Magnetic field of brushless DC fan

[sajti]

Hi,

is there anybody, who check the magnetic field, generated by the typical axial DC fan?
I will use it for amplifier cooling, but I don't know how close the line level section can be.

Thanks:Sajti

 

[Willi Studer]

It is a DC current so it will not cause any EMI.

 

[Cortez]

It's DC, isn't it?

 

[sajti]

It is a DC current so it will not cause any EMI.

Tha FAN is DC 12V, but the current is fluctuating. Check the attached picture!

Sajti

 

[dragonweed]

Place it in an other room.... 😀 Seriously, you are a lucky guy if this is your biggest problem in amp building.. The charge current induced pulses in your PS filter cap circuit are magnitudes bigger. The fans in my SE class A amp are sitting from 2" of the amp panels, and there is no trace of any spikes on the scope, nowhere (they are 24V fans run on 12V from a separate transfo and PS for quiet operation).

 

[dragonweed]

If it really worries you, do as I did, separate transfo and ps, run them on about half of their rated voltage, and replace the fan's wires with a 2 conductor shielded (microphone) cable.

 

[sajti]

This is not the only problem, this is one of the many problems 🙂

I will use separated power supply (even just another windings on the main transformer), and temperature depended fan speed adjustment.

My design let 50mm distance between the fan, and the input stage on the main pcb.

Sajti

 

[dragonweed]

...I love this age of information .... three hungarians exchanging ideas in english on an american forum

 

[sajti]

...I love this age of information .... three hungarians exchanging ideas in english on an american forum

Hungarians everywhere... 🙂

Sajti

 

[lcsaszar]

😉

 

[euro21]

Sajti, have you read this?

http://www.diyaudio.com/forums/chip-amps/184523-buzz-noise-dc-brushless-fan-tda2822m.html

 

[sajti]

Hi,

thanks! This was useful information.

Sajti

 

[Cortez]

Or you could use an EMI detector like this for "measuring" the field. That's the best way to figure it out.

 

[sajti]

I will do some measurement, but the best way to move the fan away from the input stages...

Sajti

 

[richie00boy]

DC brushless fans are not DC. They have a circuit inside that creates 3 phase pulsed AC.

Shielding the input wire is worth trying, as is adding a ferrite to the wire.

 

[djk]

Years ago I designed an amplifier for a computer, it had the DC fan on top of the heatsink and blowing down into the fins. It was dead silent.

The board house changed the design so that the fan was under the heatsink, in the same plane with the board. It was noisey.

 

[sajti]

Thanks,

I changed the idea too. The fan will be on the other end of the heatsink. It will close to the output stages, and the protection relay.

Sajti