Alternator Whine, Ground Loops, Noise
• 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.
• 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 don’t
have access to a scope for testing. There is another way if you have
a DVM. Most DVM’s will respond to AC voltages with frequencies up to
5 KHz. You can read the AC voltage component of the DC output from
• 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.
• 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 opposed to the
battery helping out. Cleaning the terminals solved this elusive
• 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 best place to start, it to make sure all
cables and connectors are clean and tight, on the battery,
alternator, injectors, and even your spark plugs. A lot of times
this will cure the problem, and sometimes you will have to dig
• 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.
• 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 immediate but at
some point in time.
• 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.
• 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.
• 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.
• 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.