Designing for high operational reliability is critical in ensuring that power supplies can support the continuous operation of equipment, particularly in demanding environments such as industrial settings. In this blog, we’ll take a look at operational reliability: what it is, how to measure it, and how RECOM power supplies are designed to maximize it.
Table of Contents
- What is operational reliability for power supplies?
- The industrial environment and its effects on power supplies
- Measuring operational reliability
- How to maximize operational reliability for power supplies in the industrial environment
- Conclusion
What is Operational Reliability for Power Supplies?
Operational reliability is a measure of how well a power supply can fulfill its intended function without failure. Key aspects of operational reliability in power supplies include:
Consistent Performance
The power supply must provide stable and accurate voltage and current without fluctuations that could disrupt the operation of connected devices.
Durability
The power supply should be able to withstand the environmental conditions in which it must operate.
Minimal Downtime
The power supply should have a low failure rate and be designed to minimize the likelihood of interruptions, ensuring that equipment remains operational as much as possible.
Longevity
The power supply should have a long operational life, reducing the need for frequent replacements or repairs, which contributes to overall system reliability.
Compliance with Standards
The power supply should meet relevant industry standards and certifications, which often include requirements for reliability and safety.
The Industrial Environment and its Effects on Power Supplies
Designing for the application environment is key to maximizing the operational reliability of the power supply. The harsh industrial environment features a wide variety of conditions that can spell doom for poorly designed power supplies. Climate-related stresses can include extreme hot and cold temperatures, temperature cycling, dust, humidity, and moisture including salt spray. Mechanical stresses can include shock and vibration. And electrical stresses can voltage surges, dips and transients.
Let’s Look at Some of These Stresses in More Detail.
- Electrical stresses include frequent or extreme variations in input voltage such as surges, sags, or spikes. These can cause stress on power supply components, particularly capacitors and semiconductors, resulting in premature failure. In AC/DC power supplies, poor quality input AC power can cause harmonic distortion, electrical noise, and transient disturbances in the input power leading to stress and degradation of power supply components over time.
- Many industrial environments have high levels of electromagnetic interference (EMI) that can come from numerous sources. Typical EMI generators include switching equipment such as variable frequency drives (VFDs) and power inverters; industrial equipment such as welders, plasma cutters; industrial generators; or even other power supplies. High levels of EMI can significantly affect the reliability of power supplies.
- Other electrical stresses include missed cycles where one or more AC cycles are not delivered to the input of the AC/DC power supply. This can happen due to temporary faults, interruptions, or switching operations in the power distribution network. Missed cycles can lead to DC power dropouts that accelerate aging and degradation of components.
- Temperature extremes. A common cause of failures is excessive temperature or temperature cycling. Most are a result of thermal stress brought on by differences in the coefficients of thermal expansion (CTE) of different materials. Temperature extremes affect both electrical and mechanical components.
Measuring Operational Reliability
Measuring the operational reliability of industrial power supplies involves assessing their ability to consistently perform under the specified conditions over time. There are several methods to assess operational reliability, but statistical reliability measurements such as MTBF (Mean Time Between Failure) are not a good indicators of true operational lifetime.
MTBF only provides a general indication of reliability and does not specify the types of failures or their causes. More importantly, MTBF is typically calculated under controlled test conditions that may not fully replicate the diverse and harsh environments in which power supplies operate. The application environment can significantly affect actual reliability.
Based on the experience of RECOM’s customers, most early failures are due to input voltage surges, not due to component aging, so they are not adequately accounted for by MTBF and similar calculations.
How to Maximize Operational Reliability for Power Supplies in the Industrial Environment
RECOM power supplies include many features to reduce electrical stresses and maximize operational reliability.
Wide input voltage range
RECOM power supplies also feature wide input ranges. Typical examples include AC/DC supplies with 85 – 264VAC inputs and DC/DC supplies with 4.0 – 36.0VDC inputs.
Voltage interruptions and dips
RECOM AC/DC power supplies for industrial use satisfy IEC/EN61000-4-11:2004+A1:2017, Criteria B for voltage dips and interruptions. Contact us for the details.
Input voltage surge protection
Since input voltage surges are the number one cause of early failure, industrial power supplies must include several protections.
They also must have robust input filtering. Apart from RECOM power supplies, the company has also developed a range of surge protection modules for PCB mounting that conform to specific industrial standards such as the RIA12, NF F 01-510 and EN50155 specifications for railway rolling stock, or the MIL-STD-416G or MIL-STD-1275E surge protection military standards. The RSP series are available in 20W, 45W, 150W, 200W or 300W continuous power ratings for either 110VDC or 24/28VDC nominal input voltages. The RSPxxx-168 series can handle input voltage surges of up to 385VDC.
EMI Filtering
If EMI protection is required, most RECOM datasheets include suggested filter circuits that meet industry specifications. RECOM has also designed a range of cost-effective inductors which have been optimized for use with DC/DC converters and verified for EMC performance by conducted and radiated EMI measurements in our in-house EMC test facility. Paired with converters they provide a one-stop solution to EMI reduction.
Output Overcurrent Protection (OCP)
OCP minimizes the effects of missed cycles and drop-outs by electronically limit the load current to protect the power supply. Typical techniques are to limit current to a set value, ‘foldback’ the current to a safe value with increasing load or ‘hiccup’ protection (the output is turned off and then back on again after a delay. If the overcurrent condition still exists, the cycle repeats).
Ease of Replacement
Of course, failure comes to everything – even RECOM power supplies. When the inevitable finally happens, ease of replacement is important to reduce downtime to a minimum. One way to simplify replacement is to use a standard form factor such as a DIN rail power supply.
Conclusion
A high level of operational reliability is a key criterion in a power supply for industrial use. This blog has reviewed some of the factors that affect operational reliability and some of the design features that RECOM builds into its power supplies that ensure a long operating life in the challenging industrial environment.