Feasible to use 3 panels instead of 2 or 4? 48 volt system.

softdown
softdown Solar Expert Posts: 3,985 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
Say “45 volt” panels. Currently I only see 45 volt output or 135 volt output when employing three 50 volt panels. 

When does voltage become significantly “inefficient” for a 48 volt system?  135 volts too much? 
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,152 ✭✭✭✭✭
    #2
    That all depends on charge controller type and voltage range some of the charge controllers in the all-in-one inverters wouldn't even accept 135 volts is being too low so we need to know what charge controller you're using

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • softdown
    softdown Solar Expert Posts: 3,985 ✭✭✭✭
    edited August 7 #3
    Considering this one:

    POWLAND 80A MPPT Solar Charge Controller,12V/24V/36V/48V Auto,Max Input 150V LCD Display


    Almost no way the very inexpensive, light weight charge controllers are going to last for years and years. But I only need additional solar for 2 months out of the year right now. I need to pare down my freezing and refrigeration demands. Takes a long time to empty a freezer.

    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,152 ✭✭✭✭✭
    edited August 8 #4
    At 135 volts open circuit you getting dangerously close to the Charge controllers maximum limit so if you have cold cold weather where you are I wouldn't recommend three in series but why don't you go 2s2p, two in series twice with  your four panels

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • softdown
    softdown Solar Expert Posts: 3,985 ✭✭✭✭
    #5
    littleharbor2 said:
    At 135 volts open circuit you getting dangerously close to the Charge controllers maximum limit so if you have cold cold weather where you are I wouldn't recommend three in series but why don't you go 2s2p, two in series twice with  your four panels
    40 volt panels so margin of safety.
    No room for 4 panels due to roof adjoining sunroom.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,152 ✭✭✭✭✭
    edited August 10 #6
    45 volts open circuit* 3 equals 135 volts at 75° F you put those in cold temperatures like you were talking (-21 f) about they're going to burn up your charge controller

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • softdown
    softdown Solar Expert Posts: 3,985 ✭✭✭✭
    #7
    I was guessing at the 45 volts. I have 35 and 40 volt panels. Assumed that the larger panels would be higher voltage. They are lower voltage. 

    I said 40 volts on Aug. 9th post. 
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,702 admin
    #8
    With electrical/electronics... "No Guessing"!

    -Bill  :)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • softdown
    softdown Solar Expert Posts: 3,985 ✭✭✭✭
    #9
    Good point. I’m trying to schedule knee surgery. Climbing ladders can be onerous. Made sense, to me, that panels that are 25% larger would be higher voltage. A clear mistake in retrospect. 

    Now I don’t think there is any way to approximate panel specifics without looking at the information label on the back. Which the sun may have eroded fwiw.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
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