# Calculating input power of ACDC power supply

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!

• Welcome! Does it really say typical for the AC current? Commented Feb 24 at 19:00
• 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. Commented Feb 24 at 19:00
• 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. Commented Feb 28 at 17:03

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: