“Has it really been ten years since that was installed?”, is a question that comes to my mind quite often.  I look around sometimes and wonder where the time has gone.

We install control systems and they run without failure for many years, most of the time, and it is easy to become complacent with the reliability of our control systems.

When systems do decide to fail, many times it can be in a power supply component of the system. Through many a year of 24/7 operation, power cycles, power surges, extreme temperatures or other reasons, power supplies will tend to fail after some time.

So how can we know or predict when that will be? Should we run the system to failure or attempt to be predictive in our approach to the power supplies of the control system?

ControlLogix 1756-PA75

This goes for any of the line of ControlLogix Power Supplies, but based on my experiences alone, they can generally fail between ten and fifteen years.

Some run longer, but if I were setting up preventive maintenance on any important system, I would replace after ten years.

If this is a critical system with redundancy, then I would implement a redundant power supply configuration as well.

A-B 1606-XXX 24VDC Power Supplies

From my experience, most of the time when a 24 VDC power supply fails and control system analog signals are lost, I have no idea how old the supply is and when it was installed.

No label is usually present on the power supply. I did some checking in the manuals and the life expectancy for one of these is greater than fifteen years, although, it shows that it can be less at higher temperatures and/or higher output current.

For instance, the failure is greater than fifteen years at 25 deg C (77 deg F) but could be less than 15 years at higher temperatures than 40 deg C (104 deg F).

So, we must take into consideration the atmosphere, temperature and overall conditions of the installed power supply to make an educated guess at when to replace the power supply before failure.

Based on this data, in a good operating atmosphere, I would change the power supply after fourteen years to prevent system downtime and after ten years if in a harsher atmosphere.


There can be a fine line between spending money that is not needed and replacing systems before they fail to ensure that we get the most out of the money that we have spent towards our control systems to perform the desired automation.

Having the forethought to be proactive and implement a preventive maintenance approach to our control systems is, in my mind, an important mindset to have to keep systems reliable and that can only be measured by the fact that you don’t get called in the middle of the night.

Written by Brandon Cooper
Senior Controls Engineer and Freelance Writer

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Brandon Cooper