Building a simple Alternator whine / ignition filter

[Whiplash-265]

I'm looking to give this a try, but I'm unable to find a similar style of cap

what i did find were a couple of differently rated ones but the wires are both on the same end and there's no flow shown on them

both are 4700uf 25v
one is marked 18x35 7mm CAP LYT RDL
the second is 16x32mm CAP LYT RDL

the arrows going down the band shown in the other pics are merely rectangles

again i appreciate the feedback

thanx

 

[K1LA]

What a wonderful suggestion!
I've got mine built and ready to throw in line but (and I realize this may sounds stupid), I just am a little confused on the best way to connect. My wiring all terminates to powerpoles and comes direct from the battery --> powerwerx in line 15amp fuse --> radio (using a T connector). I get that the red/black not on the capacitor side goes to the radio (easy enough to power pole them and throw in line) but how do I connect the other end? Just put it only on the red side of the wire and have the black side continue along ?

my apologies for such a novice question.

 

[Moleculo]

I'm looking to give this a try, but I'm unable to find a similar style of cap

what i did find were a couple of differently rated ones but the wires are both on the same end and there's no flow shown on them

both are 4700uf 25v
one is marked 18x35 7mm CAP LYT RDL
the second is 16x32mm CAP LYT RDL

the arrows going down the band shown in the other pics are merely rectangles

again i appreciate the feedback

thanx

The side of the electrolytic cap with the bars going down the side is the negative side.

I get that the red/black not on the capacitor side goes to the radio (easy enough to power pole them and throw in line) but how do I connect the other end? Just put it only on the red side of the wire and have the black side continue along ?

The capacitor side goes to the radio. If you you're using an anderson power pole on the filter connection, you need to add a run of black wire inside the filter to ground also attached to the cap. This cap in this circuit is shunting any AC noise present on the line to ground while letting the DC current pass.

 

[K1LA]

The capacitor side goes to the radio. If you you're using an anderson power pole on the filter connection, you need to add a run of black wire inside the filter to ground also attached to the cap. This cap in this circuit is shunting any AC noise present on the line to ground while letting the DC current pass.

hmmm...... could be a little late for that now that I've glued this thing in strong enough to outlast world war three. That being said, say I skip the powerpoles, would I just solder the connections in line? The radio side seems straight forward enough, red to red, black to black, but on the other side just solder the the red in line correct?

Thanks much!

 

[ghilliesnpr]

I just built one and out of curiosity decided to measure the inductance. I got 135mH but I'm sure that could vary a bit. I hope it takes care of my noise problem.

Thanks

 

[Moleculo]

hmmm...... could be a little late for that now that I've glued this thing in strong enough to outlast world war three. That being said, say I skip the powerpoles, would I just solder the connections in line? The radio side seems straight forward enough, red to red, black to black, but on the other side just solder the the red in line correct?

Thanks much!

Solder it, use butt connectors, whatever you want. Remember, the black wire is going to need to go to ground somewhere, for both the radio and this filter.

 

[Beetle]

See Post #15 for connection clarification.

Also, for the newer guys, this filter won't work on noise coming in via the antenna. Before you invest the time making the filter, turn your radio and engine on so you're experiencing the noise.

Then disconnect the antenna. If the noise is still there, the filter will probably help. If the noise isn't present with the antenna removed, look elsewhere for the source.

 

[bwharper78]

I know this has been discussed, but I am still a little confused about the hookup. Right now I have power going from my battery terminals to the radio (red and black wire). Do I need to cut the red wire and put the filter inline, then ground the black filter wire to my chassis?

 

[Blue Jay]

I know this has been discussed, but I am still a little confused about the hookup. Right now I have power going from my battery terminals to the radio (red and black wire). Do I need to cut the red wire and put the filter inline, then ground the black filter wire to my chassis?

Yes that is the way to do it.

 

[BrianJ]

Another satisfied DIY customer. This filter solved my alternator noise problem.

Thanks for the guidance!

Brian
N5BRJ

 

[slarty42]

"I just built one and out of curiosity decided to measure the inductance. I got 135mH but I'm sure that could vary a bit. I hope it takes care of my noise problem."

hey ghilliesnpr are you sure thats not micro henrys or nano henrys that you measured?

I had some round enclosed cores ( ceramic) kicking around so I wound a bobin with about 12 ft ( all I could fit inside the ceramics) of 14 gauge enameled wire & it only measures about .23 milihenrys.

I am going to try it later today or tomorrow & see if it helps, if it does I may wind another one & make up a T filter ( my intent is to use this coil as the centre of a PI filter btw)

So far I have found defective diodes in the alternator, had that rebuilt & its MUCH quieter but there is still an audible whine, tried several different ground points & methods with no appreciable results, it has been suggested that a new battery may help as well but this one is not showing signs of weakness

This is all to feed a stereo head (kenwood after market) that is just being used as a preamp to drive the stock amplifiers

Thanks for posting this project by the way, its great to see there are still hobbiests out there !

Cheers
Howard

 

[slarty42]

just an update, I tried making one of these as noted on a link, used the 12 ga wire etc, mine measured .046 milli henrys , also tried 2 of my small coils & made a "T" filter total of about .5 mh total, neither unit helped much with the whine but I found that when I flexed the plug on the radio upwards it made the noise come in louder & disappear depending on how much I flexed it so I replaced that plug on the adapter with the new one from the new stereo I bought & all is fine now without the filter.

Would still like to know if I am missing something on the wound coil as my inductance values are so different to the ones stated on earlier posts

Cheers

 

[oldslowchevy]

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

i just made this yesterday and installed it last night........ amazing. all noise is GONE. i do still have alittle noise when i use the windsheild wipers though. but i am very pleased on how this works. thank you so much for this.

 

[Beetle]

If you can live with the wiper motor noise, well and good. If you'd like to try eliminating or reducing it, get some disc ceramic capacitors (value not really critical). Voltage rating AT LEAST 50 volts; most are rated around 200V so that's fine. There used to be a place near downtown in Seattle (Radar Electric) that sold mixed-value disc ceramics by the POUND! I invested five dollars for five pounds of them and I still have four pounds or so left, after using them on Navy ships for three decades or so for applications very much like this!

I'd look for capacitance values anywhere from 0.05 μf to 0.5 μf to start. Then get access to the wiper motor itself. Check the brushes and make sure they are in good shape. They could be the cause of the problem if they're worn or the slip rings aren't messed up. Assuming slip rings/brushes are okay, add one capacitor from the hot terminal of the motor to ground. Then check to see if the noise level has gone down. If so, try adding a second capacitor in parallel with the first one.

You might never eliminate ALL the noise, but as you reported, a lot of it is gone.

 

[skidrow]

If you can live with the wiper motor noise, well and good. If you'd like to try eliminating or reducing it, get some disc ceramic capacitors (value not really critical). Voltage rating AT LEAST 50 volts; most are rated around 200V so that's fine. There used to be a place near downtown in Seattle (Radar Electric) that sold mixed-value disc ceramics by the POUND! I invested five dollars for five pounds of them and I still have four pounds or so left, after using them on Navy ships for three decades or so for applications very much like this!

I'd look for capacitance values anywhere from 0.05 μf to 0.5 μf to start. Then get access to the wiper motor itself. Check the brushes and make sure they are in good shape. They could be the cause of the problem if they're worn or the slip rings aren't messed up. Assuming slip rings/brushes are okay, add one capacitor from the hot terminal of the motor to ground. Then check to see if the noise level has gone down. If so, try adding a second capacitor in parallel with the first one.

You might never eliminate ALL the noise, but as you reported, a lot of it is gone.

seems a long way to go around just install a better ground or bond everything...Maybe that was to easy?