simple alternator / regulator wiring question

Discussion in 'Shop - Electrical' started by PSmith, Feb 28, 2008.

  1. PSmith

    PSmith Member

    Joined:
    Apr 3, 2007
    Location:
    Upland, CA
    i've never wired a car with an externally regulated alternator so please pardon my ignorance.

    in the diagram below (mopar transistor type external regulator) could wiring the (+) lead labeled "ignition" to fused "battery-on" power cause any problems?

    could any damage to the regulator occur if the field side of the alternator is receiving battery voltage (12v) with the engine off (not charging) for an extended period of time?

    any idea on what kid of draw could be expected in a "battery-on / engine-off" situation?

    first time working with an external regulator, any input would be appreciated.

    thanks [/n00b]

    [​IMG]
  2. iwire4uBDR

    iwire4uBDR Member

    Joined:
    Feb 25, 2008
    Location:
    Fountain Valley, CA
    The switched ignition wire turns on the field coil when the alt is spinning to allow the alt to charge the battery. When the battery is charged the regulator shuts off until the volts drop and begans to charge again. The field coil is really just a no/off switch so that the battery cant back feed and drain its self.

    BDR Brian
  3. PSmith

    PSmith Member

    Joined:
    Apr 3, 2007
    Location:
    Upland, CA
    i understand the principals of the voltage regulator and the diagram i posted, but my question was in regard to the possibility of damaging the regulators transistor, field circuit wired directly to the battery and the alternator not charging for an extended period of time...

    essentially the transistor will remain closed, grounding the field wire in the alternator while the battery remains at 12.6 or less.

    could this lead to premature charging system failure??

    thanks.
  4. philofab

    philofab Powered by Optima

    Joined:
    Jun 13, 2006
    Location:
    JRod's livingroom.
    If you hook the +12 to contant rather than the IGN switch it will keep the charging system on (Alt excited). No only will it discharge the battery while the alt is not spinning it could also damage the alt or regulator depending on how tough they are (what model - some are better than others).

    If you have a main battery shut off and use it ALL the time when the vehicle is not running it is ok to connect the +12 to contant. I personally would wire it to the IGN switch in either circumstance.
  5. philofab

    philofab Powered by Optima

    Joined:
    Jun 13, 2006
    Location:
    JRod's livingroom.
    The draw of the regulator is approx 250-500 ma. Use you meter to test your type of ext. regulator.
  6. PSmith

    PSmith Member

    Joined:
    Apr 3, 2007
    Location:
    Upland, CA
    the input is appreciated, first time utilizing a stand alone ECU and not tapping into a factory management system for me... or wiring up an alternator that isn't the single wire self exciting type.

    i suppose giving the supplier of the computer a ring would be the my best bet to see if any of the key on powers out are capable of being used for a field signal.

    if not, adding another circuit (likely with an inline fuse) to my already packed DPST for the ignition would be my best option then?

    thanks again
  7. philofab

    philofab Powered by Optima

    Joined:
    Jun 13, 2006
    Location:
    JRod's livingroom.
    It should be just fine if you hook it to your existing DPST switch. If the vehicle won't shut off add a diode inline. The +12 to the regulator is only used as a voltage "sense" input... no real load. If you don't want to do it this way, switch the DPST to a DPDT switch and use the second set of terminals to excite the alt.

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