Running a 5vDC fan on 9vDC

[Ambient]

check the spec sheets on the fan if you can. That may be of some help.

 

[moody07747]

Audio parts working and I just finished wiring the fan power circuit today.
but now there's a new problem...fan works great but when it spins it induces a nice sound into my amp circuit.

what do you guys suggest I do about this?
I could put some copper tape around the amp board and ground it but it would cut the air circulation out of the unit.

I have the amp circuit as far away from the fan as I could get it but when I crank the gain on the amp i get the sounds from the fun still........

 

[picbits]

Stick some 10nf, 100nf, 1uF and 10uf capacitors in parallel with the fan and see if that helps.

 

[Richard Principal]

Another option;
6 or 7 1N4001 (silicon diode) in series. 6Volt drop across each diode * 7 diodes will drop about 4 Volts

 

[Ambient]

last time I used a fan like that it caused a ripple on my power line that I could not get filtered for some reason. I was running op-amps on the same bus so the fan had to be tossed aside, but the diodes may prevent that. I will have to try that sometime.

 

[Ambient]

Another thing you could try is to use a brushless fan instead. Someone here once mentioned that brushed motors will cause spikes on the power rail when their commutators conduct as the motor spins. I believe it was in the discussion about measuring motor rpm. I believe they said that brushless will not do that.

 

[Speakerguy]

4.9V Zener should fix this whole thing yes? For the fan voltage thing anyway. Haven't read the whole thread yet about the regulator.

 

[ThermalRunaway]

A Zener diode makes for a poor voltage regulator, and is not suitable for high current applications. I wouldn't suggest you use one to try and supply a D.C. motor.

Brian

 

[moody07747]

Stick some 10nf, 100nf, 1uF and 10uf capacitors in parallel with the fan and see if that helps.

I have a good ammount of caps laying in the box so ill try this.

do they have to all be different ratings like posted above or can they all be the same?

Reason being is I have a good mmount of 22uF 50V, 100uF 50V, and 33uF 550V Radial Electrolytics but if I need something thats non polarized I can try some Ceramic or Dip Micas and I have loads of them too.

 

[Hero999]

It doesn't matter providing they're rated for more than 16V.

Their values aren't critical but you need at least an electrolytic and a ceramic disc capacitor.

Electrolytics work at low frequencies and ceramic disc work at high frequencies.

Go for something like a 100nF ceramic disc and a 100:mu:F electrolytic.

A ferrite bead on the fan's leads is often a good idea too.

 

[moody07747]

thanks, ill install that later

 

[moody07747]

OK I finally got to installing those caps and it took the noise away.....kind of...

With the unit turned on its quiet,,,but if I turn the volume knob anywhere past 2 o clock the fan starts to slow down a little and I get some noise out of the speaker.
The gain does not effect this in any way.

Now this little amp gets so loud that I'll never have to turn it up past 12 o clock...But I was just wondering if I should be worried about this little side effect.

 

[audioguru]

if I turn the volume knob anywhere past 2 o clock the fan starts to slow down a little and I get some noise out of the speaker.

The 7805 regulator needs to have a 7.5V minimum input voltage or it drops out. When you turn up the volume then the LM386 amp uses more supply current. Your supply cannot keep its voltage up above 7.5V when it supplies this much current.

Isn't your supply a 9V/800mA AC adapter? It should have plenty of current. A 200mA AC adapter or a little 9V battery can't supply the high current and it would cause this problem.

 

[moody07747]

That's what I was thinking...not enough power but on the other hand, I'm using the 9V/800mA supply which as you said is plenty of power for the circuit.

This never happened until I put the two new filter caps in though.