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Discussion in '348/355' started by RSO1091, Nov 26, 2015.

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  1. RSO1091

    RSO1091 Formula 3

    Mar 31, 2012
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    Henry S.
    #1 RSO1091, Nov 26, 2015
    Happy Thanksgiving everyone! As many of you know, I have had occasional electrical issues with my 95 F355 and have rebuilt the alternator three times in three-plus years of ownership. Those issues cleared up after I took out my high-dollar stereo system and replaced it with a digital voltmeter about two years ago.

    Fast forward to our last Stooge Day at Chuckawalla Raceway earlier this month and my voltmeter showed occasional spikes into the mid-fifteen range. The car runs fine (wouldn't have even noticed if the digital display wasn't staring me in the face), but I do get a flicker from the battery light on the dash now and again.

    So I have ordered replacement parts and intend to rebuild the alternator yet again. I am assuming that the spikes are attributable to a bad regulator. I will be changing out the rectifier as well, but was wondering what each part is responsible for inside the alternator itself. I have a Fabspeed heat shield in place and really have not had any problems since i put it in along with my FS headers. So does everyone think that a day of hard driving put it over the edge? Seems like it to me.

    Anyway, I hope everyone has (or had) a blessed day surrounded by friends and loved ones.

    Henry
     
  2. cf355

    cf355 F1 Rookie

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    #2 cf355, Nov 26, 2015
    did all these alternator failures coincide with the installation of the fabspeed headers?
     
  3. taz355

    taz355 F1 Veteran
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    #3 taz355, Nov 26, 2015
    Henry we all drove our cars hard and no-one elses alternator failed yet. I dont think it relates at all. My experience with racing is it might increase the likely hood of something failing sooner but it was going to fail anyway.

    My understanding of the whole system is that the alternator also senses feed back from the battery. Maybe a wire is loose on the battery or alternator that provides the feedback so the alternator knows to cutout.
     
  4. RSO1091

    RSO1091 Formula 3

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    #4 RSO1091, Nov 26, 2015
    Absolutely not, in fact this is the first incident I've experienced since the Fabspeeds were installed. No correlation.
     
  5. RSO1091

    RSO1091 Formula 3

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    #5 RSO1091, Nov 26, 2015
    I guess you're right Grant. Guess I'm a little gun shy when it comes to the alternator. I'll double check everything I can find between the battery and alternator.
     
  6. m.stojanovic

    m.stojanovic F1 Rookie
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    #6 m.stojanovic, Nov 27, 2015
    The rectifier is a set of diodes that convert the AC current (from the stator windings) to DC current (the alternator is basically a 3-phase AC generator). Rectifier faults (a failed diode) will result in lower alternator voltage output.

    The regulator controls the output voltage by controlling the DC current through the "field coil" which is on the rotor.

    I wouldn't worry about the spikes recorded by the digital voltmeter if they are just momentary and if the voltage stays at the normal levels most of the time. There are many brief voltage spikes in the car electrical system, even as high as 200 volt like those produced by the relays at the moment of disengagement. An analogue voltmeter would not register such spikes (as they are extremely short) but a digital voltmeter may jump a few digits up and immediately come back down to normal.

    The charging light coming on is something to look into. In addition to the regulator, proper operation of the voltage control also depends on the condition of the brushes - replace if worn (shortened, not providing good pressure on the slip rings).
     
  7. RSO1091

    RSO1091 Formula 3

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    #7 RSO1091, Nov 27, 2015
    Thanks for the explanation Miroljub. While it makes me feel a bit better, I think I'll still replace the parts this time, including the brushes. I appreciate everyones input.

    Henry
     
  8. taz355

    taz355 F1 Veteran
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    #8 taz355, Nov 27, 2015
    Henry I never thought about the brushes but if you look at them they might be the only problem since you rebuilt everything but the brushes last time.
     
  9. RSO1091

    RSO1091 Formula 3

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    #9 RSO1091, Nov 28, 2015
    Good possibility. Does anyone have a part number/source for the brushes? I can go back to Regitar I guess.
     
  10. hjp

    hjp Formula Junior

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    #10 hjp, Nov 28, 2015
    I'm not doubting that the 355 alternators use brushes. Its just that I remember the old DC generators used in the old days all had brushes and I thought the switch to alternators did away with them. Am I completely wrong about this or was this true for some but not all?
     
  11. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    #11 Steve Magnusson, Nov 28, 2015
    DC generators use brushes running on a segmented commutator = high wear (and more need for maintenance replacement)

    Alternators use brushes running on a continuous slip ring = low wear (far less probability of a problem)
     
  12. WATSON

    WATSON Two Time F1 World Champ
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    #12 WATSON, Nov 28, 2015
    How old is the battery?
     
  13. RSO1091

    RSO1091 Formula 3

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    #13 RSO1091, Nov 30, 2015
    Battery is less than two years old and shows a charge in the 12v neighborhood.
     
  14. Mitch Alsup

    Mitch Alsup F1 Veteran

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    #14 Mitch Alsup, Nov 30, 2015
    The rectifier(s) and the voltage regulator are not related.
    I would start with the regulator unless the alternator was displaying some other irregularity.
     
  15. RSO1091

    RSO1091 Formula 3

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    #15 RSO1091, Dec 1, 2015
    That's the plan Mitch, thanks.
     
  16. taz355

    taz355 F1 Veteran
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    #16 taz355, Dec 1, 2015
    Yes since you have the parts and you can change it while in the car(that takes talent) change those and see if it fixes it. You will have to take the alt out to change the brushes I think.

    Keep us posted.
     
  17. RSO1091

    RSO1091 Formula 3

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    #17 RSO1091, Dec 3, 2015
    I've always managed to change out the rectifier, regulator and brushes while the alternator was in place. Not sure when I'll get to it however. Lots of preparation around here getting ready for what is supposed to be record winter precipitation. Course if I get snowed in, I'll have nothing but time on my hands...

    Henry
     

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