Description
The Allen-Bradley 1756-PB72 is a non-redundant, slot-mounting DC power supply designed to provide regulated backplane power to a single 1756 ControlLogix chassis. It installs directly onto the left-hand side of any standard ControlLogix chassis (such as the 1756-A4, 1756-A7, 1756-A10, 1756-A13, or 1756-A17) and connects directly to the backplane connectors. Operating from a nominal 24 V DC input source, the unit provides internal current to the 1.2 V, 3.3 V, 5.1 V, and 24 V DC backplane rails to power processors, I/O modules, and communication adapters.
Commercial Availability & Procurement Terms
- Condition: New Original (Factory Sealed Surplus)
- Warranty: 12-Month Functional Warranty
- Availability: In Stock
- Standard Lead Time: Ships within 1–2 business days via global couriers (DHL, FedEx, UPS)
- Pricing Policy: Indicative pricing only. Price fluctuates based on component availability and global market conditions. Contact our sales department for a formal, time-bound quote.
Technical Specifications
| Parameter | Specification / Value |
| Model Number | 1756-PB72 |
| Product Series | ControlLogix System |
| Manufacturer | Rockwell Automation / Allen-Bradley |
| Input Voltage Range | 18 to 32 V DC |
| Nominal Input Voltage | 24 V DC |
| Maximum Input Power | 95 W |
| Output Power | 75 W maximum at 0 to +60 °C (+32 to +140 °F) |
| Backplane Current Load (1.2 V DC) | 1.5 A maximum |
| Backplane Current Load (3.3 V DC) | 4.0 A maximum |
| Backplane Current Load (5.1 V DC) | 13.0 A maximum |
| Backplane Current Load (24 V DC) | 2.8 A maximum |
| Isolation Voltage | 250 V continuous (reinforced insulation type), input-to-backplane |
| Mounting Position | Left side of 1756 chassis (Dedicated power slot) |
| Operating Temperature | 0 to +60 °C (+32 to +140 °F) |
| Weight | 0.93 kg (2.10 lb) |
Deployment Constraints & Engineering Notes
1. Backplane Current Capacity Calculations
The 1756-PB72 provides a cumulative maximum output power of 75 W, but each individual voltage rail has strict current limitations.
Field Warning: Do not exceed the rated current limit for any individual voltage rail (e.g., 13.0 A for the 5.1 V DC rail) when populating a large chassis with high-density analog or specialty modules. Exceeding any single rail limit will trigger thermal or overcurrent protection, dropping the entire backplane offline even if the total wattage is under 75 W. Use the Rockwell Automation Integrated Architecture Builder (IAB) tool to calculate total backplane draw before deployment.
2. Inrush Current and Power Sourcing
During initial power-up, the 1756-PB72 exhibits a high inrush current spike that can reach up to 30 A for up to 20 ms.
- Sizing Upstream Power Supplies: Ensure the 24 V DC bulk power supply feeding the 1756-PB72 can handle this inrush without voltage sagging or entering a current-limiting hiccup mode.
- Wire Gauge: Use a minimum wire size of 2.5 mm² (14 AWG) solid or stranded copper wire rated for 75 °C (167 °F) or higher for the input power connections to minimize voltage drop across long wire runs.
3. Non-Redundant Restrictions
The 1756-PB72 cannot be used in a parallel or redundant configuration with another power supply on the same chassis. If your application mandates high-availability power uptime, you must upgrade to a redundant power supply system utilizing a 1756-CPR2 cable and a pair of 1756-PB75R redundant power modules linked to a 1756-PSCA2 chassis adapter card.
Frequently Asked Questions
Can the 1756-PB72 be hot-swapped while the chassis is running?
No. You must isolate the 24 V DC input power supply before removing or installing the 1756-PB72. Disconnecting the power supply while the backplane is energized can cause electrical arcing, which can permanently damage the chassis backplane connectors and any active controllers or I/O modules installed in the slots.
What causes the green “INPUT OK” LED to turn off or blink?
The “INPUT OK” status indicator monitors the incoming DC voltage. If this indicator turns off, it indicates that the input voltage has dropped below the minimum operational threshold of 18 V DC or has been disconnected entirely. If it blinks, there may be an internal fault or overcurrent condition on the chassis backplane; isolate the system and verify the module power requirements.
Does this power supply require a specific chassis revision?
The 1756-PB72 is physically compatible with all standard ControlLogix Series A and Series B chassis (such as the 1756-A10). However, always cross-reference the physical dimensions and clearing recommendations in the Allen-Bradley installation manual to ensure proper convection cooling space inside your enclosure.
