Alt test?

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Feb 14, 2008 | 08:28 PM

Jason

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Alt test?

Is there an easy way to test your alternator? What voltage should be showing on the DIC?

Feb 14, 2008 | 09:28 PM

noahdr

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From: New Bern NC

somewhere between 13.6 and 14.2 is good

Feb 14, 2008 | 09:31 PM

JoeyG

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Voltage on the DIC should be 12.8 to 14.6 when the car is running. There will be about 0.5 to 1.0Measured voltage difference between the actual alt output and the DIC reading.

Feb 14, 2008 | 10:35 PM

middlebrookgt

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my DIC displays about 14.2 with lights off, 13.8 with multiple accessories running

Feb 14, 2008 | 10:54 PM

Fastbird

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What the DIC isn't telling you though is the amperage output of the alternator and if the diode is still good. Either one of those will cause issues. Low amp output won't allow your battery to charge enough, bad diode will let the alternator drain your battery.

If you suspect it's going out, hit your local Auto Zone, Advance Auto, ect and have them bring the cart out to the car and test it. It's free.

Feb 15, 2008 | 09:01 AM

BLOWNBLUEZ06

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From: Forney Texas

Quote:

Originally Posted by Fastbird93

The voltage out is directly related to the amperage out. If you have a bad diode, or a anything in the alternator that would reduce it's output, the voltage will drop under load. Turn the car on and then turn on some accessories and look at your voltage. If the alternator can't put out the current or if you have a wiring issue, the voltage will drop below the charging voltage. Check wiring connection tighness at rear of alternator and at starter. Those and the grounds and on occasion the ign switch are the main points that cause problems if it's wiring.

Feb 15, 2008 | 10:32 AM

Fastbird

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I work part time at an auto parts store and test these things all the time. Time and time again I see a car coming in complaining of a dead battery. I slap the tester on the car, and voltage output from the alternator is 13-14 volts but the amperage output is only like 2-10 amps. You can easily have an alternator that quits putting out enough amperage to consistently charge the battery that still puts out enough voltage to run the car once you get it fired up.

The bad diode will not always cause voltage fluctuations. I've seen this more times than I can count also.

Feb 15, 2008 | 10:26 PM

BLOWNBLUEZ06

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From: Forney Texas

Quote:

Originally Posted by Fastbird93

Voltage is only electrical pressure. Once the demand for current comes, at some point, the voltage will always drop. At what point the voltage drops relative to the current demand and draw is the determining factor as to whether an alternator has a current supply problem. A corvette probably wouldn't run with an alternator only able to provide 2-10 amps. Just at idle, you have the fuel pump, computer, injectors and whatever else. This is, by the way, why I said to turn on some accessories. This way, you are loading down the alternator. This is a good real world test. If you take a poll, you will find that many have taken their alternators to the local auto parts store to have them tested, been told they're good only to find out in the end that they're defective. FWIW, I worked in aftermarket automotive electronics professionally for 14 years full time and for last 10 years, specialized in DC power distribution systems for the phone company. Not trying to argue, just discuss and provide this guy with some answers that might help get his problem fixed.