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  1. #1
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    Default Testing battery capacity

    Hi folks

    This may also go under camping/fridges etc...

    What is the correct way to test my camping trailer's batteries ito capacity etc.?

    I want to determine how many days/hours I can run my fridge on the two batteries.

    The theoretical calculation would look something like this: 2x 100Ah batteries = 200Ah. Fridge current draw at 2.5A. Thus, 80 hours run time max. 40 hours if one only wants to deplete batteries to 50%. This calculation does obviously not take into consideration the fridge being opened at irregular intervals.

    So what I did is the following:

    Charged the batteries full with AC charger (13.96V)
    Cooled down the fridge down to 2'C on AC
    Took the batteries of charge and swithed the fridge to DC - battery voltage at this stage 13.02V

    The fridge has now been running for around 24 hours (obviously not all the time, have not been opening it at all) - battery voltage 12.35V

    At what voltage do I assume 50% battery discharge? 12.1V?
    This test I assume will just reflect the theoretical calculation - and proves the batteries are good or not.

    What if I want to do a real time, worst case scenario test? Should I do the same, but set the fridge to -10'C or so, so it needs to run constantly?

    This will show me the shortest possible time I can go without charging batteries, correct?

    Input from the gurus appreciated!

    Thanks
    2014 Hilux D4D dc 4x4
    2013 Metalian Maxi

  2. #2
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    Default Re: Testing battery capacity

    Quote Originally Posted by KrokODell View Post
    Hi folks

    This may also go under camping/fridges etc...

    What is the correct way to test my camping trailer's batteries ito capacity etc.?

    I want to determine how many days/hours I can run my fridge on the two batteries.

    The theoretical calculation would look something like this: 2x 100Ah batteries = 200Ah. Fridge current draw at 2.5A. Thus, 80 hours run time max. 40 hours if one only wants to deplete batteries to 50%. This calculation does obviously not take into consideration the fridge being opened at irregular intervals.

    So what I did is the following:

    Charged the batteries full with AC charger (13.96V)
    Cooled down the fridge down to 2'C on AC
    Took the batteries of charge and swithed the fridge to DC - battery voltage at this stage 13.02V

    The fridge has now been running for around 24 hours (obviously not all the time, have not been opening it at all) - battery voltage 12.35V

    At what voltage do I assume 50% battery discharge? 12.1V?
    This test I assume will just reflect the theoretical calculation - and proves the batteries are good or not.

    What if I want to do a real time, worst case scenario test? Should I do the same, but set the fridge to -10'C or so, so it needs to run constantly?

    This will show me the shortest possible time I can go without charging batteries, correct?

    Input from the gurus appreciated!

    Thanks
    12.1V should be 40% SOC. Don't think you want to go lower than this on a lead acid battery

  3. #3
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    Default Re: Testing battery capacity

    What chemistry ?

    AGM
    SLA

    Deep cycle, high cycle, normal ?

    There will be small variances.
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  5. #4
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    Default Re: Testing battery capacity

    2x Exide SMF100 batteries
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  6. #5
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    Default Re: Testing battery capacity

    Hope this chart will help
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  8. #6
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    Default Re: Testing battery capacity

    I would incorporate a coulometer from Electromannsa into your setup. It has been discussed in the Electrickery thread.
    Last edited by petewill; 2023/11/15 at 07:46 PM.
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  10. #7
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    Default Re: Testing battery capacity

    Quote Originally Posted by petewill View Post
    I would incorporate a coulometer from Electromannsa into your setup. I has been discussed in the Electrickery thread.

    Will have a look
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  11. #8
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    Default Re: Testing battery capacity

    Quote Originally Posted by ChrisH View Post
    Hope this chart will help
    Thank you. Very handy indeed.
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  13. #9
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    Default Re: Testing battery capacity

    This is from the Hcdp manual. I assume this lockout refers to the voltage level when the system shuts down? Why would they have set it so very low? That is surely a recipe to ruin the batteries.

    Click image for larger version. 

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    The newer National Luna fridges has an option for various cut out voltages - 11.5 being the highest option. Unfortunately my older National Luna does not have a cut out setting and onlu cuts out at 10.5. Again, way too low.

    Is there an option to install some inline cut out device?
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  14. #10
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    Default Re: Testing battery capacity

    The list ChrisH provided is under no load. While running 50% is perhaps around 11.8V?

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    Default Re: Testing battery capacity

    Donít blame yourself over past mistakes. Itís like driving down the N1 while looking in the rear view mirror only.

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  18. #12
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    Default Re: Testing battery capacity

    Quote Originally Posted by ekkekan View Post
    The list ChrisH provided is under no load. While running 50% is perhaps around 11.8V?
    Correct. Also.... Your fridge might also measure a lower voltage than say when you measure at the battery due to losses in the cable to the battery caused by length or thickness of the cable.
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  20. #13
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    Default Re: Testing battery capacity

    If it helps, in my experience, my NL 90l dual uses around 700Wh over 24 hours while camping in moderately hot Gauteng weather.
    This is with freezer set around -5 and fridge around 0 or 1, that's how I usually set it for a weekend camp, and plenty lid openings cause how else will you get beer?
    Before you judge a person, first walk a mile in their shoes.

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  22. #14
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    Default Re: Testing battery capacity

    Quote Originally Posted by bigboy529 View Post
    If it helps, in my experience, my NL 90l dual uses around 700Wh over 24 hours while camping in moderately hot Gauteng weather.
    This is with freezer set around -5 and fridge around 0 or 1, that's how I usually set it for a weekend camp, and plenty lid openings cause how else will you get beer?
    Yip and that is just within the reach of a 200 W fold up solar panel. One or 2 shady days you need to take a long drive to charge batteries

  23. #15
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    Default Re: Testing battery capacity

    Quote Originally Posted by Tiaan Pot View Post
    Yip and that is just within the reach of a 200 W fold up solar panel. One or 2 shady days you need to take a long drive to charge batteries

    On a good sunny day I usually get around 1000Wh charge from 200W on a Victron MPPT and that's nogal without moving the panels around at all.
    Before you judge a person, first walk a mile in their shoes.

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  25. #16
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    Default Re: Testing battery capacity

    So I am not sure what my test tested as I think it had many designs flaws...

    After 96 hours the battery is at 12.15V.

    How can I do a better test?

    Should I pack the fridge full of cold items., then over the course of a weekend open it every hour or so, remove a cold beer... and pack a warm one back. This would be a more realistic test I think.

    Any other ways?
    2014 Hilux D4D dc 4x4
    2013 Metalian Maxi

  26. #17
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    Default Re: Testing battery capacity

    Quote Originally Posted by KrokODell View Post
    So I am not sure what my test tested as I think it had many designs flaws...

    After 96 hours the battery is at 12.15V.

    How can I do a better test?

    Should I pack the fridge full of cold items., then over the course of a weekend open it every hour or so, remove a cold beer... and pack a warm one back. This would be a more realistic test I think.

    Any other ways?
    The real life situation.

    After 96hrs @ 12.15V is plenty good

    Edit...you read my thread about the older AGM battery...it survived the whole Tankwa trip and still going strong
    Last edited by Prof; 2023/11/17 at 07:37 PM.
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  27. #18
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    Default Re: Testing battery capacity

    Quote Originally Posted by KrokODell View Post
    So I am not sure what my test tested as I think it had many designs flaws...

    After 96 hours the battery is at 12.15V.

    How can I do a better test?

    Should I pack the fridge full of cold items., then over the course of a weekend open it every hour or so, remove a cold beer... and pack a warm one back. This would be a more realistic test I think.

    Any other ways?
    https://electromannsa.co.za/product/...pacity-tester/
    Cheers

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  28. #19
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    Default Re: Testing battery capacity

    Quote Originally Posted by Prof View Post
    The real life situation.

    After 96hrs @ 12.15V is plenty good

    Edit...you read my thread about the older AGM battery...it survived the whole Tankwa trip and still going strong
    Maybe we should distinguish between testing a batteries capacity and a batteries capacity to fulfil a specify users needs.
    Cheers

    NAGOF

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  30. #20
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    Default Re: Testing battery capacity

    For wot, R2k, you can have Bluetooth acces, App on your phone and data for the life of the battery.
    https://www.sunstore.co.za/products/...-battery-shunt

    Know your battery usage. Measure it.

    Just saying.
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