Problem With Solar - Fiberglass RV


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Old 05-25-2019, 11:46 AM   #1
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Name: Huck
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Problem With Solar

I have had my solar panel and wiring working fine for over 4 years. I noticed the other day that the batteries were not being charged by my rooftop solar panel. I thought it was likely the panel and some testing seemed to confirm it. The panel was brittle and cracked, so I removed it and ordered a new panel.

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 portable panel. I connected the new solar panel to the wiring where the portable panel plugs in, and the charge control 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 were 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 and 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 y connectors, it works.

I thought maybe I had a polarity problem, but if I did, the 2nd scenario shouldn't 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 so that's not a solution, plus I lose the ability to use a 2nd panel.

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

I have 2 y connectors (positive and negative) that connect to the charge controller.
One leg of each y connector (+-) connects to the panel on the roof and the other leg on each y connector (+-) connects to wiring for a 2nd portable panel.

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.

I realize this is hard to picture, but does anyone have an idea on what else I can look at?
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Old 05-26-2019, 11:29 AM   #2
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Just a guess but it sounds like leg 1 Y connector is the problem
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Old 05-27-2019, 03:17 AM   #3
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Name: Duane
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I agree with Larry C.
Do a voltage check on Y1 with the second panel connected. There should be voltage at the feed end of Y1. Polarity is the same with the siamesed cables. No voltage means an open circuit on Y1. Check for corrosion too.
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Old 05-27-2019, 07:57 AM   #4
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I found the specific problem, but still don't understand.

I checked each segment of leg 1 that goes from the roof solar panel to the controller. I connected the positive probe on multimeter to male connector and negative to female connector for each cable segment. I read positive 18+ v and 6+ a.

I did the same for leg2 and read -18+ v and 0 a. I swapped the leads and put positive on female and negative on male connectors and got 18+ v and 6+ a.

Further checking showed that these 2 cables were wired incorrectly and 1 had a male on both ends and the other female on both ends. In other words, they reversed polarity.

I thought leg 1 should work and leg 2 fail, but it's just the opposite. leg 2, that reverses polarity works and leg 1, that doesn't reverse polarity doesn't.

At that point I thought I must have wired the charge controller wrong and reversed polarity, so the 2 wiring errors cancelled out, but the controller is wired correctly.

Ideas on where to go next?

Remember this wiring has been working for 4 years with no changes to wire or connectors. Same controller as well. The only thing that has changed is the solar panel.
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Old 05-27-2019, 11:07 AM   #5
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Name: Huck
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Finally figured it out.

For some reason, the MC4 male connector uses a female pin and vice versa. This means what looks like a male connector is actually negative and the female is positive.

To make a very long story short, this resulted in me reversing the connections to the charge controller. I have no idea why it worked for 4 years, unless there were some solar panels that corrected for polarity.

Anyway, I switched the 2 leads going to the controller and problem is fixed for rooftop panel.

I found a pair of cables for the portable panel that were wired wrong - male instead of female and vice versa. That's why that leg worked - the 2 mistakes (cables with wrong connectors and miswired controller) cancelled each other out.
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Old 05-27-2019, 12:30 PM   #6
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Great detective work. Just goes to show that we can not take anything for granted.
Happy Trails
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Old 06-08-2019, 10:00 PM   #7
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The MC4 connectors can be confusing and to make it worse some are marked +/- or have a red band (for +). However, if you have them on portable panels then use an intermediate cable to the controller, you will be plugging male to female or vise versa and if marked, it looks like you are connecting + to -! As a result I marked all the positive conductors with red electrical tape. Now I just the marked cables and not worry.
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Old 06-09-2019, 12:16 AM   #8
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Name: K C
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I have seen some solar fittings from a solar company that were deliberately the reverse of the normal polarity. That is how they dealt with creating an "exclusive" designed system where you had to buy all of the fittings from them in order to get it set up and working. That sure had me shaking my head at that company and deciding I would never buy products from them.


Basically a cheap method to prevent people from buying cables and fittings that are lower in cost elsewhere.
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Old 06-09-2019, 12:21 AM   #9
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Quote:
Originally Posted by k corbin View Post
That sure had me shaking my head at that company and deciding I would never buy products from them.

Why not name the company?
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Old 06-09-2019, 10:20 AM   #10
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Quote:
Originally Posted by k corbin View Post
I have seen some solar fittings from a solar company that were deliberately the reverse of the normal polarity. That is how they dealt with creating an "exclusive" designed system where you had to buy all of the fittings from them in order to get it set up and working. That sure had me shaking my head at that company and deciding I would never buy products from them.


Basically a cheap method to prevent people from buying cables and fittings that are lower in cost elsewhere.
I’m not sure if this is deliberate. The problem is the female connector is defined as “positive” (the pin inside the housing defines sex, not the housing), but what are you plugging it into? If you are connecting panels in series, connecting positive to negative makes sense, but what about the connection to the controller, then it appears to be wrong. The following link has more info. https://en.m.wikipedia.org/wiki/MC4_connector.
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