pv volts

whitetiger32whitetiger32 Registered Users Posts: 4 ✭
in Off Grid Solar & Battery Systems #1

I have nine 370 watts monopolarise solar panels,midnite classic 150 controler and a Schneider 6848 xw+

inverter and 8 deka 8g8d/t975 gel batteries.my problem is that,when I turn on

the pv breaker my midnite volts in  numbers decrease and when I turn it off they go up

any body know why that happen? im a noobie on this.i will appreciate any help.thanks a lot.
everything was working fine before.


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  • EstragonEstragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
    It may help if you could post the numbers (ie pv in voltage goes from what to what?), and what the battery voltage is.

    Assuming the voltage drop is not huge, it may just be the normal operation of the classic.  It picks the best combination of amps and volts for max watts.  This almost always means voltage will be lower than open circuit.
    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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  • whitetiger32whitetiger32 Registered Users Posts: 4 ✭
    edited January 2019 #3

    the battery voltage was like 51.2 and the volts in drops from 110 to 98,97.

    thanks for your answer. any other suggestion? 


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  • whitetiger32whitetiger32 Registered Users Posts: 4 ✭
    #4
    im new on this site and I love it already
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  • EstragonEstragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #5
    Yes, at that battery voltage, that order of magitude drop in pv voltage would be quite normal.

    Assuming you have panels in a series string of 3, that would be a panel open circuit voltage (Voc) of ~ 36-37v ~ typical for that size panel in full sun with no load.  Under load, the voltage at max power (Vmp) of ~ 33v sounds right.  You could check panel specs for Voc and Vmp, but they sound about right.

    In a "normal" climate, I'd expect each string to put out roughly 370w x 3 x .75 = 833w, ÷ ~100v = 8.3a into the controller. An mppt  controller like a classic bucks that down to battery voltage, so roughly 833w x .95 ÷ 51.2 = 15.5a per string into the bank.

    In a cold climate, with a bit of wind, voltages would be a bit higher.  Warmer /no wind, a bit lower.  My climate is pretty severe, and voltages are ~ +/- 15% between summer and winter.  The spread between Voc  and Vmp stays about the same (10%ish) though.
    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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  • whitetiger32whitetiger32 Registered Users Posts: 4 ✭
    #6

    thanks for the imfo.i didn't answer before because my internet was down for a few days and I

    was waiting for the cable company to fix it thanks a lot.

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