I'm trying to calculate the input power draw of an ACDC power supply that we are using in a control chassis and am confused by what to me looks like conflicting information in the datasheet.

The power supply is an HDR-30-24 with datasheet here. I'm confused because I see two ways to calculate the input power to this power supply (assuming drawing the full rated output power for this example).

Method 1: The power supply has an output power rated at 36 W. The input efficiency (Typ.) is listed as 89%. So 36 / 0.89 = 40 W of input power I would expect if the load is drawing the full 36 W rated output.

Method 2: The datasheet also says that the input AC current (Typ.) is 0.88A at 115VAC. The 115VAC is rms, so I would expect the input power to be 0.88*115 = 101 W from this calculation.

Which one is correct? What am I misunderstanding here? Thanks!

  • 1
    \$\begingroup\$ Welcome! Does it really say typical for the AC current? \$\endgroup\$
    – winny
    Commented Feb 24 at 19:00
  • \$\begingroup\$ Until someone comes along with a proper answer this might be relevant: the power rating of the unit is only 30 W so it doesn't need to meet a minimum power factor value in the EU. \$\endgroup\$ Commented Feb 24 at 19:00
  • \$\begingroup\$ Yes it does actually say typical (more specifically it says "typ") for the input AC current. Also I didn't realize at 30 W it might not need to meet a minimum power factor in the EU but that could be why the real and apparent power are so different. \$\endgroup\$ Commented Feb 28 at 17:03

1 Answer 1


HDR-30-24 is the manufacturers web page.

It has a link to the test report shows the input current (typical) from the specification as well as the measured input current (which is less than the specification value) for the maximum output load:

enter image description here

The datasheet shows a RECTIFIERS & FILTER block on the input, but doesn't list a power factor. The power factor of the assumed combination of rectifiers and smoothing capacitor may explain why the result of:

  • 0.54 A * 125 VAC = 67.5 W input power
  • is greater than the 36 W output power / 90.9% efficiency = 39.6 W

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