easy way to test if an alternator works.. off a car
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    MR UN-POPULAR sqweaka's Avatar
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    easy way to test if an alternator works.. off a car

    how can i test if an alternator works on the bench? bought a used small denso alt of a aixam 2cyl diesel engine, via ebay, but i need to make sure it works before my 15min warranty runs out! no good going back to them in a year when i finally get the pop finished!

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    Official RnS Addict D COUPE's Avatar
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    Take it to your local Alternator repairer and ask him to check it ...........
    ITS NOT WHAT YOU DRIVE ITS HOW GOOD YOU LOOK IN IT

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    MR UN-POPULAR sqweaka's Avatar
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    i live in rural northumberland... 100mile round trip!!

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    Official RnS Addict V8Devon's Avatar
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    The local guy I use has an alternator bracket on the bench next to a starter. He's got a standard plug with a lamp to earth off the small terminal and a volt meter on the large terminals. Alternator bolted to bracket, belt around the starter, some leads from a battery, and hey presto, a spinning alternator showing the output voltage.

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    I'm Not Jed Clampett stueeee's Avatar
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    The only way to be sure is to run it up in circuit; but a couple of quick tests with a 12v battery and bulb will give you a good idea whether it's a worker or not.

    First up, earth the alty to the battery negative, now take a lead with a 12V bulb in it from the battery positive to the B terminal (the big one) it shouldn't light the bulb. Now reverse the battery connections so that the positive is earthed, touch the bulb lead from the negative to the B terminal -the bulb should light now. Reverse the alternator connections again so that it's negative earthed. Now touch the bulb lead to the field terminal, the bulb should light again.

    If these tests go OK, there's a very good chance that the alty will work, but the battery and bulb stuff won't find any issues with shorted wiring or the internal regulator.
    Last edited by stueeee; 25-07-2013 at 07:15. Reason: typo corrected in red
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    Semi Proffessional Prat sidspop's Avatar
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    Could you do the above, and spin the alternator up with an electric drill, and socket on the pulley? If the light goes out, it's charging. Shove a voltmeter on battery, and you will see how much. If you need a load on battery, half a dozen headlight bulbs should draw 20amps or so.
    Anybody agree?

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    I'm Not Jed Clampett stueeee's Avatar
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    Quote Originally Posted by sidspop View Post
    Could you do the above, and spin the alternator up with an electric drill, and socket on the pulley? If the light goes out, it's charging. Shove a voltmeter on battery, and you will see how much. If you need a load on battery, half a dozen headlight bulbs should draw 20amps or so.
    Anybody agree?
    That should work -may need to run the electric drill on its fast speed though, most alty's charge cut in speed is about 1000 RPM
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    Gym Junkie chrisvs's Avatar
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    Be careful if your using a drill to test an alternator, make sure the alternator is securely fixed down and hold on really tight to the drill because when it comes "on load" it will probably try to spin the drill out of your hand.

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