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Thread: Battery Drain

  1. #1
    Join Date
    Oct 2017
    Posts
    31

    Default Battery Drain

    Hi guys,

    Need your input into something that is really confounding me.

    I recently bought 3 x 110 Ah batteries to replace my old ones. Yesterday I spent 24 hours in a marina on shore power. I then motored to my destination.

    In 12 hours (since anchoring), my batteries went from 12.9v to 12.1v (50% SOC). So basically used 170Ah.

    All that was running during this time was the mast light, fridge and freezer. My battery monitor states that 5A constant drain which raises to 10A when the fridge compressor runs.

    Even if the compressor ran constantly, this would only equal 120Ah which doesn’t explain the 50Ah gap in battery drain.

    Does anyone have any tips or can point me in the right direction?

    Thanks

  2. #2
    Join Date
    Mar 2006
    Location
    Manchester
    Posts
    17,198

    Default Re: Battery Drain

    Make and model of batteries? Make and model of battery monitor?

    Entirely possible that their capacity isn't 330Ah, and is much less, even though you only fitted them recently.

    From what information you have, what would you calculate the apparent capacity to be? Based on the info you give, it looks like the capacity could be around 240Ah, or 80Ah each.

    Alternatively, something might be using power that your monitor isn't monitoring?
    Narrowboating From Stretford!!

  3. #3
    Join Date
    Oct 2017
    Posts
    31

    Default Re: Battery Drain

    They are 110Ah Exide Sealed Dual batteries.

    I have two monitors. One on my main distribution panel that just reads voltage. The other is a Victron BMV700.

  4. #4
    Join Date
    Apr 2005
    Location
    Exmouth, Devon
    Posts
    745

    Default Re: Battery Drain

    How many amps does the battery monitor say you have used?

    Edit - just re-read. What total amp hours does it record for the period? If you switch everything off and run the engine, does it show amps going in?

    Is the alternator wired the correct side of the shunt? Ditto for solar if you have it.
    Last edited by MikeCC; 03-09-19 at 12:07.
    allGadgets Marine
    www.allgadgets.co.uk

  5. #5
    Join Date
    Mar 2002
    Location
    Greenwich
    Posts
    7,593

    Default Re: Battery Drain

    Quote Originally Posted by lawrence_craig View Post
    They are 110Ah Exide Sealed Dual batteries.

    I have two monitors. One on my main distribution panel that just reads voltage. The other is a Victron BMV700.
    Is the monitor shunt the only connection to your service batteries - it should be. If anything else at all is connected on the battery side of the shunt then you need to move it to the supply side or you will be missing some part of the drain.

    My other thought is how full the batteries really were when you anchored. How long had they been at float?

  6. #6
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,614

    Default Re: Battery Drain

    Quote Originally Posted by lawrence_craig View Post
    Hi guys,

    Need your input into something that is really confounding me.

    I recently bought 3 x 110 Ah batteries to replace my old ones. Yesterday I spent 24 hours in a marina on shore power. I then motored to my destination.

    In 12 hours (since anchoring), my batteries went from 12.9v to 12.1v (50% SOC). So basically used 170Ah.

    All that was running during this time was the mast light, fridge and freezer. My battery monitor states that 5A constant drain which raises to 10A when the fridge compressor runs.

    Even if the compressor ran constantly, this would only equal 120Ah which doesn’t explain the 50Ah gap in battery drain.

    Does anyone have any tips or can point me in the right direction?

    Thanks
    Were the batteries on load when you measured 12.1 volts or had they even been on load prior to taking the reading. If so 12.1 V may not be so bad.

    To get a really meaningful estimate of the state of charge from a voltage measurement you need to allow the batteries to stand with no load or charging for at least 12 hours , preferably 24 hours, before taking the reading, Then you would expect a fully charged battery to read at least 12.7 V and a 50% discharged battery to read around 12.2 V

  7. #7
    Join Date
    Oct 2017
    Posts
    31

    Default Re: Battery Drain

    Quote Originally Posted by RupertW View Post
    Is the monitor shunt the only connection to your service batteries - it should be. If anything else at all is connected on the battery side of the shunt then you need to move it to the supply side or you will be missing some part of the drain.

    My other thought is how full the batteries really were when you anchored. How long had they been at float?
    Hmm... no, nothing is connected directly to the battery. Everything comes off the main distro panel.

    The alternator is wired directly to batt and so is solar.

    The batteries must have been full as I was on shore power for 24 hours and then motoring for 3 hours.

  8. #8
    Join Date
    May 2007
    Posts
    38,210

    Default Re: Battery Drain

    Quote Originally Posted by lawrence_craig View Post
    ....

    The batteries must have been full as I was on shore power for 24 hours and then motoring for 3 hours.
    I'm not sure that necessarily follows.
    It depends on how your shore power charger decides the battery is full.
    Possibly it has been fooled into thinking the battery was partly charged when the charger was switched on (e.g. some solar going in) and set only a short period at boost volts before going into float mode?

    You may need to read the mind of your shore power charger!

  9. #9
    Join Date
    Mar 2002
    Location
    Greenwich
    Posts
    7,593

    Default Re: Battery Drain

    Quote Originally Posted by lawrence_craig View Post
    Hmm... no, nothing is connected directly to the battery. Everything comes off the main distro panel.

    The alternator is wired directly to batt and so is solar.

    The batteries must have been full as I was on shore power for 24 hours and then motoring for 3 hours.
    Why is the alternator and solar connected directly to the battery? If you do that then the battery monitor can only measure amps out not amps in. You need to have the battery monitor shunt attached to the battery and the solar and alternator attached to the non-battery end of the shunt.

    I also agree that you can’t tell if a battery is full or close to it just because it’s been on mains charge then engine. Connect the shunt and inputs correctly and you will be able to see how much net goes in and out.

  10. #10
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,614

    Default Re: Battery Drain

    Quote Originally Posted by lawrence_craig View Post
    Hmm... no, nothing is connected directly to the battery. Everything comes off the main distro panel.

    The alternator is wired directly to batt and so is solar.

    The batteries must have been full as I was on shore power for 24 hours and then motoring for 3 hours.
    In view of this statement and Rupert W's comments you should check that there are no connections, including the charger and the solar system , directly to the service battery negative. The only connection allowed is the Victron shunt.

    The negatives of all circuits circuits: load, charging and the engine start battery , must be connected to the "load" terminal of the shunt.

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