my battery couldn't start my cat the other day so i got a new battery and bingo i got it back on the road. So i went to my auto electrician who put an analog multimeter on the new battery whiles the the cat was still running and the gauge moved to the RED which he explains means that my alternator is overcharging the battery.
now he tells me i need a new alternator, else my new battery too will be gone in a few weeks time. This is my third battery in 1yr
is this very common on your cars?what can i do to this overcharging alternator apart from replacing it?

 

so can someone show me stepwise procedure as to how to remove the alternator from the engine if i have to replacce it. thanks

 

ok so it turned out that the alternator has no problem at all rather the cells in my battery were weak due to drying out of the acid. In fact a series of test were done to confirm this and this include removing the negative terminal from the battery whiles the engine is still running and placing it back on. If there are not sparks whiles u palce the terminal on then the alternator is fine. Am sure this is a primitive way of checking but it really helps if u don't have all those digital stuff> Currently i have a new battery on and all seem to be going very well with no battery light on the dash.

 

good to hear. wish we could have helped you sooner. happy driving.

 

Nice to hear you have solved it. I want to comment that jag alternator starts giving 15,3 V for a few minutes, when car runs hot then goes down to 14 V. Any body that does not know it should think the alternator is damaged if measures the V at the begining.

 

thank you PEREZ i will keep that in mind

 

Once an engine is running, if the alternator is producing the battery is only a standby storage device. You should be able to pull the earth lead off, and you shouldn't get a spark unless the battery is flat.

The other point is that if the alternator was producing high on line voltage, it's working fine. The problem would be the regulator on the back of the alternator. Its job is to limit the output voltage so that the battery isn't overcharged, which will cause it to 'boil' and thus dry out the cells. Another indication that you may experience with a dud regulator is more frequent bulb failure where filament type lighting is in use. Bear in mind that modern alternators can have the regulating cicuitry built internally to the back of the alternator, so it may have to be removed to get to the problem.

As an aside, the most common cause of failure in alternators is brought on by bearing failure allowing the rotor to come into contact with the field coil and thus shorting out the alternator. I would personally strip the alternator down every 100,000miles & fit new bearings, which are quite cheap. You do need to take it to a workshop with a press to get the bearings both off & on, but other than that, they are pretty simple to overhaul. Most 'caged' ball bearings will comfortably last that long under such usage, and it's much cheaper than buying a new or reconditioned alternator. If the alternator is not of 'brushless' design, replace the brushes at the same time. They wear, and lose operating tension because of this. The armature may need dressing at the same time.

cheers,

Languid

 

I don't think disconnecting the battery with the engine running is a good idea as this would cause the regulator to spike and may damage onboard electronics, just check with a meter that you get between 13.8 and 14.4 Volts at the battery when the engine is running,

 

Perez is right. The alternator is controlled by the motor ECU and generates 15.3 V when the engine is cold and in several other rapid charge conditions. A warm engine should have 13.5 to 14 V. This is more complex than a simple alternator.

P.S. Disconnecting the battery on a modern running engine is asking for DISASTER.

 

My alternator actually IS overcharging, and I am looking at replacing it this weekend. Ordering a new Bosch alternator from Advance Auto Parts and having my cousin put it in for me. Wish me luck :/ Spitting out like 400dollars for it :x

 

How do you know????

 

I took the car to my cousin's garage. He is the manager at a garage in town which is a college town, and it is one of the two garages that operate on foreign cars. So I happen to have an advantage. Anyhow back to the story, he just hooked a machine up to the battery and we did a full test, involved turning my blowers on high, my high-beams on and my heated seats and such. And whenever they were all on, it was running at average voltage. But whenever it was all off, it was running too high of a voltage. You can also take your car to any auto parts store and they can do this as well. Such as Advance Auto Parts.

 

Which almost certainly means the the regulator on the alternator is what is actually faulty, not the alternator itself. It's clearly working well, producing current, but the voltage is out of control. By replacing the alternator in total, you are actually throwing the baby out with the bath water.

Cheers,

Languid

 

As I said previously, the alternator has two charge modes. After you turned off all the loads the battery was somewhat discharged so the alternator probably went into the rapid charge (higher voltage) mode and is working properly but producing a high reading. What were the battery voltages in volts? Spend you're money and then if you're brave repeat the tests with the new alternator and see what you get.

Languid, the X Type alternator has two charge modes controlled by the ECU so it will look like a regulator problem.

 

The tests were ran properly. In fact here are the results; When the car is running loaded, it is putting out 14.83V, and whenever everything is off, it is putting out 15.18V. That is most certainly overcharging, you can't tell me it's not. And the tests were run for quite a while.

 

As Languid points out, there is a regulation problem. And, Tony_H says that regulation is externally influenced by the ECU and the perception of demand by the ECU. That makes the testing more complex, and the tester must account for the ECU influence.

There are many situations where a charging problem can be fixed without replacing the entire unit. A self rebuilt unit is often better than taking a crapshoot on a purchased rebuilt.

 

I know I'll never convince QuintonChester, but for the rest of us on Page 52 of this link there is an explanation of how the charging system works.

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This is a great document and it used to be on the FAQ but has now been replaced by a later and less useful version.

 

I don't know why everybody is criticizing me, it's great to know that I'm the bad guy here... Anyway, I drove to my girlfriend's house today, and my car straight out died. Wouldn't turn over at all, jumped the car and my battery light came on instantly as well as my engine light. No clue what in the world is wrong with my cat :/ My alternator is already on the way though, and was on the way before this happened. Any clues?

 

Quintonchester...have you had a load test done on the battery also? this will tell you the condition of the battery...do you own a check engine light reader?..if not...the best $50-90 you can spend...hope you get it sorted soon :+)

 

QuintonChester, you're not "the bad guy" but I was insistent that the readings you were posting were within specifications. At the least you might have been wasting your money. That said, this is a public forum and we owe it to others not to post erroneous information. By all doing that we will get good information when we need it.

Sorry that your car has died.