PLEASE help!

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greenthumb76
greenthumb76 Solar Expert Posts: 40 ✭
in Solar Beginners Corner #1
I just bought this 15A controller, and will be attaching it to my 110 watt solar panel array (on 10 & 12 awg wire) and to my batteries (on 4 awg).

Unlike my previous controller, this one has no leads, so I will need to make short leads myself (4 awg wire will not fit into the small holes).

(40 watts of solar panels on 12awg and 70 watts of panels on 10awg join just before a 20A ATC fuse.
Then about 6" of wiring that came with the fuse holder (12g?) will attach the fuse holder to the solar controller lead that I make.
The batteries are on 4 awg and there is no fuse between the batteries and the controller).


My questions are:
    will it be ok to make each of the leads from about 4-6" of 12awg wire?
  1. Where can I find info on the correct gauge wire to use with a fuse (so the wire I use doesn't act as a fuse instead?)?

Thanks for your help!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: PLEASE help!

    110 Watts of panel total? No worries: @ 14.2 Volts charging and 77% efficiency it probably won't exceed 6 Amps. 10 is clearly the upper limit here, not 20 Amps.

    You could almost wire that with 18 gauge lamp cord. :p

    You wouldn't need 4 gauge going from the controller to the battery at all, and there's no trouble joining your two array leads into one either.

    Also, that array won't charge much of a battery; it might keep a 100 Amp hour going with mild usage.
    Expectations: 110 Watts @ 77% = 84.7 / 14.2 Volts charging = 5.9 Amps likely peak output.
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  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    #3
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    Re: PLEASE help!
    greenthumb76 wrote: »
    I just bought this 15A controller, and will be attaching it to my 110 watt solar panel array (on 10 & 12 awg wire) and to my batteries (on 4 awg).

    Unlike my previous controller, this one has no leads, so I will need to make short leads myself (4 awg wire will not fit into the small holes).

    (40 watts of solar panels on 12awg and 70 watts of panels on 10awg join just before a 20A ATC fuse.
    Then about 6" of wiring that came with the fuse holder (12g?) will attach the fuse holder to the solar controller lead that I make.
    The batteries are on 4 awg and there is no fuse between the batteries and the controller).


    My questions are:
      will it be ok to make each of the leads from about 4-6" of 12awg wire?
    1. Where can I find info on the correct gauge wire to use with a fuse (so the wire I use doesn't act as a fuse instead?)?

    Thanks for your help!

    Just remember that the wires must be able to handle more current than the fuse/breaker that is set to protect them. So for the #4 gauge wire you're ampacity rating would likely be 70-95amps (depending on what kind of wire, and before any deratings for temperature and conduit fill). Your #10 wire would be 30-40amps (before derate), and #12 would be 25-30amps before derate. If you're not sure of the wire type, I would assume lower ampacity and size your breaker/fuse accordingly. The way you describe it, it sound like your two PV panels are wired in such a way that you would need to size this fuse/breaker to protect the #12 wire (since it is the smaller of the two).

    What kinds of ambient temperatures will the wires be exposed to, any heat sources nearby (like a rooftop), are they to be in conduit... etc? These factors will all combine to derate the safe current carrying capacity of your wires to as little as 33% in some cases.
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  • phred01
    phred01 Solar Expert Posts: 35 ✭
    #4
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    Re: PLEASE help!

    If there is room put a circuit board brass pin of the correct hole size then solder a 4 gauge wire to it. If the wire breaks then solder it to the pin again thus saving any damage to the hole. Btw a short under gauge wire is ok but don't keep the supply and return wires too close as will radiate any temperature increase due to the current flow
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  • greenthumb76
    greenthumb76 Solar Expert Posts: 40 ✭
    #5
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    Re: PLEASE help!

    Cariboocoot,
    I followed what you said, except for this:
    and there's no trouble joining your two array leads into one either.
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  • greenthumb76
    greenthumb76 Solar Expert Posts: 40 ✭
    #6
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    Re: PLEASE help!

    Phred,
    Thank you. I followed what you were saying about the wires being close together, but don't understand what you're getting at here:
    phred01 wrote: »
    If there is room put a circuit board brass pin of the correct hole size then solder a 4 gauge wire to it. If the wire breaks then solder it to the pin again thus saving any damage to the hole.
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  • greenthumb76
    greenthumb76 Solar Expert Posts: 40 ✭
    #7
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    Re: PLEASE help!

    hillbilly,
    you lost me here:
    I would assume lower ampacity and size your breaker/fuse accordingly.
    how does one size a fuse accordingly? To protect
    and #12 would be 25-30amps
    would I use a 25 or 30 amp fuse, or . . . ?

    What kinds of ambient temperatures will the wires be exposed to
    , Outdoor Virginia temps: Anywhere from -10 to 95F.
    any heat sources nearby (like a rooftop)
    no.
    are they to be in conduit... etc?
    no.

    Thanks for your help!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: PLEASE help!

    Reread your original post.

    You've got one 40 Watt panel and one 70 Watt panel, yes? 110 Watts total.

    Okay, both the 12 gauge and 10 gauge are over-kill for these. 12 Gauge will handle about 20 Amps and 10 gauge 30 Amps. The two panels together won't come close: 110 Watts / 17.5 Volts (typical Vmp of a "12 V" panel) = 6.2 Amps. Your 20 Amp fuse is overkill too (and no fuse is really needed here, but always a good idea).

    I take it your use of a 15 Amp controller is to allow for future expansion? Be wary of mixing different panels: parallel connections with vastly different Vmp's are inefficient as are serial connections with different Imp's. Also, more than 2 panels/strings of panels in parallel should have a fuse per panel.

    I don't see you needing 4 gauge from the charge controller to the battery even at 15 Amps (max output of he controller). My method would be to use the largest wire the controller would accommodate straight to the batteries, with a fuse (this is where your 20 Amp fuse would be, if you had enough panel to approach that level of output). Unless it is a particularly long wire run, 12 Gauge will probably handle it. If 8 AWG will fit the controller and you can get some, use that. Just be sure the fuse is no larger than the max the wire will handle.

    In short, the wire size should be large enough to accommodate the maximum current + safety margin (someone remind me again about NEC rule: 120%? 125%). The fuse should be less Amperage than the wire can handle.
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  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    #9
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    Re: PLEASE help!

    Greenthumb,
    Remember that the idea is that the fuse/breaker will blow BEFORE the wire does; thus it needs to be rated at an ampacity equal to or less than the wires ampacity. So if your wire has an ampacity of 25 amps you could in theory use a fuse of any size LESS than 25 amps (the only issue is that it must be sized large enough to handle what ever currents will be supplied by your PV, or required by your loads)

    So in the case of #12 wire taking it's 25amp rating (there are some types of wire that would have a 30amp rating, but I don't know what you have) and derate for temperature:
    Derating factors for various types of copper wire at that temp would be near 80-90% depending on the type of wire and max temp. So you're looking at a "safe" current carrying capacity of that wire being about 20-23amps. Therefore a 20 amp fuse would in theory blow before your wires get too hot from excess current flow.
    Does this make sense?

    Also you if you don't have it, may I STRONGLY recommend the following reading material http://www.solarenergy.org/bookstore/photovoltaics-design-installation-manual . It's a really good book that covers the whole system, one piece at a time and does a pretty good job of making it all fairly simple (heck, even I understood it :-) ).
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  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    #10
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    Re: PLEASE help!
    greenthumb76 wrote: »
    I just bought this 15A controller, and will be attaching it to my 110 watt solar panel array (on 10 & 12 awg wire) and to my batteries (on 4 awg).

    Unlike my previous controller, this one has no leads, so I will need to make short leads myself (4 awg wire will not fit into the small holes).

    (40 watts of solar panels on 12awg and 70 watts of panels on 10awg join just before a 20A ATC fuse.
    Then about 6" of wiring that came with the fuse holder (12g?) will attach the fuse holder to the solar controller lead that I make.
    The batteries are on 4 awg and there is no fuse between the batteries and the controller).


    My questions are:
      will it be ok to make each of the leads from about 4-6" of 12awg wire?
    1. Where can I find info on the correct gauge wire to use with a fuse (so the wire I use doesn't act as a fuse instead?)?

    Thanks for your help!

    I'm also confused by the #4awg wire??? Do you mean to say that:
    A) you've joined the leads from your PV into #4?
    B) that the batteries are interconnected with #4?
    C) is that #4 wire running to your inverter?

    If it's A, then I'd use a smaller wire for that as Coot's right; you really don't need that big of a wire for so little PV. (I would do a voltage drop calculation just to be sure and take into account your length of run, and any future expansions you may have planned). I'd still want a fuse between the PV and charge controller personally, and it's not like they are all that expensive for the small sizes you'd be looking at.
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  • greenthumb76
    greenthumb76 Solar Expert Posts: 40 ✭
    #11
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    Re: PLEASE help!

    hillbilly,
    Remember that the idea is that the fuse/breaker will blow BEFORE the wire does. . . Therefore a 20 amp fuse would in theory blow before your wires get too hot from excess current flow.
    Does this make sense?

    Yes, that made sense.

    As it turns out, the 40 watt array's wire seems to be 16 awg. And, it will be running 40-45 feet before connecting to the 70 watt array's 10g wire at the fuse holder.

    What size fuse should I use here then?
    I'm also confused by the #4awg wire??? Do you mean to say that:
    A) you've joined the leads from your PV into #4?
    B) that the batteries are interconnected with #4?
    C) is that #4 wire running to your inverter?

    A) no
    B) yes
    C) yes
    and the wire from the solar controller to the batteries is #4
    I'd still want a fuse between the PV and charge controller personally, and it's not like they are all that expensive for the small sizes you'd be looking at.

    Yes, I presently have a 20amp fuse there and will plan to keep it (unless, in the question above, you recommend a smaller one).
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  • hillbilly
    hillbilly Solar Expert Posts: 334 ✭✭
    #12
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    Re: PLEASE help!
    greenthumb76 wrote: »

    As it turns out, the 40 watt array's wire seems to be 16 awg. And, it will be running 40-45 feet before connecting to the 70 watt array's 10g wire at the fuse holder.

    What size fuse should I use here then?

    Your 16awg wire should be able to pass 16 amps, so you would want to protect it with a 15amp fuse. The issue to be careful with is that while now you only have say 110watts of PV, if/when you start adding more PV then I could see a situation develop where you have:
    1) undersized fuses that blow whenever the PV panels start pushing higher currents through those same wires and fuses that you have installed now
    or
    2)you have unprotected wire runs that are now possibly subject to higher currents that could damage them.

    One of the reasons I was recommending a fuse or breaker between the PV and Charge controller is facilitate the ability to disconnect the PV array from the Charge controller. The typical big need for a fuse on any wire would be to protect it from excessive currents that it's not sized to be able to handle; which in your system right now sounds like a minimal issue (hazarding a guess that your total array short circuit currents are less than the wires can handle). This would obviously change if you add in one or two more PV panels... meaning you might then need to change some fuses and possibly some wires (or at least the 16awg). Just make sure that if your PV increases, that your fuses or breakers can handle the additional current AND that your wires are still able to handle more current than your fuses.

    As for the rest of the system, let me see if I have this right:

    You have a 40watt PV with ~40' of 16awg wire and a 70watt PV with 10awg wire (of a presumably similar length?)
    these then meet at a 20amp fuse, and continue some distance to your charge controller, where you have 4awg wire running to the batteries
    and another run of 4awg to your inverter (distance?)

    The questions that I would have would be how long are your wire runs and what sorts of loads do you have now (and how much might they grow in time). The 4awg from your batteries to your inverter for example *might* be a bit on the small side depending on how large your loads are and how long this run is (ie, you may have some excessive voltage drop).
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  • greenthumb76
    greenthumb76 Solar Expert Posts: 40 ✭
    #13
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    Re: PLEASE help!
    As for the rest of the system, let me see if I have this right:
    You have a 40watt PV with ~40' of 16awg wire
    I have shortened it to 30', but yes--40 watts, #16 wire.
    and a 70watt PV with 10awg wire (of a presumably similar length?)
    only 15 feet of cable (#10) on that array.
    these then meet at a 20amp fuse, and continue some distance to your charge controller,
    I changed it to a 15 amp fuse, and it is less than a foot from the controller.
    where you have 4awg wire running to the batteries
    and another run of 4awg to your inverter (distance?)
    yes and no
    • (2-4') of #4 from controller to the batteries
    • about 2' of #4 between the batteries
    • about 6' of #4 from batteries to inverter.
    The questions that I would have would be how long are your wire runs and what sorts of loads do you have now (and how much might they grow in time).
    When the hours of sunlight increase, my max draw will be about 600 watts, for a short period of time (an hour or two).
    The 4awg from your batteries to your inverter for example *might* be a bit on the small side depending on how large your loads are and how long this run is (ie, you may have some excessive voltage drop)
    .
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