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Alternator Whine

Alan Applegate (K0BG) on November 8, 2006
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Alternator Whine

I want to revisit this problem, because there seems to be a lot of poor advice floating around on these pages. Let's start out with a few basic facts, but keep in mind this is NOT an alternator primer. If you need or want more data, the internet is your best friend.

The average alternator's output is between 13.9 and 14.2 VDC. It might be less if there is a problem with the alternator. In some cases it may be a little higher, but voltages over 14.6 VDC should be considered abnormal.

Continuous output and peak current ratings vary quite a bit. The requisite amperage ratings selected by OEMs are largely based on content. That is to say, how many features like rear window defrosters, premium sound systems, electric windows, and heated seats any given vehicle is equipped with. Heavy duty and high-end vehicles usually have larger ones as do those with extra-cost trailer towing packages.

Nowadays, the smallest OEM ones are rated about 90 amps peak, and the larger OEM ones about 150 amps peak. There are a few exceptions, but the highest rated OEM units are about 225 amps peak. The reason I use the term peak is this; very few OEM alternators will deliver their rated output continuously, and contrary to popular belief, there isn't any standard rule for peak versus average.

\Almost all alternator stators (the non-rotating part) are wired in a wye configuration (as shown), and the rest are wired in a delta configuration (primarily Ford products). Rotating within the stator is the field. The field current and/or voltage is varied by the regulator so the output voltage is constant, regardless of the load, up to their peak amperage rating. There are several different regulation strategies employed. Some simply use a pass transistor, others use pulse width modulation, and some almost defy definition.

Depending on the engine type (diesel or gas), alternators are driven from two to five times engine speed, up to a maximum of about 16,000 rpm. As a general rule, the output frequency of an OEM alternator is equal to the engine rpm. That is to say, 1,000 rpm equals 1KHz. Their efficiency is about 90%. Thus, an alternator rated at 130 amps, with an output of 14 vdc, will have an input of around 2 KW, and will require about 3 HP to drive.

\In a never-ending quest to reduce weight, and improve efficiency, most new-generation OEM alternators are double wound, and use twelve diodes instead of six. This not only reduces size and weight, the lower mass of the rotating field allows the alternator to be driven faster, which improves low rpm power output. It also doubles the ripple frequency.

As long as the diodes are doing their job, the output ripple is nearly nonexistent, as the battery is acting like a very large capacitor. When they don't do their job, the result is what we commonly call alternator whine. To be sure, there are other causes which will be discussed later.

While alternator whine can be a bane for us amateurs, as long as the alternator delivers its rated output, dealers don't care, and typically will not replace noisy ones under warranty. So this leads those who are plagued to seek other avenues of relief. For example, using RG8 as a power cord, or twisting the factory power cords of their transceivers. Doing so is junk science. Let's visit this in more depth.

First, any technique we use to shunt alternator whine to ground must present a low impedance at the frequency we're trying to suppress (less than 8 kilohertz typically). Further, it must be of lower impedance than the circuit it is attached to. In the case of vehicle DC wiring, that's seldom higher than a few tenths of an ohm.

An average power cord is ten foot long. A ten foot piece of RG8 has 250 pF of capacitance. At 8 kHz, 250 pF has a reactance of about 1,500 ohms. In terms of suppression, this amount is insignificant.

Twisted or not, a 10 foot power cord made from two number 10 conductors will have about 2 pF of capacitance per foot. Ten feet of it is an insignificant reactance even at 80 kHz! What's more, those who support twisting the power cord as a fix for alternator whine, and a host of other maladies, ignore some basic facts. Twisting works to reduce noise pickup only if both inputs and outputs are balanced, and neither end is grounded. That's not the case here.

Brute force filters offer some help, but there is a big downside too, and that's voltage drop. Radio Shack used to sell one that was rated at 20 amps. Inside its tubular construction is 20 feet of what appears to be number 16 Thermalese wire wound around a laminated steel core about 3/8 of an inch square, and and 2 inches long. A 1 uF coaxial capacitor completes the package. The input and output are size 10. The voltage drop at 20 amps is almost 2 volts. At 8 kHz, the suppression is less than 2 dB.

In some cases, a 1 Farad cap, like those used in mobile sound systems will suppress alternator whine if they're placed near the radio end of the power cord. However, they have a lot of drawbacks, not the least of which is their propensity to explode if dead shorted.

The best place to cure alternator whine is at the source. If you think it is a leaky diode causing your problem, use an O scope to look at the alternator output directly at the output terminal. If it is a diode, you'll easily see it. The fix is obvious.

As alluded to above, there are another situations which can cause what ripple there is to invade the circuitry of your transceiver. One of those is a ground loop. Ground loops occur when there is a differential in current flow between the positive and negative power leads feeding the radio. This is typically caused by incorrect wiring techniques. Poor bonding of body on frame vehicles, and poor coax connections can also cause the problem.

Another problem altogether, which is often incorrectly identified as alternator whine, is the switching transients from the alternator's regulator. While diode induced whine directly varies with engine speed, regulator whine normally does not. It will appear louder at low rpms, and when there is a high amperage load. Since it is radiated RF energy, removing the antenna will cause it to go away. The only fix is to replace the regulator.

Distractors will surely point out that they fixed their alternator whine with one of the aforementioned anecdotal remedies. If that is indeed the case, then the original wiring was amiss.

Alan, KBG

Member Comments:
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Alternator Whine  
by K0CBA on November 8, 2006 Mail this to a friend!
Let me be the first to compliment you on this article. It is well written, well researched and informative. Alternator whine can be a real booger-bear to isolate the exact source (within the device itself) and even more of a challenge to eliminate especially as the parts makers make every effort to cut cost with no regard to the quality issue.
RE: Alternator Whine  
by AA4PB on November 8, 2006 Mail this to a friend!
Great article, Alan. I did an experiment with a high impedance headset. I hooked a 0.1 Mfd capacitor in series with one side just in case I accidently got across 12 Volts. Connecting one side to the master ground terminal near the battery, I "probed" other grounds with the other lead. I found many places where I could hear the alternator whine, proving that all vehicle grounds are not the same. There are alternator currents flowing in the ground connections. Put the headset between the two grounds and some of the AC current flows thru the headset.
Alternator Whine  
by WI7B on November 8, 2006 Mail this to a friend!


First, thanks again for you article. As always, it hits on a present and pratical problem faced by many amateurs.

I have noticed that in using two different rigs my late model SUV with two different antenna schemes, I either have no alternator whine or a noticeable whine. In both case, using the noise blanker eliminates most of what I take for this "engine noise" or whine.

In one scheme, with a poor 20m mag mount radiator on the roof (half-a-wet-noodle) there is no egrecious whine.. However, when I moved to a more-efficeint system using an externally-mounted autotuner (SGC/ICOM type) with a high voltage end-fed design that requires good grounding, whine becomes an important factor in receiver noise.

What I've done is to keep my receiver tuned without the noise blanker being "on" as I tighten and secure grounding cable to the chassis. In this way, I've been able to elimnate most noticeable whine effect.


---* Ken

Alternator Whine  
by KI0QM on November 8, 2006 Mail this to a friend!
Nicely done and interesting. -- Thanks!
RE: Alternator Whine  
by AH6RR on November 8, 2006 Mail this to a friend!
Great article! Excellent advise. Now if I can get rid of my computer noise I will be in top shape in the mobile.

Roland AH6RR
Alternator Whine  
by KB1KIX on November 8, 2006 Mail this to a friend!
Great article, and just in time!

I'm now having to dig a little deeper to solve my issues with alternator whine.

I have tried all the usual routes and this gives me a different' approacth.

Thanx for a great, well researched article.

RE: Alternator Whine  
by K6AER on November 8, 2006 Mail this to a friend!

Great article. Many hams have asked how do I know if my alternator is producing audio whine. Alan mentioned you can spot a defective diode in the diode matrix with a scope buy many hams dont have access to a scope for testing. There is another way if you have a DVM. Most DVMs will respond to AC voltages with frequencies up to 5 KHz. You can read the AC voltage component of the DC output from the Alternator.

Place the DVM in the AC auto range position. Place the leads on the large output connector that connects the alternator output to the battery positive lead and alternator frame ground. The DVM will read the AC ripple, super imposed on the DC output. The most common problem with alternator wine is one or more diodes have opened up or worse a diode has shorted. Typical AC ripple on a healthy alternator/battery system is about 10-20 mV as read on a DVM. A single open diode can produce in the Y diode matrix, anywhere from 200 mV to 800 mV ripple depending on the age of the battery. A shorted diode will produce much higher ripple until the shorted diode is blown open by excessive current draw.

Also the age of your battery is a factor in Alternator whine. Alan had mentioned that your battery is a large capacitor and this is true. The frequency reactance of a battery to alternator whine changes with age. The battery impedance increases with age and your battery will become less of a filter as the years pile up. Buying a new batter will reduce the effects of alternator whine but that is masking the problem for a properly working alternator should produce very little AC output ripple.
RE: Alternator Whine  
by W5FAE on November 8, 2006 Mail this to a friend!
Very relavent article, Alan. I experienced a case of alternator whine that was present only when the headlights or the rear window defroster were on. Since these were a pure resistance, I could only blame the alternator... Wrong. The whine was fixed by cleaning the battery terminals. I believe the ultimate cause was, in fact, the high resistance between the battery cable and the alternator. It caused the load to be taken up by the alternator as oppossed to the battery helping out. Cleaning the terminals solved this elusive problem.
Thanks for the info, alternator whine is annoying to both the source and the listener.

Thanks and 73,

RE: Alternator Whine  
by KC8VWM on November 8, 2006 Mail this to a friend!

Just as a sidenote.

Not only is alternator whine just a mere general annoyance for radio operators, there have been documented cases of FCC citations issued based on it.

73 Charles - KC8VWM
RE: Alternator Whine  
by K0BG on November 8, 2006 Mail this to a friend!
Michael, thanks for bringing up the DVM idea. While I thought about that, I did not include it. After reading your comments, now I know I should have. Thanks again.

Alan, KBG
RE: Alternator Whine  
by K8MHZ on November 8, 2006 Mail this to a friend!
Great article!

It should help to get rid of a bunch of whiners, an that is always a good thing.

I would like to add that a bad alternator belt can produce noise too. This was the case in a friends Intrepid. We chalked it up to static being generated by the badly cracked (and dried out?) belt.

The noise was not a whine but did vary with engine speed.

Again, good write up.
Alternator Whine  
by N0AH on November 8, 2006 Mail this to a friend!
Getting a bike and going light rail-
RE: Alternator Whine  
by W4CNG on November 8, 2006 Mail this to a friend!
Good article Alan, and it is good that N0AH is going "Light Rail". It's a better place for someone whose upper parts do not go all the way up on the elevator...

Steve W4CNG
Alternator Whine  
by N0AH on November 8, 2006 Mail this to a friend!

Elevators? Moving parts? Light rail?
RE: Alternator Whine  
by KA4KOE on November 9, 2006 Mail this to a friend!
A friend of mine not only has alternator whine, but an annoying WHOOP WHOOP when his windshield wipers are running.

No sounds like he's trying to escape abduction and the UFO is hot on his tail.

RE: Alternator Whine  
by W4LGH on November 9, 2006 Mail this to a friend!
Alan did in fact write a nice article. Very accurate and informative. However in modern autos, not only is the alternator whine a problem, but the electronic multi-port fuel injectors will make almost the same sound! One bad one, with an engine running @ 3000 rpm will create a whine, and at idle and annoying tick-tick sound. I have found that the injectors on the Big Trucks are really bad, and in some cases, completely wiped out HF communications. Its easy to find this problem too. Just use a portable AM radio and move it along the intake of the engine, you'll be able to pick out the one making all the noise!

The best place to start, it to make sure all cables and connectors are clean and tight, on the battery, alternator, injectors, and even your spake plugs. A lot of times this will cure the problem, and sometimes you will have to dig deeper.

The newer cars usually have the diode pack and regulator built into the alternators, some of the older models, especially the older Chrysler products, the diodes would run hot and develop resistance in their connections. Some GM models did the same. Just remember when dealing with the current levels @ 12vdc, you need to have a very good connection. A little resistance goes a long way at the levels.

73 and Happy Hunting...
de W4LGH - Alan
RE: Alternator Whine  
by N5AX on November 9, 2006 Mail this to a friend!
My what a interesting read.
RE: Alternator Whine  
by NN6EE on November 9, 2006 Mail this to a friend!
RE: Alternator Whine Reply
by KC8VWM on November 8, 2006 Mail this to a friend!

Just as a sidenote.

Not only is alternator whine just a mere general annoyance for radio operators, there have been documented cases of FCC citations issued based on it.

73 Charles - KC8VWM
Charles, I was one of those guys you were referencing about concerning a citation issued from the "Top Radio-cop" though subsquently it was PROVEN to be unwarranted & bogus because of an on-going vendetta by a FEW local OOs which by the way were ultimately fired by Rosalie White of the ARRL back in 2003!!! :-)))

RE: Alternator Whine  
by W1RKW on November 9, 2006 Mail this to a friend!
Also, if you do have a whine and you do have shorted or open diodes it should be safe to say that you're going to have battery problems as well. Maybe not immidiate but at some point in time.

A typical car battery requires the correct charging terminal voltage to maintain longevity. A few tenths of a volt in either direction can shorten the life of an automotive type battery.

From a maintanance perspective it's a good practice to monitor the charging voltage across the battery terminals over the life of the battery. Any deviation should be questioned and investigated.
Alternator Whine  
by KC0RBX on November 9, 2006 Mail this to a friend!
Thanks for being a "Myth Buster" and debunking the junk science fixes. You saved me some time cause I was willing to try it! Another cause for noise which I found on my Yahoo Yaesu ft-857 users' group is electric fuel pumps. Ford Motor had issued a fix for this by putting ferrite beads or toriods around the power leads as close to the fuel pump as possible.
RE: Alternator Whine  
by THERAGE on November 9, 2006 Mail this to a friend!
Just as a sidenote.

Not only is alternator whine just a mere general annoyance for radio operators, there have been documented cases of FCC citations issued based on it.

73 Charles - KC8VWM

NN6EE comes to mind...along with a few other things. :)
RE: Alternator Whine  
by NN6EE on November 9, 2006 Mail this to a friend!
To the "MORON"/Rage :-)))

What did I earlier say and EXPLAINED that you don't understand???



RE: Alternator Whine  
by THERAGE on November 9, 2006 Mail this to a friend!
You got kicked off a repeater too, didn't you?? :-)))
RE: Alternator Whine  
by W8DPC on November 9, 2006 Mail this to a friend!
I like a little radiator cheese with my alternator whine.
Alternator Whine  
by W1WMP on November 9, 2006 Mail this to a friend!
Excellent article!!
I've been a mechanic for over 40 years and have found,in my experience,that bad and inadequate grounding is the number one source/cause of noise.
A couple other things I've observed
Be aware of where you're putting your wiring so it stays as far away as possible from noise sources.If you have to cross any other wiring,try to cross it at 90 degrees.
I have found a source of noise that is a non-electrical component.The fuel filter.As the filter gets full of contaminates it requires more pressure to pass the fuel. Eventually the filter partially clogs,putting a greater strain on the fuel pump.More strain more amps more E.M.noise.
Another good reason to keep it changed.

RE: Alternator Whine  
by W6TH on November 10, 2006 Mail this to a friend!
A great post and you can also confirm this post by looking into the ARRL handbooks and this will verify how the correction works.

The ARRL handbook has said for many years that a 0.5 microfarad coaxial capacitor in each leg of the alternator will cure the whine. Just don't ever put a capacitor across the field winding.

Most mobile information you find on eHAM is taken from the ARRL handbooks. This helps those that do not have a ARRL handbook or time to read.
Alternator Whine  
by N4OYO on November 10, 2006 Mail this to a friend!
I have found in my 2000 Ford Exploder that the fuel injection system induces noise that is very similar to alternator wine, it will very in frequency with engine RPM. One give away that it is the injection system and not the alternator is that while the frequency varies with engine RPM, the amplitude will vary with throttle position. If the RPM is held steady, and the amplitude goes up with a heavy throttle, it is fuel injector noise.

Of course, with my HORRIBLE Ford fuel pump noise, my injector noise is down in the weeds.

Alternator Whine  
by W6VPS on November 10, 2006 Mail this to a friend!
As usual...well done Alan.
Thanks for the informative piece.
RE: Alternator Whine  
by AE6RO on November 10, 2006 Mail this to a friend!
Regarding alternator diodes, I have an other amusing story.
Back in 1984 or '85 I had a 1967 GMC pickup given to me by my father.
The battery would go dead if I didn't drive the truck for a few days. If I remember right the charging voltage was normal, or near normal.
It turned out to be a very subtle problem. There was a bank of eight diodes in the alternator. The junctions on two of them had gone soft in just such a way that a small discharge current flowed from the battery to ground just like leaving the glovebox light on. A new/rebuilt alternator took care of that.
Other cars had glove box lights turn themselves on and discharge the battery when the vehicle was left alone for a few days. And perfectly good batteries discharge themselves overnight. Just jumpstarting and driving would make them good as new. Oh, and cleaning battery terminals with Coke doesn't work. Moving to another city did.
Amazing what modern technology can do! Oh brave new world! Why am I a libertarian?! Oh, d@mn, forgot my meds again.
RE: Alternator Whine  
by KC8VWM on November 10, 2006 Mail this to a friend!
lol take your meds John.

Good comments.

73 Charles - KC8VWM

RE: Alternator Whine  
by KT6K on November 11, 2006 Mail this to a friend!
All good...but do any of you have a solution for mobile xyl whining?
Alternator Whine  
by WA8MEA on November 11, 2006 Mail this to a friend!
I hope Alan soon writes on the following:

-Reducing heater blower motor noise....
-killing air conditioner compressor noise....
-Stopping the noise emitting from cell phone charger in cigarette lighter....
-Ending mobile laptop computer noise
-Ceasing Sony Playstation running through inverter noise....


-eliminating QRN from two 11 year olds in the back seat.....

73, Bill - WA8MEA
RE: Alternator Whine  
by WA2JJH on November 11, 2006 Mail this to a friend!
Many times I hear mobile stations with alt.whine.
Simply by listening to them, you can tell if they are stopped at a light, accerating(too fast sometimes) or
decelerating(too fast...then off the air = accident)
They give their location often. Who needs GPS! Hi-Hi
Well sorta.

RE: Alternator Whine  
by W9WHE-II on November 13, 2006 Mail this to a friend!
Simple superb. Very well written. Thank you!
RE: Alternator Whine  
by KC8VWM on November 13, 2006 Mail this to a friend!
All good...but do any of you have a solution for mobile xyl whining?


Replace the YL in the passenger seat with radio equipment?
RE: Alternator Whine  
by W5GM on November 13, 2006 Mail this to a friend!
Good article! My friend Rick N5DXT got rid of 98.5% of the injector noise in his PowerJoke Ford by grounding the exhaust system to the frame/chassis of his truck. There are a few radios, the yaesu ft-2600 comes to mind, that just hav3e ZERO filtering on the dc input and will amplify noise no matter how clean or alternator output.
RE: Alternator Whine  
by WA2JJH on November 13, 2006 Mail this to a friend!
Another solution to X(YL) whine....Gaffers tape across
the XYL's speaker(mouth) However you might have some expaining to do if pulled over by the police or state

A less invasive proceedure is to turn around to the XYL and yell at 125db.........Will you kindly shut the
"F" up!!!!!!!!!!!

A rocket powered 007 style ejection seat works well too. Just make sure you are driving over a bridge over water. You could just pull a TED Kennedy! This works well after the divorce lawyer makes that first call!
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