Basic Solar Panel Question

[Surviver76]

I am full time and met another full-timer who has a solar Panel issue.
He is in an older C-Class Ford and picked up a panel and got it twisted. Apparently, he reversed the polarity and tried to hook into his controller and of course something blew.
I built my own solar system so offered to lend a hand in sorting things out. The panel is off the roof and so I metered the pigtails while the sun was on the panel and got a one. No good signal. So then I dug the insulation out of the junction box on the back of the panel and again let the sun on it, got underneath and metered the terminals and still got a one on my meter.
My question is this. In a case such as this, is it possible for the cells to get somehow ruptured to where the panel is ruined? I never thought so but with no signal, I wonder. Then I thought well looks like some diodes or something in that junction box. If they were fried, could that cause the panel to show no signal when the terminals are metered directly? Any help appreciated.

[red31]

try probing the 3 sections of the panel separately.

[CapnCampn]

It looks to me like that is the J-box that is on the back of every solar panel, and it has 2 wires coming from it, Probably negative on the left, Positive on the right. (is that the one with the + tag on it?)

If that's the case, you won't see any wires from this box to the panel, since they will come through the back of the panel from the cells into the box.

So, put your DVM into the 100V DC range, and put the black lead on the left wire (in the J-box) and the red lead on the Right Wire in the box, and you should see voltage, somewhere around 40-50V.

if the meter reads 1, with no tenths etc, that usually means out of range. Even with the leads touching nothing, your meter should read 0.00 or so.

If all else fails, maybe try a different meter?

Good luck.
CC

[time2roll]

Unless you see something obvious I would not attempt to repair the solar panel or the junction box.

I would not know how to test without separating everything like cutting the diodes out. But then you need to replace them with new. I would look for a new panel if the voltage and amps cannot be found at the end of the pigtails.

[2oldman]

Tom_M wrote:
There are no wires between this junction box and panel.

Well, then the OP has a worse problem than I surmised.

[Tom_M1]

Tom_M wrote:

2oldman wrote:
So you're saying that jct box is just fine.

I never implied that the junction box is fine. Just that cutting off the pigtail wires will make no difference in troubleshooting the problem.

I think I just figured out what our problem may be. The junction box is attached to the back of the panel. The wires in the picture are the pigtail wires that have the MC4 connectors on them. There are no wires between this junction box and panel.

[Tom_M1]

2oldman wrote:
So you're saying that jct box is just fine.

I never implied that the junction box is fine. Just that cutting off the pigtail wires will make no difference in troubleshooting the problem.

[2oldman]

So you're saying that jct box is just fine.

[Tom_M1]

2oldman wrote:
What difference does it make if it's disconnected from the system?

If the panel is connected, there may be a short in the wiring or controller. This would result in a near zero voltage reading at the terminals of the panel. Disconnecting the panel should give the open circuit voltage (Voc). No need to cut off the pigtails.

[2oldman]

Tom_M wrote:
so are you suggesting that he clip off the connectors? Doing so would have no effect on his measurements.

That box looks so corroded I don't think I'd trust any measurement coming from there, which is what I understood him to say he did. What difference does it make if it's disconnected from the system?

[Tom_M1]

2oldman wrote:

Tom_M wrote:
Since the panel is off the roof it is probably unplugged, so clipping the wires would accomplish nothing.

I have no idea what your response means.

Perhaps I'm interpreting "clipping the wires" incorrectly. The OP stated that the panel is off the roof so it is most likely disconnected from the system. Most panels have a pigtail with MC4 connectors, so are you suggesting that he clip off the connectors? Doing so would have no effect on his measurements.

[2oldman]

Tom_M wrote:
Since the panel is off the roof it is probably unplugged, so clipping the wires would accomplish nothing.

I have no idea what your response means.

[Tom_M1]

2oldman wrote:
I would clip the wires just like I said and see if the panel is ok. You can get by sans junction box.

Since the panel is off the roof it is probably unplugged, so clipping the wires would accomplish nothing.

[2oldman]

Surviver76 wrote:
If this were your panel doing this,what would you do?

The jct box looks like somebody tossed acid in it. I would clip the wires just like I said and see if the panel is ok. You can get by sans junction box.

[coolmom42]

Surviver76 wrote:
Time2Roll, Yes, I immediately took the meter as set to my rig and got 14 volts on the batt terminals of my controller.
No, he did not physically bump or drop the panel.
So I had believed as you say that a reverse of polarity could not fry the panel itself. Seems odd to me, metering the terminals in the junction box with full sun on the panel should be the ultimate test of the panels output right? Direct metering...

You could get 14 V on your meter and still not have it set to a large enough range to read the voltage off the solar panels. I don't know what the ranges are on your meter but generally it's multiples of 10 so set yours at 100 or higher.