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  1. #1

    Best way to wire up dual batteries?

    Bought a Jetski that already is rigged to fish with rod holders everywhere, it has a fish/depth finder as well that is powered by a second battery up front but the two batteries arenít connected. Iíd like to hook both batteries up so both are charged, one for starting and one for the depth finder and add a radio. Is the west marine blue sea systems add a battery the best solution for this? My only issue with that is not being able to select between each individual battery like I see on most boats? I guess I donít need to if the engine is off itíll draw from the batteries and once it reaches 13.5v the ACR will cut off the draw from the starting battery so Iíll never have to worry about being dead in the water? Just want to order the right stuff and have it wired up correctly so I donít get stranded on the water, planning on going offshore.


  2. #2
    Click avatar for tech links/info K447's Avatar
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    There are a number of good threads and posts covering this.

    Search for combiner across all the forums on here. That should reveal several useful threads.

    https://lmgtfy.com/?q=site%3Agreenhulk.net+combiner

  3. #3
    Believe me, I searched, but doesn’t come up with much. Everyone that has dual batteries doesn’t show what they used or how it’s setup, just they have dual batteries. Thanks for the link though! Much help!

  4. #4
    Click avatar for tech links/info K447's Avatar
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    This link might work for a little while

    http://greenhulk.net/forums/search.p...rchid=14657055

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  6. #6
    Thank you, those are actually helpful! How did you search for those? When I searched, none of them came up, very few on the subject matter.

  7. #7
    So you suggest just a combiner or ACR and no switch? I was looking at this setup to buy... https://www.westmarine.com/buy/blue-...B&gclsrc=aw.ds

  8. #8
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by JetSkiJeffC View Post
    So you suggest just a combiner or ACR and no switch?

    I was looking at this setup to buy... https://www.westmarine.com/buy/blue-...B&gclsrc=aw.ds
    With a combiner, the factory wiring between engine and battery remains 100% original. Every cable and connection remains as it was.

    The combiner cables are added alongside. New battery negative cable and the combiner negative go to the engine ground. The only point where the new touches the original is where one + wire from the combiner connects to the original battery + terminal.

    So the additional battery and/or the combiner itself can fail or even be removed from the hull and the engine will still start and run.

    In my view, a mechanical switch connected into the heavy battery cables creates potential additional sources of failure. When hooking up a mechanical switch, the heavy cables to the engine are instead routed through the switch. There are more cables and they become critical to normal engine operation.

    A loose connection or bad contact inside the switch can render the engine inoperable.

    In my opinion there is no significant upside to having the switch. The combiner already handles battery charge control for the aux battery. The engine start battery is protected against discharge via the auxiliary equipment.

    I will also mention that I often see mechanical battery switches connected into the positive battery side. Which can be dangerous. Safer to connect a big switch into the negative cables, so that an accidental short to the engine does not cause sparking and/or possible electrical fire.

  9. #9
    I understand the switch adding another failure point. I’ll have to get 2 new batteries since the two I currently have are completely different. So I’ll only need this ACR and some 6 gauge cable then? https://www.amazon.com/Blue-Sea-Syst...61841438&psc=1

    I see quite a few different diagrams on wiring too, is this accurate and do I need both fuses?


    I will add the second battery in the front since that’s where the tray is already mounted and the depth finder cables ran to.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  10. #10
    Click avatar for tech links/info K447's Avatar
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    Quote Originally Posted by JetSkiJeffC View Post
    ... So Iíll only need this ACR and some 6 gauge cable then?

    https://www.amazon.com/Blue-Sea-Systems-Automatc-Charging/dp/B000OTIPDQ/ref=asc_df_B000OTIPDQ/?tag=hyprod-20&linkCode=df0&hvadid=312697294768&hvpos=1o1&hvne tw=g&hvrand=2127553463590158292&hvpone=&hvptwo=&hv qmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9007458& hvtargid=aud-801381245258la-489561841438&psc=1


    I see quite a few different diagrams on wiring too, is this accurate and do I need both fuses?


    I will add the second battery in the front since thatís where the tray is already mounted and the depth finder cables ran to.
    The attached wiring diagram looks about right.

    The 100 amp fuses (or whatever average is appropriate) are there to protect the heavy wires against potential fire (short circuit current heating the wire). And to protect the ACR similarly.

    The fuses should be inline and very close to the battery posts. Wiring between the battery post and the fuse is unprotected, should a short occur there.

    The fuses themselves add more connections and potential failure points, so some installations use fusable link wiring rather than a discreet fuse.

    Some ACR installations just use heavy gauge battery wiring and no fuse protection. They rely on sturdy and tidy installation and mechanical protection for the wires and the ACR. If nothing breaks loose during heavy wave bashing and nothing ever damages the cables or becomes disconnected, there is no problem. Right ...?

    If you want to reduce parasitic (milliamp) current drain when the ski is just sitting (overnight or longer term storage), a low current disconnect switch can be installed inline with the ACR ground wire. Without ground the ACR internal electronics cannot draw current.

    Unlike a heavy battery switch failure, ACR without ground just isolates the two batteries. Engine still starts just fine, auxiliary electrical gear on the second battery still works. Just no charging when engine is running.

    BTW, many PWC come without any sort of cover for the battery. The energized posts and cable end connections are exposed. I prefer to have some sort of tough plastic cover over each battery. So that dropped tools, or loose whatever inside the hull, cannot contact a battery post.

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