Alternator Problem?/ Symptoms:

[mthomas58]

I've posted questions previously noting that I have begun to notice my headlights dimming at low rpm and brighten during acceleration. Today I noticed the same symptom with my Kuehl variable speed fan control on the A/C. Fan speed slows at low rpm or when compressor kicks in and then speeds back up when rpm increaser or when compressor cycles off.

I've got weak electrical system skills. What gives?

Recent changes - replaced interstate battery with new yellowtop optima (deepcycle). Significant after market adds that draw amp above factory specs: (two sound system amps and 5 spal consenser fans tied into A/C system all relay activated when comressor cycles on). Alt is a reman unit replaced at about 90k....now at 180k.

Note: no probs with the interstate battery - just replaced for more room when gas tank was pulled to repair a leak

[Sunroof]

Hey Mark, I am no authority either, but did you check the fan belt tension? Crazy, I know, but a loose belt can be an issue and affect the alternator. If this just happened after installing the new battery I wouold try the Interstate again to see if that changes anything. It would not be costly to get the system checked.

I am horrible with meters, scopes and all things electrical in my Porsche!!

Bob
73.5T

[mthomas58]

Originally Posted by Sunroof

Hey Mark, I am no authority either, but did you check the fan belt tension? Crazy, I know, but a loose belt can be an issue and affect the alternator. If this just happened after installing the new battery I wouold try the Interstate again to see if that changes anything. It would not be costly to get the system checked.

I am horrible with meters, scopes and all things electrical in my Porsche!!

Bob
73.5T

Hi Bob. The issue started before the battery replacement. I'll check the belt tension just in case.

Thanks!

[steely]

You might be pulling a little too much juice with the new stuff you added.

Then again, your voltage regulator (on the Alternator) may be strained.

Try getting one of those voltmeters for the cigarette lighter (Vector at amazon for one) and monitor the output during a drive.

Good luck,

[86911cab]

If the belt is not slipping, I would suspect your voltage regulator. I had the same symptoms, replaced the regulator and the problem went away. Your regulator is probably unable to produce enough DC voltage at lower engine RPMs. Also try shutting down your amps and see if it is draining your system, your alt may not be rated high enough.

[mthomas58]

Originally Posted by steely

Try getting one of those voltmeters for the cigarette lighter (Vector at amazon for one) and monitor the output during a drive.

Good luck,

Great suggestion. Amazon reviews on the Vector were not that good.....this one was highly recommended:

http://www.amazon.com/Equus-3721-Battery-Charging-Monitor/dp/B000EVWDU0/ref=sr_1_1?ie=UTF8&s=automotive&qid=1236737671&sr=1-1

[mthomas58]

Just had my old MB mechanic run a diagnostic test using Midtronics tester.

Results: Good Battery/ 690 CCA/ Cranking Voltage Normal 11.78V/ Chargin Test - Charging System Problem: Low Voltage Charging/ Load off: 14.01V Load on: 12.68V/ Diode Ripple Normal.

Looks like I need a new alternator. Is there a higher amp alternator option than stock on a 3.2?

[rick-l]

Originally Posted by mthomas58

Just had my old MB mechanic run a diagnostic test using Midtronics tester.

Results: Good Battery/ 690 CCA/ Cranking Voltage Normal 11.78V/ Chargin Test - Charging System Problem: Low Voltage Charging/ Load off: 14.01V Load on: 12.68V/ Diode Ripple Normal.

Looks like I need a new alternator. Is there a higher amp alternator option than stock on a 3.2?

How big was the load for the charging test? was it a resistor or a current source? What RPM?

[mthomas58]

Load for the charging test was lights/fogs & A/C running (incl 5spal fans) at 2500 rpm.

This was the test unit (actually it was an earlier model Midtronics mdx-500 series) - resistor source I guess.