Cummins Marine Diesel Repower Specialists Forums Instrumentation & Electronics Converting 6B5.9M from 12 to 24 volts

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  • #50472

    Robert Cart
    Participant
    Country: United States

    My 6B5.9M was manufactured in 1994 but installed new in 2004 in my sailboat. I’m now converting my electrical system to 24volts and was originally planning to just swap out the alternator and leave the rest of the relatively simple engine electrical systems at 12V. However, as it turns out only a few electronics items need 12V and a simple DCDC converter can handle them nicely. In many ways it would be simpler to convert all to 24V, but how to do it?

    I have two panels which I think are B type and after looking at the diagram, it appears they can be wired for 24V without replacement.

    I would also like to get rid of one of the panels, but am unsure about the senders and if they are designed for one or two panels and must be replaced?

    The starter looks like a Delco Remy 28MT but not certain. It isn’t clear whether the same starter supports either 12VC or 24V. Any clues?

    So, what must I do to end up with a complete 24V electrical system conversion and a single panel?

Viewing 11 replies - 1 through 11 (of 11 total)
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  • #58474

    Robert Cart
    Participant
    Country: United States

    further thoughts

    I am still battling with a dual voltage system and have not decided where I land. My latest thought is this. What about using a 24V alternator and starter motor with but keep the 12V panel and starter solenoid? I already must provide low current 12v loads for NMEA2000 and etc. It is then easy to power the panel with that system. This means I can have a 24V start and house batteries and this greatly simplifies charging and redundancy, etc. The 12 and 24V grounds are common so should be no problems there. I serve the 12V loads with a 24V to 12V DCDC converter and in a pinch, I could get home by pulling off a 12V battery to drive the 12V loads if the converter failed. This is all around a nice solution and means I don’t have to replace panels, circuit boards and senders. The solenoid switch on a 24V starter motor might even be able to be rewired for 12V. Alternatively, I use the 12V one off the existing starter. What’s the catch?

    #50799

    Corey Schmidt
    Forum Moderator
    Vessel Name: Rebel Belle
    Engines: Cummins
    Location: Oxnard, CA
    Country: USA

    I would not make any assumptions regarding how the engine is setup… verify everything 100%, then make decisions.

    The panel takes inputs directly from senders for “indication” and the PCB interprets the signals for alarming.

    We always recommend have redundant alarms:

    https://www.sbmar.com/articles/redundant-alarms-least-expensive-engine-insurance/

    #50786

    Robert Cart
    Participant
    Country: United States

    You should not have to replace the tach due to voltage IMO… can you verify 100% what device is driving the tach gauge? Alternator? Mag Pickup? Generator drive?

    Corey, I am away from the boat and can’t check now. I assume the alternator drives it. It is a very simple engine. No ECM or turbo or anything complicated so I’d be surprised if its not driven by the alternator.

    My list is getting slightly shorter because the starter includes the solenoid/mag switch.

    I am still wondering about the engine side of things. Does the circuit board use the water pressure sender for the gauge and the alarm or is there a separate alarm switch? What about for the oil pressure? Do you have a wiring diagram for the engine itself a 1994 6B5.9M?

    I’m a data hound and am also interested in adding additional sensors like transmission oil pressure and raw water flow rate and maybe even exhaust gas temp. Can you guys help with the parts I need?

    #50785

    Robert Cart
    Participant
    Country: United States

    Thanks, Tony. A second alternator would offer a hot backup. Also, if one of these 100 amp units failed, it would be easier to find a replacement in some far away port even if not 100 amps it would be something.

    I only hesitate now because I”m almost overwhelmed with all the work on deck now. The added cost and complexity of the belting and bracket and wiring isn’t enticing. I’d probably also have to rework the cover on the front of the engine to protect the passageway there. Not easy. I’ll keep it in mind as a future upgrade. Thanks again!

    #50772

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

    What not add a 2nd 24VDC alternator for your 24V house?

    Tony

    #50707

    Corey Schmidt
    Forum Moderator
    Vessel Name: Rebel Belle
    Engines: Cummins
    Location: Oxnard, CA
    Country: USA

    You should not have to replace the tach due to voltage IMO… can you verify 100% what device is driving the tach gauge? Alternator? Mag Pickup? Generator drive?

    #50697

    Robert Cart
    Participant
    Country: United States

    Tony and Corey, thank you so much. To switch to 24V, I now understand that I need to swap out the following:

    1) alternator
    2) starter
    3) mag switch for starter
    4) panel circuit board
    5) lights on panel (alarms and in gauges)
    6) fuel solenoid
    7) water temp sender
    8) oil pressure sender

    Anything else? What about the tach? Are you sure I need a new one???

    #50690

    Corey Schmidt
    Forum Moderator
    Vessel Name: Rebel Belle
    Engines: Cummins
    Location: Oxnard, CA
    Country: USA

    A few valuable points to consider:

    Sending units for boats with more that one station are setup as DUAL station senders and the resistance values will not work for a single panel configuration. You will need to replace these… they are not voltage specific.

    The panel controls all power distributed to the engine. If your cranking battery is 12V, then the panel will also receive 12V power… same for 24V battery system.

    RED wire is always hot voltage to the panel from the engine/battery directly. Then, the PURPLE wire will be switched power (typically from the KEY) through the panel and back to the engine. This power also handles the solenoid, & mag switch. GREY wire is the tach SIGNAL only, no power involved… it is a straight AC square wave signal. The lamps in the panel will all need to be changed to 24V if you convert to 24V batteries.

    The PCB boards provided from Cummins are voltage specific and from our experience, you must replace this component so it alarms and functions correctly.

    Panel wiring: https://www.sbmar.com/wp-content/uploads/2015/11/B-C-Panel-wiring.pdf

    #50689

    Robert Cart
    Participant
    Country: United States

    Thank you, Tony. Your advice would be spot on if it weren’t for some crazy requirements I have. I’m on the bleeding edge and am doing quite a few things common only to the most modern boats. For one thing, I’m upgrading the house battery bank to LiFePO4 batteries. I have already pulled and rewired most of the boat for 24V with a distributed two wire bus. I’ve yanked out the generator and I’m not putting one back. I’ll run AC loads off a 3kW inverter. I have water maker, electric winches and windlass, refrigeration, etc. This all leads to needing 200 amps from the alternator at 24V. A 160A 12v alternator and a 300w DC converter wouldn’t make a dent in the demands for this 62′ boat.

    On your specific comments, I found a wiring diagram for the B series panel on your site and elsewhere. I don’t have the diagram for how the harness connects to parts on the engine. What I have shows the grey wire from the tach to be connected to either W12 for 12V or W24 for 24V. Since it has those two voltage options, it suggests the panel may be wired for either 12 or 24V? I’m assuming the grey wire is power from the battery via the alternator connection and is energized once the ignition is switched on. I guessed that W24 connection is the midpoint of a simple voltage divider so as to deliver 12V to the panel.

    I’ve found this to be a common approach for both dual voltage products. I now know a lot about buying 24V pumps, motors, lights, fans, etc. They often are not clear about whether a product may be purchased in one of two voltages or whether it is dual voltage. The latter was luckily true with my autopilot and fridge compressors.

    A new 24V starter cost $124 new so I won’t sweat that or the labor to replace it. A new new mag switch and fuel shutoff solenoid may not be necessary if the panel voltage remains at 12V? As I only want a single panel, $300 would be unpleasant, but not the end of the world.

    Questions:
    1) Do you know if the voltage source for the panel is delivered via the grey wire from the alternator? Ity appears the purple wire serves as the power supply wire within the panel, but I cannot tell how this is powered.

    2) Do you have a diagram showing how the harness connects to the engine components?

    Thanks in advance!

    #50481

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

    Voltage Conversion

    Robert,

    I really think you need to rethink this out if $$, time, complexity & and hassle are part of what you’d like to keep at a minimum..

    1) Converting the panels is not cheap-The 24VDC PC board will set you back over $300 each. Then you have the lights and the tach.

    2) You need a new starter, new mag switch, and a new fuel solenoid

    3) then the new alternator…….

    Way better and easier to go exactly the other way.. Go ahead and upgrade, if needed, to a HD 12VDC alternator ( like a Delco 24SI 160A ) and then for less than $200, you can buy a high-end 250-300W 12-24VDC DC-DC converter..Cheap ones are about $50.

    Think about it..

    Tony

    #50473

    Luke Nelson
    Participant
    Vessel Name: Southern Image
    Engines: QSC 8.3 540hp
    Location: Perth
    Country: Western Australia

    I did a similar change on a pair of QSC’s. Corey sorted all the bits I needed.
    Alternator, starter, 24/12 convertor for gear shift and smart craft, a new voltage gauge, new fuel lift pump.

    The only issue I had was the firmware upgrade on the ECU. Cummins say there is not a 12v and 24v firmware and the ECU senses the voltage and adjusts to suit. My mechanic said this was not the case when he worked at Cummins. My lifts pumps didn’t like this and ran slow and I had fuel low pressure alarms.

Viewing 11 replies - 1 through 11 (of 11 total)

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