Solar AWG to MPPT

gqrootgqroot Registered Users Posts: 22
Hello,

I currently have two 205watt solar panel (using a MC4 Y-connection) hooking up to about 10 feet Morningstar MPPT45. Would a 10 AWG PV cable 50 - 75 feet be okay or would I need to get a bigger cable?

If the 10AWG cable run from the PV to the MPPT is able to handle that far of a run would it still be okay at 615watts?

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar AWG to MPPT

    You need to do some Voltage drop calculations: www.solar-guppy.com/forum/download/voltage_drop_calculator.zip

    Understand it's not a case of just one factor. You have to take into consideration Voltage, expected maximum Amps, and the length of the wire run to determine what gauge wire to use.

    Are the panels wired in parallel or series? If parallel, the Voltage will be lower and the current higher; not good for longer wire runs. If series, the Voltage will be higher and the current lower; better, providing the Voc of the panels together does not exceed the input limit of the controller.

    If you're planning on future expansion, figure out the best design for that now and see how it works with your existing set-up. It may be possible to add more panels in series and increase power that way, but depending on how much more you add (and what the specs are) you may have to make parallel connections as well. The additional Amps from that needs to be taken into account for wire sizing.
  • gqrootgqroot Registered Users Posts: 22
    Re: Solar AWG to MPPT

    Thanks Cariboocoot for you help.

    The panels are currently in parallel config. I guess I can put them in series to get 48 volts and get away with a smaller gauge and longer run.

    So if I decide to add two more panels in parallel config with separate runs (from the first pair of panels) to the MPPT45 - is that correct?

    The MPPT45 I have is able to hand about 3k watts. Can I then add different make/model of panels to the same MPPT45 or will I need to buy another charge controller?
  • mike95490mike95490 Solar Expert Posts: 9,363 ✭✭✭✭✭
    Re: Solar AWG to MPPT
    gqroot wrote: »
    ....
    The MPPT45 I have is able to hand about 3k watts. Can I then add different make/model of panels to the same MPPT45 or will I need to buy another charge controller?

    Very odd. I have a 3KW array on a 48V system and it pushes about 58A, from a 60a controller:confused:
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar AWG to MPPT
    gqroot wrote: »
    Thanks Cariboocoot for you help.

    The panels are currently in parallel config. I guess I can put them in series to get 48 volts and get away with a smaller gauge and longer run.

    So if I decide to add two more panels in parallel config with separate runs (from the first pair of panels) to the MPPT45 - is that correct?

    The MPPT45 I have is able to hand about 3k watts. Can I then add different make/model of panels to the same MPPT45 or will I need to buy another charge controller?

    What is your system Voltage and what type of controller is that?
    Ideally you'd keep all panels the same on any one controller and run as many in series as possible (avoiding the Voc problem). Normally you join all panels up at the array (with appropriate fusing as needed) and run one set of wires to the charge controller. When adding different types of panels it's important that they be close (with 5%-10%) of the original panel specs: Vmp being most important for parallel connections and Imp for serial ones. If we had the panel specs (Voc, Vmp, Imp, Isc) it would be possible to suggest a plan.

    The 45 Amp rating of a charge control is for its output. On a 12 Volt system that's about 540 Watts. On 24 Volts about 1080, and on 48 Volts 2160. Don't try to put a 3kW array through that if your system is only 12 Volts.
  • gqrootgqroot Registered Users Posts: 22
    Re: Solar AWG to MPPT

    The two Siliken panel is a 24 volt 60 cell with a capability of 205 watt.

    The controller is a Morningstar MPPT45. I read the Morningstar MPPT45 and it said that it is capable of 2400 watts (thanks mike90045 for the correction - my mistake).

    The inverter is a Sunforce 2500watt pure sine.

    So far I have the two panel hooked up to the lattice top (back of the house) and will need to run the PV cable all the way to the garage which is about 50 - 75 feet away.


    In the earlier posts, the smell was as you folks suspected was the battery. So I am going to return the Optima battery. I am going to get a Concorde Sun Xtender 59AH unless you folks recommend something better. I found a local place where I can do a local pick up.


    I am learning a lot from you guys - thanks! :D
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar AWG to MPPT

    Siliken 205 Watt: Voc 36.4, Vmp 28.7, Imp 7.15, Isc 7.9
    So it's one of those "in between" panels - too high Voltages for a 12 Volt system, too low for a 24. Probably meant for grid-tie applications, but can be used off-grid with MPPT controller.
    The Tristar 45 MPPT has a V in limit of 150. That would mean 4 panels in series at most, and not if your in an area where cold temps are likely to cause super conducting.

    For now, putting the two panels in series would give you Voc 72.8, Vmp 57.4, and Imp 7.15. That would work with either a 12 Volt or a 24 Volt system (not for 48 Volt - Vmp too low). Using 48 Volts as the nominal and 8 Amps as the current and 75' for the length I get 10 AWG as being sufficient to keep the V drop below 3%.

    If you want to add one more panel in series for 615 Watts total you could with the same wire, a the Voltage would go up but the current would remain the same. If you plan to add another string of three in parallel to that you should probably install 8 AWG or even 6 AWG for the run to the controller. I can't do a precise calculation with the limitations of my netbook.
  • gqrootgqroot Registered Users Posts: 22
    Re: Solar AWG to MPPT

    I'll put them up in series then and run the 10 AWG.

    The Tristar MPPT45 dip switch is set to 24 volt system, does that mean I will just leave it at 24 volts since the solar panel I have isn't capable totaling 48 volts? Just clarifying.

    Much appreciated for your help.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar AWG to MPPT
    gqroot wrote: »
    I'll put them up in series then and run the 10 AWG.

    The Tristar MPPT45 dip switch is set to 24 volt system, does that mean I will just leave it at 24 volts since the solar panel I have isn't capable totaling 48 volts? Just clarifying.

    Much appreciated for your help.

    System Voltage is on the output side of a charge controller, not the input. If you used this with a 12 Volt battery (the Optima) with the system Voltage set to 24 it would fry the battery. Maybe that's what happened the first time.
  • gqrootgqroot Registered Users Posts: 22
    Re: Solar AWG to MPPT

    I am so dumb! Someone shoot me :blush:

    For some reason I set the system voltage to 24 thinking it was the panels. Dip switch (#2 On/# 3 Off). I'll put it to 12 (#2 Off/#3 On).

    Could I have damaged the Controller by doing this?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Solar AWG to MPPT
    gqroot wrote: »
    I am so dumb! Someone shoot me :blush:

    For some reason I set the system voltage to 24 thinking it was the panels. Dip switch (#2 On/# 3 Off). I'll put it to 12 (#2 Off/#3 On).

    Could I have damaged the Controller by doing this?

    Doubtful. Basically it tells the controller to try and bring the Voltage up to 24 Volt levels. Since those panels have a Vmp of 28.7 it would shove as much current as it could come up with to the battery to try and raise its Voltage. By the time the Voltage reached 14.4 (normal charge for 12 Volt) the controller could still be pumping 20+ Amps, and would still be doing so as it pushed the Voltage past 15.5 (EQ level on a 12 Volt system). By that time the battery would be cooking, its safety valve would blow, and that's when you'd get that eau de batterie in the air.

    Since the output current would not have exceeded the controller's max and the input Voltage would not be above the V in limit the controller itself should be okay. BTW: fuses are good things.
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