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Building a simple Alternator whine / ignition filter

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Old 12-18-2008, 11:56 AM
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Default Building a simple Alternator whine / ignition filter


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







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.


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.

Above is the finished wrap


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)

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.

+12V Side with the capacitorto radio
Black Ground +12V to battery


Measured Filter Response:

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



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Old 01-22-2009, 01:15 PM
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Thanks for the heads-up. This thing works great. I copied your design and now have zero alternator/whatever internal noises.
Lil'Yeshua and sanjosebay21 like this.

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Old 01-09-2010, 11:46 AM
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Quote:
Originally Posted by moleculo View Post
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







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.


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.

Above is the finished wrap


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)

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.

+12V Side with the capacitorto radio
Black Ground +12V to battery


Measured Filter Response:

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

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????????

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Old 01-09-2010, 12:34 PM
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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.
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Old 01-09-2010, 01:43 PM
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If you want to use more capacitance, that's "more better" / OK to a ridiculous point. Less will work, well....less. LOL.

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Old 03-01-2010, 10:42 PM
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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$

Last edited by psalejandro; 03-01-2010 at 11:00 PM.

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Old 08-29-2010, 04:24 PM
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Default 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.

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Old 09-07-2010, 11:07 AM
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Mole, lets make this sticky.

Also, did you ever measure the L of that coil? I bet its high like a MH or so.
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LinkBack to this Thread: http://www.worldwidedx.com/home-brew/31492-building-simple-alternator-whine-ignition-filter.html
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