OK, I have a computer PSU powering a 100w amp. The system works great, but if I connect the cooling fans (2 x 12v DC brushless), I get a loud whine in both channels.
What is the best solution to reduce or eliminate the whining? I am limited for space, but could easily add caps or coils to do the job. I cannot put another psu in to run the fans, not enough space for that.
All useful input is appreciated....
Thanks,
- Tim -
-- Email - tempowl@nospam.nbnet.nb.ca (remove the nospam part)
Ok, I have found that adding about 12,000 mfd capacitance across the 12v line going to tye fans reduces the noise a lot. Adding more does not make any difference. I am concerned about the turn on load though, and I am still looking for a better alternative.
- Tim -
-- Email - tempowl@nospam.nbnet.nb.ca (remove the nospam part) And If I Forgot To Mention My Location, I\'m In The Fredericton Area
First you need to find out whether the noise is radiated or conducted !
If its radiated then you will need to provide some kind of screening between the fans and the rest of the circuit. Probably easier to screen the amp front end rather than the fans.
If its conducted you will need to find some method of preventing the conducted signal. Usually some kind of choke, maybe a coil + capacitor combination.
The other thought crosses my mind that the noise could actually be conducted down the power feed. Computer switch mode PSU are not renound for being the quietest of devices.
As a test stick 1kuf 16V cap across the fan terminals as close as you can get to the motor itself. Make sure that you get the polarity correct or it could get messy very quickly.
--
Best Regards:
Baron.
RC filter. No need for coils.
Line in > to resistor.
output end of resistor to cap Plus, neg tied to chassis or ground.
That same output node goes to both fans plus in, in parallel.
We used like a 2 Ohm resistor and a 35µF cap. Not sure on those values, but we definitely made an RC filter for 3 12V fans. I will get the values for you Monday if needed.
We were at 10GHz, so those spurs had to be quelled.
That seems HUGE.
Try to refrain from being a top posting dope.
That suggests that the noise is radiated ! Looks like screening could be needed ! 1kuf across the fans would kill just about any hf noise that could get onto the power lines.
--
Best Regards:
Baron.
Problem has been solved.
As with almost all noise issues, this one was ground related. I had the input ground attached to the frame of the amp, as was the AC ground and the DC minus. I found that if I also attached it to the ground of the amp module itself (the car amp), all noise was eliminated.
The unit is now pumping out clean audio!
Thanks to all whom responded.
- Tim -
-- Email - tempowl@nospam.nbnet.nb.ca (remove the nospam part)
Just saw this thread and was about to suggest checking ground connections. Glad to see you solved it yourself.
The best solution is to use a separate power supply for the fans. Mark
The best solution is to use a separate power supply for the fans. Mark
AND WATCH OUT WHERE YOU PUT EXCLAMATION MARKS!
I find it hard to believe you can't find 3 cubic inches for a little swittcher.
AC powered fans perhaps.
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