Motor Control

Eaton offers a full line of 24V dc power supplies in the PSS, PSG and ELC series. Eaton also has the EZ Power product line, which provides low amperage solutions for 12 and 24 Vdc applications requiring a shallow panel depth or the look of the EZ Relay. Lastly, Eaton offers specialized 27V dc power supplies for the material handling industry as part of the Sensors product line with the PG series.

In general, the PSS series power supplies are best suited for use with the IT. contactors/starters, S801/S811 soft starters, and PanelMate® ePro™ operator interface products. The high start-up (inrush) currents with these products would require a user to oversize a general purpose power supply, thereby increasing system costs. The PSS series provides a high current surge (outrush) to power such devices at a more economical price point.

The ELC power supplies are very economical and are available with 1A and 2A outputs. The PSG series picks up at 2.5A through 20A, and offers a metal frame and more advanced features.

How do I determine the size of power supply required for an application?
The most important factors in determining the size of the power supply are nominal current draw, peak inrush current, peak inrush time, and input voltage. The chosen power supply must be capable of providing the nominal current for the combined load, as well as the combined peak inrush. It is good practice to allow about 20% overhead for high life expectancy and future expansion. An example calculation is as follows (115 Vac input):

Load Description	Nominal Current Draw	Peak Current Draw/Inrush
ePro PS – 12"	1.5A	7A for 50 mS
XT contactor – 25 HP	0.1A	1A for 50 mS
Total	1.6A	8A for 50 mS

At 24V dc, you would need a power supply capable of 1.6A nominal current. With a 20% buffer, the power supply should be about 2A or 48W. A 48W power supply should be adequate, but you would next need to make sure the power supply could provide the 8A (216W) of outrush. A 60W PSG (PSG60E) can only provide 90W of peak surge current, so a larger size would be required. In the PSG series, you would have to step to a 10A (240W) to cover the 9A peak. The PSS55A would provide 2.3A of nominal current and 10A of peak surge for 180 mS and would probably be the better choice.

These are simple guidelines and all factors, such as operating temperature and other environmental factors must always be considered when choosing a power supply.