Excessive Ripple???

98E9GT

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Dec 16, 2007
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I had my charging system tested today and it failed, tester read Excessive Ripple. Isnt that basically telling me my alternator is shot?
 
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trinity_gt

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Jan 31, 2003
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When they talk about ripple, they're probably referring to the waveform coming out of alternator. The alternator is really a small 3-phase AC generating station. Three windings in it produce alternating current output that are 120-degrees out of phases. These outputs are fed through a rectifier block and the result is a waveform that has peaks and valleys but which always stays positive. As one phase maxes out and begins to drop in output, the next is rising and when the next one has a greater output than the falling one, the rectifier output follows it. The term "ripple" refers to the difference between the peak and valley voltages at the output of the rectifier. As a simple example of ripple at work, most who've installed aftermarket stereos have heard that annoying whine in the speakers... That whine is caused in part by the ripple nature of the alternator output (and bad grounding...)

Excessive ripple may mean that one winding of the alternator is open or that a rectifier has gone bad. In any event, if the diagnosis is correct, you're probably looking at a new alternator.
 

GDawg

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Mar 22, 2002
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Back to life...

Your car wants VDC (volts direct current). Alternators produce a small amount of VAC (volts alternating current) that your computers don't like. There is a diode in the alternator that is supposed to suppress the VAC ripple. No more than .4 vac is acceptable. Once it goes above this you will start to have driveability issues.

I found this thread cause I have that problem and I'm looking at rebuilding the alternator instead of replacing it.
 

stang_ed

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Aug 5, 2009
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Back to life...

Your car wants VDC (volts direct current). Alternators produce a small amount of VAC (volts alternating current) that your computers don't like. There is a diode in the alternator that is supposed to suppress the VAC ripple. No more than .4 vac is acceptable. Once it goes above this you will start to have driveability issues.

I found this thread cause I have that problem and I'm looking at rebuilding the alternator instead of replacing it.

Slight correction from an EE. Alternators only create alternating current (AC). The diodes in the alternator rectify the AC to create direct current (DC) needed to power the car and charge the battery. The DC created is not pure and has AC superimposed upon it. The amount of AC on the DC is called the ripple. If one of the windings is bad or if a diode is bad the amount of ripple will be more than normal with the result the effective DC will be low potentially causing malfunction and poor charging of the battery.
 

GDawg

Founding Member
Mar 22, 2002
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Colorado Springs, CO
Slight correction from an EE. Alternators only create alternating current (AC). The diodes in the alternator rectify the AC to create direct current (DC) needed to power the car and charge the battery. The DC created is not pure and has AC superimposed upon it. The amount of AC on the DC is called the ripple. If one of the windings is bad or if a diode is bad the amount of ripple will be more than normal with the result the effective DC will be low potentially causing malfunction and poor charging of the battery.

Thanks for the insight... I'm still learning... :nice:

What causes a diode to go bad?
 

joshjwc9

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Jun 12, 2006
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If I am hearing loud speaker whine (as well as cutting out and distortion of the driver tweeter) and I have been for probably a year now, is this caused by an alternator on its way out, or something like bad grounding, a bad amplifier (Mach 460) or a bad battery?
 

stang_ed

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Aug 5, 2009
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Thanks for the insight... I'm still learning... :nice:

What causes a diode to go bad?

Semiconductors can go bad without there being a specific external cause. Otherwise, over-current through them and higher than normal temperature can cause failure. Unnatural events such as improper connections (like shorts) can cause failure also. Very high and damaging currents can flow from these causes. Generally, today our auto's charging systems are very rugged and can take a lot of abuse.