Meanwell PSU fan output

[joerice01]

I'm currently building a project with the Meanwell EPS-120-27 power supply.
There is a dedicated fan output rated at 12v 0.5A, however when I plug in my Sunon 12v 40mm fan it does not spin.
I can feel it pulsing though.

I measured the voltage of the fan connector as 10.8V and is within the tolerance of the stated value (-15% to +10%).

When I power the fan by another source with 10.8V it turns on fine and only draws 0.050 amps.

PSU Datasheet: https://www.meanwell-web.com/content/files/pdfs/productPdfs/MW/EPS-120/EPS-120-spec.pdf
Fan datasheet: https://docs.rs-online.com/1531/0900766b815d9a49.pdf

Is there something I am missing here?

Thanks in advance.

[AmnevaR]

It's weird. Have you tried to put some load on power supply when the fan is connected to it?

[BrokenYugo]

I'm assuming you're testing this fan supply with no load on the main output?

Note how in the block diagram the fan supply has no regulation. With little to no load on the main rail only a very small amount of current will be available on the fan supply, since only a very low amount of power is being driven into the switching transformer.

The 10.8 volts you measured would probably disappear if you put a test load on the fan output, something like a 220 ohm 1 watt resistor. Put a few watts load on the main output and it will come right up.

[joerice01]

It only has a dps3003 buck at this point. I'll load that up and see if it comes on. I did try it with a small fan and that came on with no load. Must be just big enough to need it.

Thanks

[NiHaoMike]

Maybe the fan output supplies more current as the supply heats up?

[TimNJ]

Motors always draw more current to start them up. Usually stall current and start-up current are roughly the same. You'd think with enough bulk capacitance on the fan supply that it should be able to supply the transient start-up current...but maybe not.

I looked at some images of EPS-120. I don't see any electrolytic caps near the fan output connector. Maybe it's just 1 or 2 1206 caps on the bottom, in which case, would probably not have enough storage to supply the start-up current.

Just a guess.