Rattling BLDC fan when used with low voltage? Delta AFB0712VHD

[cybertronicify]

I'm trying to put a second fan inside my Korad to cool the transformer as it is getting quite hot. The fan i'm using is a Delta AFB0712VHD, voltage range 5v-13.2v The Korad's fan controller outputs 6v idle 12.03v full power. But i noticed that the Delta fan rattles when it idles at 6v, any idea why is that? It works perfectly when the fan speeds go up and when it drops down to idle it rattles. It shouldn't be vibration as the fan does not physically rattle, it just makes a rattling sound. The stock fan that came with the Korad doesn't have this problem.

When i power the Delta fan with the Korad's output it spins as low as 4.3v before it stalls.

[Rufus]

I'm trying to put a second fan inside my Korad to cool the transformer as it is getting quite hot. The fan i'm using is a Delta AFB0712VHD, voltage range 5v-13.2v The Korad's fan controller outputs 6v idle 12.03v full power. But i noticed that the Delta fan rattles when it idles at 6v, any idea why is that?

Probably because when you say it idles at 6v it is actually idling at 12v applied half (or less) of the time. The 12v pulses create an audible mechanical impulse. It probably depends on where the motor armature is in relation to the poles at the time of the pulse which makes it sound like a random rattle rather than a continuous buzz.

[cybertronicify]

Ahh i see, so a cap won't help?

[wraper]

Ahh i see, so a cap won't help?

It depends on fan and control circuit. Try it.

[cybertronicify]

nope added a 16v 1000u cap. didnt do a thing

[cybertronicify]

Ok i tried to put a inline resistor with the Delta fan and it seems to be fine. Not sure why is that.