Trailer connected to truck creates alternator AC noise

Having rebuilt 10,000+ alternators...

I really suggest having this diagnosed electrically not by guesswork.

A shorted or open rectifier will cause an ugly ripple in DC output never mind chop alternator capacity by 30% or more. Bad rectifiers WILL destroy the stator if not repaired rather quickly.

Have a competent shop test the alternator at 100% output. A 120 amp alternator MUST be load tested for at least a half minute at full load, not a Kragen job.

Bad rectifiers or bad stator CAN cause the symptoms you describe. Professionals groan when a customer starts throwing around buzzwords. You may or may not be dealing with EXCESSIVE VOLTAGE RIPPLE due to a bad rectifier or stator. Save the alternator sine wave lingo for an alternator diagnostic laboratory. An otherwise useless term.

If the alternator is load tested PROFESSIONALLY and is found to be good...

Check to make sure the firewall to hood bonding STRAP is in good repair and tight. Wires are next to useless. A flat braided strap is used for a reason. But you say your instruments are affected. Keep reading...

Overwhelmingly when multiple instruments are affected on a single board, the instrument panel, the prime suspect is a bad ground wire and or connection running between the instrument panel circuit board and the interior firewall.

This needs professional diagnosis to cut to the chase...

Hope this helps

KATOOM wrote:
Its not noise you hear with your ears or in the radio but a sin wave created by the alternator diodes which causes various electrical senders to read incorrectly or not work right at all.

See the sine wave where?

You realize the alternator has three windings and six diodes and is spinning faster than your engine , at 2000 engine RPM, the sine wave is about 18000
I can't see that sine wave without an oscilloscope

If you are getting some "NOISE" on a display when the tt is attached, you have a grounding shielding issue and the noise signal is being radiated by the tt

What is AC noise?
EDIT: you described what your issue is while I typed. There should be no RFI or EMI issues between your RV 12V system and the truck's alternator. The power circuit from the truck to the trailer is terminated through the truck's battery which is a big filter. You may get some spurious RFI into radio frequencies but nothing that would cause your senders to go wonky.
It sounds like your RV's battery is bad and the loss of current may be your major issue.

Its not noise you hear with your ears or in the radio but a sin wave created by the alternator diodes which causes various electrical senders to read incorrectly or not work right at all.

We don't know what you're talking about.

Are you talking about picking up a "whine" on AM radio, or after-market amplifiers? I've experienced whine when there is a grounding problem ... energy is being radiated by the positive wiring, but not being absorbed by the ground wiring, because there is high impedance in the ground somewhere.

Use an multi-meter set to ohms and test the resistance on your 7-way cable's ground pin to the trailer frame, and on your truck's 7-way connect ground pin to the truck's frame. corroded connectors or a lose / broken wire can cause high impedance.

some folks say the trailer grounds through the hitch... if there's too much lube or paint in the way, you'll have a high impedance path there as well.

Is the alternator belt making noise? That can indicate that the amperage is pretty high, and it might be worthwhile to charge the trailer batteries a bit before leaving camp with a generator or with a solar system.

SunElec.com


Good luck!

Fred.

PLEASE DEFINE THE SYMPTOM WHAT NOISE IN WHAT SYSTEM IS THE ALTERNATOR "CREATING?"

Noise entering ear, radio, cellular, etc?