A Change of Power

Is It Time to Upgrade to High-Efficiency Power Supplies?

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The capability (and complexity) of our packaging machine designs have evolved over time and now have multiple power supplies. We think we should upgrade to newer, higher-efficiency power supplies that we've heard about. We understand that overall machine power consumption will be reduced, but are there any drawbacks in terms of cost, heat generation, form factor, flexibility or other areas?

—From April '11 Control Design

ANSWERS

Selection Guidelines

The change comes with few downsides and many upsides besides the efficiency itself.

Efficiencies vary by load, so look for specifications of minimum efficiencies that will guarantee worst-case conditions. Beware of claims of "up to" certain efficiencies. Although not necessarily false, the claims might drive you to unrealistic expectations.

Heat generation is a byproduct of inefficient supplies, so as efficiencies rise, dissipated heat falls. Space savings and reduced cooling hardware are side benefits from the improved technologies. As less heat is generated, the size of power supplies can be reduced using components that can be smaller and mounted closer together. Mounting options increase because less attention is required to air flow and cooling.

Because of the advanced technologies, built-in diagnostic features for preventive maintenance can be added that would otherwise not be possible or would be cost-prohibitive. Such features include switched alarms or onboard displays for voltage, current, run-time, temperature or life-time monitors. In addition, newer models come with compliance to newer versions of standards—UL, CSA, CE or SEMI—and green standards like RoHS.

Finally, consider block-type power supplies that provide redundant bussed power or smart power supplies that provide multiple output branches with integrated overcurrent protection. These types may be more suitable for applications with multiple power supply requirements.

Jeff Jurs, program manager,
Omron Industrial Automation, www.omron.com

Switch Your Mode

Traditionally, machine builders used big linear power supplies to make up for surges and large current draws from the loads on the machines. But as the technology changed, many of those current-hungry components have become more efficient and allow the machine manufacturer to switch out the bigger, bulkier power supply for a switch-mode power supply to take advantage of the features it brings to the application.

New switch-mode power supplies also provide the flexibility to run on ac/dc input voltages. Many offer a status relay output as an alarm that the builder can use to activate a beacon or audio alarm in case there are issues in the panel.

Andrew Barco, product specialist,
Weidmüller, www.weidmuller.com

Longer Life

Higher-efficiency power supplies might cost a bit more upfront, but the investment can help prolong the overall life of your product, reduce panel-space requirements and improve machine uptime.

Heat generation inside the power supply shortens the life of panel components such as capacitors, eventually limiting the overall life of the power supply. The more heat generated, the faster the capacitors dry out. A temperature increase of just 10 °C, for example, can cut the life of a capacitor in half. Higher-efficiency power supplies consume less energy and therefore generate less heat, helping extend the life of your product.

Derrick Hinds, product manager,
Rockwell Automation,
www.rockwellautomation.com

Benefits Outweigh Cost

With the evolution of machine design and controls technology, the need for more dc power becomes ever more prevalent. Older linear-style power supplies typically had an efficiency rating of 40-60%. Today's primary switch-mode power supply (PSMPS) designs are more than 90% efficient.

With efficiency comes reliability. From input voltage sway tolerance to output regulation and monitoring, the newer power supplies are designed for long service lives. It is not uncommon to see mean time between failure (MTBF) ratings of more than 600,000 hours.

Updated power supply designs also allow flexibility in the cabinet. Many PSMPS available now have the ability to work across the globe on different voltage networks and configurations. Power supplies have dual voltage settings, auto ranging inputs or even ultra wide operating ranges. Also, these power supplies offer an adjustable output voltage, which allows one design to be used in multiple applications. Some 12 Vdc output power supplies can be adjusted as low as 5 Vdc for logic applications or as high as 18 Vdc.

The one typical drawback with today's power supply designs is cost; there can be a substantial cost differential between a linear power supply and a PSMPS. However, with the cost of operation over several years, the stout design and the intelligence built in, the benefits offered easily outweigh the initial purchase price of some power supplies.

Ken Allwine, product marketing,
Phoenix Contact, www.phoenixcon.com

No Downsides

A 240 W load shouldn't need an additional 60-80 W to operate. That 240 W is all that is required and everything else that it takes to operate the load is a waste.

Comparing a highly efficient 240 W supply to a lower-efficiency 240 W supply by using a watt meter shows that the highly efficient supply has a heat loss of only 10 W compared with 42 W on the other. Using one of the many online enclosure sizing software tools, a comparison can be made of the required enclosure sizes. Keeping this simple, only the power supply will be installed inside the enclosure. The outside temperature is 40 °C, and the maximum allowable temperature inside is 60 °C. The result shows that the highly efficient supply could fit in a 6x3x6 in. enclosure. If the lower-efficiency supply were installed in the same enclosure, the inside temperature would be 124 °C, greatly exceeding the manufacturer's maximum operating temperature. To allow a temperature not greater than 60 °C, the enclosure size for the lower-efficiency supply would have to be 10x10x10 in. or 826% larger by volume. This adds substantial cost for sheet metal and takes away valuable real estate on the wall or floor.

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