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  • #26760

    David Wesner
    Participant
    Vessel Name: Monarch
    Engines: 6BTA
    Location: Newport
    Country: USA

    What is the D+ lug on the K1 Bosch alternator for? It was jumped over from the B+ lug when I inherited this boat. It had a parasitic drain on the battery that was identified as the alternator. First suspicions and advise was that a diode was bad. But, I am now thinking the jumper wire from the D+ lug was the cause. I “now” understand this to be the field exciting lug also used in conjunction with a charge indicator light. The light fed from the ignition switch excites the field which when running then has zero potential with the B+ lug. This will extinguish the light when running, but when not the field is grounded or close to it causing current flow.

    Should this D+ lug be fed off the ignition either the same lead that goes to the fuel solenoid (purple) or another charge indicator light run outside of cummins wiring loom.

    Engine is an older 250hp 6bta JWA.

    Also, how do I determine the current rating for the alternator? I believe it can be 95 or 120 amps. AL9971N / AL9972N

    D

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Viewing 8 replies - 1 through 8 (of 8 total)
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  • #27328

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Glad you sorted it out.. Yes, an LED will accomplish this too.

    Tony

    #27326

    David Wesner
    Participant
    Vessel Name: Monarch
    Engines: 6BTA
    Location: Newport
    Country: USA

    Update: Fed alarm board off ignition circuit. The wire from the raw water alarm went to the D lug on the alternator. Powered up and charging. The lamp being a LED prevents the back feeding and the fuel solenoid works fine.

    #26864

    David Wesner
    Participant
    Vessel Name: Monarch
    Engines: 6BTA
    Location: Newport
    Country: USA

    Got it, thanks

    #26857

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    You can use a diode and / or a 12VDC warning light ( maybe 1 watt max )………..Although they work differently, they both accomplish the same thing……………………Remember old cars that had a warning light on the dash that was bright when then engine was off ( or not working) , at idle it would flicker, and about 1000-1200 RPM or so, it would go out.. The “D” terminal ( or #1 terminal on a “Delco unit” ) is at ZERO potential when the unit is off.. .Once the unit is energized and working properly, that terminal goes to about 13-13.5VDC.. The light does two thing at this point.. It shuts off (both the input , the IGN, and the “D” are at the same potential.. But then, when you turn off the ignition, the LAMP limits the CURRENT going back (back feeding) to the fuel solenoid to about 1-2 watts and that IS NOT enough to keep it energized…………………………. Make sense?

    This is my suggestion, as it looks like you are working with an “unknown” alternator as to its real condition–Take it to a local alternator repair shop an have it looked at, tested and then pick the techs brain as to how it needs to be hooked up..

    If you want a diode you can wire into the circuit, send me a self-addressed & stamped envelope w/ $5 in it and I’ll send you one …………………..

    Proper wiring diagrams on on my web site.. I would not deviate from this as they are very simple an easy to deal with..

    Tony

    #26828

    David Wesner
    Participant
    Vessel Name: Monarch
    Engines: 6BTA
    Location: Newport
    Country: USA

    OK, diode makes sense. I didn’t think about the energizing the ignition circuit from the alternator, just was concentrating on the charge warning lamp. The diagram indicates a diode “or” lamp. I understand the purpose of the diode, but does the warning lamp provide any other function beside being a warning lamp. The word “or” is puzzling me.

    Another way around the energized ignition circuit from the alternator excitation lug “D”, would be to remove the plunger and spring from the fuel solenoid and use a pull cable for the stop lever on CAV pump. Which I believe would be good to do anyway.

    The alarm board gets power from the ignition circuit to terminal 5. Terminal 2 can feed the excitation circuit “lug D” on the back of the alternator. I believe a diode will still be needed if the fuel solenoid is to stay in place.

    I’m not familiar with buying diodes, any sort of specs or sources to purchase from?

    D

    #26823

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Your ??? is real simple……………………………….Before the BOSCH K1 is actually rotating and is “Turned ON”, the “D” terminal ( #1 terminal on a Delco unit) is at ZERO volts ) or ZERO potential…………….. Once the unit is energized and “turns on”, that terminal goes to about 13-14 VDC , and if you do not have a diode ( or an indicator light bulb) in the circuitry, it will back feed into the IGN circuit and the engine will not shut down when you turn the key off ( it will keep the fuel solenoid energized)…………. Look a tad closer at the diagrams I attached ( not the Bosch manual) and think about how it all works…….Make any sense?……………………………..Tons of this stuff on the internet , but you have to spend the time to sort thru it all………

    Alarm: Tel me EXACTLY what you want to accomplish,

    Tony

    #26817

    David Wesner
    Participant
    Vessel Name: Monarch
    Engines: 6BTA
    Location: Newport
    Country: USA

    Thanks.

    I don’t fully understand the theory why a lamp (resistance) or a diode is needed for the excitation circuit, but…I do believe you. Maybe because it would be direct short to ground when not generating power? Regardless, I am going to do that. Seaboards site was handy with the drawing, I did see some of those you attached while I was researching this.

    I recently ordered the SMX deluxe alarm panel. The boat is keel cooled and I will not be using the raw water alarm on the board. Do you think it would be feasible to utilize that lamp circuit for the “D” excitation circuit and relabel the alarm on the face panel? Thanks

    D

    #26805

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    David,

    Look over all of the attachments.. It should explain how this unit operates and is wired.. The “D” terminal is similar to the #1 terminal on a Delco 3-wire unit.. BTW, Cummins does not always follow their own wire coloring listed in the factory diagrams.. The TACH has always been a GREY wire / “W” terminal on the Bosch K1.

    Tony

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