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Old 12-28-2018, 07:54 AM   #1
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Series or Parallel

I am preparing to add a 3rd solar panel to the two that were factory-installed on my 2018.5 23T Fuse. There is a 3 port roof cap on the RV roof and only 2 ports are in use so it seems like it ought to be a simple thing to do. The existing solar panels are SunPower 100 watt panels and I thought I would use the same brand as those already installed, although I know that is not necessary. I just think it would look more professional to use the same panels.

I am curious as to whether the existing panels are connected in series or parallel. I assume parallel as I do not know why increasing the voltage would be useful to the solar controller, but I do not know. I know that the installation only requires changing the MC4 to SAE connectors and, I think, reversing the polarity, and then plugging the panel into the unused roof port and that the series or parallel wiring is probably done internally, and not under my control, but I was wondering. Can anyone tell me?
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Old 12-28-2018, 08:37 AM   #2
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The only time you would go in series is to increase the output voltage. This is done in commercial installations. Parallel is how these are done with the controllers in RV's.
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Old 12-28-2018, 11:35 AM   #3
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The only time you would go in series is to increase the output voltage. This is done in commercial installations. Parallel is how these are done with the controllers in RV's.
Thanks. Confirms what I thought, but it is nice to have confirmation.
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Old 12-28-2018, 11:56 PM   #4
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... I assume parallel as I do not know why increasing the voltage would be useful to the solar controller, but I do not know. ...
As I have heard it explained, the answer is a solid, "It depends!", specifically on the controller type used, PVM or MPPT. As I understand it, the MPPT controller is able to channel the higher voltage into more amps delivered to the battery bank in full sun, then when the panels have partial blockage and the individual panel voltages go (way) down, the combined (serial) voltage can still be sufficient to sustain useful charging, while the parallel panel installation might drop below the useful charging threshold. (Assuming I have that right, a single panel/MPPT controller should be more effective than a single panel/PVM controller, as most panels I've seen are rated at 18V or higher, and the PVM controller might be dissipating the excess voltage as heat. Experts?)

This is given multiple panels and a single controller. I have recently seen the case where each panel gets its own controller, to some advantage but the explanation was not clear to me, perhaps just redundancy.
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Old 12-29-2018, 04:49 AM   #5
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You could always measure the voltage at the input to the controller with a multimeter. In order to do this, you'll need to be in the sun and have access to the connections at the controller but you shouldn't have to disconnect anything. Parallel will measure something in the range of your panels' rated output voltage. Series will measure something close to double the rated voltage. Since there are many issues affecting actual output voltage vs. rated output voltage, don't expect that you're going to get an exact, even multiple of your panels' rated output voltage.

Your Sunpower panels look like they're rated at 17.1V if I have the model right. Even if you don't know your panel's output rating, it should be fairly obvious. voltage readings at the controller input are either going to be in the teens (parallel) or the thirties (series).
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Old 12-29-2018, 08:00 AM   #6
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The Zamp 3-port portal Winnebago installs on its RVs is parallel.

And generally the portal is connected to a Zamp 30-amp PWM solar controller. But, they also generally install Zamp solar panels. So, it’s surprising that your panels are another brand.

When buying your additional panel take note of the connectors on the panel. The Zamp 3-port connector uses SAE connectors, most solar panels use MC4 connectors.

My RV came with only one 100-watt panel (Zamp) and the 3-port portal on the roof. I purchased 2-additional 100-watt panels and installed them about a year ago. It was an easy job. I did buy non-Zamp branded panels getting mine from Renergy. The most difficult part was changing the Renergy’s MC4 connectors to SAE. Even that was easy enough it’s was just the most difficult part. The Renergy panels were a lot cheaper than Zamp panels.
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Old 12-30-2018, 07:14 AM   #7
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And generally the portal is connected to a Zamp 30-amp PWM solar controller. But, they also generally install Zamp solar panels. So, itís surprising that your panels are another brand.
The later Fuse models all seem to come with 2 panels instead of one and a Zamp roof cap to plug in to, and all of them that I looked at (that is, climbed to the roof to look) had SunPower solar panels. I assume that Winnebago, when they decided to add a second panel, also decided to save some money and use less expensive panels. When I called SunPower to try to get a single panel they told me that they do not generally sell panels for RVs but that Winnebago probably made a large purchase of those flexible 100 watt panels and that is why they are being used on their RVs.

I am guessing that they are using the Zamp controllers with the non-Zamp panels because they have a ton of the controllers and want to use them up. Perhaps soon they will stop using the Zamp controllers as well.

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When buying your additional panel take note of the connectors on the panel. The Zamp 3-port connector uses SAE connectors, most solar panels use MC4 connectors.
Yes. Among other things I have been looking for an MC4 to SAE connector. Amazon has those and I expect to get one of those. They are not cheap, but it is a one time purchase and I don't generally put the words "RV" and "cheap" in the same sentence.

One thing that has continued to puzzle me is the polarity of the solar panels and that of the Zamp controller. The threads on adding solar panels all seem to say that Zamp uses the reverse polarity of all (or most) of the other systems and that if I use non-Zamp panels I will need to make sure to reverse the leads, but the Zamp web page says that is not true. Here is one of the FAQs on the Zamp page and their response:

4. Is the solar port reverse polarity?

No, but they are different from other brands of solar ports because all of our SAE plugs are polarity-protected for safety reasons. That means the positive pin on all of our SAE plugs is set back and covered to prevent accidental contact that could damage your panel, short your battery, or give you a pretty nasty shock. So, because of the polarity protection on our plugs, Zamp Solar ports are only compatible with Zamp Solar SAE plugs.


Based on this I do not know if I need to worry about reversing the polarity or not. I know I should be able to connect an MC4 to SAE adapter to a SunPower panel, check the polarity with a multi-meter and compare it to the other SAE connectors plugged into the roof cap, but that means that I have to be prepared for either case (reverse polarity or no reverse polarity) and that seems to mean that I have to have both adapters ready for use. Just one more thing to have to be prepared for and one more thing to buy which I may or may not need.

In light of the Zamp FAQ any information you have about the polarity issue would be appreciated.

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Originally Posted by creativepart View Post
My RV came with only one 100-watt panel (Zamp) and the 3-port portal on the roof. I purchased 2-additional 100-watt panels and installed them about a year ago. It was an easy job. I did buy non-Zamp branded panels getting mine from Renergy. The most difficult part was changing the Renergyís MC4 connectors to SAE. Even that was easy enough itís was just the most difficult part. The Renergy panels were a lot cheaper than Zamp panels.
I have played around with 3 choices. First, buy a Zamp panel which should have all of the proper connections already attached and which should just plug into the roof cap without issue. Second, buy a SunPower panel so that all 3 panels will match. Not that it would make any difference electronically, but it might look a bit more professional having all 3 panels the same type and that might (I stress might) make a small difference when and if we trade in this RV down the road. Third, buy an inexpensive panel and save some money.

I do not know the price of the Zamp panel since all of the prices that I have seen are for roof install kits and seem to include a lot of stuff, including the roof cap, that I do not need. I plan to call Zamp on Monday (or perhaps Wednesday since they may be closed on Monday). The SunPower panels seem to be about $260 from Amazon and slightly less from other retailers, and other panels are about half of that. I assume the 3rd party panels are probably all equivalent and, for all I know, are identical with only the names being different. The Zamp are all made here in the US.

In any case I am trying to get all of this done before our trip to the Quartzsite RV show in late January since I figure that will be a 3 day dry camping trip and I could use the extra power.
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Old 12-30-2018, 09:51 AM   #8
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Here's some things.

Zamp say, they are not reverse polarity - well, not in their world. But SAE connectors NORMALLY have the positive "male" side exposed and the negative "female" side covered. That's just what's normally expected in those connections. Zamp does the opposite, as they told you. They wire the positive terminal to the female connector.

To me that's reverse polarity - except that the SAE connector can be wired either way. It's just common or normal to be wired the other way.

So, be aware that the MC4 to SAE adapters from Amazon are wired incorrectly. I found this out the hard way and I had to reverse the connections which means I had to actually cut the wire on my amazon connectors and flip them around to make the polarity correct for the Zamp portal.

If you have the flexible panels I'm not sure that Zamp even offers them. So, that might not be an option. And, it's probably why WBGO switched from Zamp to SunPower for the panels. But you can find other flexible panels by other folks.

I'd say if you can find them, buy them without connectors at all. I know some brands can be purchased that way. Then you can buy pre-wired SAE to bare wire kits from Zamp and you can wire them the way you want them - positive to the female / negative to the male side.

Flexible panels are losing a lot of favor because they are not as efficient as standard flat panels. But if your RV has the flexible panels it would make the most sense to buy the same for your RV.

I think WBGO put one flat panel on the Fuse at first and switched to the two flexible panels in later models.

When I bought my two extra panels Zamp panels were $400 each and Renergy were $120 each. So, I bought two new panels for a little more than 1/2 of what one panel would cost had I stayed with Zamp. Then I bought the MC4 to SAE adapters from Amazon and thought I was all set - only to find the polarity on the adapters was wired the "normal" way for SAE with positive being on the male side of the connector.

It all sounds more difficult than it is. Buying the MC4 to SAE adapters was a waste of time and money and if I had taken the advice I posted above about buying panels with bare wires I would have saved myself time, trouble and money.

Best of luck!

Here is my RV roof with 300w of panels - I have a lot more room for more panels but I still want to be able to access more things on the roof AND the Zamp 30-Amp controller would only support 400 to 450 watts of panels.
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Old 12-30-2018, 10:03 AM   #9
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One thing I forgot to mention. Winnebago seems to have issues with the SAE Zamp polarity too. When I bought my RV the Zamp 30-Amp PWM Solar Controler showed an error code P01 on the display. That means the polarity was reversed. So, I switched the wires at the back of the controller and all was good.

I figured it was just on my RV. Then one day I was watching a YouTube video from a dealer on a brand new Winnebago RV they were trying to sell. They mentioned the solar panel and then trained the camera on the solar controller. Sure enough it read P01. So, it wasn't just my WBGO that was wired backwards.

I'm assuming that your Fuse is wired correctly.

By the way, I tested the Zamp panel, and the 3-port portal on the roof to determine which part was wired backwards - it was the wiring from the port on the roof to the solar controller. I should have removed the portal and changed the wires there but it was so easy to flip the wires at the back of the solar controller. I put red and black tape on the wires to remind myself which was actually positive and which was actually negative.
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Old 12-31-2018, 06:47 AM   #10
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I found this on Amazon:

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

It is a polarity reverser and I assume I could just use the MC4 to SAE adapter and then plug this onto the end to solve the problem. Any reason that should not work? It is certainly inexpensive enough.
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Old 12-31-2018, 08:27 AM   #11
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Mike, that looks like it would work fine. However, I bet somebody makes a correctly wired MC4 to Zamp SAE adapter by now. When I got mine there were only a few available and it never occurred to me that the adapter I purchased would arrive with the wires not "zamp ready" before I purchased. If the polarity had been right it would have been easy to plug and go.

Maybe you can buy an adapter that has the correct polarity and you'll be all set.
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Old 12-31-2018, 08:58 AM   #12
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Mike, that looks like it would work fine. However, I bet somebody makes a correctly wired MC4 to Zamp SAE adapter by now. When I got mine there were only a few available and it never occurred to me that the adapter I purchased would arrive with the wires not "zamp ready" before I purchased. If the polarity had been right it would have been easy to plug and go.

Maybe you can buy an adapter that has the correct polarity and you'll be all set.
I have plans to check with several solar panel dealers as soon as they are open, and can ask. But the polarity reverse seems like a pretty inexpensive solution to the problem. I did Google "MC4 to Zamp SAE adapter" but got only hits for regular MC4 to SAE adapters and reverse polarity adapters like the one I mentioned.
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Old 01-02-2019, 04:55 PM   #13
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To clear up a couple things:

Wiring dissimilar panels in series or parallel is a poor practice and your output wattage will suffer some. In series, the current will be limited by the lowest current panel in and in parallel, the output voltage will be clamped by the lowest voltage panel.

Personally I am a fan of wiring panels on the RV roof in series if possible. This yields a higher voltage to the controller which is favorable due to the voltage drop experienced on the wires. Of course, check the input voltage limit to your controller to ensure it is not exceeded. If you will frequently have one panel shaded however, that benefit is negated and wiring in parallel would be better.
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Old 01-02-2019, 05:05 PM   #14
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As an example the Zamp 30-Amp 5-Stage PWM Charge Controller has a maximum DC input voltage of 25VDC. First if you do series you would need to keep the strings equal 2 x 2. If you can only fit three panels you would be inefficient. This is why the KISS principle applies IMO. Parallel as the roof is the same plane and shading affecting only one panel of three or four panels is negligible IMO.
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