battery, alternator?

EpidemicEvan

Registered User
my battery light came on so I thought my alternator was going bunk. When I got it checked at the parts store they said that it was good as well as the battery. I had it checked again then they said the battery was getting bad but alternator was good, then the alternator was bad but the battery good, and then the last time they said that they both were running perfect while the battery light was on. I have no clue whats going on is there anyone out there that can help me solve my problem? thanks
 
Step 1. Buy a battery tester from any auto parts store. They look like a medicine dropper with a plastic tube. They are cheap. Check your battery's electrolyte level and charge. Charge the battery with a charger and retest after a suitable charging time. A 2amp trickle charger should be left on for about 3-4 days. A 10amp charger could be left on for about 1. I personally don't recommend recharging a battery faster than 4 amps. If it won't hold a charge, its the problem.

Step 2. Borrow/buy a voltmeter.. with the engine idling, check the voltage across the center of the battery posts. If its less than 14volts, your alternator is bad.

When the alternator is going out, the battery light will come on occasionally and become more frequent until it stays lit.
 
EpidemicEvan said:
I have no clue whats going on is there anyone out there that can help me solve my problem?
Most likely your alternator is on its way out. A common mistake when troubleshooting is to perform voltage measurements only... this however does not tell you what the true power output is.

Our alternators have a bank of diodes that convert AC to DC, and usually one or two sets of diodes in the bank go faulty. The alternator will still produce the correct voltage, but cannot supply the needed current. The "battery light" signal comes direcly from the alternator regulator and is telling you it has detected an internal fault.

ricardoa1 said:
Run the car without the battery. If it runs good then the alternator is good
You should NEVER perform this test on a modern car. The battery is an integral part of modern system design and acts as a giant filter capacitor. This is needed because the alternator output has high ripple (think of it as pulsed DC). Modern solid-state electronics can burn out easily without proper regulation and filtering.

In the old days of non-computers and old kettering ignition systems this was OK, and often a quick way to check for alternator failures.

One other tip: when giving someone else a "boost", you should shut your car off completely. If left running, when they go to crank their engine, they can (and often do) cause a sudden drop in your electrical system voltage which plays havoc with the voltage regulator. This has been known to burn out ECMs, alternators, and other sensitive electrical components on occasion.
 
Well it worked for me. The alternator/generator is what feeds the power to the car when it is running, and charges the battery at the same time.
The battery allows the car to start and then the alternator takes over. If the alternator is bad the battery lamp will start to light up because not enough voltage is being put out, but only once the battery has drained to a certain level.
It just happened to me last friday so I am not talking out of my ~~~, the alternator needed to be replaced.
 
If you have an aftermarket alternator in the car DO NOT start it with a dead battery. Even if you jump it, the alternator will be working overtime and probably fry. I know because I've been through 3 or 4 this year. Those tards at the parts shops don't know jack about cars or charging systems so don't listen to them. They told me my alternator passed a bench test at one autozone so I put it back in my car and had the same problem. I brought it back to another autozone slightly sabotaged this time, and it failed. So they replaced it under warranty, I installed the new one and bingo, no more problems. Those machines don't test alternators under loads or after they've gotten too hot to touch. Mine was so hot after a couple minutes that I couldn't touch it. That was running no accessories.
 
Heed Paul93SC and Jeremy K advice...

It is no longer an acceptable practice to run a car with a discharged, or weak battery. There are way to many electronics to feed. The battery is both a reserve storage device as well as a giant electrical 'cushion' to 'smooth out' voltage and current. The biggest problem is you can damage the alternator and won't know it for 6-months down the road. Then it will die a slow, painful death in 90 degree heat at night on a lonely stretch of road when you need it most!!!!
Just because others say they've done it and didn't have a problem doesn't make it O.K.

Paul93SC gives good info on checking the system, but you can also go to one of the parts stores for a good diagnostic check. The trick is bring someone to work the throttle and hold the RPM while you watch the machine. Pay close attention to the voltage and the AMPs output. If you don't get at least 100 AMPs, get an alternator.

Hope this helps!
 
do any of u guys think that it could be a wire going bad since the last time i went to the parts store they said that both alternator and battery good. Like a bad cable or maybe the wires that connect to the alternator and go to the engine block? I noticed that the wires that go to the alternator were kinda bad and the coating of the wires were off (I was seeing some bare wire). I put electrical tape around them but that didnt work the battery light still goes on and off.
 
Inspect all wires and cables, add on battery rerminal ends are a no no. If you need to replace the cable ends replace the whole cable. In my 35+ years of being an auto tech I find that is the problem most of the time. I am retired from that now and am one of those TARDS that work at Auto Zone. I will bet that the test was accurate and you have or had another problem. The test machine doesnt know how to lie. If it wasnt hooked up properly it wont test. If your alt. is getting hot in your car it is probably something in the car causing it. {see above} The system is called a charging system it has more than 1 or 2 components. Good Luck
 
EpidemicEvan said:
I noticed that the wires that go to the alternator were kinda bad and the coating of the wires were off (I was seeing some bare wire).
Well, this is never a good thing to find, but it depends on how bad the existing wires are.

If you're talking about the two wires which go into the plug on the top of the alternator, and they are simply losing their sheath, then taping them up will probably suffice. These are the "battery voltage sense" and "diagnostic output" wires.

If you're talking about the main "battery" cable which bolts to a post on the back, then you should follow Garry's advice and just replace it. This cable carries the main power from the alternator to the battery.

---------------

The bench tester at the parts house is probably not lying, but cannot simulate all the "real world" conditions an alternator has to live through. Often failures are intermittent and don't show up with a quick test like that. You can't blame the guys at the counter for this.

Our alternator design is fairly standard and well known. It employs a "3-phase" output and has a bank of diodes which form a full-wave rectifier bridge. Two diodes rectify each phase and all three rectified outputs are combined together for the total power output. If you lose one phase, maximum power output will fall by 1/3rd. Lose two phases and maximum output will fall by 2/3rds.

However, even in this condition, if the load does not exceed the power output of the phases still functioning, correct output voltage will still be maintained.

The diode bank dissipates a large amount of heat (due to their internal voltage drop) and they get real hot. Often these diodes will return to normal operation after cooling down, but they are still faulty diodes. Our internal diagnostic circuit is not your simple "voltage" detector, but rather a somewhat sophisticated phase monitor and is designed to monitor the balance of the three phases. The "battery" lamp is triggered when it detects a power output imbalance between the phases.
 
The bench tester at the parts house is probably not lying, but cannot simulate all the "real world" conditions an alternator has to live through. Often failures are intermittent and don't show up with a quick test like that. You can't blame the guys at the counter for this.







I retract my statement about parts employees. I apologize if I offended anyone. It just urks me that some punk kid tries to make me look like the jacka$$ because my alternator passes their bench test and they don't honor my warranty. I know how to test an alternator while it's in the car and I know when one's not performing correctly.
 
Jeremy no offense taken. Alternator output can be real world tested in the car by you with a simple voltmeter, voltage should be between 13.8 and 14.2 below that alternator is queationable, much above that the internal regulator is bad. I like to rest alternators in the car so I can inspect the system myself.
 
I retract my statement about parts employees. I apologize if I offended anyone. It just urks me that some punk kid tries to make me look like the jacka$$ because my alternator passes their bench test and they don't honor my warranty. I know how to test an alternator while it's in the car and I know when one's not performing correctly.
Thats standard. Unfortunately, these Mitsubishi alts fail intermittantly and usually when they're hot. Eventually (and that can mean you get stranded somwhere), they will fail completely. I've had to argue with more than one store manager about this very thing. :mad: As odd as this sounds... you're better off with a used working alt than with a new rebuilt one. :eek:
 
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