 500 project. Document the module slot number and existing output addresses. Photograph the existing connector wiring and the old module label (including series letter).
Stage 2: Removing the Old Module (5–8 minutes)
- Remove the front cover if present.
- Label every field wire or note the 1492 cable orientation, then carefully disconnect the 40-pin connector. Do not pull on individual conductors.
- Release the self-locking tabs on the top and bottom of the module and pull it straight out of the chassis. Avoid rocking the module to protect the backplane connectors.
- Inspect the chassis backplane pins for bent contacts or debris. ⚠️ Keep the old module available until the new unit is verified and running under process conditions.
Stage 3: Installing the New Module (8–12 minutes)
- Put on the ESD wrist strap and ground it. Confirm the replacement is exactly 1746-OB32 and note the series letter.
- Configuration Note: The 1746-OB32 has no DIP switches or jumpers. Output behavior is controlled solely by the ladder program addressing the output image bits.
- Seat the new module firmly into the same chassis slot until the locking tabs click.
- Reconnect the 40-pin connector or 1492 prewired cable exactly as photographed. For maximum current capacity on Series D modules, connect both VDC pins of each group to the DC supply. Apply appropriate surge suppression (typically a reverse-biased diode across inductive loads). Self-Checklist: [ ] Connector fully seated and keyed correctly [ ] Both VDC pins connected if high group current is expected [ ] Locking tabs engaged [ ] Total module and group currents within temperature limits
Stage 4: Power-On & Testing (10–15 minutes) Pre-Power Check: With a multimeter, verify no short circuits exist between the field supply and DC commons or chassis ground. Power-On Steps:
- Restore power to the chassis only (field devices still isolated if possible).
- Observe the module status and individual output LEDs. Each output LED should illuminate when the corresponding output bit is commanded ON.
- Connect the programming terminal, go online with RSLogix 500, and verify the module appears correctly in the I/O configuration.
- Force or toggle individual output bits and confirm field devices respond. Measure voltage drop and current on representative points under load.
- Restore full field power and run a controlled process test. ⚠️ Troubleshooting Note: If an output LED is on but the field device does not energize, check field supply voltage, wiring polarity, and load current. Series A/B/C modules contain non-replaceable fuses; a blown fuse requires module replacement. Series D modules have no internal fuses—external fusing is required. Exceeding the 0.25 A per point rating at elevated temperature is a common cause of premature failure.
6. Frequently Asked Questions (FAQ)
Q: Can the 1746-OB32 be hot-swapped under power? No. Inserting or removing the module with chassis power applied risks damaging the backplane connectors and the module. Always remove power first.
Q: Is the 1746-OB32 obsolete, and is stock genuinely new? Yes, the SLC 500 platform and this module have been discontinued by Rockwell. Available units are typically new surplus or carefully tested new-old-stock. Verify series letter (especially Series D versus earlier fused series) and date code on the label before installation.
Q: What is the recommended direct replacement if 1746- stock is exhausted? Within the SLC 500 family the 1746-OB32E (electronically protected version) is the closest functional equivalent, though voltage range is narrower (10–30 V DC). For new designs Rockwell directs users to CompactLogix or ControlLogix high-density DC output modules. Wiring, addressing, and connector style will change, so plan a program and terminal revision.
Q: Will I lose my programming logic when I replace the module? The processor retains the user program. Output addresses remain the same provided the module stays in the same slot. No configuration words need to be rewritten because the 1746- has no programmable parameters.
Q: Why is the price often lower than original Rockwell list prices? Because the module has been obsolete for years. New surplus and tested stock from reputable channels typically sell below original factory list. Condition, series, and included connector or cable affect pricing.
Q: Does this module require external fusing or special cabling? Yes. Series A/B/C modules have internal non-replaceable 2.5 A fuses per common; Series D modules have none. External fusing is required for short-circuit protection on all series. The module uses a 40-pin keyed connector rather than a standard removable terminal block. Allen-Bradley 1492 prewired cables and interface modules are commonly used for field wiring.
Q: What are the main current and temperature limitations I must respect? At 30 °C ambient each point is rated 0.50 A and the module total is 8.0 A. At 60 °C these drop to 0.25 A per point. Each common is limited to 4.0 A, and each common pin to 2.0 A. To reach the full common rating on Series D modules, both VDC pins of the group must be connected. Exceeding these values shortens life or causes thermal limiting.
