1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Automotive noise filter, choke and capacitor

Discussion in 'Automotive Electronics' started by kinarfi, Apr 24, 2011.

  1. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    I have a toroid choke out of a server power supply that has 2 windings on it separated by a plastic divider. For sake of description, both winding 1 and 2 have their wires go into the center at the bottom, as it sits on it's base, on the A side of the core and after several loops, go out of the center at the top on the B side. I plan to connect the two winding to make 1 winding and add a capacitor.
    Which set up will have the best filtering?
    #1 Tie the top of winding 1 to the bottom of winding 2, so the current is always entering the center from one side and connect the capacitor at that tie point in the middle and ground.
    #2 Same as #1, except the capacitor is at the load end of the choke.
    #3 Same as #1, except the capacitor is at the feed end of the choke.
    #4,5,6 Same as #1,2,3, except the choke has the two leads at the bottom tied together so the current ends up going into the center on one side and then at the middle of the single winding, it goes into the center from other side.
    Hope I was clear, if not, I'll have to take pictures or make a drawing.
    Thanks all,
    Kinarfi
    PS Capacitor is 10,000uf, 25 v electrolytic and I don't know what the value of the choke is.
     
    Last edited: Apr 24, 2011
  2. carbonzit

    carbonzit Active Member

    Joined:
    Mar 19, 2011
    Messages:
    1,958
    Likes:
    13
    Are you sure that's a tapped choke? From your description it sounds like an autotransformer (which I guess could be used as a choke).
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,590
    Likes:
    952
    Location:
    Canada, of course!
    A choke with a small inductance that was used in a SMPS that operated at 50kHz is not useful to filter low frequency alternator whine.
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. carbonzit

    carbonzit Active Member

    Joined:
    Mar 19, 2011
    Messages:
    1,958
    Likes:
    13

    While what you wrote is true, the O.P. didn't say what they were trying to filter. Don't you think it would have been more useful to ask that, rather than ASS-U-ME something?
     
  6. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,590
    Likes:
    952
    Location:
    Canada, of course!
    "Automotive Noise Filter".
    I didn't guess that the car tires or exhaust system were noisy.
    About the only electrical noise that somebody wants filtered in a car is alternator whine that is heard on a stereo that has poor filtering.
     
  7. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    I went back to an earlier post and got this drawing, it may be what I have. And while it will handle any current thrown at it, it may very well not work at audio frequencies. Still, if it would work at audio frequencies, which set up would have the most effect?
    Thanks,
    Kinarfi
     

    Attached Files:

    • new.png
      new.png
      File size:
      45.5 KB
      Views:
      1,856
  8. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    Not tapped, two separate windings.
    Kinarfi
     
  9. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,590
    Likes:
    952
    Location:
    Canada, of course!
    The balanced inductor filters high frequency switching noise produced by a switched-mode high frequency power supply so it doesn't pollute the electrical line. It will be useless at audio frequencies.
    Please describe the "automotive noise" that you want to filter. Isn't it "alternator whine"?
     
  10. MikeMl

    MikeMl Well-Known Member Most Helpful Member

    Joined:
    Mar 17, 2009
    Messages:
    11,139
    Likes:
    566
    Location:
    AZ 86334
    Your choke is a "common mode choke", and is likely used to filter 50KHz to 500KHz, not audio frequencies. Try using just one of the windings as a series inductor, but I predict it wont do much.

    The correct solution to your alternator whine problem is isolating everything related to audio from the frame of your vehicle (no local grounds), and then cross connect your audio ground to the vehicle ground in only one place (at the negative battery pole, this is called a single point ground). The root cause of your problem is a "ground-loop". Usually, no amount of filtering will do much.
     
    Last edited: Apr 24, 2011
  11. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    Audioguru, Yes, definitely alternator whine plus I can hear the radiator cooling fan in my head phones, I powered my amp up with an alternate battery and the whines were gone. Guess I'll have to make a better filter.
    Mike, What I have for audio and audio amp is that circuit you gave me, http://www.electro-tech-online.com/threads/shorting-left-channel-to-right-channel.112018/#post917149 and an Ipod nano 3, I put the circuit in an old lighter to USB module with a stereo jack in and a cable out, thus only one power and one ground connection. The headphones are self contained battery operated by Lynx Aviation. I'll have to pull it apart and make an accurate schematic of how I hooked it up.
    Kinarfi
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,590
    Likes:
    952
    Location:
    Canada, of course!
    In the other thread an LM386 amplifier is shown that is missing a filter capacitor to grouns at pin 7. Maybe with the capacitor added the noises will be gone.
    Are the headphones connected with the earphones in parallel (in-phase) or connected in series (then maybe they are out-of-phase).
     
  13. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    Parallel, as shown in the drawings, I plan to build a better audio filter later today and use that filtered voltage as power for my amplifier and some USB receptical which are powered by a 12 - 5 volt LM317 to drive some of my electronic toys, GPS, Ipod, etc.
    Thank you,
    Kinarfi

    It's been a long time since I designed a transistor amplifier, but why wouldn't this work just as well? I think I have a gain of 5 on this, correct?
     

    Attached Files:

  14. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,590
    Likes:
    952
    Location:
    Canada, of course!
    You sketched a PNP transistor but a 2N4401 is an NPN transistor.
    Without an emitter resistor that is the collector resistor value divided by 5 (200 ohms) then the gain would be about 220 if it was biased properly. But it is biased so that the transistor is turned on as hard as it can which is saturated and it amplifies Nothing.
    It is a preamp, not a power amp so it cannot drive a low impedance speaker.
     
  15. canadaelk

    canadaelk Active Member

    Joined:
    Jan 31, 2010
    Messages:
    772
    Likes:
    29
    Well, I hope you are not driving around listening to headphomes. This would be just plain stupid (illigal here) and you should get all the noise you deserve! Just my opinion. E
     
  16. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    Like I said, it's been a long time, how ever, if I had drawn and designed it correctly, is there any advantage to using an LM386 over using a 2N4401 or similar? How would like to include a circuit using a 2N4401 with a gain of 5 for me to look at or copy?
    Thanks, (for doing my work), Actually, I always do my own work so I understand what's happening.
    Kinarfi
     
  17. audioguru

    audioguru Well-Known Member Most Helpful Member

    Joined:
    Mar 16, 2004
    Messages:
    32,590
    Likes:
    952
    Location:
    Canada, of course!
    An LM386 is a power amplifier and is designed to drive an 8 ohm speaker.
    A single 2N4401 transistor can drive the input of a power amplifier if you need more voltage gain. It cannot drive a low impedance speaker because it is not a power amplifier circuit. The LM386 has a voltage gain of 20 which can be increased to 200 if you add one capacitor.

    I could easily sketch a single transistor circuit that has a gain of 5 and a load of 10k ohms or more. But why? You don't need it.
     
  18. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    10-4 ,Thank you, over and out! Got my filter built and it works dandy, now to get it all in and mounted.
    Kinarfi
     
  19. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    Oh but I am, however, I driving around listening and talking while driving off road, but your concern is definitely valid and I agree with you, completely. My head phones are aviation type and used for communicating with my passenger, and listening to music. You can see the headphones on the hood next to the blanket.
    Thanks for your concern,
    Kinarfi
    [​IMG]
     
  20. killivolt

    killivolt Well-Known Member

    Joined:
    Mar 12, 2008
    Messages:
    3,213
    Likes:
    121
    Location:
    U.S.
    Post deleted.

    He's being safe.

    Edit: You beat me with your post. Bam, bam. hahaha :D
     
    Last edited: Apr 25, 2011
  21. kinarfi

    kinarfi Well-Known Member

    Joined:
    Jul 7, 2009
    Messages:
    1,514
    Likes:
    30
    Location:
    P. G., Utah, United States of America
    Been there, done that, had it happen to me also.
    Kinarfi
     

Share This Page