voltage readings

higgins
higgins Solar Expert Posts: 56 ✭✭✭✭
in Solar Beginners Corner #1
I have a 20 watt polycrystalline panel,10 amp charge controller PWM type,12 volt
86 Ah battery new from last week and an 12 volt 11 watt energy bulb.When i first got the battery i measured it with a digital multimeter before and after resting the reading was 12.80 .I connected everything up and used the bulb to discharge the baterry for a while and left the panel connected although not sunny,it shows the battery's voltage was rising.After a couple of days i'm getting readings of 14.plus so i put the bulb on for a few hours but i still have high readings even though the panel has stopped charging because it's dark,is this normal or could the multimeter be giving a false reading?
Higgins:blush:
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #2
    Re: voltage readings

    Could be false reading. Unplug everything from battery, then measure it again. Then connect light bulb while measuring battery voltage. Then connect charge controller while dark outside and measure battery voltage again. Note any changes in battery voltage.
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #3
    Re: voltage readings

    Have disconnected CC as my light load is connected and controlled through that,i've noticed the multimeter's baterry is low(could this be the cause?),anyway just connecting to the battery now the reading i am getting is 14.56!:confused:
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #4
    Re: voltage readings

    To further confuse me the CC was displaying a low voltage status led while multimeter and light was still on,the reading was 14.2!
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #5
    Re: voltage readings

    Would not be the first meter that failed with strange readings... I assume the meter is correctly setup and leads plugged in the correct locations. You are measuring the battery voltage right at the battery posts and not somewhere else.

    Try connecting the meter to a car battery and see what you read. When charging you will probably see somewhere between 13.8 and 14.2 volts.

    Turn off the car and turn on the head lamps, and you should see around 12.5 volts or less.

    The only other question I may have is the sizing of the wiring... It is possible with small gauge wire and/or long wire runs that you have voltage drops that cause issues too.

    With a reasonable load on a 12 volt (6 cell) battery, there is no practical way it can read over 13 volts with no charging currents going into the battery while driving a load (after the "surface charge" has been dissipated by resting and/or loads)...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #6
    Re: voltage readings

    well i am suspecting the multimeter,it still reads 14.56 after some 20 mins or so,i'm going to measure a few other batteries and see what readings i get,oh yes it is connected to the battery posts!
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #7
    Re: voltage readings
    higgins wrote: »
    To further confuse me the CC was displaying a low voltage status led while multimeter and light was still on,the reading was 14.2!

    Your multimeter is bad. CC showing low voltage is most likely correct.
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #8
    Re: voltage readings

    I have measured a 9 volt battery and got a reading of 9.24 volt,so i have put the light load back on for now to run the battery down will measure it again after an hour or two.This is an abnormal reading as far as i'm concerned,i have seen those readings when a charger is plugged in and connected but there is nothing charging it and it has been a dull sort of last couple of days so i'm stumped for now,
    Higgins
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #9
    Re: voltage readings
    higgins wrote: »
    I have measured a 9 volt battery and got a reading of 9.24 volt,so i have put the light load back on for now to run the battery down will measure it again after an hour or two.

    Don't do that, your battery is already dead as reported by your charge controller. Find another multi meter.
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #10
    Re: voltage readings
    AntronX wrote: »
    Don't do that, your battery is already dead as reported by your charge controller. Find another multi meter.
    have connected the CC and light back,switched the light bulb on CC status led is green for normal full battery,i think the multimeter is playing up here but why,could a low battery in the multimeter cause this reading even though i got a normal reading on a 9 volt battery?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #11
    Re: voltage readings

    This is a 6 cell battery--correct?

    Some folks wire up 14 volt (7 cell) battery packs for running video cameras, sail plane avionics (and even that is debatable as to needed or not), etc.

    You don't have an AC wall mount transformer/charger wired in somehow as backup--and it is still turned on?

    The batteries are based on physical chemistry--so they should be operating on Lead Acid principles... This is not some other battery chemistry is it? (NiCad, NiMH, etc.)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • AntronX
    AntronX Solar Expert Posts: 462 ✭✭
    #12
    Re: voltage readings
    higgins wrote: »
    have connected the CC and light back,switched the light bulb on CC status led is green for normal full battery,i think the multimeter is playing up here but why,could a low battery in the multimeter cause this reading even though i got a normal reading on a 9 volt battery?

    Yes, low battery could cause bad readings. Or your multimeter could be not calibrated right and add 2 - 3 Volts to the readings. A lead acid battery will not be over 13V when not being charged. Normal resting voltage is usually 12.5 - 13 V.
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #13
    Re: voltage readings

    This is a standard 12 volt six cell leisure battery of the sealed lead acid type,bought new last week,
    Higgins
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #14
    Re: voltage readings

    just took a reading after the light been on for a while reading showed a drop at 13.67 but then reading started to rise until as i look now it's14.04 and still rising!What could be causing this?
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  • higgins
    higgins Solar Expert Posts: 56 ✭✭✭✭
    #15
    Re: voltage readings

    Well the culprit turned out to be the digital multimeter's low battery,i put a fresh battery in and i am getting normal readings of 12.79,:D
    Higgins.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #16
    Re: voltage readings

    DVM battery--who would have thought? :roll: :D

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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