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The CompactLogix Power Supply Selection Guide

Allen Bradley offers CompactLogix power supplies to meet the power requirements of CompactLogix controllers. Allen Bradley has two families of CompactLogix power supplies, 1768 CompactLogix, and 1769 compact input/output (I/O) expansion power supplies. These power supplies are specifically for powering the 1768 CompactLogix controllers, 1768 I/O modules, 1769-L3x CompactLogix controllers, and 1769 compact I/O modules.

The first section of this article will discuss the specifications and benefits offered by these families of power supplies in detail. The second section will discuss the procedure for the selection of a suitable power supply as per system architecture.

Specification of CompactLogix Power Supplies 

These supplies deliver power to controllers via the CompactLogix backplane. The backplane is built into the Allen Bradley’s 1768 and 1769 families of controllers, I/O modules, and power supplies.

While selecting a power supply, it is essential to analyze its specifications to pick one with the appropriate functionality. Let’s discuss the specifications of CompactLogix power supplies.

Supply Type: The 1768 CompactLogix power supply family offers both dual-input and single-input power supplies. Whereas the 1769 power supply family only has single-input power supplies.

The 1768 dual input power supply is operable by both alternating current (AC) and direct current (DC). The 1768 single-input power supply, on the other hand, can only be powered by either alternating current or direct current.

Input Voltage: For both power supply families, the nominal input voltage for AC to DC power supplies is 120 /220 volts and for DC to DC power supplies is 24 volts.

However, the input voltage has multiple ranges depending on the power supply’s catalog number. The 1768-PA3 is a dual supply and offers an input voltage range of 108 – 132 volts DC or 85 – 265 volts AC. The input voltage range is 16.8 – 31.2 volts DC for 1768-PB3, 19.2 – 31.2 volts DC for 1769-PB4 and 1769-PA2, and 85 – 265 volts AC for 1768-PA2. The 1768-PA4 power supply has two switch-selectable input ranges, 85 to 265 volts AC or 170 to 265 volts AC.

Input Frequency: The input frequency range for all AC CompactLogix power supplies is 47 hertz to 63 hertz.

Output Voltage and Current: The 1786 CompactLogix power supplies can provide a maximum of 3.5 amperes and a minimum of 0.25 amperes at an output voltage of 24 volts DC. The 1769 compact I/O power supplies can either supply an output current of 2 /0.8 amperes at an output voltage of 5 /24 volts DC or 4 /2.0 amperes at an output voltage of 5 /24 volts DC. For example, 1769-PA2 and 1769-PB2 can supply 2 amperes at 5 volts DC and 0.8 amperes at 24 volts DC.

All CompactLogix power supplies provide backplane power, but some power supplies come with an external output terminal. Only 1768-PA3, 1768-PB3, and 1769-PA2 power supplies come with an external output terminal. This user-accessible terminal block is rated at 24 volts DC and can supply a maximum of 0.25 amperes.

Output Specifications of CompactLogix Power Supplies 

Catalog No  Output capability 
1768-PA3  3.5 amperes backplane current at 24 volts DC 
1768-PB3  0.25 amperes external current at 24 volts DC 
1769-PA2 /1769-PA2K  2 amperes at 5 volts DC 
1769-PB2 /1769-PB2K  0.8 amperes at 24 volts DC 
1769-PA4 /1769-PA4K  4 amperes at 5 volts DC 
1769-PB4 /1769-PB4K  2 amperes at 24 volts DC 

Power Specifications: The 1768 CompactLogix power supplies have a typical efficiency of 75% to 80%. 1768-PA3 can consume a maximum power of 120 volt-ampere /120 watts. 1768-PA3 supplies a maximum of 90 watts and dissipates 30 watts maximum. 1768-PB3 can consume a maximum of 112 watts at 24 volts DC, deliver a maximum of 90 watts, and dissipates 22 watts maximum.

1769 compact I/O power supply family offers power supplies with a power consumption of 50 to 240 volt-ampere and power dissipation of 7.5 – 15 watts at 60 degrees Celsius.

Power Specifications of CompactLogix Power Supplies 

Catalog No Power Consumption Power Dissipation 
1768-PA3 120 volt-ampere at 120 /220 volts AC 120 watts at 24 volts DC  30 watts 
1768-PB3 112 watts 22 watts 
1769-PA2 /1769-PA2K 100 volt-ampere at 120 volts AC 130 volt-ampere @ 240 volts AC  8 watts at 60 degrees Celsius 
1769-PB2 /1769-PB2K 50 volt-ampere at 24 volts DC 7.5 watts at 60 degrees Celsius 
1769-PA4 /1769-PA4K 200 volt-ampere at 120 volts AC 240 volt-ampere at 240 volts AC  18 watts at 60 degrees Celsius 
1769-PB4 /1769-PB4K 50 volt-ampere at 24 volts DC 14.5 watts at 60 degrees Celsius 

Overcurrent Protection: The 1768 CompactLogix power supplies come with overcurrent protection. When overcurrent happens in these supplies, their outputs latch off till the overcurrent is cleared. Reasons for the overcurrent condition can be short-circuiting or line transients.

The 1768 CompactLogix power supplies come with a soldered fuse. It offers overcurrent protection of 15 amperes. However, this fuse is not replaceable. The 1769 compact I/O power supplies have fuses that can be replaced easily. The compatible fuses for 1769 power supplies are listed below;

Compatible Fuses for 1769 Compact I/O Power Supplies 

Catalog No Fuse Type Specifications 
1769-PA2 /1769-PA2K Wickmann 19195 Littelfuse 02183.15MXP 3.15 amperes, 5 millimeters x 20 millimeters 
1769-PB2 /1769-PB2K Wickmann 19193 Littelfuse 021706.3MXP 6.3 amperes, 5 millimeters x 20 millimeters 
1769-PA4 /1769-PA4K Wickmann 19195 Littelfuse 02183.15MXP 3.15 amperes, 5 millimeters x 20 millimeters 
1769-PB4 /1769-PB4K Wickmann 19193 Littelfuse 021706.3MXP 6.3 amperes, 5 millimeters x 20 millimeters 

Inrush Current: Inrush current is the high current drawn by a power supply from its mains for an infinitesimally short time interval /instant. It is also known as a switch-on surge as the power supply draws this current on turning on. It is required to charge capacitors to avoid voltage sag.

The CompactLogix power supply from Allen Bradley allows for a brief inrush current ranging from 25 amperes to 80 amperes. The inrush current values for each catalog are listed below.

CompactLogix Power Supplies Inrush Current Data

Catalog No Maximum Inrush Current 
1768-PA3 50 amperes at 85 to 132 volts AC 80 amperes at 195 to 265 volts AC 
1768-PB3 50 amperes at 16.8 to 31.2 volts DC 
1769-PA2 /1769-PA2K 25 amperes at 132 volts AC 
1769-PB2 /1769-PB2K 30 amperes at 31.2 volts DC 
1769-PA4 /1769-PA4K 25 amperes at 132 volts AC 
1769-PB4 /1769-PB4K 30 amperes at 31.2 volts DC 

Status Indicators: Allen Bradley’s CompactLogix power supply comes with a PWR LED status indicator. This indicator helps you to identify the issue and take appropriate actions accordingly.

PWR LED Interpretation 
OFF The power source has been switched off or there is insufficient input power. The system has a short/overload fault. The power supply has to be replaced. 
GREEN The power supply is functioning. 
RED The power supply is unable to give genuine 24 volts of power to modules. 

Power Source Loss: Allen Bradley’s 1768 and 1769 power supply may handle momentary power outages without disrupting the performance of the system. The ride-through time is the amount of time during which the system is completely functional during a power outage. This time ranges from 5 milliseconds to 25 milliseconds for both families.

If the power supply is still off after ride-through time, a new period, known as the hold-up time, begins. The power supply partially supports the power of the system for some time, known as hold-up time. For both families, the hold-up time is typically 5 milliseconds to 10 milliseconds. If the power outage lasts longer than the hold-up time, the power supply can’t cater to the system power requirements properly.

Power Supply Position In the System: The 1768 CompactLogix power supplies distribute power from their right side. That’s why they must be the system’s leftmost module.

The 1769 CompactLogix power supplies are capable of distributing power from both the supply’s right and left sides. Input/output modules for the 1769 power supply can be mounted on either side of the power supply. Up to 8 I/O modules are allowed on either side of these power supplies. It implies that a maximum of 2 banks of I/O modules or 16 I/O modules can be supported.

Distance Rating: The 1768 CompactLogix power supply series does not have a distance rating. Because the 1768 modules do not take into a distance rating to the 1768 power supply and the 1769 input/output modules in the 1768 system have a distance rating from the controller rather than the 1768 power supply.

The 1769 Compact I/O power supply has a distance rating. It is a crucial consideration when connecting a 1769 I/O module. Each module must be placed within the distance rating indicated for it. The 1769 compact I/O power supplies have a power supply distance rating of 8 modules. It means that 8 input /output modules can be connected on either side of the supply, up to 16 modules.

Environmental Specifications: Allen Bradley’s 1768 and 1769 power supply families’ operating temperatures are 32 degrees Fahrenheit to 140 degrees Fahrenheit. When these power supplies are not ON or functional, you must store them in place, having temperatures of -40 degrees Fahrenheit to 185 degrees Fahrenheit.

These power supplies come with T3C, T4, and T5 American temperature codes.

Physical Dimensions: The physical dimensions of Allen Bradley’s CompactLogix power supplies are tabulated below.

Catalog No Weight (pounds) Dimensions (H x W x D) (millimeters x millimeters x millimeters) 
1768-PA3 2.15 131.25 x 132.75 x 105.50 
1768-PB3 2.22 131.25 x 132.75 x 105.50 
1769-PA2 /1769-PA2K 1.16 118 x 70 x 87 
1769-PB2 /1769-PB2K 1.16 118 x 70 x 87 
1769-PA4 /1769-PA4K 1.39 118 x 70 x 87 
1769-PB4 /1769-PB4K 1.39 118 x 70 x 87 

How to Choose CompactLogix Power Supply for your CompactLogix Controllers 

These steps can help you decide on a power supply for your system quickly. 

  • Choose a CompactLogix controller as per your system requirements. If it is CompactLogix 1768 or 1769 controller, move to step 2. 

As mentioned above, these supplies are specifically designed for 1768 and a769 power systems. 

  • Check which power supply is compatible with your chosen controller. The table below includes the possible 1768 and 1769 CompactLogix controllers and compatible CompactLogix power supplies. 

Controllers versus Compatible Power Supplies 

Controllers1768-PA3   1768-PB3 1769-PA2 1769-PB2 1769-PA4 1769-PB4 
1768-L43     
1768-L43S       
1768-L45     
1768-L45S     
1769-L30ER    
1769-L33ER   
1769-L37ERM   
1769-L38ERM   
1769-L30ERM   
1769-L31    
1769-L32C   
1769-L32E   
1769-L32EK   
1769-L35E   
1769-L35CR   
  • Refer to the specifications of power supplies mentioned in section 1 while linking it with the “Controllers versus Compatible Power Supplies” table. If you have chosen the power supply. It’s time to determine the number of power supplies needed for a system. 
  • The two main scenarios while estimating the number of power supplies for your system can be; 

Case 1: If you have chosen CompactLogix 5370 L3 controller, known as the 1769 CompactLogix controller. Then you need 

  •  One 1769 compact I/O power supply is required for the controller and local input /output (I/O) modules. 
  • One 1769 compact I/O power supply is required for each added bank of input /output (I/O) module. 

Case 2: If you have chosen the 1768 CompactLogix controller. Then you need 

  •  One 1768 CompactLogix power supply is required for the controller and 1768 modules. 
  •  One 1769 compact I/O power supply is required for each added bank of input /output (I/O) module. 

Note: As mentioned in section 1 that 1768 CompactLogix power with irreplaceable fuse. It is highly recommendable to use an external replaceable fuse in line that connects incoming power to the input block of the power supply. 

  • While connecting the power supply with controllers refers to the specifications such as distance rating, power supply position in the system, etc. 

Final Remarks: Allen Bradley CompactLogix power supplies are highly recommendable if you are trying to avoid the hassle of dealing with momentary power losses, over-current protection, and higher inrush currents. These supplies are highly efficient, offering 75 to 80 % efficiency.

This entry was posted on May 3rd, 2022 and is filed under Allen-Bradley, Hardware Comparison, Uncategorized. Both comments and pings are currently closed.

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