1. In celebration of the launch of the new redesigned site, we just gave away a FREE antenna! Click Here to See Who Won!

Building a simple Alternator whine / ignition filter

Discussion in 'Home Brew' started by Moleculo, Dec 18, 2008.

  1. Moleculo

    Moleculo Administrator Staff Member

    Joined:
    Apr 14, 2002
    Messages:
    8,460
    Likes Received:
    574
    This was posted by Beetle in another thread and I thought others would find it useful, so I'm cross posting it here. This is courtesy of Jim KB1MVX, and the original may be found here: New Page 1

    I recently installed a new transceiver in my truck. On the first day of using the new radio I got reports that I was transmitting very noticeable alternator whine. I could also hear it on receive and when the radio was quiet. I checked the diodes in the alternator, verified I had good grounds, and I even ran the truck with the alternator removed to be sure that the whine was indeed from the alternator.

    The alternator produces AC, which is rectified into DC. The problem is the rectification is not perfect. The DC output will have a small AC signal riding on it. That AC signal will have 9 cycles for each revolution of the alternator. Suppose your engine is idling at 600 RPM and the drive pulley ratio to your alternator is 1:3. At that engine speed your alternator is turning 1800 RPM, which is 30 rotations per second. Each rotation gives you 9 cycles of AC. Do the math and you get a 270 Hz sinusoid (not a perfect sinusoid but close enough). Cruise down the road at 2000 RPM and you get a 900 Hz sinusoid riding on your DC power supply.


    I tried an off the shelf filter from Advance Auto. It did very little so I decided to build a filter. The first filter I built worked VERY well. The problem is that not everyone has the tools required to build that filter so I decided to figure out a filter design that could be built in less than an hour by anyone with basic tools, have a cost under $20, and handle a current of at least 20 Amps.

    Parts List:
    1/2" Quick Link from Lowe's $2.98
    6x3x2" project box from Radio Shack
    $3.79
    20' roll 12 gauge red hook up wire from Radio Shack
    $4.99
    4700 uF 35V
    capacitor from Radio Shack $5.29
    18" of black 16 gauge wire
    electrical tape
    GOOP or similar glue
    3 zip ties

    Total: $17.05

    Directions below
    [​IMG]






    1/2" Quick Link will be used as the inductor core. A fellow
    ham, Dave KC1LT, suggested using a shackle. I went to get
    a shackle and came across this quick link. I went with the
    quick link to make more efficient use of project box space.

    [​IMG]
    Beginning the winding
    Wrap the hook up wire around the closed side of the quick link starting
    from the left as shown. Leave about 9" of wire free on the left end. Try
    to keep the winds as close together and tight as possible. On the last layer
    space the winds so that you have 9" of wire left on the right end. Use all 20' of wire.
    [​IMG]
    Above is the finished wrap

    [​IMG]
    Wrap the coils in electrical tape and close the quick link. About 1.5" from the right
    end of the inductor strip 1/4" of insulation off the red wire and solder in the + lead
    of the capacitor. Make sure you observe the capacitor polarity. In the picture you
    can see the negative arrow on the capacitor pointing down. Solder the 18" piece of
    black wire to the negative lead of the capacitor. (Above)
    [​IMG]
    Cover the solder connections and capacitor leads with electrical tape.
    Drill a 3/16" hole in both ends of the project box for the red wires. Drill
    an 1/8" hole in one end of the project box for the black wire. Run the
    wires through the holes. Put a zip tie on each of the three wires to limit
    how far the wires can be pulled out of the box. Make sure to leave a little
    slack in the wires inside the box. Using GOOP or some other thick strong
    adhesive, glue the capacitor and inductor into the project box. Leave the
    cover off until the glue dries.
    [​IMG]
    +12V Side with the capacitorto radio
    Black Ground +12V to battery


    Measured Filter Response:
    [​IMG]
    I made this measurement using a low frequency signal generator and an oscilloscope. At 25 Hz the filter has better than 30 dB of attenuation. In other words for frequencies above 25 Hz the noise power has been knocked down by more than a factor of 1000.
    I am new to practical electronics. By answering basic questions and making suggestions several folks contributed to this. In particular Dave KC1LT was very helpful. I hope this information is useful. If you use this design to build a filter or if the information presented was useful please send an email to kb1mvx@comcast.net and let me know it was worth the effort to put this together.



    73
    Jim
    KB1MVX

     
    #1
    1 person likes this.
  2. HomerBB

    HomerBB Well-Known Member

    Joined:
    Jan 4, 2009
    Messages:
    2,496
    Likes Received:
    405
    Thanks for the heads-up. This thing works great. I copied your design and now have zero alternator/whatever internal noises.
     
    #2
    2 people like this.
  3. hacksaw

    hacksaw Active Member

    Joined:
    Jan 25, 2009
    Messages:
    149
    Likes Received:
    4
    Ok guys, what about using this basic design but instead, using a smaller cap, and shorter wire wrapped on a ferrite? I only have about 4' of wire laying arround so I wrapped it as many times through a ferrite as I could and used a 1800uF 35v cap. This is all I had laying arround for today. I havent tried it yet on the Jeep either. Is this even worth my effort????????
     
    #3
  4. Robb

    Robb Yup

    Joined:
    Dec 18, 2008
    Messages:
    8,208
    Likes Received:
    1,016
    A noise filter is worth the effort if you are experiencing noise!
    But your cap value isn't correct; this will adversely affect the outcome. Try what you have and if it works a bit - the rebuild it to Moleculo's specs here so that iit is a keeper.
     
    #4
  5. Moleculo

    Moleculo Administrator Staff Member

    Joined:
    Apr 14, 2002
    Messages:
    8,460
    Likes Received:
    574
    If you want to use more capacitance, that's "more better" / OK to a ridiculous point. Less will work, well....less. LOL.
     
    #5
  6. psalejandro

    psalejandro Member

    Joined:
    Mar 2, 2010
    Messages:
    1
    Likes Received:
    0
    hi everyone. i'm from the philippines, I came across this thread while desperately looking for a solution to cure the alternator whine of my portable lcd tv (chinese made). i use a fm transmitter to hook-up the sound to my car's stock audio system. the lcd tv is producing the annoying alternator whine (thru the cigar lighter socket). i even tried connecting the tv direct to battery but the whine is still there.

    moleculo's post solved the problem, only, since i'm a cheapskate and a quick link costs more than 10USD here, so I just used tie wire rolled like a rope as inductor core, and a 4700 uF 25V capacitor (can't find a 35V) and it worked like a charm. that's why I signed up just to say THANKS! :)

    here are the materials i used:

    5 meters of tie wire .30$
    4700 uF 25V cap .60$
    6m gauge 14 wire 3$
    project box .30$
    electrical tape
    super glue

    total: less than 5$ :D
     
    #6
    Last edited: Mar 2, 2010
  7. kb3kwy

    kb3kwy Member

    Joined:
    Jul 18, 2010
    Messages:
    2
    Likes Received:
    0
    noise filter

    Looks great just found this thread. I am using my Yaesu vx6r in my car. The battery never lasts long so purchased a new battery and gutted out the old one and put a lighter plug in it with cord to run directly from the car. I get reports of noise now. Hope this solves the problem sounds like it will.
     
    #7
  8. linearone

    linearone King of NY

    Joined:
    Apr 2, 2005
    Messages:
    614
    Likes Received:
    4
    Mole, lets make this sticky.

    Also, did you ever measure the L of that coil? I bet its high like a MH or so.
     
    #8
  9. GunSlinger338

    GunSlinger338 Active Member

    Joined:
    Feb 26, 2006
    Messages:
    101
    Likes Received:
    1
    definitely gona give this a try .
    I drive a 06 F250 powerstoke ..
    with radio wired into the fuse panel i get a very loud "buzz" in the TX .. to the point that some thought i was in close proximity to lawn mower ! LOL
    rewired strait to the battery with some success , but still a slight "buzz" in the TX

    Would you be better off mounting this as close to the radio as possible ?? I'm thinking ..YES

    thanks for the INFO!
     
    #9
  10. Moleculo

    Moleculo Administrator Staff Member

    Joined:
    Apr 14, 2002
    Messages:
    8,460
    Likes Received:
    574
    No, I never did measure it...that would be interesting though. Maybe the next time I do this I'll stick it on the antenna analyzer and see what it says.
     
    #10
  11. Moleculo

    Moleculo Administrator Staff Member

    Joined:
    Apr 14, 2002
    Messages:
    8,460
    Likes Received:
    574
    Yes, it needs to be as close to the radio as you can reasonably get it.
     
    #11
  12. CamoRedneck

    CamoRedneck KJ4PUF

    Joined:
    Feb 28, 2008
    Messages:
    87
    Likes Received:
    2
    Built one

    Okay fellas I just built one, with this new cherokee I have my radio picks up the whine bad. I'll hook it up tomorrow and report if it works or not.
     

    Attached Files:

    #12
  13. linearone

    linearone King of NY

    Joined:
    Apr 2, 2005
    Messages:
    614
    Likes Received:
    4
    were you able to measure the choke's inductance?
     
    #13
    1 person likes this.
  14. crmzendrgone

    crmzendrgone CB newbie

    Joined:
    Nov 29, 2010
    Messages:
    108
    Likes Received:
    1
    Ok I am learning a lot! But I am not quite up to par on my vocab and all.

    What does this mean. +12V Side with the capacitorto radio
    Black Ground +12V to battery

    Does this need to be put in line with the power cord of the radio or on the alternator??? And is it good to have even if you have no idea if your radio has noise or not?

    So the real question is how do I know if I have noise or not. Cause as of now I have my radio wires to the junction box under the dash. THANKS!!!!
     
    #14
  15. Beetle

    Beetle Well-Known Member

    Joined:
    Dec 7, 2005
    Messages:
    2,514
    Likes Received:
    378
    It goes in series with the power lead to the radio from the battery. The end closest to the capacitor should go to the radio.

    And only YOU can tell if you have noise.
     
    #15

Share This Page