Inverter and CC battery voltage reading

Masterjoe
Masterjoe Registered Users Posts: 86 ✭✭
in Solar Beginners Corner #1
Does it make a difference if the inverter and CC read the battery voltage .1 to .2 volts off? For example inverter reading 25.4 and CC reading 25.2? Thanks
4.5kw 24v System
18 Solartec 250w polycrystalline panels
Xantrex XW4024 Inverter/Charger
Conext MPPT 80-600 Charge Controller
12 Trojan L16G-AC 20 hour 390ah batteries tied in 3 strings at 1170ah total
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    If you are referring to two separate measuring devices, inverter and CC, there would be decrepancy as they, the inverter in particular, is not a precision reading, usually rounding off to the next decimal point, so 25.44 would be 25.4 and 25.46 would be 25.5. To get an accurate assement, use a digital meter to read both points, if the inverter is turned on you would likely see a slightly lower reading athe inverter, which will drop futher under load.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • MichaelK
    MichaelK Registered Users Posts: 236 ✭✭✭
    #3
    I agree that the measurements need to be made with a multimeter.  With my own system I see a bit of variation of the readings of one device versus another.  With a multimeter, if you still see differences, that would suggest to me that your wiring is too small a gauge and you are getting a bit of voltage drop.  Can you say offhand what size wire you're using?
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #4
    The main issue with the different reading is charging may not be getting done properly.  For example, if the controller thinks voltage higher than it really is at the battery posts, it will go to absorb and float at lower actual voltages, which could lead to undercharging.  Same problem if you use an inverter to charge, but less so as you would normally only bulk charge that way.

    Some inverters and charge controllers have a setting to compensate for this.  You would take a reading at the battery terminals and at the controller output posts when in bulk, and enter the difference in the offset setting.  Also, some charge controllers have voltage sense wires that connect to the battery independent of the big charging cables to avoid the issue.  

    If the offset is more than a couple tenths of a volt, it would be worth checking and retorquing connections, and looking at wire size and length.  
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • Masterjoe
    Masterjoe Registered Users Posts: 86 ✭✭
    #5
    No I can’t I’ll have to ask my installer. I’ll post updated information soon. Thanks all for the help.
    4.5kw 24v System
    18 Solartec 250w polycrystalline panels
    Xantrex XW4024 Inverter/Charger
    Conext MPPT 80-600 Charge Controller
    12 Trojan L16G-AC 20 hour 390ah batteries tied in 3 strings at 1170ah total
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  • MichaelK
    MichaelK Registered Users Posts: 236 ✭✭✭
    #6
    It might be a good time to point out that there are aspects of your system that appear to be seriously unbalanced.  You have a 1170AH battery bank with 3 strings of L-16s.  More than 2 strings is never a good idea.  Three will result in ruined batteries if you don't manage them very, very carefully.  Conventional wisdom about charging lead-acid batteries is to charge them at between 1/8 to 1/12th of the stated capacity, written in shorthand as C8 to C12.  1170/12= 97.5amps  1170/8=146.25amps.  Multiply that 29.6V = 2886 to 4329 watts.  Your Conext 80-600 can only put out a maximum of 80 amps of charging current, or roughly half of your solar capacity.  It seems to me that you'd need a second Conext controller to supply enough amps to properly charge that size battery bank, and really utilize your array.  What kind of configuration are your panel wired into?

    You can possibly get around this somewhat by periodicly isolating individual 24V strings and charging/equilizing them separately, one at a time.  A better way to have accomplished this is to use 2V L16s.  A single string of 12-2V L16's would have to same capacity as your three strings, but there would be no resistance inequilities to deal with.  I am surprised that a system this large is tethered to a 24V system voltage.  My system is about the same size as yours, but I'm operating at 48V.
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
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  • pdh
    pdh Registered Users Posts: 31 ✭✭
    #7
    > Does it make a difference if the inverter and CC read the battery voltage .1 to .2 volts off? For example inverter reading 25.4 and CC reading 25.2?

    That's a difference of just under 1%, which is probably within the error tolerance for those displays.
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