Alternator whine

Capacitor - small one goes right on the output terminal of the alternator and/or the battery terminal of the regulator (if externally regulated.) Another small one goes on the positive wire to the coil. (that one suppresses ignition noise, if you don't have any ignore that one.) Big capacitors go in the power wires to the amps, as close to the amps as possible. If that doesn't work, then you start worrying about ferrite rings and suchlike.

good luck,

nate

Well, first off make sure that the alternator doesn't have a popped rectifier diode or two. A dead diode really increases the whine because it increases the "ripple" on the ouput voltage from the alt.

A "choke" (inductor) installed in series with the power leads to the amplifiers, followed by a capacitor from the power lead to ground is a good noise filter. You can buy choke/cap combos pre-packaged at most stereo stores. 3 wires to connect and you're done.

"Steve Massey" writes in article dated Wed, 21 Sep 2005 09:05:43 -0700:

The following is based on my electrical engineering education and *not* any actual experience with car stereos:

Put the capacitors across the power inputs to the amps (i.e. in parallel with the amp), + side to 12V and - side to ground. Some caps can go either way so it doesn't matter which is which. The closer you get it to the amp itself, the better. For example, downstream of the fuse is better than upstream.

The WVDC rating should be at least 12V (or whatever you use for an input voltage). Higher won't hurt but it won't help either.

The uF rating is a measure of the noise-absorbing ability. Bigger is better. However, if the amps (and caps) are wired to an always-on power source, be aware that they do "leak" and can drain the battery if you let the vehicle sit too long.

A choke goes in series with the amp, either on the 12V line or ground line. Upstream of the cap, if you're using both.

A filter designed for this purpose is probably a choke+cap combo.

If you're drawing more current than the alternator can handle, the best thing to do is get a bigger alternator. Test this by pulling the fuses on 2 of your 3 amps and see if the remaining one gets better.

-- spud_demon -at- thundermaker.net The above may not (yet) represent the opinions of my employer.

Do you still get noise in the amplifiers if you unhook the audio source and crank it up with ablsoultely nothing being input to the amp?

Just curious.

There are all sorts of things that cause this ... when I was younger and into car stereo, we used to call this a "ground loop problem" and would buy a "ground loop isolator" to fix it. Most of the time it worked, too ... basically it was caused by signal wires running too close to power or ground wires. This was often solved by proper planning (running power wires down one side of the car and signal wires down the other).

When that didn't work, sometimes grounding all components to the same place worked (made for extra wiring, but much less hassle trying to track down noise). When neither of those worked, having the alternator rebuilt usually did. There was one shop where we sent all our alternators and they did their thing.

Later, after owning a shop where I rebuilt alternators, I came to realize there was a capacitor one could put in (the older GM and Ford alternators had them as factory equipment ... most alternators can be modified to take one) that would often solve the problem. When that didn't work, it was usually because one or more phase of the alternator stator was out of "sync" and installing a new one would work out beautifully.

That's what I meant ... just couldn't think of the phrase off the top of my head. Thank you. "Sync" was the only thing I could come up with at the time that made sense to me and I thought would make sense to someone else, too.

I hope it never stops working ... for you or for whoever you sell that tractor to in 100 years.

I assume you mean that one or more arms of the three phase circuit was open or had high resistance, giving a lot of ripple? Or have I misinterpreted what you are saying?

By the way, Walter, my CS130 on the John Deere is working fine so far, but we will see how long it lasts. The old deep discharge battery was refilled with water, and took a charge just fine. It's fixed, for today anyhow.

That's an inductive loop, where noise is transmitted inductively across space to another conductor. The ground loop problem is caused by the various components--stereo, amps and so on-- being grounded at various points of the car's body. Old body joints cause resistance, and there can be varying ground potentials at the different points anytime current is flowing through the body. Alternator noise is often picked up at such points and fed back to the amp. The solution is to ground all of the associated components to the same point. Poor grounding at the alternator, regulator, engine-to-frame, and such can also cause ground loops. Some noise can be fed back from the alternator field, through the regulator and into the car's system. A capacitor across the field terminal and alternator ground stops that.

Dan