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Dedicated Starting Battery For 2 Generators

Discussion in 'Generators' started by DOCKMASTER, Feb 9, 2023.

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  1. Capt J, Feb 10, 2023
    #21
    Capt J

    Capt J Senior Member

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    The problem with this entire scenario is if you lost shorepower or a generator while sleeping at night, or a bad battery charger and large house load, it's entirely possible to not be able to get anything started. I'd want a 31 for generators only, 12 v house bank as usual and a battery switch that can pull from either bank or both.
  2. DOCKMASTER, Feb 10, 2023
    #22
    DOCKMASTER

    DOCKMASTER Senior Member

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    I think you misread or misunderstood something. I will have a dedicated battery that does nothing but start either gen. Then I will have a manual emergency crossover switch to the house bank in the event the dedicated battery fails. In addition to that I have back-up 24v to 12v chargers that can charge the house bank from the 24v starting banks (from engine alternators or shore fed charger) in the event of a failure of the house bank charger. If that isn’t enough redundancy and back up for you I also carry a set of heavy jumper cables. So in total, that gives me 11 batteries, 4 alternators, 2 a/c powered chargers, 2 24v to 12v chargers and a set of jumper cables. Oh yeah, I forgot I also have a small portable battery charger as well. And I’m not even counting the battery and alternator in the tender . I think I’m good.

    I’m only installing one gen starting battery as that is all that’s needed. It’s not about saving a couple of bucks. I am running low on space though with everything I’ve added to the engine room. I see no need to crowd things more just for the sake of doing it.
    Capt Ralph likes this.
  3. mapism, Feb 11, 2023
    #23
    mapism

    mapism Senior Member

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    Coming to think of it, since in terms of redundancy you are clearly covered, why fit a starting battery for the genset at all?
    I mean, having now understood that your house bank is 12V, I sort of wonder why don't you keep the wiring as you said it is now, with the house bank starting either genset...
    ...you could even go as far as stripping the alternators from the gensets and sell them on eBay! :)
  4. alvareza, Feb 11, 2023
    #24
    alvareza

    alvareza Senior Member

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    All the battery redundancy described sounds like a dream. My Ocean is currently the opposite of redundancy. 4 group 31s, 2 serve the house and 2 serve Flybridge and electronics, both banks parallel at 12 volts when starting either engine. The starters for the MTU 60 Series are definitely 12v. I thought for awhile the parallel on start was to get 24v, but not so. Battery charger charges both banks. Generator starts off one side. Trying to find gyre out an efficient way to add an inverter with additional battery capacity to run fridges at night/anchor and provide a redundant battery bank w/o rewiring everything
  5. DOCKMASTER, Feb 11, 2023
    #25
    DOCKMASTER

    DOCKMASTER Senior Member

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    I don’t have to change anything. The boat has worked like this for the 11 years I’ve had it and who knows how long before that. I’m simply adding another level of safety, redundancy and more importantly, piece of mind. When we anchor at night I prefer to shut down the gen when we go to bed. With our cooler temps it’s not a problem for fridge and freezers to sit overnight. I don’t worry too much about house bank draw overnight as I’ve never had an issue starting a gen in the morning. That being said, it’s always in the back of my mind. With a dedicated gen starting battery I have one less thing to have to worry about or even think about.
    cleanslate likes this.
  6. Capt J, Feb 11, 2023
    #26
    Capt J

    Capt J Senior Member

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    Then you should be covered with just a Gen battery.
  7. cleanslate, Feb 12, 2023
    #27
    cleanslate

    cleanslate Senior Member

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    How many 31s do you have ?
  8. rtrafford, Feb 14, 2023
    #28
    rtrafford

    rtrafford Senior Member

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    One each for two 12v Gens. Two in parallel for house 12v electronics. Two each for 24v to each main. Two each for house 24v. Four for 24v thruster. Total 12 units.
    cleanslate likes this.
  9. cleanslate, Feb 14, 2023
    #29
    cleanslate

    cleanslate Senior Member

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    That's all ? :) My boat...it's a so small..:rolleyes:
    Well it's something for me to consider down the road. I'm thinking for me ; two 31s in parallel would equal one 8D for one side and another two 31s for the other side 8D. Then get a group 27 for the 8kw generator? Would like to have an independent battery for the Gen. some day. Problem I have is limited room in my engine room. Yeah I'll think it over while I'm plugging away in the bilge.
    Thank you all for the info.
  10. ranger58sb, Feb 15, 2023
    #30
    ranger58sb

    ranger58sb Senior member

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    On our previous boat, we used an Odyssey Extreme PC1500 for our 8kW genset. That battery is a Group 34 (or 78, or some such) and I think just a tad smaller than a Group 24.

    I've seen something somewhere (maybe on the Odyssey website) about fitting the G34 into a G24 box or tray... think that was maybe for a fitted "fence" inside a G24 tray to keep the think from sliding around. Maybe.

    Anyway, the battery worked fine for the genset.

    -Chris
  11. ranger58sb, Feb 15, 2023
    #31
    ranger58sb

    ranger58sb Senior member

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    Speaking of that, our current 21.5 kW Onan needs 625 CCA minimum, and the PC1500 is rated at 850... so it'll likely be the choice I look at first when I need to replace our genset battery too.

    -Chris
  12. rtrafford, Feb 15, 2023
    #32
    rtrafford

    rtrafford Senior Member

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    No worries. Modern electronics are quite sensitive. I put them on a bank of their own to be clear of any feedback from thrusters, house systems, starters...might be overkill, but better safe than sorry. Yeah, I could shrink the population a bit, but the better plan would be to refit the thruster with hydraulics and get it off the batteries altogether.
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