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  1. #1
    Join Date
    Nov 2009
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    Default What's the R connection for on a Yanmar / Hitachi alternator?

    I'm looking at the circuit diagram in the Yanmar workshop manual (page 12-20). Most of it I understand, but I cannot figure out the purpose of the R terminal.

    The basic setup I carried in my head was much like this: http://www.tb-training.co.uk/images/altcct.gif , where the lamp wire provides the initial current to energise the coil. So at first, I thought that R was just a minor enhancement to this, duplicating the lamp circuit with a resistor (mounted inside the regulator casing for practicality) so that the alternator would still work if the lamp blew or was removed.

    Then I noticed that BAT is connected to R inside the alternator. This implies two things - firstly that a cable from R is unnecessary, as the R terminal (and hence the coil) will always be energised whenever the battery isolator is connected (which is undesirable anyway), and secondly that the "ignition switch" (engine electric power only, not starting) is being completely bypassed by the cable from switch to BAT to R to the other side of the switch.

    Either I'm missing something fundamental or the circuit diagram in Yanmar's own manual is just wrong.

    Pete

  2. #2
    Join Date
    Jul 2002
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    Home: Kent. Boat: Chichester
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    43,826

    Default

    You don't say what engine or what manual you are looking at or where it is to be found but IIRC Tb training only covers positive regulation. The Hitachi alternator is however negative regulated.

    Maybe this diagram of the regulator and internal wiring of the alternator which I found in one of the Yanmar manuals for the YM series will help.


  3. #3
    Join Date
    Aug 2007
    Location
    Falmouth
    Posts
    399

    Default Yanmar Hitachi alternator

    My workshop manual shows more detail of the internals with some notes on how the regulator works.


  4. #4
    Join Date
    Aug 2004
    Location
    Cumbria; U.K.
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    3,319

    Default

    The alternator diagram in the Yanmar GM manual does show the "B" terminal internally connected to the "R" terminal, then to the regulator. Initial exitation of the alternator would therefore seem to be independent of the lamp, whose only function is to confirm that a charging voltage is present
    edit :- All as in post above!!

  5. #5
    Join Date
    Aug 2007
    Location
    Falmouth
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    399

    Default

    There are one or two mistakes on the diagram in my manual - one is that the capacitor connected between Bat and E has got mixed up in the reproduction with the chained lines outlining the AC Generator unit (note how it is shown differently in the diagram Vic has found). Another is that the three dots, indicating connections are missing in the output commutation diode bridge. (Note that these are even worse in the bridge in Vic's diagram)

    The draftsman or printer has been inconsistent in applying the standards to the indication of lines crossing (not connected) and lines crossing (and connected) - he has drifted between the two standards. Therefore, I suspect that the dot on the line between R and R1 is a misprint also. I think there is not a connection between Bat and R at all. If there were, the charge lamp would be on even though the ignition switch was off.

    If that dot were correct, with the ignition switch off, but the main battery switch on, current would flow from the battery, via Bat to R, then through the lamp and the Rotor coil and the Darlington pair Tr1 (conducting because of base current through R4) back to the battery via E. We know the charging lamp does not light unless the ignition switch is on, so the dot indicating connection between Bat and R must be a mistake as well, it should be shown as a "bridge" where these lines cross.

  6. #6
    Join Date
    Aug 2004
    Location
    Cumbria; U.K.
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    3,319

    Lightbulb

    [QUOTE

    We know the charging lamp does not light unless the ignition switch is on, so the dot indicating connection between Bat and R must be a mistake as well, it should be shown as a "bridge" where these lines cross.[/QUOTE]

    Agreed, that didn't occurred to me,. However, the answer to the OP still seems to stand, that the "R" terminal is to provide excitation current, independently of the lamp.

  7. #7
    Join Date
    Oct 2003
    Location
    N. Wales
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    2,884

    Default

    Quote Originally Posted by earlybird View Post
    However, the answer to the OP still seems to stand, that the "R" terminal is to provide excitation current, independently of the lamp.
    It's the voltage sense feedback to the regulator. <<Deleted>>

    Andy
    Last edited by misterg; 06-01-10 at 13:17.
    No boat no more...

  8. #8
    Join Date
    Aug 2007
    Location
    Falmouth
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    399

    Default

    I suspect that the value of R1 would be too high to pass sufficient excitation current in the absence of the charge lamp.

  9. #9
    Join Date
    Nov 2009
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    Southampton
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    Default

    The diagram I'm looking at is the same one Eygthene posted - thanks.

    Sounds like my second hypothesis is correct then - the diagram is wrong as printed and there is no connection between BAT and R, that wire being only for the smoothing capacitor between BAT and E. Makes sense. If R is indeed for excitation current then everything is cleared up, but then Andy reckons it's actually for battery-sensed regulation. In that case, should it not be connected directly to the battery (or at least battery isolator) rather than the charge lamp still inside the engine loom?

    Pete

  10. #10
    Join Date
    Nov 2009
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    Southampton
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    Default

    Quote Originally Posted by Eygthene View Post
    I suspect that the value of R1 would be too high to pass sufficient excitation current in the absence of the charge lamp.
    What is the value of R1? It's not stated on the diagram. If R is for excitation then some resistance is needed or the lamp would never light. It doesn't need to let much power through, because as soon as the alternator is generating anything at all it supplies itself independent of R. Indeed Tony Brooks is of the opinion that an alternator at sufficient revs will usually get going without any external exciter current, presumably due to some residual magnetism stimulating the first few milliamps to kickstart things.

    Pete

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