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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Input Voltage | 85–132 V AC / 170–250 V AC, 47–63 Hz |
| Typical Line Power | 240 VA |
| Max Inrush Current | 45 A |
| Backplane Current @ 5 V DC | 10 A |
| Backplane Current @ 24 V DC | 2.88 A |
| User Power Output | 1 A @ 24 V DC (20.4–27.6 V DC range) |
| Total Output Power Limit | 70 W (5 V + 24 V backplane + user combined) |
| Fuse Protection | Soldered in place (non-replaceable) |
| Isolation | 2600 V DC for 1 s |
| CPU Hold-up Time | 20 ms (full load) / 3000 ms (no load) |
| Operating Temperature | 0 °C to +60 °C (no derating) |
| Dimensions (H × W × D) | 140 × 110 × 145 mm (5.5 × 4.3 × 5.7 in) |
| Weight | Approx. 1.1 kg (2.5 lb) |
| Mounting | Left side of 1746 chassis (does not occupy a slot) |
4. Product Introduction
The Allen-Bradley 1746-P4 is the highest-capacity AC power supply in the SLC 500 family. It mounts on the left side of any 1746 chassis and supplies up to 10 A at 5 V DC and 2.88 A at 24 V DC to the backplane, plus a 1 A isolated 24 V DC user output.
Total combined output power must stay under 70 W. The unit accepts selectable 120/240 V AC input via jumper and provides 20 ms hold-up under full load. It is the standard choice for larger SLC 500 chassis with higher I/O and processor current demand.
1746-P4
1746-P4
1746-P4
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No POWER LED, chassis dead | No AC input or internal fuse open | ✅ High | Measure AC at L1/L2; confirm jumper position | Verify line voltage and jumper first |
| POWER LED on, modules drop offline | Overloaded supply or exceeded 70 W limit | ✅ High | Calculate total 5 V + 24 V + user watts; measure voltages | Reduce load or replace if voltages sag under load |
| Intermittent power loss | Thermal stress or failing internal components | ✅ High | Monitor chassis temperature and voltage under load | Replace if unit runs hot or voltage sags |
| Fuse opens immediately on power-up | Shorted module or wrong input jumper | ❌ Low | Isolate all modules; re-check 120/240 V jumper | Correct wiring/jumper before installing new unit |
| User 24 V DC missing or low | Overloaded user output or internal fault | ✅ Medium | Measure user terminals; confirm load ≤ 1 A | Reduce external load or replace supply |
| Chassis runs but CPU faults on power cycle | Insufficient hold-up during line dips | ❌ Low | Check for sags longer than 20 ms | Address upstream power quality |
If the unit still fails after these checks, provide voltage readings, load calculations, and photos to technical support.
6. Frequently Asked Questions (FAQ)
Q: Is the 1746-P4 still available new from Rockwell? No. The SLC 500 platform is discontinued. Available units are New Surplus or refurbished. Confirm current stock and lead time before ordering.
Q: Does the 1746-P4 require a voltage jumper? Yes. Set the jumper for 120 V or 240 V before applying power. The jumper location differs from the 1746-P1/P2. Wrong setting can damage the supply.
Q: Can I hot-swap the 1746-P4? No. Remove power to the entire chassis first. Hot-swapping risks damage to the backplane or the new supply.
Q: What is the absolute maximum load? 10 A at 5 V DC and 2.88 A at 24 V DC on the backplane, plus 1 A on the user 24 V output. Combined power of all three must not exceed 70 W. Exceeding this limit causes voltage drop or shutdown. Always calculate total module current first.
Q: Is this a direct replacement for an existing 1746-P4? Yes, provided the input voltage range and total current demand match. Confirm the jumper setting and verify the chassis load stays under 70 W total. Mounting is identical on the left side of any 1746 chassis.
Q: Why is New Surplus priced lower than original list? These are genuine Allen-Bradley units from excess inventory or cancelled projects. They are unused and typically supplied in original or anti-static packaging. They are not refurbished unless explicitly stated.
Q: Can the internal fuse be replaced? No. The fuse is soldered in place. If it opens, the entire power supply must be replaced.
