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  1. #11
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,612

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    Quote Originally Posted by Chanquete View Post
    Before operating the glow plugs 12Volts

    Whilst operating the glow plugs 10 Volts

    After operating the glow plugs, without starting the engine 12 Volts

    The engine starts immediately in much less than a second.
    If the battery is only reading 12 volts with no load and without having been on load for several hours previously it is almost flat ... at least down to about 25% of fully charged

    Maybe as, lw395 suggests it merely needs a spell on a good automatic, multistage charger, with an appropriate maximum amps output, to recharge it fully

    HOWEVER

    The fact that the engine cranks and starts easily suggests that the redaings may not be accurate, Are they readings taken directly from from the battery terminals with a decent reliable meter

  2. #12
    Join Date
    May 2001
    Location
    UK East Coast
    Posts
    36,520

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    The fact that the OP wrote "12 Volts" rather than 12.0 makes me wonder if he's using a simple analogue voltmeter, which is usually fairly inaccurate. Readings with a decent multimeter might be more relevant.

  3. #13
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,612

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    Quote Originally Posted by pvb View Post
    The fact that the OP wrote "12 Volts" rather than 12.0 makes me wonder if he's using a simple analogue voltmeter, which is usually fairly inaccurate. Readings with a decent multimeter might be more relevant.
    Good point
    Although an analog meter need not be inaccurate, but if the readings are from a crude panel meter they may well be.

    The fact that the engine cranks and starts easily suggests they are inaccurate and the OP may be trying to fix something that is not broken
    Last edited by VicS; 14-09-19 at 12:55.

  4. #14
    Join Date
    Jan 2013
    Location
    Buenos Aires, Argentina
    Posts
    131

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    The battery was full charged with an intelligent charger. The battery is 6 years old. The engine starts immediately in much less than a second.
    I will check the volts with an electronic tester.
    Thanks!

  5. #15
    Join Date
    Jan 2013
    Location
    Buenos Aires, Argentina
    Posts
    131

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    Quote Originally Posted by VicS View Post
    Good point
    Although an analog meter need not be inaccurate, but if the readings are from a crude panel meter they may well be.

    The fact that the engine cranks and starts easily suggests they are inaccurate and the OP may be trying to fix something that is not broken
    Thanks! . My Volt data comes from the instrument panel meter.
    I will measure Volts again with an electronic voltmeter.

  6. #16
    Join Date
    Apr 2018
    Location
    Mooring, Faro
    Posts
    1,669

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    Quote Originally Posted by VicS View Post
    Good point
    Although an analog meter need not be inaccurate, but if the readings are from a crude panel meter they may well be.

    The fact that the engine cranks and starts easily suggests they are inaccurate and the OP may be trying to fix something that is not broken
    You may well be right, our panel analogue volt meter is out by 0.8 volts!

  7. #17
    Join Date
    May 2016
    Location
    Suffolk
    Posts
    7,967

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    Quote Originally Posted by PaulRainbow View Post
    Take the following voltage readings from the battery terminals ;
    Quote Originally Posted by Chanquete View Post
    Thanks! . My Volt data comes from the instrument panel meter.
    I will measure Volts again with an electronic voltmeter.
    Accurate data is important.
    Rainbow Marine.
    www.rainbowmarine.co.uk

  8. #18
    Join Date
    Oct 2001
    Posts
    1,419

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    Note that cheapo electronic volt meters can be out of calibration. So worth a double check if readings seem wrong.

    0.8v wrong for one of mine.

  9. #19
    Join Date
    Aug 2010
    Location
    Bristol
    Posts
    945

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    Most GPS chartplotters (if you have one) have built in voltmeter which can be displayed and much more accurate than panel volt gauge.

    My eberspaker heater doesnt start up if less than 10.5v and I normally cant get it to start without running engine, and thats on a brand new battery. The hot plug load current drops the voltage much the same as engine glow plug. Battery gives about 12.5v to just under 13v under normal loads but rises to 13.5 to 14.1 if engine running. Thats on both of our boats.
    A boat is for going places

  10. #20
    Join Date
    Jul 2003
    Location
    West Australia
    Posts
    11,664

    Default Re: Voltage drop curve of lead acid batterry with increasing discharge

    I find this obsession with batteries and voltage in our typical boats strange. Ideally and usually the boat has a 2 battery system leaving redundancy. So with a back up you have much less to worry about than your car. I understand that keeping voltage up and minimising depth of discharge can enhance the life of the battery. However I reckon people worry too much. When a battery has reached the end of it's life it will be obvious. Don't worry till then. ol'will

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