Pv voltage drop

mountainman
mountainman Registered Users Posts: 439 ✭✭
in Caravan, Recreational Vehicle, and Marine Power Systems #1
With a 3% voltage drop on pwm using a panel vmp of 17.4.  20 foot on 8 gauge gives me 16.87 volts compared to a panel with 18.9 vmp on 70 foot run about  10% drop gives me 17 volts according to calculator voltage drop.net. If with pwm the battery regulates voltage and any thing above that is just lost would a 3% drop on a 18.9 panel give me more amps or watts compared to a 10% drop? 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    The volt drop is due to the resistance of the conductors, which results in lost energy dissapated as heat, but in order to create heat there needs to be current to complete the equation, power equals voltage multiplied by current (P = V × I )  so if there was a 2 volt drop at 10 amps the power lost would be 20 watts, obviously as the volt drop increases so dose the power loss. This is why it's important to keep the volt drop to a minimum, regardless wether the PWM controller pulls the voltage down, the losses will still occur in the conductors resulting in lower output.
    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.  
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  • NANOcontrol
    NANOcontrol Registered Users Posts: 276 ✭✭✭
    #3
    This question comes in conjunction with why panels are 18V and my battery is 12V. While you may loose 20W, It probably has absolutely  no effect on charging. It isn't going to effect charging until the voltage at the charger drops below what the battery needs. Lets say worst case is 1V loss in the charger, 2V in lead loss gets you to needing 17.5V at the panel.  Of course panel volts will drop when they get hot in the sun.  However, it is unlikely the battery will draw 10A at 14.5V unless you have an external load. With PWM you have no way to measure the voltage drop with just a meter as it will likely be pulsed.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #4
    So if that is the case, why not use the lightest gauge of wire available, with no current shouldn't be a problem, but wait the battery is discharged, example 11V and needs current, all of a sudden the current demand is 10A, hypothetically speaking, the wire now becomes a fuse, because it's incapable of supporting such currents, why?,volt drop rears it's ugly head, 
    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.  
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #5
    The reason for my question I had to go 70 foot 9.5% drop on 8 gauge because of a pecan tree. Now a storm has taken the tree down.Anyway if I shorten to 35 ft and by parralleling 8 gauge cables I can get 2.5% drop. With 400 watts I'm seeing 308 watt 22 amp peaks with a 250 watt load. For short periods on cloudy days 340 and 24 amps.So can I expect a 7% increase in amps and watts. 9.5% -2.5%
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #6
    There will be a reduction in losses which will improve overall output potential, the percentage of which will be determined on losses not overall production, reducing the volt drop will be benificial especially on hot days when panel voltage drops, 9.5% is too much 2.5% is much better, you may not notice a dramatic increase in overall output, but will have the peace of mind that in extreme conditions the system is designed to minimize potential problems associated with volt drop.
    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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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #7
    Thanks mcgivor you gave me an  answer I can understand.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • NANOcontrol
    NANOcontrol Registered Users Posts: 276 ✭✭✭
    #8
    Do you? There is no technical reason to change the existing wiring.
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #9
    In winter there's no reason to change wire in summer I can see where voltage drop can be a concern when it's 100 degrees. A 2 volt drop puts me at 16.9 volts factor in temp coefficient of my panels and I can barely Equilize at 15.5
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #10
    Nano if I had to cut the tree the wind took down  or buy the biggest wire I wouldn't. But since I can double the wire I have at half the distance and get some extra watts by digging a hole. Time for the shovel 
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #11
    mountainman said:
    Nano if I had to cut the tree the wind took down  or buy the biggest wire I wouldn't. But since I can double the wire I have at half the distance and get some extra watts by digging a hole. Time for the shovel 
    Sounds like a lot of work to me. I'd be very tempted to save the $ of the wire, and just slap another panel in parallel.
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #12
    Problem is my 30 amp controller is maxed out at 400 watts . I'd have buy another controller and panel. My panels are on a pole I can remove with one bolt. Cut the wire I have and parralle them.then dig a 3 ft hole.
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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  • Plucka
    Plucka Registered Users Posts: 130 ✭✭
    #13
    I had solar output suddenly drop to 9.5 volts and no amps -was faulty mc4 connector
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  • mountainman
    mountainman Registered Users Posts: 439 ✭✭
    #14
    Mine still had full voc 22.4 but only .9 amps
    2kw array 6 345 q cells  make sky blue 60 cc
     6 230ah GC @36 volts 
    18 amp accusense charger. 3650 champion 
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