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Did I destroy this alternator?

Discussion in 'Automotive Electronics' started by coop1er, Feb 20, 2016.

  1. coop1er

    coop1er New Member

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    Hey all.

    I had a car that wasn't charging. So I chucked another 2nd hand alternator in it. It still wasn't charging and I was a little surprised but then I remembered that the battery light on the dash never illuminates. So I replaced the globe. The light came on with the ignition ok but when I started the car, it was charging at 18v. I checked the globe and I had fitted a 12 volt 5 watt globe to what had originally been a 12 volt 3 watt globe.

    Even after fitting the correct globe, the alternator still charged at 18v. There is no external regulator.

    My question is, did I destroy the alternator by fitting the wrong globe or was there likely something already wrong with it?

    Thanks for all replies.
     
  2. Diver300

    Diver300 Well-Known Member

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    It is highly unlikely that a 5 W lamp would do damage.

    If you are getting 18 V with a battery fitted, either that has damaged the battery or the battery was damaged already. Alternator regulators can fail, causing the output voltage to rise too high, but the output current that an alternator can produce is limited by its design, and that current shouldn't take the voltage up to 18 V at all quickly.
     
  3. coop1er

    coop1er New Member

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    Ok thanks for that.

    I should have mentioned in my original post, the battery was newish but flat from not being charged.

    Also in the end, I fitted a reconditioned alternator, charged the battery, fitted the correct globe as previously mentioned, and everything was ok after that.
     
  4. dave

    Dave New Member

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  5. rfranzk

    rfranzk Member

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    Hello Coopier,
    It is unlikely that the burned bulb caused any problems. Likely the internal voltage regulator or diode on the alternator failed first causing the lamp to burn out. Any other lights on the vehicle failed recently??? Did the charge lamp illuminate dimly when it was overcharging?? That would indicate one or more leaking diodes. Also typically the excite circuit for the alternator is through the lamp in series to the alternator so with the lamp out the alternator cannot be excited properly to operate or output any voltage.

    You failed to mention make and model of vehicle. Late model electronics are pretty reliable but still can fail.

    rfranzk.
     
  6. coop1er

    coop1er New Member

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    Thanks rfranzk.
     
  7. strantor

    strantor Active Member

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    wait, what? Did you resolve the problem before or after creating this thread? Are you still looking for help/input or can we consider this "SOLVED"?
     
  8. coop1er

    coop1er New Member

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    The car was fixed prior to creating this thread. My query was whether I caused the damage to the 2nd hand alternator by fitting the wrong globe. I would always welcome more input but I guess it could be considered solved.
     
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  9. strantor

    strantor Active Member

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    Ok gotcha.

    According to a discussion in the link below, fitting the wrong globe can indeed fry the alternator, as the globe current draw is what excites the alternator. Too many watts, the regulator craps out. The recommended 2W for the alternator in question on that thread. I don't know what alternator you have, but your 5W globe is over double what they were discussing.

    http://www.aussiev8.com.au/bodywork-styling-wiring-sound/60833-alternator-upgrade-hz-308-a.html

    Keep in mind they are talking about a specific car with a specific alternator with a specific circuit. Not all car/alternator/circuit configurations use the globe to excite the alternator. Not knowing what car you have or what's under the hood, I cannot speculate as to whether you did or did not damage the alternator, but I can say that it is entirely possible.
     
  10. b.james

    b.james Member

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    Your lack of understanding of this process has led you to an incorrect conclusion.
    The current that flows through the diode via that lamp starts the alternator producing output and as soon as the output voltage rises above that coming through the lamp and diode it stops flowing and the lamp goes out . the diode current flows through the field winding and is limited by that resistance to ground.

    So no, the bulb did not contribute to your problem, is the correct and only answer.
     
  11. debe

    debe Active Member

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    Not all altenators will handle the wrong wattage globe. Some as in this Bosch altenator, the reg can be damag BOSCH 85A Altenator.1.jpg BOSCH 85A Altenator.2.jpg ed by wrong globe.
     
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  12. strantor

    strantor Active Member

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    cool story, bro.
     
  13. debe

    debe Active Member

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    Those pages I posted Strantor come from the Ford Workshop manual & relate to the Altenator in the V8 link you posted
     
  14. strantor

    strantor Active Member

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    Thank you Daryl. I appreciate you backing up my suggestion with a textbook reference after b.james sought once again to adulterate a contribution of perfectly valid content with doubt and contempt.
     

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