Interesting Alternator Ripple

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  • greasybob
    Senior Member
    • May 2008
    • 1590

    Interesting Alternator Ripple

    Had an 03 Town and country with a complaint of battery light on. Found code P1594 in the PCM, charging system voltage too high. I checked alternator out put and the voltage was in normal range, around 13.5. So it must be an intermittent condition. I checked grounds doing voltage drop tests from everything I could see that might cause an over charge, nothing. So I did a ripple test and found a rather strange looking pattern on the scope. I checked from the alternator post to the battery ground. The pattern looks like something you get when your scope isn't grounded properly. I checked the ground again. This was the pattern, not a lot of spikes but way too wavy. Not sure of the cause. The field strength in the alternator is controlled by the PCM. But the control pattern was normal, So I gotta believe something in the alternator shorting, not sure if diodes will cause a pattern like this or over charging. I included a normal ripple pattern for comparison. Replaced alternator, was week ago. No complaints since. I realize the time sweeps are a little slow for a ripple test, but it shows the waviness better.
    Attached Files
  • Crusty
    Senior Member
    • Dec 2007
    • 2450

    #2
    Sometimes when the alternator case itself isn't grounding cleanly where it mounts to a bracket, or the cylinder head or intake manifold, things can get a little dicey.
    Might be worth adding a jumper from the alternator case to a "known good" ground if I ever see another funky alternator ripple. I've seen it before, but not often.

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    • badcoupe
      Senior Member
      • Jan 2011
      • 218

      #3
      Had one like that on a pacifica that would make the speedo read even while sitting still and had the trans in limp mode. Was charging fine but the ripple was crazy looking.

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      • greasybob
        Senior Member
        • May 2008
        • 1590

        #4
        Just wondering ? According to the component description in the PDF below, The PCM powers the rotor at 250 Hz up to 100 % duty cycle. But is the ECM actually supplying the full current load to the rotor or is it just activating the gate or base in a transistor in the alternator and the actual current is coming from the battery cable (or alternator batt +) ? If it's supplying the current, you should be able to current ramp the control wire as well. Maybe this is why so many Chrysler PCM voltage regulators bite the dust.
        Attached Files

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        • Witsend
          Banned
          • Nov 2012
          • 2942

          #5
          Any Voltage drop between the B+ stud at the alternator and the cable that attaches to it? Also I believe some of the alternators have a goofey sprag clutch (one way clutch built into the pulleys and seen some Alternators causing a strange objectionable engine noise accompanied with vibration at idle "Wub" "WUB" "WUB", so who knows if the sprag pulley being turned is doing some sort of Mambo with the serpentine belt that affects the ripple pattern too.( If I remember, I will attach my Counselor 2 to a 2003 Chrysler Town and Country with what I believe still has a good quiet alternator when I see it later, for a comparison.
          Last edited by Witsend; 04-06-2016, 07:21 AM.

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          • Witsend
            Banned
            • Nov 2012
            • 2942

            #6
            2003 Chrysler Town and Country alternator waveform

            As far as i know this alternator is a good one, waste spark system divide rpm in half
            Attached Files

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            • greasybob
              Senior Member
              • May 2008
              • 1590

              #7
              This one was so bad even my EECS750 charging system tester picked it up measuring from the battery posts. This was another Caravan around the same year. Everything looked fine measuring with the Vantage ultra from the alternator post until I did the draw test again this time I made sure the AC was on so that the radiator fan would be running. That was enough to get things wavy.
              Attached Files

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