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115Ah Alternator and the service batteries

Discussion in 'Technical Discussion' started by vivariva, Apr 3, 2012.

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  1. vivariva, Apr 3, 2012
    #1
    vivariva

    vivariva Senior Member

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    We're planning to install two 12V-180Ah deep cycle service (parallel) batteries to our boat.

    The engine is a Volvo Penta D2-75 with a 115Ah Alternator with an electronic charging capacity sensor. It has a starter battery on its own.

    Do you think the above-mentioned battery amperage is too much for this engine? What is the normal battery capacity (ies) for an alternator of 115 Ah, or any other one in terms of percentage?

    Thank you in advance, regards
    Vivariva
  2. AlfredZ, Apr 3, 2012
    #2
    AlfredZ

    AlfredZ Senior Member

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    Hi there,

    I think the alternator should count to 25% of the total of deep cycle output, so addup all the amps together and see if it within range. You will also need a regulator (I think you already have one installed), not to mention that the cables should be in proper rating also in order not to heat up and fail.

    Cheers,

    Alfred
  3. Marmot, Apr 3, 2012
    #3
    Marmot

    Marmot Senior Member

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    You need to determine how much power your normal use of the boat will consume. Figure that you don't want to use much more than around 60 percent of the battery capacity. You can go deeper (some people say 80%) with an AGM but the deeper you discharge, the shorter the battery life in terms of cycles.

    When you know how much power you normally use, figure out how much engine running time you have to recharge. Do you have a generator on the boat?

    Try not not mix battery types as in AGM house bank and flooded wet cell for starting and hope to recharge them with the same charger or alternator as the voltage requirements are different. You can use an "echo charger" to automatically recharge the start battery and house bank in sequence according to which has the lower voltage.

    This is a popular and continuous "hot topic" among the small boat cruising community and if you Google the subject of charging house banks you will find a few months worth of interesting reading. Much of it should be taken with a grain of salt but all of it is enlightening one way or another.
  4. vivariva, Apr 3, 2012
    #4
    vivariva

    vivariva Senior Member

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    Thank you for your answers, it is a continuous topic as you have mentioned, I trust the answers on YF more than anywhere else on the net.

    The power consumption at anchor is mostly the big fridge, water pump and lights at night. It is a 47 footer sailboat.

    At cruise, the autopilot and the 8hp bow thruster come into play however the engine runs mostly at the same time.

    Regards, thanks again Marmot&3ala2
  5. Marmot, Apr 3, 2012
    #5
    Marmot

    Marmot Senior Member

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    Why would you use the bow thruster "at cruise"?
  6. vivariva, Apr 3, 2012
    #6
    vivariva

    vivariva Senior Member

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    I meant the 'cruise' mode not at cruise from one point to another. I would'nt use the thruster except in the marina/close quarters..

    If you're trying to outsmart a post or a user, use your free time at another thread.
  7. Marmot, Apr 3, 2012
    #7
    Marmot

    Marmot Senior Member

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    It looks like I wasted my time. Won't let that happen again, have a nice day.