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High Voltage Reading On Alternator

Discussion in 'Technical Discussion' started by CaptOz, Jun 11, 2014.

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  1. CaptOz, Jun 11, 2014
    #1
    CaptOz

    CaptOz Member

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    Hi,

    Last weekend I noticed that my Simrad Auto pilot high voltage alarm was going off. I didn't even know it had one. When I looked at the Gauge I saw it was pegged passed 40 Volts. Normally I see 34-36 volts off the alternator. I have a relatively new 32 Volt Bank.

    Now I am not able to turn off my Simrad. The power button will not shut it down. I have to flip the breaker on the panel and it shuts off. Could I have damaged the Simrad head unit?

    What do you think about alternator? The voltage is fine at low RPMs, but as soon as I get on Plane, the voltage starts to climb and goes past 40 volts. Is there a voltage regulator inside the Alternator that perhaps when bad? Or is it external?

    The Boat is a 1986 54' Bertram. Thanks in Advance...

    Admin Edit: Ridiculously Oversized Image Removed. See post from Old Phart below.
  2. Pascal, Jun 11, 2014
    #2
    Pascal

    Pascal Senior Member

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    Definitely an alternator or regulator issue.. You need to start by checking the wiring to see if you have an internal or external regulator. This varies and on older boats alternators may have been replaced since new with different type.

    In the meantime I would disconnect the alternator, and charge using the generator and charger.

    Always always scan your gauges regularly especially while accelerating on plane
  3. K1W1, Jun 11, 2014
    #3
    K1W1

    K1W1 Senior Member

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    Hi,

    Does the voltage go up when you rev it up to cruise RPM at the dock? The alternator doesn't know if you are underway or not as its function is in relation to the speed of the crank not the engine load.

    If disconnecting the alternators wiring and you are going to run the engine don't forget to take off the drive belt as well.

    This is in case it is self exciting which can get pretty exciting if left going with nowhere to deliver it's charge.
  4. Capt J, Jun 11, 2014
    #4
    Capt J

    Capt J Senior Member

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    Most likely a bad voltage regulator for the alternator. You can disconnect it temporarily as Kiwi said. However, sending that kind of voltage to the batteries will cook them pretty quickly.
  5. Old Phart, Jun 11, 2014
    #5
    Old Phart

    Old Phart Senior Member

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    I dunno
    My contribution:

    too big pixels redo-high-voltage-reading-alternator-highvoltage-jpg.jpg
  6. K1W1, Jun 11, 2014
    #6
    K1W1

    K1W1 Senior Member

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    Good effort but it doesn't do much unless the offending one is resized.
  7. Old Phart, Jun 11, 2014
    #7
    Old Phart

    Old Phart Senior Member

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    I dunno
    True.

    The admin has the task.

    Just trying to make life a little more tolerant.

    1847 x 1385 pixels is just a little too excessive.

    Should be an easy switch for someone of authority. ;)
  8. Chasm, Jun 11, 2014
    #8
    Chasm

    Chasm Senior Member

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    Sounds like a regulator problem.
    The alternator voltage is depending on the field current the regulator supplies. More field current, more alternator voltage. No current, no voltage.

    After you have located the regulator, before touching anything else:
    Measure the voltage on the battery voltage sense connection of the regulator. If that wire is broken the regulator "thinks" that the batteries are really low and puts out max field current. -> Oops.

    Also: Do not use the yacht with this fault - unless you have to. Currently the batteries get overcharged really hard. Or in or in words, cooked to death.
  9. Capt Ralph, Jun 11, 2014
    #9
    Capt Ralph

    Capt Ralph Senior Member

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    Lets go over a few things. Delco 31-SI alternators? (31-SI's are strange and box looking) Both engines go over 40Vdc? Do you have a battery isolator between your batteries and alternators?
    Fresh batteries, problem since?
    Any regulator feedback leads loose? (if external external regulator or diode isolators are used).
    What AP system control box. Thought Simrad stuff ran at 12 & 24Vdc. Could a 24Vdc strap been placed on the top battery?
  10. Capt J, Jun 12, 2014
    #10
    Capt J

    Capt J Senior Member

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    I just thought of this. BUT, also try turning off your battery chargers and see what the voltage is. It could be a battery charger issue as much as an alternator issue.
  11. captholli, Jun 12, 2014
    #11
    captholli

    captholli Senior Member

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    This is sounding more like a old system, is there a shunt in the circuit?
  12. Capt Ralph, Jun 28, 2014
    #12
    Capt Ralph

    Capt Ralph Senior Member

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    Any updates?
  13. CaptOz, Jul 2, 2014
    #13
    CaptOz

    CaptOz Member

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    Update

    Thanks for all the Input guys...

    Only the Starboard alternator has the issue. The voltage builds as the rpms climb. If I keep boat off plane, voltage stays around 38-40 at 1000 rpms.

    There were two wires on the back of the alternator, I disconnect the Red one.


    I will go to the boat this weekend and take a closer look.

    How do I test out regulator?


    Thanks!

    Attached Files:

  14. Capt Ralph, Jul 2, 2014
    #14
    Capt Ralph

    Capt Ralph Senior Member

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    Ah, The original 31SI Delco. Usually two cables to it. Batt + out & ground.
    Simple things on this model.
    questions; the batt + goes directly to the top battery of a good bank? No battery isolator or combiner in the system? No other wires to the alt that the two cables?
    If there was a small wire used for an exciter, we need to start our test there.

    Let me ask again about that good batt bank. All flooded cells? Hydro'd good? 4 x 8V batts and good connects including a real good bond back to the block, usually to where the starter and alt negative straps are.
  15. CaptOz, Jul 2, 2014
    #15
    CaptOz

    CaptOz Member

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    Yes, The bank is just a year old and is very good condition. The Red wire from the alternator goes straight to the Alternator on the same pole that has the 2/0 battery cable connected to it.

    Only two cables to the alternator.

    I see not small wires, perhaps if I remove the back cover plate there might be one?

    The bank is almost new, water has been kept on it.

    The wiring I have not touched other than when I replaced the bank. It pretty much original.

    The engine fires up instantly, so I don't think there is a grounding issue.
  16. Capt Ralph, Jul 2, 2014
    #16
    Capt Ralph

    Capt Ralph Senior Member

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    the small wire if there was external.
    I would recommend pulling the alt and sending it to a shop. If you feel adventurous, order and replace the regulator yourself. part # 1987518.
  17. CaptOz, Jul 2, 2014
    #17
    CaptOz

    CaptOz Member

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    Is that Part number an AC Delco part number or Detroit Diesel?
  18. CaptOz, Jul 2, 2014
    #18
    CaptOz

    CaptOz Member

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  19. Capt Ralph, Jul 2, 2014
    #19
    Capt Ralph

    Capt Ralph Senior Member

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    delco part number
  20. Capt Ralph, Jul 2, 2014
    #20
    Capt Ralph

    Capt Ralph Senior Member

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    hold on, maybe 24, be rite back.
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