# Solar Problem That Has Me Stumped



## MoonRiver (Sep 2, 2007)

I posted this on an RV forum and didn't get a single response. I think I might be missing something simple, so hope you can help.

I have had my solar panel and wiring working fine for over 4 years. I noticed the other day that the trailer batteries were not being charged by solar. I thought my rooftop flexible panel had failed and some testing seemed to confirm it. The panel was brittle and cracked. 

My testing showed something strange going on, but I figured I needed a new panel so ordered one. When I received it, I first tested it with multimeter and it tested OK. I connected it to existing wiring, and the charge controller solar panel light didn't come on (and battery was not being charged).

I tested voltage (18+ volts) and amps (6+) through the wiring. I was stumped. It should be working. 

My system is wired with 2 y connectors, so that I can plug in an additional panel. I connected the new solar panel to the wiring for the 2nd panel, and the charge controller light came on and I could see the battery was getting charged.

I kept switching things around until every piece of cable plus the y connectors was tested. Here's the part that has me completely stumped.

If I use the existing wiring for the rooftop panel and plug into y connector (or even remove y connector and go directly to controller), the light doesn't come on and no charging.

But if I leave all that wiring in place and add 2 10' jumper cables so that I can loop back on the wiring for the 2nd solar panel, it works. What I am saying is in both cases I use the same wiring up to the y connector. If I plug into the y connector it fails, but if I add 2 10' jumper cables which then connect to 2 3' cables and then into the same y connectors, it works. I've tried both connectors on the y cable with the exact same results.

I thought maybe I had a polarity problem, but if I did, the 2nd scenario should not fix the problem. The way I have it wired right now it is going across every piece of wire there is and it works, but the jumper cables are running out the door to connect to the wiring under the trailer, so that's not an option, plus I lose the ability to use a 2nd panel.

I realize this is hard to picture, but does anyone have an idea on what else I can look at?

ETA: Here's a simpler way to look at it.

I have 2 y connectors that connect to the charge controller.

One leg of each y connector connects to the panel on the roof (leg 1) and the other leg on each y connector connects to wiring for a 2nd portable panel (leg 2).

If I plug my new panel into leg 1, it fails

If I plug my new panel into leg 2, it works

If I plug into leg 1, but instead of connecting leg 1 to y connector, I route it through leg 2 and then into y connector it works. 

Note: Here's the only 2 things I can think of that might be causing the problem.

1) A possible bad connection that only occurs when certain specific connectors are plugged in to each other. I ordered some extra MC4 pin sets so I can try redoing the MC4 connectors in leg 1.
2) A polarity problem that somehow is being corrected by the leg 2 wiring. Tomorrow I plan on using the multimeter to make sure the polarity on leg 1 and leg 2 is the same when the panel is connected to each one.


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## farmrbrown (Jun 25, 2012)

It does sound a little confusing, but maybe I can simplify it.
I think your MC4 y connector is the problem, leg 1 got toasted, either when the 1st panel cracked or due to corrosion from weather.
There are some sharp solar guys on here, but looking at some threads in this forum........
https://www.solarpaneltalk.com/foru...5480-how-common-is-it-to-have-connectors-fail
..........that's where I'd start first.


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## MoonRiver (Sep 2, 2007)

farmrbrown said:


> It does sound a little confusing, but maybe I can simplify it.
> I think your MC4 y connector is the problem, leg 1 got toasted, either when the 1st panel cracked or due to corrosion from weather.
> There are some sharp solar guys on here, but looking at some threads in this forum........
> https://www.solarpaneltalk.com/foru...5480-how-common-is-it-to-have-connectors-fail
> ..........that's where I'd start first.


Thanks. I took the y cables out and went directly to the controller and it still failed, so not the y connectors.

But still along the same line, I do have 1 more test I can do which will hopefully isolate it to 1 of 2 connectors. They are the ones on the roof that the panel's connectors plug into. They are the ones exposed to weather and also would potentially be the ones most likely damaged by the failing panel. I can bypass them with the jumpers but still use the rest of the wiring on leg 1. If it works, then I know 1 (or both) of those connectors are bad.


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## MoonRiver (Sep 2, 2007)

I identified problem, but still don't understand it.

ETA: Here's the problem. The 2 cables that go from underneath the trailer to the closet are wired incorrectly One cable has a male MC4 on both ends and the other has female MC4 on both ends. The problem is this causes it to work!

Leg 1 is wired correctly and doesn't work and leg 2 is wired incorrectly and does work. In leg 2, polarity is reversed.

For 4 years, this wiring has worked for both leg 1 and leg 2. I have not changed any of the wiring or connectors during that time.

Below is the testing I did to specifically identify the problem.

*Test 1*

I tested each segment of cable on leg 1 with multimeter - dc volts and amps
Leg 1 has these segments

Solar panel
2 short cables that go through roof into bathroom (I don't remember why I did this)
2 short cables that go from bathroom to closet (as 2 segments instead of 1)
2 y connectors that connect to cable that is hardwired to controller
Note: Going through the bathroom ceiling was really the only option, plus had the benefit of protection if the roof cable bladder leaked. The cables are at ceiling level and don't get wet from shower.​I used the red probe on meter on positive mc4 and black on female mc4 and tested each segment.
Results were +18 v on each segment including solar panel and 6+ a on each segment. Plug into controller and no connection.

*Test 2*

I tested leg 2 with these segments

Same solar panel
2 10' jumper cables (to connect roof panel to under trailer connectors)
2 short cables that go from under the trailer into the closet
The same 2 y connectors
Same test - red probe into male and black into female. Results were *-18 v and 0 a.
Switched the meter leads and got same results as leg1 (+18 v and 6+ a).*

Connected leg 2 as is to controller and it works. So positive on female and negative on male works, but I don't understand why?

I'm going to go double check, but I assume the connectors on the cable going from under the trailer into the closet has the connectors on 1 end reversed. (Rechecked and that was problem. One cable had a male MC4 on each end and the other had female on each end, so reversed polarity.

*Why and What Now?*

I could just switch 1 male to female and 1 female to male on leg 1 and it should work. But why? I'm still missing something.

Am I correct in the way I described testing the segments?
Am I correct that the male connector should be positive and the female negative?
How can it be that this same wiring (both leg 1 and leg 2) worked fine for 4 years, and now has different polarity on each leg?

I have tested using both connectors on the y cable, plus tested without it, and I get the same results, so the y cable is not the problem.

Like I said, I think I am still missing something. What other tests can I run?


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## Bearfootfarm (Jul 13, 2006)

MoonRiver said:


> How can it be that this same wiring (both leg 1 and leg 2) worked fine for 4 years, and now has different polarity on each leg?


The only thing I can think of is the insulation on the wire has worn through somewhere.


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## MoonRiver (Sep 2, 2007)

Bearfootfarm said:


> The only thing I can think of is the insulation on the wire has worn through somewhere.


I updated while you were commenting.

I found that cables that go from under the trailer into the closet reverse polarity. One cable has male male connectors and the other female female. They should be cable 1 male female and cable 2 female male. So the leg that is wired correctly (leg 1) doesn't work and the one that is wired incorrectly (leg 2) does work.


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## MoonRiver (Sep 2, 2007)

Just had an Aha moment.

On MC4 connectors, female pins are used in male plugs and vice versa.

What looks like a male connector is actually a female connector and vice versa. When I said I was testing the positive male connector, I was actually testing the negative female connector. Why would they do that?

At this point, I am more confused than I was yesterday.










Notice the female pin on left goes into the connector next to it that appears to be a male connector. Since the pin is female, the connector is also called female. 

I walked away for a couple of minutes and everything suddenly made sense, well almost everything. Since what I assumed was the male connector is actually the female connector, what I thought was a positive 18v on leg1 was actually -18v. And what I thought was -18v on leg 2 was actually 18v. That explains why leg1 fails and leg2 works. It doesn't explain how leg1 worked for 4 years, but I'm OK with that.

I am 99% sure I know what the problem is. I reversed polarity going into the controller when I connected what I thought was the positive MC4 to the positive on controller and what I thought was female to negative. I need to replace the connectors male with female and vice versa. That should fix leg1. Then I need to fix the miswired cable pair on leg2 and then leg2 should also work.


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## MoonRiver (Sep 2, 2007)

Pop Quiz

Which is the male connector and which is the female?












Answer: The one on top is female because it has a female pin and the one on the bottom is male because it has a male pin.


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## farmrbrown (Jun 25, 2012)

Glad you're getting thru it. I was going to post a few links about wiring 2 panels, in series vs. parallel but I didn't want to insult you with basic DC wiring since you already had yours installed.
I was getting more confused too with male/female since it only matters what is positive and negative.


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## MoonRiver (Sep 2, 2007)

farmrbrown said:


> Glad you're getting thru it. I was going to post a few links about wiring 2 panels, in series vs. parallel but I didn't want to insult you with basic DC wiring since you already had yours installed.
> I was getting more confused too with male/female since it only matters what is positive and negative.


Everything works now. Thanks for playing along.


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## Bearfootfarm (Jul 13, 2006)

MoonRiver said:


> Which is the male connector and which is the female?


The correct answer these days is to ask them how they self identify and accept whatever they tell you.


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## MoonRiver (Sep 2, 2007)

Bearfootfarm said:


> The correct answer these days is to ask them how they self identify and accept whatever they tell you.


MC4 connectors were ahead of their time.


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