05704-A-0144 | Honeywell 620 Series 24V Power Supply

Description

Product Introduction (Anti-Template)

Every 620 series rack needs clean, regulated DC power. The 05704-A-0144 (also known as 620-0044) is the module that delivers it. This is the standard power supply for the Honeywell 620 series programmable logic controller systems, converting plant AC to the 24 VDC logic power required by the CPU and I/O modules.

The module slides into the dedicated power supply slot on the left side of the 620 rack. Its value is in its simplicity and isolation. It provides a dedicated, fused power source for the rack, isolating the sensitive logic from plant power fluctuations. For a plant still running a 620 system, this module is the foundation—without it, nothing else works.

4. Key Technical Specifications

5. Compatible Replacement Models

The 620 series had several power supply variants for different voltages and rack configurations.

• ✅ Drop-in Replacement: 05704-A-0144 (any revision)
  Any module with the base part number 05704-A-0144 is a direct physical and electrical replacement. It fits the same rack slot, uses the same backplane connector, and provides identical 24 VDC output. Minor hardware revisions (suffix letters) do not affect compatibility.
• ⚠️ Hardware Compatible: 05704-A-0145
  This is a higher-wattage version for larger racks or systems with more I/O. It fits the same slot and provides the same 24 VDC output but with higher current capacity. It can replace a 05704-A-0144 as long as the rack’s power budget doesn’t exceed the original supply’s rating. The reverse (putting a lower-wattage supply in a high-current rack) is not recommended.
• ❌ Hardware Incompatible: 05704-A-0142
  This is likely a 5 VDC output power supply for older 620 systems or specific applications. The output voltage is different, and using it in a rack expecting 24 VDC will not power the modules and may damage them. Verify output voltage before installation.

6. Frequently Asked Questions (FAQ)

What happens if the 05704-A-0144 fails?
The entire rack loses power. All I/O modules in that rack will de-energize, outputs will go to their off state, and the CPU will fault. For critical processes, this is a trip event. This is why we recommend keeping a verified spare on the shelf. The replacement procedure is straightforward: power down the rack, swap the module, power up.

Can I replace this power supply with the rack powered?
No. This is the main power supply for the rack. Removing it while powered will cause arcing on the backplane connector and an immediate loss of power to all modules. You must remove AC input power to the rack before swapping the power supply module. Follow LOTO procedures.

How do I know if the power supply is working?
Look for the green “PWR OK” LED on the front of the module. If it’s lit, the supply is producing DC voltage. If it’s off, check the AC input power at the source. If AC is present and the LED is off, the supply has likely failed. You can also measure 24 VDC at the test points or on the backplane (carefully) to verify.

What causes a 05704-A-0144 to fail?
We see several common failure modes. Input power surges (lightning, switching transients) can damage the input rectifier or filter capacitors. Overheating—if the rack is in a hot, unventilated cabinet, the supply can cook over time. Output overload—if the total current draw of the rack exceeds 2.5 A, the supply will run hot and eventually fail. Capacitor aging is also common in units over 10-15 years old.

My rack has a 05704-A-0145. Can I use a 05704-A-0144 as a spare?
Only if your total rack current draw is less than 2.5 A. Calculate the current draw of your CPU and all I/O modules from the 620 series manual. If it’s under 2.5 A, the -0144 will work. If it’s over 2.5 A, you need the -0145. Using an undersized supply will cause it to overheat and fail prematurely, and may cause intermittent rack resets.

What is the difference between 05704-A-0144 and 620-0044?
Nothing. They are two different numbering systems for the same module. Honeywell used both the 05704-A-xxxx catalog numbers and the 620-xxxx series numbers interchangeably. The module itself may be labeled with one or both numbers. When ordering, either part number will get you the correct supply.

We are upgrading from 620 to C300. Can we reuse this power supply?
No. The 620 series power supply is not compatible with Series C or C300 racks. The form factor, backplane connector, and voltage requirements are completely different. The 620 system is obsolete; the power supply is only useful for maintaining existing 620 installations. For a C300 upgrade, you need new Series C power supplies (like CC-PPS01 or similar).

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