QuestionQUESTION: Hi, I am not sure if I have an Alternator charging problem. The LCD light on my radio started flashing off and on when I was driving at night. When I stopped driving and was idling, the LCD light got very dim but when I turned my headlights off, the LCD light on the radio got very bright. When I turned my headlights back on, the LCD light on the Radio got very dim. This also happened 3 months ago and the next day the alternator went bad and they replaced it. I am afraid that the alternator is acting up again. The car battery reads 12.6v when the car is off. It reads 14.2v at idle which should all be normal. But if I turn the headlights on at idle, the voltage (across the battery) is only 13v. If I turn the lights on and the rear defroster at idle, I am only getting 12.2v (I read on several website that I should be getting at least 13.8v in this scenario). If I increase the speed of the engine to 2000rpm, I get 14.2 volts even with the lights and defroster on. I am guessing that if I idle the car for too long with the lights on and defroster, I will be draining the battery. My mechanic supposedly tested the charging system under load and he said that it is fine. I think the alternator has a problem. What do you think? Thanks in advance.
ANSWER: Hmmm. Something definitely does not sound right about this. I think the first thing I would do is check your battery cable connections. I would clean them and tighten them. Then I would replace my alternator belt (unless it has been done recently) and make sure it is tightened correctly.
All of the above can cause the type of problem that you are having. Since your alternator is not that old I would hope that it has not gone bad already.
I'm not sure why the mechanic did not find that your alternator was bad under load. What you are doing with the tests you have done is a load test, just without the fancy machine. Your testing is telling you that there is a problem in the system somewhere. It very well might not be the alternator though. It could even be a bad battery. To test it I would remove it and have just the battery load tested. You can get your own load tester for a decent price. You can check it out on my website (it is under "electrical system diagnostic tools):
http://www.myautorepairadvice.com/cool_tools.html
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QUESTION: Hi again, the cable connections and belt seem fine but I will double-check them tomorrow. The battery is only 4 months old. I did more testing today. The car was cold (it was about 42 degrees out), I started it and the rpm's were about 1500. I was getting 14.2v at idle even with the headlights on. After about 15 minutes the rpm's automatically lowered to about 800 rpm's. I was getting 14.2v. Then I turned on the lights and saw the voltmeter drop to about 13.5 volts and then it went back to 14.2v within a few seconds. I kept turning the headlights off and on to make sure that it was consisent. At first it was but then sometimes the voltage would lower to 13.3v or so and stay there even after turning the headlights off. Sometimes it would jump back to 14.2v while sometimes it would stay at 13.2v or so. Then I turned on the headlights, rear defroster and put the fan on high. The voltage lowered to about 11.8v at idle. Then I turned off the rear defroster and the fan and just left the headlights on. I guess that the alternator couldn't recover though since the voltage wouldn't go higher than 12.4v. Can an alternator have an intermittent problem like this? If the alternator is on its way out, how long do you think it can go on like this before it totally fails? Is it possible that the alternator is a cheap one (it was rebuilt) and is made to not output a lot of amps at low rpm's? Thanks again for your help!
AnswerIt doesn't matter how old the battery is. It might be just fine, but you need to verify that it is working correctly. The test is super easy and doesn't take long and it will rule the battery out quickly.
That being said, your alternator is most likely just a bad rebuild. If I were you I would probably just buy a new one. Yes, alternators can be bad intermittently and it sounds like yours probably is.
It's hard to say how long this one might last. Most likely it would last for a while, but I'm not sure that it is a good idea to drive it like this. An alternator like this is hard on a battery.
