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Car Alternator speed?

  1. Jul 28, 2011 #1

    sophiecentaur

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    I have looked all over in the search for the optimal speed to run a 12V alternator. I have a diesel engine on my boat which is never run above 2500 revs and I have a feeling that the drive pulley is too large - so the alternator runs slower than optimum.
    Does anyone know the speed range that I should be aiming at for the alternator?
     
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  3. Jul 28, 2011 #2

    dlgoff

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    It would depend on what alternator you have. For Delco Remys 21SI Alternators Series, it would be in accordance to this:
    21siAlternatorPCDelcoRemy.jpg
    http://www.newindo.com/delcoremy/20si-21si-26si-delcoremy-generators.htm" [Broken]
     
    Last edited by a moderator: May 5, 2017
  4. Jul 28, 2011 #3

    sophiecentaur

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    Thanks. That tells me that I should have around a 2:1 diameter ratio for the alternator to be rotating fast enough at normal running speed. From memory, the diameter of the existing alternator pulley is much more than half of the flywheel pulley so it looks as though I could do a lot better than at present. As the very maximum engine revs are 3k, it looks as if a 2:1 ratio would not over rev any of the alternators on those graphs. The make of my alternator is a Valeo, btw, but I'd bet the speed curves are much the same. It's 12V and probably a 40A max output (as are all the old ones) but I've never measured more than about 10A from it on my 'tong' meter. The warning beep only stops when the engine's doing over 1k.

    I shall have to do some measuring when I'm next aboard and then look around for a smaller pulley at a breaker's.
    Cheers.
     
  5. Jul 28, 2011 #4

    dlgoff

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    Go for it. :smile:
     
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