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Padlin's avatar
Padlin
Explorer
Mar 02, 2015

Cable size for 160W portable solar panel

Have 2 trailers. Trailer #1 has an existing 30A PWM charge controller being fed by a single 160W roof mounted panel. The controller is about 2' from the 2 6v batteries with a shunt between them for the monitor. Trailer #2 has no solar.
Have a 160W portable solar panel with rear mounted 10A controller, came with 20' or 12awg to use from controller to the batteries.
Want to use trailer #1 late fall/winter bypassing the portables controller and running the cable to the existing 30A controller. Will use trailer #2 this summer feeding it's batteries directly from the panel mounted controller.

Portable Panel specs
Open Circuit Voltage (Voc): 21.0V
Short Circuit Current (Isc): 9.4A
Maximum Power Voltage (Vmp): 17.0V
Maximum Power Current (Imp): 10A


Fixed Panel Specs
Voc 22.2V
ISC 9.46A
Vmp 18.5V
Imp 8.65A


Using 10A of current I believe the following max cable lengths are correct.
12awg = 20'
10awg = 30'
8awg = 40'

Am I correct in assuming that the cable gauges and lengths mentioned above would work for both scenarios?

Do you see any other issues?

14 Replies

  • NinerBikes's avatar
    NinerBikes
    Explorer
    Mar 03, 2015
    Bend wrote:
    OP-

    The secret of good solar PWM charging performance is conserving voltage. Once that is done, amps will take care of themselves. You need at least 16.5 volts at the controller for it to work and usually 14.8 volts at the batts. Your winter RV will probably need more solar watts and battery voltage due to low temps.


    This, and sometimes you need even more at the battery with problematic batteries like group 31's or Trojan T-1275's, something aroud 15.0 to 15.3V at the batteries. See the "My screwy 31" thread by landyacht318.
  • time2roll's avatar
    time2roll
    Nomad
    Mar 03, 2015
    A couple wires and some battery clamps is fine. Just let it dangle.
    Could get fancy and mount it on a small piece of wood to provide wire strain relief and a hook of sort to keep it out of the mud.
  • BFL13's avatar
    BFL13
    Explorer II
    Mar 03, 2015
    Solar controller needs air-it gets warm- so don't put it in a plastic bag :) You can get the kind that you can leave out in the rain. Most need to be kept dry.
  • Padlin's avatar
    Padlin
    Explorer
    Mar 03, 2015
    smkettner wrote:
    Controller is on the back of the panel? Don't use it that way. Controller should be within 3' of the battery.


    Thinking of doing such if I can come up with a place to put it on a bumper pull with front mounted batteries. Don't think it'd fit in the little black battery boxes.
  • time2roll's avatar
    time2roll
    Nomad
    Mar 03, 2015
    Controller is on the back of the panel? Don't use it that way. Controller should be within 3' of the battery.
  • Salvo's avatar
    Salvo
    Explorer
    Mar 03, 2015
    No, not when using a pwm controller. The PV voltage going into the controller needs to be greater than battery voltage plus voltage drop from cables.

    Padlin wrote:


    With the 2 panels connected to the controller, does the lower voltage of the two drag down the higher?
  • BFL13's avatar
    BFL13
    Explorer II
    Mar 02, 2015
    IMO rip the 10a controller off the back of the portable panel set and use the existing 30a controller to run the new panels as well as the roof top ones so you have 320w when doing that. You can have 160 on the roof and 160 on the ground doing that. Just need access to the controller for the wires from the ground panels like through the cargo bay, whatever.

    If just using the 160w portable with the other trailer, mount a new 20a controller from eBay ($15 ?) near the batts and some #8 from it to the batts. Use #8 or better from panel to controller. Eg I use #8 or better jumper cables out to the portable panel. If too far I use more sets of jumper cables clamp to clamp. It all gets the job done.
  • Bend's avatar
    Bend
    Explorer
    Mar 02, 2015
    "... does the lower voltage of the two drag down the higher?"

    You should be fine. You have all summer to test it.
  • Padlin's avatar
    Padlin
    Explorer
    Mar 02, 2015
    Bend wrote:
    OP-

    The secret of good solar PWM charging performance is conserving voltage. Once that is done, amps will take care of themselves. You need at least 16.5 volts at the controller for it to work and usually 14.8 volts at the batts. Your winter RV will probably need more solar watts and battery voltage due to low temps.


    With the 2 panels connected to the controller, does the lower voltage of the two drag down the higher? there is just one set of input connectors so I;ll be doubling it up, at least that's the plan. I do intend to see what I have room for on the roof of winter trailer once all this snow melts. Space is pretty limited, maybe another 100w, maybe.

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