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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Input Voltage | 85–132 V AC / 170–265 V AC, 47–63 Hz |
| Typical Line Power | 135 VA |
| Max Inrush Current | 20 A |
| Backplane Current @ 5 V DC | 2 A |
| Backplane Current @ 24 V DC | 0.46 A |
| User Power Output | 200 mA @ 24 V DC (18–30 V DC range) |
| Fuse Protection | 1746-F1 or equivalent (3 A, 250 V) |
| Isolation | 1800 V AC RMS for 1 s |
| CPU Hold-up Time | 20 ms (full load) / 3000 ms (no load) |
| Operating Temperature | 0 °C to +60 °C (derate 5% above 55 °C) |
| Dimensions (H × W × D) | 140 × 58 × 145 mm (5.5 × 2.3 × 5.7 in) |
| Mounting | Left side of 1746 chassis (does not occupy a slot) |
4. Product Introduction
The Allen-Bradley 1746-P1 is the standard AC power supply for SLC 500 modular chassis. It mounts on the left side of the 1746 chassis and delivers regulated 5 V and 24 V DC to the backplane plus a limited 24 V DC user power source for external devices.
It supports 120/240 V AC selectable input via jumper and provides 2 A at 5 V DC with 0.46 A at 24 V DC. Hold-up time of 20 ms under full load helps ride through brief power dips. Common in existing SLC 500 installations where a direct drop-in replacement is required.
1746-P1
1746-P1
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No POWER LED, chassis dead | No AC input or blown fuse | ✅ High | Measure AC at L1/L2 terminals; check fuse continuity | Verify line voltage and jumper setting first |
| POWER LED on, no module LEDs | Overloaded backplane or failed supply | ✅ High | Calculate total 5 V/24 V draw; measure backplane voltage | Replace if voltages out of tolerance under load |
| Intermittent power loss | Thermal derating or failing capacitors | ✅ High | Monitor temp; check for voltage sag under load | Replace if unit exceeds 55 °C or sags |
| Fuse blows immediately on power-up | Shorted module or wrong input jumper | ❌ Low | Isolate all modules; confirm 120/240 V jumper position | Fix wiring/jumper before installing new supply |
| User 24 V DC missing or low | Overloaded user output | ✅ Medium | Measure user terminals; confirm load ≤ 200 mA | Reduce external load or use separate supply |
| Chassis runs but CPU faults on power cycle | Insufficient hold-up time | ❌ Low | Check for line sags longer than 20 ms | Address upstream power quality |
If the unit still fails after these checks, pull diagnostic photos and voltage readings and contact technical support.
6. Frequently Asked Questions (FAQ)
Q: Is the 1746-P1 still available new from Rockwell? No. Rockwell discontinued the SLC 500 line. Remaining units are New Surplus or refurbished stock. Lead times and availability vary; confirm current inventory before ordering.
Q: Does the 1746-P1 need a voltage jumper set? Yes. Set the jumper for 120 V or 240 V before applying power. Wrong position can damage the supply or blow the fuse. Always match the jumper to the actual line voltage.
Q: Can I hot-swap the 1746-P1? No. Kill power to the chassis first. Hot-swapping risks damaging the backplane or the new supply.
Q: What is the maximum load this supply can handle? 2 A at 5 V DC and 0.46 A at 24 V DC on the backplane, plus 200 mA on the user 24 V output. Exceeding either rating causes voltage drop or shutdown. Calculate total module current before installing.
Q: Is this a direct replacement for an existing 1746-P1? Yes, provided the input voltage range and current demand match. Confirm the jumper setting and total chassis load. It mounts the same way on the left side of any 1746 chassis.
Q: Why is New Surplus cheaper than original factory pricing? These are genuine Allen-Bradley units that were excess inventory or project overstock. They are unused and typically come with original packaging or anti-static protection. They are not refurbished unless specifically stated.
Q: What fuse does the 1746-P1 use? 1746-F1 or equivalent 3 A, 250 V fuse. Keep spares on hand; the fuse is intended for short-circuit protection and may open under certain fault conditions.
