Battery Perfomance

Discussion in 'Motorhome Chat' started by CJB, Sep 22, 2014.

  1. CJB

    CJB Funster

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    Good Afternoon,

    I was at the "Paws in the Park" show in Kent this past weekend with no EHU.

    I am a bit concerned about how my battery bank performed. I have dual Banner batteries totaling 200A, both are less than 2 years old. I also have a 100W Solar panel to help charging.

    The batteries were fully charged when I arrived. Over a 24 hour period the most power I believe I could have consumed was about 7Amps for 5 hours. However the batteries were reading 12.4V which I believe it about 50%, there was thick fog over this period so I don't think the solar panel was contributing much if anything at all.

    I woke up the next morning at 8AM and once again checked the batteries they read 12.9V which is 100% full I think. Now it was a very sunny morning however it had only been daylight for a couple of hours.

    I am confused on two fronts.

    1) Why did my batteries drop so quickly?

    2) How did they charge so quickly?

    The battery readings were taken from the solar controller and checked by a meter reading directly from the batteries.

    Any ideas would be much appreciated.
     
  2. Bartyfixedit

    Bartyfixedit Funster

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    Was anything running at the time you took the 12.4V reading? Terminal voltage is only a guide to charge level, and only then under no load with the battery rested for a few hours. If anything were running this would explain the 12.4V.
    By the same rule the terminal voltage is automatically higher during charging hence the apparent rapid charge in the morning.
    Your batteries are probably fine. If it worries you then fit a Nasa or Victron Battery monitor. The Nasa is probably best for a novice battery watcher. You can scrap the telly and just watch the battery monitor:D
     
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  3. Jaws

    Jaws Funster Life Member

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    12.4 v is fine.. After several hours with 300w of solar panel power going in to my 290aH worth of batteries that is pretty much what I would expect unless it is a reasonably sunny day.....
     
  4. CJB

    CJB Funster

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    So without a battery monitor there is no real way to see how much charge is left in a battery.

    Also am I correct in saying that a battery should not be discharged more that 50%.
     
  5. andy63

    andy63 Funster

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    Hi cjb I think a batt monitor is the best solution for keeplng an eye on leis batt usage. Fitted a sterling power management panel ln mine and it displays batt voltage and shows the amp hour usage.
    Ive also read that 50% discharge on lead acid batt is about as much as you should to get the best life out of them. Its important not to leave them in a discharged state for any length of time
    do you have a good multi stage charger that charges them when on hook up....??
    ta andy
     
  6. Jaws

    Jaws Funster Life Member

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    Interestingly a true leisure / marine battery is advertised as a deep discharge unit.. Actually there is not really such a thing unless you go to traction batteries.

    This from a well known source:

    I do not agree wih everything this particular company say on their faq ( some is a little dated for some reason ) but the above is spot on.. So a 50% discharge is the safe bet
     
  7. mitzimad

    mitzimad Funster

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    if you were taking battery voltages with the solar panels in operation you are probably measuring the charge voltage, batteries need to be left after charging to get a true reading which may explain the diffence in voltage from day and night time readings
     
  8. CJB

    CJB Funster

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    So how does everyone else tell how low their batteries are when they are off grid?
     
  9. Daz n Tina

    Daz n Tina Funster

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    when all my electrics go off I know my batteries are flat
     
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  10. PhilandMena

    PhilandMena Funster

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    Nothing to worry about here! All sounds normal. If batteries are in use you will see a voltage drop, so 12.4 V sounds OK. It's only after the batteries are rested after being used you get an indication of the amount of power left and the reading will climb depending on how much power has been taken from them.

    You are correct in not letting your batteries fall below 50%. 20% would be even better, if possible. (Battery life is governed by number of cycles and the manufacturer should state how many cycles at what ever % so you have an indication of what to expect from your battery).
    You will find this guide attached of great help: http://www.campingandcaravanningclub.co.uk/helpandadvice/technicalhelp/power/your-leisure-battery/

    Incidentally, Banner batteries are the dogs bollo*ks.
     
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  11. PhilandMena

    PhilandMena Funster

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    Whoops missed this question. Simple, use a volt meter (£14.00 approx) assuming there is no direct reading from your control panel. The attachment in my previous post will provide you with the information you require.
     
  12. CJB

    CJB Funster

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    Thanks for all replies. I have read some more information on the charge / discharge if 12V batteries, it is much less straight forward than I had thought. Perhaps I will go for a Battery Monitor!!
     
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  13. mitzimad

    mitzimad Funster

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    same cost efficent method i use although its never happened since i bit the bullet and bought trojan batteries
     
  14. pappajohn

    pappajohn Funster Life Member

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    2) How did they charge so quickly?

    They dont....what you measured was the solar input voltage.......and the same would happen on hookup, charger voltage.

    If you had jumped on the roof and covered the panel the battery would have shown its true voltage after a short while.
     
  15. dave newell lvs

    dave newell lvs Trader-Vehicle Services

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    What you need to understand is that voltage readings are a very crude and rudimentary measure of state of charge. 12.4 is fine for a battery in service. If you want to use voltage as a rough guide then 14 is full, 12 is 50% and 10 is completely dead but as I said voltage is a crude measure. When a fully charged battery (12.7 volts after standing with no load for 24 hours) is put under load ( say some lights or the water pump is on) then it will show a lower voltage, possibly 12.4 for example, switch the load off and it will soon resume to 12.7. Likewise and as PJ said when your meter was showing 12.9 it was showing the charging voltage coming from the solar, not the true battery voltage. Think of your battery(ies) as a fuel tank, but its a fuel tank whose capacity varies depending on how fast you draw fuel out of it, the faster you drain it the less capaclty it has.

    D.
     
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