New Allen Bradley 1756-PA75 ControlLogix AC power supply

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FAQs

Q1: What is the primary function of the 1756-PA75?

It is a backplane power supply that mounts on the left end of a ControlLogix 1756 chassis. It converts AC input power to regulated DC voltages (5V, 3.3V, 1.2V, and 24V) and distributes them through the chassis backplane to power all installed modules, including processors, communication cards, and I/O modules .

Q2: What input voltage does the 1756-PA75 accept?

The power supply accepts 85–265V AC at 47–63 Hz. The voltage input is auto-sensing, meaning no jumper or manual voltage selection is required — simply connect the AC line power and the supply will automatically adjust .

Q3: What are the output current capacities of this power supply?

The 1756-PA75 provides:

• 5V DC: 13 A

• 3.3V DC: 4 A

• 1.2V DC: 1.5 A

• 24V DC: 1.75 A (for field devices) 

Q4: What should I check if the power supply fails to start or trips intermittently?

Common causes include:

• Blown upstream fuse — ensure a 15A time-delay fuse is installed on ungrounded power connections 

• Overcurrent protection triggered — check for shorted I/O modules or backplane faults 

• Aging electrolytic capacitors — if the unit is over 10 years old, capacitor degradation can cause intermittent trips 

• Toggle switch operation — the front toggle switch is a hard power switch, not a reset button; cycling it performs a full power-on self-test 

Q5: What is the difference between the 1756-PA75 and 1756-PA75R?

The 1756-PA75 is the standard (non-redundant) power supply. The 1756-PA75R is the redundant version designed for critical applications. A redundant system requires two 1756-PA75R power supplies, a 1756-PSCA2 chassis adapter, and 1756-CPR2 cables. If one supply fails, the remaining supply accommodates the entire chassis load without disruption.