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    Home » Articles » DIY

    Simple Way to Test Your Car Alternator

    by Eric · This post may contain affiliate links, its one way we pay the bills. · 9 Comments

    Is your battery or alternator light on? Here's the first step to determine if your alternator is not working.

    You will need a voltmeter - I prefer a digital one - they are all less than $20.

    Open the hood of your car/truck, set the voltmeter for 20 volts DC or whatever DC voltage setting it has between 15-25 volts DC.

    12.67 volts DC means the alternator is not charging

    Place the Black lead from the voltmeter on the negative post of the car battery - the black cable from the engine is attached to the negative side of the battery.

    Place the Red lead from the voltmeter on the positive post of the car battery - a red cable from the engine is attached to the positive side of the battery.

    Read the voltage: if it is around 12.5 volts, the alternator is not charging the battery. This may be caused by several things, it may be a loose or disconnected wire, a loose belt, the voltage regulator may be bad, or the alternator is bad. In many cars, the voltage regulator is attached to the back of, or incorporated into the alternator.

    When my Ford F150 truck battery went dead, I pulled out my voltmeter and tested the battery. I was able to tell the problem was not a loose wire or connection because soon after I started testing at the battery, the alternator started to smoke, which is a pretty good indication that it needs to be replaced.

    On many cars and trucks, if you have some mechanical ability, you can replace the alternator yourself. Look online for a discussion forum about your vehicle and search the posts for alternator replacement tips and tricks. When you go to your local parts store to pick up a new alternator, its ideal to bring in the broken one, most parts like this require a trade-in of the old part ( so they can rebuild it ) AND it is good to confirm that the new alternator is the right one. Save yourself a trip.

    Tell us your alternator stories below, be good to learn other tips and tricks from you all.

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    Reader Interactions

    Comments

    1. Keva Cilek

      October 24, 2010 at 8:25 am

      Much obliged for the information and for creating a attractive website. I have been looking for reliable info on travel tips and will put these recommendations to practice. I have found it difficult to locate good recommendations, as there are so many web sites with junk posts. Please keep the good stuff coming!

    2. willie flores

      October 28, 2010 at 8:23 am

      you also can check your alternator by pull the postive wire from your batt.
      and if your engine cuts off your alternator is not working if it stays on it is ok.

    3. Lavinia

      November 12, 2010 at 2:44 pm

      Spray WD-40 let it sit overnight, then heat the part with the torch and the bolts will come out smooth as butter.

    4. Howard

      December 02, 2010 at 2:20 pm

      One thing you didn't mention is that the engine should be running while performing this voltage test.

    5. admin

      December 03, 2010 at 11:09 am

      yes! good point. I am not always the master of the obvious. eric.

    6. raja max

      November 22, 2011 at 1:57 pm

      nice job. how to check that the car battery protection is working fine. (overvoltage protection where the batt stops charging when its is full)

    7. Nancy

      March 16, 2018 at 4:41 pm

      Would a phone charger make the alternator go bad if it is used all the time

    8. Eric

      March 18, 2018 at 10:29 am

      @nancy, no, a phone charger draws very little power. thx! eric.

    Trackbacks

    1. Is Your Car Battery Dead? A Quick DIY Fix - GardenFork - Eclectic DIY says:
      August 8, 2019 at 11:03 am

      […] You turn the key, and you just hear ‘click’. Is your car battery dead? Maybe not. Here’s a quick DIY repair that may save you some $. (If you suspect the alternator may not be charging, learn how to test an alternator here. […]

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