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Different voltage displays on different charge controllers on same battery

Discussion in 'General Electronics Discussion' started by VictorAdebayo, Jan 4, 2021.

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  1. VictorAdebayo

    VictorAdebayo

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    Dec 14, 2020
    Dear Forum, my solar system is fixed with a 30amp SunMateSolar charge Controller and a 200amhr 12 volt battery. When the bars are full on the SunMate Solar (SMS) Controller it displays 12.7 volt as full battery. I have an idle smaller 20amp Controller, if connected to battery for testing(I don't have a digital tester), it displays 12.9 volt as the same battery voltage. I use gel battery.Which one is correct please and why the difference? Hope nothing is going wrong here then?
     
  2. Martaine2005

    Martaine2005

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    May 12, 2015
    Nothing is wrong and they both seem fairly accurate.
    Average it as 12.8V.
    Unless either unit has been properly calibrated, you won’t be able to tell which is closer to actual battery voltage.
    But 12.7V vs 12.9V, I’d be happy with either.

    Martin
     
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  3. VictorAdebayo

    VictorAdebayo

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    Dec 14, 2020
    Oh ! Ok. Thank you. I have been worried, probably thinking one is overcharging and or one is under-functioning
     
  4. Martaine2005

    Martaine2005

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    May 12, 2015
    Nothing to worry about.
    Even the same two meters will vary slightly.

    Martin
     
  5. dave9

    dave9

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    Mar 5, 2017
    I'd guess that the latter charger is applying current to the battery while taking the reading to result in the 0.2V higher value. You could check this with a multimeter.

    If it is constantly supplying an extra 0.2V, that could result in shorter battery life long term from trickle charging more than it needs to. Considering the amount of this 0.2V, I wonder what would happen if you put a schottky diode in series... I mean besides it taking longer to charge. ;)
     
  6. VictorAdebayo

    VictorAdebayo

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    Dec 14, 2020
    Thank you for your suggestion. I am trying to get a digital multimeter to no avail. The analog one I have is not helping matters. The reading during the day while charging are between 13.5(+ 0.2) to 14.3(+0.2). As I said, final settling of the battery at night is 12.6(+0.2)/12.7(+0.2).
     
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