common ground wiring?

SystemSystem Posts: 2,511 admin
I have a solar panel consisting of 3 Shell 75w modules with junction boxes and blocking diodes on each. There are 4 wires. Green(ground), White, Yellow, Blue
I am not sure how to wire this to my Charge Controller.
I have used a multimeter to determine the following:

Positive Negative Voltage
Blue White ~18v
Blue Yellow ~2v
White Yellow ~16v

Positive Negative
White Blue
Yellow Blue
Yellow White

-I cannot see past the point where yellow and white stop on the diagram due to a a metal back that I would like to avoid removing.

After some more use of google I think the yellow is probably the common ground. which would make blue and white positive. When Connecting to Charge controller do I just attach the end of both blue and white to the positive input lead? and yellow to the negative of course?


  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: common ground wiring?

    That sounds like something that was made up using 3 standard SP-75 panels mounted on some kind of backplate. Not sure why all the wire colors, since all you should have is a + and -, and a frame ground.

    I am guessing that with a backplate the panels run super hot in the sun.

    Not sure why they have blocking diodes either, that might be why the voltages are a bit odd.
  • System2System2 Posts: 6,290 admin
    Re: common ground wiring?

    I may have misspoke, the junction boxes have 2 bypass(not blocking) diodes each. here is a quote from the shell pdf file for the panel:

    "The Junction Box provides a high quality, dust protected and splash proof IP54-rated housing. The housing contains a rigid connection block with screw terminals and bypass-diodes providing "hot spot" protection for the solar cells."

    How I should wire it to the charge controller?
  • System2System2 Posts: 6,290 admin
    Re: common ground wiring?
    Windsun wrote: »
    Not sure why all the wire colors, since all you should have is a + and -, and a frame ground.
    I agree 100% with the above. All you should have, is a plus, a negative and a frame ground. Nothing more. The extra wires and colours indicate to me that someone has modified the panel wiring for some reason, and it makes no sense to me, that anyone would do that.

    PS: The ground wire will have no continuity, or voltage reading - - - unless there is a ground fault somewhere in the wiring, or a panel.
    The "back plate" that was mentioned - - does that cover the backs of the panels? If so, it's my opinion that it should be removed, as heat will build up to the extreme, like mounting panels flat to a roof with no air space for ventilation, not good at all for the panels. They need lots of free air flow to keep their temps down as much as possible.
Sign In or Register to comment.