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iDude2003

Charging System Problem

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I own a 2003 Lexus LS 430. As the auto approached 150K miles the system stopped charging my battery. Symptoms: Numeorus indicator lights began to flash on the dash, the battery was completely drained and the engine stopped. I replaced the alternator, timing belt, water pump, serpentine belt, and battery. The car ran perfectly for about an 1/2 hour and the same problem occured. A friend tested the output from the alternator and all looked good. Any thoughts on what may be causing the problem?

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I own a 2003 Lexus LS 430. As the auto approached 150K miles the system stopped charging my battery. Symptoms: Numeorus indicator lights began to flash on the dash, the battery was completely drained and the engine stopped. I replaced the alternator, timing belt, water pump, serpentine belt, and battery. The car ran perfectly for about an 1/2 hour and the same problem occured. A friend tested the output from the alternator and all looked good. Any thoughts on what may be causing the problem?

Well I'd like to know how the alternator was tested. To test it you have to run it at idle speed and load it up so that it delivers maximum wattage out. I think this car has a 700-900 Watt alternator. That means about 50-60 Amps of current load. Is this what your friend did?

If the alternator is new or rebuilt its seems reasonable it should work (not always but lets take it as a starting point). If the alternator is good, the belt is good, and the engine running, then the problem is getting the energy back to the battery. Do you have loose or corroded wires from the alternator to the battery? Is the ground wire from the battery loose or corroded at either end (battery and chassis ends). To allow 60 amps of current to flow this needs to be a very tight and clean connections.

Using a DVM measure the battery voltage at its + and - terminals with engine switched off. Should be around 12 VDC. Then start up car and let it idle with everything electrical switched off you can turn off. The voltage across the + and - terminals should be around 13.3 VDC. If you are still around 12VDC or less then you have no recharge at all suggesting faulty alternator or really bad or disconnected wires. If you have 13.3 VDC then start turning on everything electrical, high beams, bun warmers, AC blower fan, rear window defrost, ... Now measure battery voltage. If it is below 13.3 volts it shows the alternator is not charging enough to keep up with the load. Maybe bad alternator (worn brushes, bad regulator or a stator diode is fried). Since your alternator is new maybe not the case then it has to be the wiring. I am assuming here your battery is good since you said it was new.

If wiring is bad it will have a voltage drop across it. While engine runs and all electrical on measure voltage from battery - terminal to a bare metal on the engine block. Should be near zero volts. Anything above 0.5 VDC suggests a poor connection from battery to ground. Next is to measure voltage from charging terminal of alternator to the + terminal of the battery. This should be near zero as well. If higher then that link is a problem. Be careful on this last measurement. Set up measurement wires before you turn on car so you don't get injured. Also shorting wires from battery + to ground can be dangerous. Be careful.

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I was surprised to see that you changed the timing belt and water pump...no trivial task and nothing to do with the battery charging. Must have just been time to change. Did you do it yourself?

On the battery charging issue it should be a relatively easy task to find out what is wrong. Either a charging issue (try the voltage tests with and w/o load as Curiousb suggests) or a discharge issue (perhaps there is excessive drain on the battery), or bad connection(s) or a bad battery (I know you replaced it but you can still get a defective unit).

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I own a 2003 Lexus LS 430. As the auto approached 150K miles the system stopped charging my battery. Symptoms: Numeorus indicator lights began to flash on the dash, the battery was completely drained and the engine stopped. I replaced the alternator, timing belt, water pump, serpentine belt, and battery. The car ran perfectly for about an 1/2 hour and the same problem occured. A friend tested the output from the alternator and all looked good. Any thoughts on what may be causing the problem?

Well I'd like to know how the alternator was tested. To test it you have to run it at idle speed and load it up so that it delivers maximum wattage out. I think this car has a 700-900 Watt alternator. That means about 50-60 Amps of current load. Is this what your friend did?

If the alternator is new or rebuilt its seems reasonable it should work (not always but lets take it as a starting point). If the alternator is good, the belt is good, and the engine running, then the problem is getting the energy back to the battery. Do you have loose or corroded wires from the alternator to the battery? Is the ground wire from the battery loose or corroded at either end (battery and chassis ends). To allow 60 amps of current to flow this needs to be a very tight and clean connections.

Using a DVM measure the battery voltage at its + and - terminals with engine switched off. Should be around 12 VDC. Then start up car and let it idle with everything electrical switched off you can turn off. The voltage across the + and - terminals should be around 13.3 VDC. If you are still around 12VDC or less then you have no recharge at all suggesting faulty alternator or really bad or disconnected wires. If you have 13.3 VDC then start turning on everything electrical, high beams, bun warmers, AC blower fan, rear window defrost, ... Now measure battery voltage. If it is below 13.3 volts it shows the alternator is not charging enough to keep up with the load. Maybe bad alternator (worn brushes, bad regulator or a stator diode is fried). Since your alternator is new maybe not the case then it has to be the wiring. I am assuming here your battery is good since you said it was new.

If wiring is bad it will have a voltage drop across it. While engine runs and all electrical on measure voltage from battery - terminal to a bare metal on the engine block. Should be near zero volts. Anything above 0.5 VDC suggests a poor connection from battery to ground. Next is to measure voltage from charging terminal of alternator to the + terminal of the battery. This should be near zero as well. If higher then that link is a problem. Be careful on this last measurement. Set up measurement wires before you turn on car so you don't get injured. Also shorting wires from battery + to ground can be dangerous. Be careful.

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Thank you very much for the response / help. I was a bit nervous about doing the wiring test myself so I took it to my mechanic. The problem in fact was the wiring between the alternator & battery. Great advice ... thanks again.

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I was surprised to see that you changed the timing belt and water pump...no trivial task and nothing to do with the battery charging. Must have just been time to change. Did you do it yourself?

On the battery charging issue it should be a relatively easy task to find out what is wrong. Either a charging issue (try the voltage tests with and w/o load as Curiousb suggests) or a discharge issue (perhaps there is excessive drain on the battery), or bad connection(s) or a bad battery (I know you replaced it but you can still get a defective unit).

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After deciding to keep the car for a few more years, I had my mechanic change the timing belt / water pump as a maintenance action only. The charging problem ended up being the wiring between the alternator / battery. Thanks for the feedback.

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Charging System questions seem to come up a lot. There is a lot you can do with just a simple digital voltmeter and basic tools. I wrote this up to help people inclinded to do some self diagnosis. These tests should diagnose 95% of the potential charging system problems.

How to test Battery and charging system.pdf

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Charging System questions seem to come up a lot. There is a lot you can do with just a simple digital voltmeter and basic tools. I wrote this up to help people inclinded to do some self diagnosis. These tests should diagnose 95% of the potential charging system problems.

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Charging System questions seem to come up a lot. There is a lot you can do with just a simple digital voltmeter and basic tools. I wrote this up to help people inclinded to do some self diagnosis. These tests should diagnose 95% of the potential charging system problems.

Good writeup curious. You might add a section on testing the AC ripple under load to possibly detect bad diodes. However a good battery may filter the ripple enough that you would just see a lower changing voltage. Essentially losing a phase (or more) of charging current and hence less voltage. And you certainly do cover that. The main thing is to load the system down. I like to turn the headlights on with the engine off and watch the battery voltage droop over a 5-10 minute period. If the battery is good, it will go down to about 11.9v +/- and hang in there for a good while. If it is bad, it will quickly drop south of 11v.

I also like to take the voltmeter and check the charge voltage under load at the battery posts then go to the head of the clamp. If I see any drop, I know the post connection is corroded or the clamp is hi-Z. In one instance, I could take my hand and hold it on the post and feel excess heat. That's a dead giveaway of a high resistance connection.

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