first timer

Sarah
Sarah Registered Users Posts: 9 ✭✭
in Solar Beginners Corner #1
Hey Everyone, Glad I found this site :) I have 3 *  24 v panels 200 watt and PWM controller 50 a. My question is should I keep the controller near the solar panel or battery for better efficiency ? The distance between the solar panel and battery is 40  feet. Also , Which size wires should i use? My load will be ( 2 )  12v air coolers connected directly to battery. Sorry for asking such a basic question, but this is my first time working  with solar.
Thanks in advance
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #2
    Welcome to the forum,

    put the controller near the battery.  Make sure you have a DC circuit breaker between the controller and the battery.

    Since you are using 24 volt panels with a 12 volt battery, you are missing out on at least half of your potential power.  You would benefit greatly from an MPPT controller such as the Midnite Kid.

    Your three panels need to be combined (near the panels) with a combiner box and a circuit breaker for each panel.  The combined output then runs to the controller.   I need the specs on the panels to advise you on the wire size. 

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #3
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  • softdown
    softdown Solar Expert Posts: 4,034 ✭✭✭✭
    edited August 2016 #4
    These stringent calls for the DC circuit breaker between the controller and battery bank seem to be relatively new. Sure does make a lot of sense though. With an FM80 on a 48 volt system, what size circuit breaker would be called for? I'd try to research the question myself but working on other projects at the moment.

    Perhaps cruising our hosts web site will point me to the right one...

    EDIT: Thinking the FM80 has circuit breakers built into it...

    Another point....the majority of the circuit breakers require "rack mounting" in a circuit breaker box. If we are going to recommend a single circuit breaker....perhaps we should point to a circuit breaker that can operate as a stand alone?


    vtmaps said:
    Welcome to the forum,

    put the controller near the battery.  Make sure you have a DC circuit breaker between the controller and the battery.

    Since you are using 24 volt panels with a 12 volt battery, you are missing out on at least half of your potential power.  You would benefit greatly from an MPPT controller such as the Midnite Kid.

    Your three panels need to be combined (near the panels) with a combiner box and a circuit breaker for each panel.  The combined output then runs to the controller.   I need the specs on the panels to advise you on the wire size. 

    --vtMaps

    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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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
    Sarah,
    Those are unusual panels.  Most 60 cell panels have a Vmp about 30 volts.  Anyway, it's good news for you because the lower voltage with higher current is better utilized by your PWM controller. 

    By the way, those are NOT 24 volt panels.  A 24 volt panel has a Vmp high enough (about 36 volts) to charge a 24 volt battery with a PWM controller.

    This would be a good combiner:  https://www.solar-electric.com/mnpv3.html
    You would also need three of these: https://www.solar-electric.com/mnepv.html  in the 15 amp size.
    One of these, mounted on the combiner box, can be a real lifesaver: https://www.solar-electric.com/suprdemn.html

    You combined current would be almost 26 amps.  Over a 40 ft distance you would have a 3.5% voltage drop with #6 copper cable, or a 2.2% drop with #4 cable.  You will need a DC circuit breaker (50 amps) on the PV input to the controller.  This is not for safety, but rather serves as a switch.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
    softdown said:
    These stringent calls for the DC circuit breaker between the controller and battery bank seem to be relatively new.
    New to you.  They have been around since the first safety codes were written.  ANYTHING and EVERYTHING connected to a battery must have OCP (over current protection = fuse or circuit breaker).
    softdown said:
    With an FM80 on a 48 volt system, what size circuit breaker would be called for?
    What size cable?  The OCP must be able to protect the cable.  When controllers fail, they may become a short circuit across the battery.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • softdown
    softdown Solar Expert Posts: 4,034 ✭✭✭✭
    #7
    4/0 copper is used for all battery connections. I am surprised at how much I have forgotten during my hiatus.

    Safety and not wanting to blow things up are the reason that I had a solar pro finalize the connections. He said that I did a "perfect job". Opinions would vary greatly of course. I've seen pictures of solar installs that looked to have costs up upwards of $60,000. Kriminy.
    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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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #8
    Thanks , Great Group 
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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #9
    Fast question, if I use a smaller wire like a 3 awg ,will it be safe until I get a 6 awg wire since 3 awg is still in the ampere range of my panels. Hope that makes sense.
    Thanks in advance
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #10
    Sarah said:
    Fast question, if I use a smaller wire like a 3 awg ,will it be safe until I get a 6 awg wire since 3 awg is still in the ampere range of my panels.
    3 awg is much heavier than 6 awg.  It is a better choice than 6 awg or 4 awg.  The maximum amps allowed through 3 awg wire depends upon the insulation and temperature, but it's at least 85 amps.  You will not come close to that, but the issue is not ampacity, but voltage drop.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #11
    What size breaker do i need between the controller and the Battery?
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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #12
    As for the breaker between the panels and controller I got it :) 50 a, the same as the controller.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #13
    Sarah said:
    What size breaker do i need between the controller and the Battery?
    Depends on the wire.  If your controller fails and becomes a short circuit on the battery, you want the breaker to trip before the wire catches its surroundings on fire.   Assuming your battery cable is at least #6 or thicker, a 50 amp breaker would be OK... your controller is rated to 50 amps and your array will be hard pressed to put out 30 amps.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #14
    Got it, Thanks :)
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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #15
    Just double checking, don't want to burn down the house :)  need basic help with breakers. Can anyone please comment on:

    • Should the  Breaker from Solar to Controller  be the same ampere as the controller and placed closer to panels?
    • Should the Breaker from controller to batteries be the same ampere as the controller and placed closer to the batteries?
    • Do I need a breaker between battery and Inverter, if so how do I know which size breaker I need , what is the purpose? :|

    I am an old lady learning something new, so please be as simple as possible. 

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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #16
    Sarah said:
    Should the  Breaker from Solar to Controller  be the same ampere as the controller and placed closer to panels?
    Breaker from PV to controller should be near controller.  It's purpose is to be a switch... it's not for safety.  As long as your cable is large enough to handle the full power of your panels, the cable doesn't need to be protected from overcurrent.

    Most controllers must be powered up by connecting to the battery BEFORE connecting to the PV.  To power down you must disconnect the PV BEFORE disconnecting the battery.  You connect or disconnect by having a switch (breaker), mounted next to the controller.  The breaker should be large enough that the PV current can never trip it... 50 amps would work for you.  
    Sarah said:
    Should the Breaker from controller to batteries be the same ampere as the controller and placed closer to the batteries?
    The breaker between the battery and the controller is very important for safety.  50 amps will work for that also.  It should be close to the battery.  The battery cables should leave the battery box in conduit.  The conduit runs to the electrical box with the breaker.
    Sarah said:
    Do I need a breaker between battery and Inverter, if so how do I know which size breaker I need , what is the purpose?
    The purpose is safety.  ANYTHING and EVERYTHING connected to a battery must have OCP (over current protection = fuse or circuit breaker).  The size breaker depends on how much current your inverter draws, and the size of the cable you are protecting.

    Most inverters come with instructions for cable and fuse size.  What inverter are you planning to use?

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Sarah
    Sarah Registered Users Posts: 9 ✭✭
    #17
    Thanks so much for your clear answer. Inverter 1500 watts 
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