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  1. #1

    Interesting 12 Volt Problem

    I’ve noticed an unusual 12v problem for quite some time now, and finally did some checking on it this past weekend. My voltage meters on the bridge typically read between 13 and 14 volts. Occasionally, they spike up to 16v. This seems to happen to both engines simultaneously, which really confuses me. The port gauge pretty much pegs the gauge, and stbd goes up to around 15.5v. Port is the supply for the flybridge panel.

    What has really brought this to light is the fact that my electronics shut down momentarily whenever I start the port engine, due to the drop in voltage. BTW, the port bank, a pair of 8d batteries, is new this season. The engines start fine. Because of this, I purchased a deep cycle 12v battery and hooked it up via a Charles 93-battcomm-a battery combiner to the flybridge panel. After a day of running, my electronics went off completely, as that battery drained and did not recharge. I put a meter on the line side of the combiner, and it read 13.1v; the load side was down around 11v, so clearly the battery combiner was not connecting and allowing the new battery to charge.

    This weekend, I noticed the volt meters pegged at16 again, so I grabbed my meter and confirmed that indeed, I had 16.1 volts at the combiner line side. I also showed around 16 v on the load side as well.

    So, my questions are
    1) Is there a minimum voltage at which the combiner will join the batteries?
    and
    2) What could possibly cause this variation in voltage?
    And
    3)Why would it affect both engines simultaneously?

    BTW, I do have a good battery charger installed (Sentry I believe) and it seems to be working properly.
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  2. #2

    Re: Interesting 12 Volt Problem

    Neither the charger nor alternators should output 16 volts. Somethings wrong with the regulation of either the alternators or the charger. Does it happen with or without the engine running.
    Scott
    41C117 "Hattatude"
    Port Canaveral Florida.


    Marine Electronics and Electrical Products Distributor.

  3. #3

    Re: Interesting 12 Volt Problem

    I've only noticed it with the engines running, but of course that's the only time I'd be looking at the gauges. The charger is down in the ER. I do always run my genny when running the boat. I guess I could shut down the genny the next time it occurs and see if the voltage drops back to the normal range.

    Edit - That said, the gauges read high when running the boat at cruising speed; they drop back to normal when I throttle back to lower rpms.

    The fact that the charger is the only link common to both engines/batteries does seem to point in that direction. (I guess the parallel switch is another common link, but I can't see any way that it could fail and cause these symptoms.)
    Last edited by Bob Bradley; 08-18-2015 at 10:24 AM.
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  4. #4

    Re: Interesting 12 Volt Problem

    Quote Originally Posted by Boatsb View Post
    Neither the charger nor alternators should output 16 volts. Somethings wrong with the regulation of either the alternators or the charger. Does it happen with or without the engine running.
    Building on Scotts question, please describe the state of the combiner, each engine, the generator and the shore charger during these events.

    Sounds like one of those devices is having a regulator failure.
    Florida
    2002 Cabo 47
    MAN mechanical 800/8's

    "You can avoid reality, but you cannot avoid the consequences of avoiding reality"

  5. #5

    Re: Interesting 12 Volt Problem

    Quote Originally Posted by Bob Bradley View Post
    I've only noticed it with the engines running, but of course that's the only time I'd be looking at the gauges. The charger is down in the ER. I do always run my genny when running the boat. I guess I could shut down the genny the next time it occurs and see if the voltage drops back to the normal range.

    Edit - That said, the gauges read high when running the boat at cruising speed; they drop back to normal when I throttle back to lower rpms.

    The fact that the charger is the only link common to both engines/batteries does seem to point in that direction. (I guess the parallel switch is another common link, but I can't see any way that it could fail and cause these symptoms.)
    The next time it happens first turn off the shore charger and check, then shut down the generator. If you still have high voltage, shut down one engine so the only thing charging is a single engine, then the other engine. Also, check all the connections at the engine and generator alternators, including the ground connections.

    Is your combiner supposed to be on all the time, switched on automatically, or only on when you switch it on?

    Please explain this extra battery that you added.
    Florida
    2002 Cabo 47
    MAN mechanical 800/8's

    "You can avoid reality, but you cannot avoid the consequences of avoiding reality"

  6. #6

    Re: Interesting 12 Volt Problem

    The new house battery is a 12v deep cycle, physically located in the fb console. At the combiner, the line (input) post is fed from the fb panel (i.e. the port starting battery). The load (output) side goes to the new deep cycle, and also to a switch that feeds the 2 circuits that run the electronics. (I installed a dpdt switch so that I could easily swap back from the new house battery to the old starting battery if I had a problem - good thing).

    The combiner is hard wired - it should combine the two batteries any time it detects 13 volts or more on the charging side. It is not switched.

    As to the state question, both engines were running, as was the genny. The genny starts off the main engine starting battery bank, (not sure if port or stbd bank) and also has its own alternator, which would be able to charge the starting batteries. The high voltage reading on both engines occurs up over 1800rpm, and slowly goes back to normal as I throttle down. I have only observed this while under way (i.e. under load), not when I rev it up at the dock. That said, it is a somewhat intermittent problem and does not always occur under way.
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  7. #7

    Re: Interesting 12 Volt Problem

    Quote Originally Posted by Bob Bradley View Post
    The new house battery is a 12v deep cycle, physically located in the fb console. At the combiner, the line (input) post is fed from the fb panel (i.e. the port starting battery). The load (output) side goes to the new deep cycle, and also to a switch that feeds the 2 circuits that run the electronics. (I installed a dpdt switch so that I could easily swap back from the new house battery to the old starting battery if I had a problem - good thing).

    The combiner is hard wired - it should combine the two batteries any time it detects 13 volts or more on the charging side. It is not switched.

    As to the state question, both engines were running, as was the genny. The genny starts off the main engine starting battery bank, (not sure if port or stbd bank) and also has its own alternator, which would be able to charge the starting batteries. The high voltage reading on both engines occurs up over 1800rpm, and slowly goes back to normal as I throttle down. I have only observed this while under way (i.e. under load), not when I rev it up at the dock. That said, it is a somewhat intermittent problem and does not always occur under way.
    Be careful with your extra battery in the FB console. If I understand what you have done, that battery could be depleted and draw a very high charging current which your panel wiring may not handle.

    The shore charger serves both banks that's why we need to check if it's the reason for this behavior on both engine meters.

    The combiner is another way that both sides can see the same behavior. I would temporarily disconnect the battery cable feeds to both posts on this device and insulate the leads to make sure that both sides cannot be combined.

    Turning off the shore charger, then genset, then one engine will help determine the source of the runaway voltage (if the prior steps did not already tell us that).

    The fact that it only happens underway tells me that you need RPM's and heat to get the symptoms. Does it happen after a hard run back at the dock out of gear, revving up the engines?
    Florida
    2002 Cabo 47
    MAN mechanical 800/8's

    "You can avoid reality, but you cannot avoid the consequences of avoiding reality"

  8. #8

    Re: Interesting 12 Volt Problem

    Quote Originally Posted by Reefgeorge View Post
    Be careful with your extra battery in the FB console. If I understand what you have done, that battery could be depleted and draw a very high charging current which your panel wiring may not handle.

    Reply - I don't think so. I am supplying the combiner with a wire directly from a breaker in the upper station panel.


    The shore charger serves both banks that's why we need to check if it's the reason for this behavior on both engine meters.

    Reply - Agreed. Next time it occurs I will kill the genny, or turn off the house A/C breaker that controls the charger.


    The combiner is another way that both sides can see the same behavior. I would temporarily disconnect the battery cable feeds to both posts on this device and insulate the leads to make sure that both sides cannot be combined.

    Reply - Again, I don't think this can happen. The upper station panel is fed only from the port starting battery bank. I am only combining the port bank with the new fb battery via the combiner.


    Turning off the shore charger, then genset, then one engine will help determine the source of the runaway voltage (if the prior steps did not already tell us that).

    The fact that it only happens underway tells me that you need RPM's and heat to get the symptoms. Does it happen after a hard run back at the dock out of gear, revving up the engines?

    Reply - Haven't tried yet. Lots of possibilities here. Hell, it could even be coincidental failure of both alternator regulators being affected simultaneously by heat - stranger things have happened. The problem predates the installation of the fb battery and combiner, so I am pretty much eliminating that as a possibility. I do think I may have a bad combiner, however. The manufacturer, Charles, tells me that it should combine the batteries when it detects 13v on the charging side. It is definitely not doing that, but is combining them when the voltage spikes to 16.

    I also remain suspicious of the Sentry charger - it is the most likely piece of the puzzle that affects both engines at the same time.

    You've made some good suggestions which I'll try next time I'm there. Thank you.
    Responses imbedded in quote. Thanks for you help.
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

  9. #9

    Re: Interesting 12 Volt Problem

    When I mentioned the combiner potentially causing the original problem I meant the one that is part of the original boat wiring not the new one that you installed at the FB.

    Of course both regulators could have failed at exactly the same time in exactly the same manner but statistics suggests that this is not the most likely cause. If it is, go buy a lottery ticket as you will be in rarified statistical territory indeed. And yes, stranger things have happened - to me I think.
    Florida
    2002 Cabo 47
    MAN mechanical 800/8's

    "You can avoid reality, but you cannot avoid the consequences of avoiding reality"

  10. #10

    Re: Interesting 12 Volt Problem

    Gotcha. I hadn't thought about the parallel switch. It doesn't seem to have much effect any more. Used to be that when I used it, the electronics would not drop out, but no more. Might be a good place to start to investigate.
    Everyone should believe in something - I believe I will go fishing - Henry David Thoreau

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