Capacitors to remove noise from PSU

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Hi

I have a transformer with a 3rd secondary winding of 6V at 1A.
I used 4 FR104 diodes to make a rectifier, then connected a PC fan to the rectifier... all working and I'm very impressed with myself.

BUT, when I do connect the rectifier to the transformer, I can hear a slight noise on the amps connected to the other windings of the transformer... sounds a bit like the fan maybe makeing noise...

Is there anyway I can suppress/filter some of the noise using small capacitors or something... I got tonnes lieing around, but I don't just want to go and add random capacitors to my circuit... also not sure where they would have to go...
 
Hi,
the fan is running on pulsed DC since there is no smoothing on the supply. That may be aggravating the noise problem.
If you add caps after the rectifier the fan will see more voltage and run faster. Is that OK?
To suppress noise on the fan line you can add small caps to the AC side of the rectifier and to the DC side. Any sizes below 100nF should be OK.
You can also add caps to the other PSU supplies but these are after the horse has bolted, better to solve at source if possible.
 
Like this?

fanpsu.gif
 
Nordic,

Eva said to put the resistor in series with the fan. A capacitor in parallel and a resistor in series with the load makes a low pass filter which will help filter out the noise from the fan that creeps onto the AC. Your diagram shows the resistor in parallel, not in series, with the load.

Dick
 
Nordic,

You still have it backwards.

Attach the 100 uF cap to points 3 and 4 on your rectifier. Then, attach a resistor to one end of the capacitor and attach the other end of the resistor to one of the fan leads. The other fan lead attaches to the other end of the capacitor.

Capacitor in parallel to the rectifier then a resistor in series, in line with, one of the fan leads.

Try drawing this for us. Thanks.........
 
separate the fan psu

i use separate supply/transformer for the fan(use small amp trafo)+use regulator and i put shielded cable for the fan.. this is my opinion, more work but it works for me... anyone maybe have better solution
best regards, opik
 
Was more of a cost issue to get some auxilary power for things like fans etc... the extra 6V winding only cost me about a dolar extra (I had my trafo made)...its pretty huge and I don't think adding anoter (even small one) is an option, due to the weight.

Lol don't laugh at my graphics... that was a 30 second photoshop jobby to get on with it... as they say a picture says a thousand words.

Below is what I use photoshop for normaly
 

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