# My Sentra Kills Alternators!!!



## manimal (Jun 16, 2005)

I've got a '92 nissan sentra that seems to kill alternators (we've gone through 3 in the last 12 months). I don't know why. I don't have a big sound system in the car or any extra electrical stuff. How do I test for problems (shorts?) in the electrical system? :4-dontkno


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## Volt-Schwibe (Jan 12, 2003)

first off, i have some questions, and then we can all come in and make some suggestions.


one, do you drive the car at a high rev? like, fast? sometimes the constant high rev's cause the alternator to put out excessive voltage, and this excess voltage is burned off in the voltage regulator as heat. obviously, you can only add so much heat to a set of diodes and resistors before they fail.


two, are all these alternators coming from the same supplier? maybe they just suck.

three, how is it failing? does it start putting out bad voltage? (less than 13.8 or more than 15.2) or does it just stop putting out voltage altogether?

and finally, does your battery go dead overnight?


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## JamesO (Mar 30, 2005)

Answers to Walt's questions would be a helpful start.

Keep in mind, the alternator really powers everything in the car, not the battery. The battery's primary purpose is to start the car, load the alternator and filter the power from the alternator.

Has the car needed to be jump started a lot since the first alternator was installed? Hook up the jumper cables backwards or hit it with 24 Volts, your alternator is history.

What leads you to the conclusion the alternator has failed? 
Charging Voltage problems?
Idiot light?
Dead battery?
Car won't start?

What is the charging Voltage, measured with a digital Voltmeter, at the battery terminals with the car running at a fast idle and the headlights turned on?

How old is the battery, if it is 3 years or older, replace it. 

JamesO


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## batty_professor (Jul 29, 2004)

I think Walt may be onto something with the 'same supplier" thing. Some rebuild houses couldn't successfully put new brushes in a vacuum cleaner. I often find I have to rebuild my own, or check out the junkyards for a low-mileage unit. The factory supplied units are often good for 150,000 miles or so.


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## manimal (Jun 16, 2005)

To answer the over-reving question, we don't really drive it extra hard or anything. It's an auto trans, and we just drive to keep up with chicago traffic. 

I am suspicious about the supplier. It's a one-year warranty rebuilt from Pep Boys (the last 3 alternators).

What happens exactly is that the alternator will stop putting out enough voltage, and eventually leave us stranded. The last time it went out, we caught it early enough (charging voltage was at 12.5 volts) and swapped it. We get a free replacement every time, but it's not really a lot of fun to replace every 3 months or so. Yesterday the stereo would turn off when the car was idling, but turn back on when the rpms picked up, so i'm assuming the voltage coming out of the alternator is low again.

The battery is about 2.5 years old.

I'm willing to believe that it's a crappy alternator supplier, but is there anything else we should check out first?

thanks!


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## batty_professor (Jul 29, 2004)

Check to make sure the battery connections aren't corroded, and the - connection at the engine block, and the lead connecting - to the body (at lug under screw with star washer) are all intact. Also suspect is the lead/lug that attaches to the stud/nut connection on the alternator itself. I have seen those burn off before on the Japanese cars.


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## JamesO (Mar 30, 2005)

Charging Voltage was 12.5 Volts, this is not right!!! A lead acid battery has a terminal Voltage of 12.6 Volts at full charge!!! So this indicates you are not charging at all. A proper charging Voltage (measured at the battery terminals) is between 13.8-14.8 Volts at a high idle with the headlights on. Some newer cars will limit the charging Voltage with a battery temperature sensor on hot days to keep the battery from overheating, so these may fool you.

What you need to confirm is if there is too much Voltage drop somewhere. This is what Batty is after. Use digital Voltmeter and measure on either end of the cables. Anything more that about 0.2 Volts and this is not good.

This link may help clairify how to measure Voltage drop:

http://www.prestolite.com/pgs_training/training_4.php

Bad grounds are common. Quick test for a bad engine/chassis ground is to take a pair of jumper cables and connect 1 end (both Red and Black clamps) to the engine block and one clamp to the negative battery terminal and the other clamp to a good body ground and see what happens to you charging Voltage. If it goes up, you have a bad ground somewhere.

Have seen problems in the German cars with the larger spade lug alternator connections and the small #10 wire. In the past had to parallel some of the output wires to eliminate high Voltage drop in poorly designed cables. 

JamesO


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## Volt-Schwibe (Jan 12, 2003)

i like the idea about checking for bad ground.

these alternators of yours are either being "backfed" power surges and spikes, is under excessive load, or are just being rebuilt badly.



a bad ground can cause the first one.

a serious short in the electrical system can cause the second.

the third is obvious.



i have a funny story to tell about auto parts suppliers actually. (it's a long story, you don't have to read it.)

there is this guy i know, and he's a little "excitable" getting angry quickly, and so on. he calls me up one day and asks me if i would help him swap his sister's alternator, and so i say yes. we get there and she has an alternator she bought at a Knecks store. (a division of shucks.)just out of curiosity, i check her voltage with it running, and then i watch as the vehicle is shut off. 12.3 volts running, 12.6 volts shut off. so, we change the part, and low and behold, no change. so we take it back, the store happily replaces it. (i've got to say they usually are great about that.) well, within 30 mins, we are headed back there again. they replace it again. (really, they are great.) and again, for the third time, it's bad. so this time when we take it back, we've given up on them, and we just wanted our money back, and, we kinda really needed the old one back too. well, there is this manager there all of a sudden, and he's got it in for us, and decides we are stupid. so, he takes the alternator, and he puts in on the test machine, and i am standing right there, and i can see the machine, and it's only lighting the one light. (which means the alternator is connected, and reading the correct ohm load, which means only that the coil is intact.) so he carries it back and says it's a good alternator. i tell the manager he's crazy, and my friend starts to get loud. after a bunch of bickering about who knows how to read the test machine, i talk him into pulling another one off the shelf, and he tests it, and it gives him one light, same as the other one. i am starting to be a little amazed that 4 of this store's alternators are testing bad, right in front of me, and this manager doesn't know how to read the machine. well, after about 10 minutes of seriously loud bickering, i start worrying about the cops showing up to arrest my friend, so i got my friend to calm down a second, and i asked the guy straight out, "where is your closest other branch? and if i get them to say this alternator is bad, can we get a refund and our core back?" he looks at me all crazy, and tells me it's about 25 minutes down the same street, so i grab my friend and out the door we go. we get to the other store, and i tell that manager all about it, and he said he had received a phone call already, and he tosses it on the machine, and the machine lights up one light, and he says "yep, it's bad" so he wrote us a receipt, took the bad alternator back from us, and gave us a full refund. and, he called the other store and asked the guy to make sure our core was where we could come get it. we get back to the other store, and i had a mindful of noise i would have loved to give that guy, but he is hiding in the back of the store, and we walk in and their counter girl has our alternator, right there at the door, and there is a policeman there with her. she handed it to us and apologized to us for the bad experience we had, and we left, fuming mad. 

so, after all that time was wasted, we drove down the street to napa, and bought a rebuild kit, and put nothing but the voltage regulator in our old broken one, and the car worked fine.

so, after seeing 4 alternators come off the shelf and out of the box and test out as bad, not much will surprise me now.


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## batty_professor (Jul 29, 2004)

Walt, while people go to those stores to buy a replacement item like that, they're depending on it being a good part. They rely on this because they typically know nothing of the inner workings of such. And are at the mercy of the vendor. So to the average Joe, the defective parts may not be obvious. This is a sad reflection on the situation as a whole. That story you shared though is PRICELESS! I once had an '89 Beretta with the 3.1 V-6. It had a rebuilt GM alternator. It got intermittent one day, and got worse fast. So I took it off, disassembled it for inspection. Brushes, slip rings, and interior in general looked new. In any alternator, the three field windings Y into a common connection. This one the three leads were twisted together, and a crimp sleeve in place. The insulation wasn't cleaned off the lead ends before the crimp was applied. This alternator must have been through the rebuild house for this problem and subsequently missed, only to fail again. i guess this is what happens when the approach is tro run these through a process like meat through a packing plant. Anyhow, I removed the crimp, prepped the leads, and crimped/soldered the connection. I'm sure it outlasted the car.


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## maddbob (Feb 13, 2005)

Check For An Intermittant Short Between Battery Cable And Exhaust Manifold.


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## maddbob (Feb 13, 2005)

Trans.in my pickup was overhauled,battery cable was installed incorrectly,it was against manifold and sheath melted and gave intermittant short until finally it drained battery and blew diodes,battery is ok not swollen so plates arent shorted,replaced alt. and repositioned cable and reinsulated with rtv,problem solved.Now some alternators diodes are directly attached to alternator case,that said,I had a car that was blowing alternators about one a week,I was lucky and had three and the equipment to rebuild them including diode replacement,it was found the car had been in a front collision and bent the alt. brackets,the severe alignment condition created so much heat in the bearings that you could recieve a severe burn by touching it after a few minutes,this heat was being transfered to diodes and exceeding there breakdown ratings and killing them,replaced brackets and problem went away.One more thing oddly enough there was no tell-tale noise associated with this condition,but was discovered accidently when eye-balling the drive belt,and I saw that the drive shiv was 1/2" back from normal,so I hpoe this helps in some way.Maddbob


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