chrage controller amps

DConlyGuy
DConlyGuy Registered Users Posts: 80 ✭✭
in Solar Beginners Corner #1
i have switched to 24 volt systems and now the best amps i can get is 10 amps, instead of the 20 plus at 12 volts. is that normal when you move up in volts the charge controller put out less amps?
600 watts of solar panels,Epever 30 mppt , 2 PWHR12500W4FR battery's in 24 volt setup
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    edited February 2017 #2
    The basic math (would be nice if I could get basic math right--Fixing below--BB edit):
    • 400 watts * 0.77 panel+controller derating *1/29.0 volts charging = 17.9 amps (typical best case maximum on clear/sunny noontime day)
    • 400 watts * 0.77 panel+controller derating *1/24.0 volts charging = 21.6 amps if battery is very discharged (i.e., charging at 24 vdc and less than 50% state of charge)
    • 400 watts * 0.77 panel+controller derating *1/29.0 volts charging = 10.6 amps (typical best case maximum on clear/sunny noontime day)
    • 400 watts * 0.77 panel+controller derating *1/24.0 volts charging = 12.8 amps if battery is very discharged (i.e., charging at 24 vdc and less than 50% state of charge)
    I would expect you to have 1/2 the current when moving from 12 volts to a 24 volt system (power=volts*amps --- I.e., 2x the voltage and 1/2 the maps gives you equal power).

    If your battery is "mostly" charged, then the MPPT controller may be in "absorb" mode--I.e., holding a constant charging voltage (29.0 volts) for 2-6 hours, then the current is not limited by the panels or the controller--it is limited by the battery bank.

    If your battery state of charge is less than ~80% SoC, and your battery voltage is less than ~29.0 volts, then the controller should be in "bulk charging" mode--And the controller will be taking the maximum amount of power from the solar array and outputting the maximum amount of current into the battery bank.

    More or less, ~10 amps (fixed BB) would be the average best case current flow I would expect from a well running system into a discharged battery bank. If you are getting ~5 amps (fixed BB) or less, then there is something not right (into discharged battery bank with full noon-time sun).

    What is the charging voltage and the battery bank's specific gravity? What is the charging voltage at the controller vs at the battery bank terminals (looking for excessive voltage drop on the controller DC cables)? What are the Vpanel and Ipanel numbers?

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • DConlyGuy
    DConlyGuy Registered Users Posts: 80 ✭✭
    #3
    on your second line of your post you are right, i just went and put the 12 volt battery back on it to see and poof there was the 20 amps at 12 volts. think ill have to add 300 more watts of panels to get what i want out of the charge controller at 24 volts. to answer you other questions im only getting 270 watts out of my 400 probably not best aligned since they are fixed usally get 38 volts out of the panels and no sg's to give as i came across 2 of these PWHR12500W4FR to try out  24 volt system with
    600 watts of solar panels,Epever 30 mppt , 2 PWHR12500W4FR battery's in 24 volt setup
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #4
    DConlyGuy,

    Sorry--I had a calculator/brain breakdown... I multiplied my numbers by x0.77 instead of divide by /0.77

    In any case, it looks like your system is working 100% correctly.

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