Hello! Are these facts about my electrical system enough to pinpoint the problem on my 99 Nissan Altima? FACTS: In early April, the following were replaced: alternator/serpentine belt, a few pulleys, and compressor belt. In mid-May, I started using the A/C, and got a very short squeal from the b…

I am wondering if the alternator has been bad for the past few months and is responsible for killing both the 4.5-year old battery and the new one that lasted three weeks. I’m not sure. You made me less than confident with Autozone’s diagnostic prowess when you said the read out “finally” said the …

Thanks for your reply, Shadowfax. I’m feeling a little silly that I wasn’t even generally aware that an owner’s manual suggests replacing certain parts on a basic schedule. I’ll check that today. Yes, it took Advance several consecutive tests before the read-out said the three-week battery was not …

The item associated with the alternator that can cause ripple when bad does not cause squeal. Squeal is caused by slippage, and that’s caused by a worn/loose/stretched belt or a component starting to fail and binding. The component could be the tensioner, the AC compressor, the power steering pump, …

The alternator will always have some “ripple.” The battery acts as a buffer/accumulator and will absorb that ripple IF and only IF the charging circuit is well connected. That means the large cable and the alternator body itself as that is part of the circuit. Battery cables, terminals etc are al…

Regulators also contain capacitive/resistive filters to modulate the ripple. According to the OP, the ripple was out of spec. I agree with the rest of your post. Actually, my commendt isn’t a disagreement as much as an explanation as to why I think the alternator should be bench tested. Especially …

I’m a technical / engineering scientific kind of person that engineers automation controls–computer science major. I used to work on heavy trucks for a living. I look at it from this perspective: The vehicle is the best place to test the alternator–the environment is perfect. A bench test is u…

I’m in agreement about not just the bench testing of alternators but starter motors also. The results on a bench can be somewhat iffy at best. Maybe there’s a problem between the alt. and the battery terminal; as in the solder in a fusible link trying to give up the ghost.

As Caddyman pointed out, the alternator is a three phase generator with a diode rectifier bridge. One of the reasons that three phases are generated is that the cosine of 60° is .5. That means that as one phase is 60° past its peak, the next phase is reaching 60° before its peak. Both are at thei…

The amount of ripple voltage you are seeing along with belt squeal indicates to me that you do indeed have a bad alternator. The ripple voltage should be less than .1 volt AC. The squeal is occuring because there is a problem with some the diodes and it is causing an excessive current load to the al…

Excessive Ripple = definitely Bad Alternator?

Maintenance/Repairs

Caddyman June 15, 2011, 1:43am 9

Alternators generate 3 phase A/C which is rectified into DC current. There is very little ripple. If one of the three big diodes that are performing the rectification gets weak or fails, there will be a LOT of “ripple” (A/C ) in the output. The output of the alternator will also be greatly reduced…

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Excessive Ripple = definitely Bad Alternator?

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