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  1. #1
    Join Date
    Oct 2017
    Posts
    31

    Default Replace batteries or look elsewhere?

    Hi guys,

    I have the following setup:

    - 3 x 125Ah service batteries (2 years old)
    - Separate fridge and freezer running 24 hours a day

    Now until last week, the fridge and freezer has been fine to run all day and overnight as long as I run the engine 2 x per day for an hour or two (I'm a liveaboard).

    Recently (as in this week), my batteries haven't been lasting 2-3 hours without needing charging. The voltage of the batteries have been dropping from 12.6v to under 12v in less than 2 hours.

    Are the batteries done for? Or should I be looking at an issue with the fridge/freezer? I find it strange I would have such a dramatic change over the period of 1 week for example.

    If it's any benefit, I did an energy calculation and my average consumption is around 180Ah per day.

    Appreciate the help in advanced as always.

  2. #2
    Join Date
    Mar 2002
    Location
    Greenwich
    Posts
    7,472

    Default Re: Replace batteries or look elsewhere?

    What amps are being put in by the engine when charging for a couple of hours? What amp hours does that add up to?

  3. #3
    Join Date
    Oct 2017
    Posts
    31

    Default Re: Replace batteries or look elsewhere?

    Quote Originally Posted by RupertW View Post
    What amps are being put in by the engine when charging for a couple of hours? What amp hours does that add up to?
    It is a 100a alternator so should be putting out enough to charge the batteries fully, no?

  4. #4
    Join Date
    May 2001
    Location
    UK East Coast
    Posts
    36,280

    Default Re: Replace batteries or look elsewhere?

    Quote Originally Posted by lawrence_craig View Post
    It is a 100a alternator so should be putting out enough to charge the batteries fully, no?
    No - the 100A capability of the alternator is irrelevant. What matters is the ability of the batteries to accept charge; this depends on the state-of-charge, the battery type, and the total Ah capacity. My guess is that you've been gradually running the batteries down. The 12.6v you mention isn't generally considered to be a fully-charged battery.

    If you install a battery monitor, you'll be able to see how many Ah you've used, and then see how many Ah you're replacing when charging.

  5. #5
    Join Date
    Mar 2002
    Location
    Greenwich
    Posts
    7,472

    Default Re: Replace batteries or look elsewhere?

    No - the chances of a normal alternator putting out it’s rated power is very low - basically if there is a huge discharged battery bank and perfect highish revs. From my own experience I’d guess 20 to 30 amps within ten minutes then dropping. Even a smart alternator would need many hours to raise a bank from discharged to above 80 percent charged.

    Solar and maybe even a generator may be a better option alongside a better alternator regulator but to work your gap you need to see what amps are flowing in under your current charging regime.

  6. #6
    Join Date
    Oct 2017
    Posts
    31

    Default Re: Replace batteries or look elsewhere?

    Quote Originally Posted by RupertW View Post
    No - the chances of a normal alternator putting out it’s rated power is very low - basically if there is a huge discharged battery bank and perfect highish revs. From my own experience I’d guess 20 to 30 amps within ten minutes then dropping. Even a smart alternator would need many hours to raise a bank from discharged to above 80 percent charged.

    Solar and maybe even a generator may be a better option alongside a better alternator regulator but to work your gap you need to see what amps are flowing in under your current charging regime.
    Ok, I think I understand.

    My main question is that previously, I didnít have an issue with the SOC of my batteries as they were fine last week based on how I was managing them. Then this week, I am struggling to keep the charge for 4 hours. What could potentially cause this change?

  7. #7
    Join Date
    May 2001
    Location
    UK East Coast
    Posts
    36,280

    Default Re: Replace batteries or look elsewhere?

    Quote Originally Posted by lawrence_craig View Post

    My main question is that previously, I didn’t have an issue with the SOC of my batteries as they were fine last week based on how I was managing them. Then this week, I am struggling to keep the charge for 4 hours. What could potentially cause this change?
    As I wrote in post 4, you're most likely gradually running your batteries down.

  8. #8
    Join Date
    May 2001
    Location
    North Wales, sailing Aegean Sea or Menai Strait
    Posts
    21,902

    Default Re: Replace batteries or look elsewhere?

    When I start my engine in the morning after the fridge has run all night the 3 x 110 Ah battery bank takes 50 amps (nominal size of the alternator) for about a minute, then slowly reduces pretty much linearly and is down to around 12 amps after an hour. This has been the pattern for years, with several different battery makes, Sterling alternator regulator always fitted.
    Answers to some technical queries at new website http://coxeng.co.uk

  9. #9
    Join Date
    Mar 2002
    Location
    Greenwich
    Posts
    7,472

    Default Re: Replace batteries or look elsewhere?

    Quote Originally Posted by pvb View Post
    As I wrote in post 4, you're most likely gradually running your batteries down.
    And that is being Lakesailored ( although you hadn’t posted when I started typing)

  10. #10
    Join Date
    May 2001
    Location
    UK East Coast
    Posts
    36,280

    Default Re: Replace batteries or look elsewhere?

    Quote Originally Posted by RupertW View Post
    And that is being Lakesailored ( although you hadn’t posted when I started typing)
    I'm not convinced that clause 10 (c) (iii) of the Lakesailoring Rules applies in this case.

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