Parallel Solar Panel Fuses

[dznf0g]

Gator, that is a very good link, I bookmarked it.

I think I know the answer, but the author is kind of cheeky about it. I have 2 X 100watt Renogy panels on the roof, in parallel. The standard 10ga solar wiring runs from each to the combiner, and 6 ga stranded marine duplex runs down to the controller, then 6 ga to the positive buss bar, through a breaker. no panel fuses.

So, if I have a shorted panel, mathematically I would not have enough current to heat anything up significantly. Do I need fuses? Code is vague in this scenario? I don't find any MC4 fuses/holders less than 10amps. Is there any scenario in this example where a 10 amp fuse would open?

[gator.bigfoot]

Originally Posted by dznf0g

Gator, that is a very good link, I bookmarked it.

I think I know the answer, but the author is kind of cheeky about it. I have 2 X 100watt Renogy panels on the roof, in parallel. The standard 10ga solar wiring runs from each to the combiner, and 6 ga stranded marine duplex runs down to the controller, then 6 ga to the positive buss bar, through a breaker. no panel fuses.

So, if I have a shorted panel, mathematically I would not have enough current to heat anything up significantly. Do I need fuses? Code is vague in this scenario? I don't find any MC4 fuses/holders less than 10amps. Is there any scenario in this example where a 10 amp fuse would open?

No you do not meet the requirements for fusing, just the disconnect. A 10amp fuse cannot open if the ISC less than 10 amps for the string. If fusing both branches with one fuse then yes a 10 amp fuse could open, but unlikely. The losses in the panel and the wiring would limit this. The panel should have an ISC of 5.86 amps. Multiplying this by 2 panels we would be 11.72 amps (under the max fuse rating), but over the 10 amps. But in reality the light coming into the panels would have to be at max (correctly tilted to the sun for this time of the year) and the panels would have to be clean (probably not 100%) and the panels would have to be fairly new so they haven't begun to degrade. In reality if they are sitting flat on your roof the best that you will see be 8 amps. So nowhere near the 10 amps.

I've run your info through my calculator and produced some graphs at 30C. You can see at this temp that the max current that could be produced under perfect conditions would be 10.85 amps (input to the controller). You can also see the effects of temperature. Mind you at very cold temps you will see an increase in performance. At -5C you will see 14.4amps at max (input to the controller).

[dznf0g]

Thanks, that's what I thought. Where is the point where I would need to fuse? I doubt I will increase my panels (I carry a suitcase for shade and the few times I need more than 200W) I was noodling at 400W I might need fusing, or be close.

Very nice calculator!!!

[jranck]

Originally Posted by daleyocum

Mine is a FC25FBT and in that model the bathroom has two 45 degree panels on either side of the door. AS uses the ne near the toilet for the black tank vent pipe. I ran my 6ga wire down from the combiner box straight down inside that chase next to the vent pipe and from there through the wall and under the twin bed to the solar charge controller with all the other electronics. I mounted the BMV712 so it’s visible in the hall and penetrating into the other chase

I used AMSolar’s combiner. You can see it circled in red in this photo. I used AMSolar’s over priced panel mounts which allow you to adjust the height to miss it.

Is there a reason you didn't just use the airstream combiner. I think I see one in your picture?

[gator.bigfoot]

Originally Posted by dznf0g

Thanks, that's what I thought. Where is the point where I would need to fuse? I doubt I will increase my panels (I carry a suitcase for shade and the few times I need more than 200W) I was noodling at 400W I might need fusing, or be close.

Very nice calculator!!!

Thanks, at 400 I would definitely add the fuses. Although, you want to ensure that these fuses are accessible and that they are very secure. With all the bouncing the RV does they can easily come loose. In my opinion you would be better to add an additional feed from the roof and then fuse those lines before combining them into one into the controller. Or just add a second controller. In all the years now of running solar and looking at the performance on multiple sites I've come to the conclusion that putting more solar on the roof is a waste. Sure it's nice and convenient but the pros out way the cons. It is far better to be portable. I know that brings a whole new layer of complexity especially in regards to where do you put it and the hassle of putting it up and taking it down. And you may even be concerned about theft, but in reality the roof of an RV is the worst place to put solar. They are at the wrong angle, they are in the wrong position, they are inaccessible, they get much hotter on the roof affecting performance and the list goes on. I'm planning to build a solar tracker and then use flex panels for mine. Then I can lay the flex panels under the bed when travelling and fold up the tracker. Anyway I something in my head and hopefully I'll get to it one day.

Good luck,

[dznf0g]

Originally Posted by gator.bigfoot

Thanks, at 400 I would definitely add the fuses. Although, you want to ensure that these fuses are accessible and that they are very secure. With all the bouncing the RV does they can easily come loose. In my opinion you would be better to add an additional feed from the roof and then fuse those lines before combining them into one into the controller. Or just add a second controller. In all the years now of running solar and looking at the performance on multiple sites I've come to the conclusion that putting more solar on the roof is a waste. Sure it's nice and convenient but the pros out way the cons. It is far better to be portable. I know that brings a whole new layer of complexity especially in regards to where do you put it and the hassle of putting it up and taking it down. And you may even be concerned about theft, but in reality the roof of an RV is the worst place to put solar. They are at the wrong angle, they are in the wrong position, they are inaccessible, they get much hotter on the roof affecting performance and the list goes on. I'm planning to build a solar tracker and then use flex panels for mine. Then I can lay the flex panels under the bed when travelling and fold up the tracker. Anyway I something in my head and hopefully I'll get to it one day.

Good luck,

Wouldn't it be simple to just add one of these in a current MC4 connector?

Agree, and I doubt I will ever add mor rooftop. I do have a suitcase as well, and quite frankly 360W total (200 roof, 160 portable) works very well for our lifestyle.

Thanks for your input, I just wanted to make sure I was currently code compliant. I knew fire was not an issue with my cabling and power.

[daleyocum]

Originally Posted by jranck

Is there a reason you didn't just use the airstream combiner. I think I see one in your picture?

In my 2018 model AS only used 10ga wire coming down from the the stock combiner. That’s not enough for five panels in parallel. On newer models AS switched to 8 gauge down from the combiner. If I was doing it over with a newer model i’d use that combiner if I had a series/parallel arrangement (and an even number of panels) or had four or fewer panels.

AirMiles on the forum has had good success with a series/parallel arrangement even using the 10ga wires. You just need an even number of panels for that to work.

[gator.bigfoot]

Originally Posted by daleyocum

In my 2018 model AS only used 10ga wire coming down from the the stock combiner. That’s not enough for five panels in parallel. On newer models AS switched to 8 gauge down from the combiner. If I was doing it over with a newer model i’d use that combiner if I had a series/parallel arrangement (and an even number of panels) or had four or fewer panels.



AirMiles on the forum has had good success with a series/parallel arrangement even using the 10ga wires. You just need an even number of panels for that to work.

With 5 panels even #6 is too small. Your voltage drop is significant.

As for series parallel it all depends on where you camp. If you're in sunshine then great, but as soon as there's any type of shading it all falls apart. You can only hope that the sun on the panels out weigh the shade and it charges your batteries. I find for my type of camping I'm lucky to see sun on one panel. If I had 2 in series I'd get nothing.

[OrangeCrush]

A few years ago I studied the MPPT turn on vs PWM for an all parallel array as I too was very concerned about the Victron MPPT turn on requirement of Vbat+5V. Am solar guaranteed they have seen no issues, but I was and still am dubious, especially at high temperature and with higher lithium battery voltages. At the time they were selling a panel they called SP100 which is basically a 100 watt panel with Sunpower Maxeon cells. You can get essentially the same panel today from Renogy (eclipse I think). Due to the cell design which is very efficient with higher voltage and no grid lines they had to build in a bypass diode at the cell level for protection. Secondary benefit to this which they are now marketing extensively is better partial shade performance. I verified this with some experimentation and chose to go series parallel 400 watt using the Airstream Zamp 10ga prewire at the time. All has worked wonderful for about 4 years until last year when my max power in excellent sun dropped to only about 150 watts. Some debug on the roof yielded no revelation as each series pair was achieving close to expected Voc and Isc. Soft conclusion at the time was something was robbing me of power from the roof box down. Since I was getting ready to do a big upgrade (Lithium, Multiplus, Orion) I decided to take all panels down and carefully test and possibly re-wire all parallel. I never found an absolute problem as my panels check out fine and wiring was all good. I did discover that the Zamp prewire module at the time my AS was built (2017) has a Bussmann thermal breaker in the box for protection and the part is only rated to 12V which is significantly below the 40V my series pairs generate. I talked to Zamp and they said they have have discontinued using the thermal breaker on new AS prewire boxes as it was causing problems.

We do camp in partial shade sometimes and the 400 watt SP combo used to do OK for us. It seams the consensus is still an all parallel array will due better in shade but I am not sure it is as big a deal as some youtube videos make it out to be, especially with a Sunpower cell panel. If I had room for 2 more panels I would stay series/parallel but I only have room for 1 more. We have had a few times in the trees where sun on the panels was scarce and combined with cold nights we were hurting a bit. I am somewhat temped to stay with 400 watts of SP and get a 200 watt Renogy portable to find the sun when I need to.

FYI - the Explorist.life guy is why I started pushing the parallel panel fuse question. Zamp told me they install fuses in all their new panels which coincides with their removal of the thermal breaker from the roof box. The head EE at AM Solar, Garret Towne, told me Zamp only does this to avoid talking to customers about it and with low voltage systems it is completely un-necessary. Good engineering is about getting information from as many sources as possible and then doing your own analysis and making your own decision. I hope we have beat this bush well enough to enlighten everyone, I know it has me.

gator.bigfoot: Love your model!

[gator.bigfoot]

The big issue with solar panels are that they are not really designed for RVs. Our company owned two factories producing solar modules (sold since). One in NA and the other in Europe. I worked on the European one in the early 2000's and then setup the factory here. We also setup factories for other clients around the world. I setup 5 factories in Germany and one in Spain at one point. But we set them up in Asia, India just to name a few. Not only that, we setup factories to produce solar cells and almost all companies in the world today will most likely use the cells produced by the factories we installed. I got a great education first hand on design and production of all of this, from the raw materials to the finished product (we did it all at one point). Both amorphous and crystalline panels. The one thing that we found is that there is no money in small panels. No one wants to produce them. They are not cost effective. The bigger the more recognition you get. The small stuff fell to the low cost producers and the fringe companies. Our company got out of the solar market in the last few years, although we still support them. And I am now working in automotive once again (currently on EV batteries).

The issue with the small panels is that you cannot get enough voltage from them. To get the voltage you need to configure them in a certain way, but then you don't get the wattage. Then no one wants to buy them because of the lower wattage and the space they take up. And on a small roof and with the AS roof already curved it makes it even harder to get two panels side by side that will not be shaded by trees on most campsites in the east. Perhaps in Colorado, Cali or Nevada you can get these wide open sites. But many of them here are shaded. So it makes it really challenging given the design of the panels. Experimentation is key. See what configuration works for your type of camping. Mine I found is the parallel approach and I will one day get to adding that portable tracker. But for now, I have enough power with my 300 watts and 420 amp hours of AGM. But I always want more. I just can't justify it. Lol.

[jranck]

Originally Posted by daleyocum

In my 2018 model AS only used 10ga wire coming down from the the stock combiner. That’s not enough for five panels in parallel. On newer models AS switched to 8 gauge down from the combiner. If I was doing it over with a newer model i’d use that combiner if I had a series/parallel arrangement (and an even number of panels) or had four or fewer panels.

AirMiles on the forum has had good success with a series/parallel arrangement even using the 10ga wires. You just need an even number of panels for that to work.

You have the same model year as me and I've looked at the 10 ga wires wondering of that is really enough. Too bad we can't use the old wires to pull new bigger gauge wires through the trailer.

[OrangeCrush]

gator.bigfoot: Sounds like you have had a lot of experience and long carrier in the solar panel industry. I bet it was interesting and hopefully a lot of fun. Makes total sense that an RV is the worst place for a panel and small potoatoes when it comes to revenue. I too am frequently in trees. Not sure what I am going to do next on top yet but probably will plan on adding a portable as I have a good place in a closet to fit a 200 watt Renogy.

jranck: Yes, it is too bad we can not pull more wire through the current Zamp port. I did find the 10 ga worked quite fine for 400 watts series/parallel until the stupid Bussmann thermal breaker in the Zamp box went resistive on me. I am now faced with pulling new wire through a new hole one way or another.

[jranck]

Originally Posted by OrangeCrush

jranck: Yes, it is too bad we can not pull more wire through the current Zamp port. I did find the 10 ga worked quite fine for 400 watts series/parallel until the stupid Bussmann thermal breaker in the Zamp box went resistive on me. I am now faced with pulling new wire through a new hole one way or another.

Can you replace the thermal breaker in the Zamp box? I've decided that I'm going to try the 400W series/parallel using the Zamp box and 10 ga wire in my rig after reading this thread and the other "show and tell" solar thread. We'll see how long that gets me.

[OrangeCrush]

Originally Posted by jranck

Can you replace the thermal breaker in the Zamp box? I've decided that I'm going to try the 400W series/parallel using the Zamp box and 10 ga wire in my rig after reading this thread and the other "show and tell" solar thread. We'll see how long that gets me.

I doubt you can bypass it without removing the Zamp box to get to it.

After thoroughly testing I have decided the wiring from My Zamp prewire down is working fine and was not my problem. I talked to Bussmann engineering about the shortstop thermal breaker operating at 40V. Inside this device is a bimetallic strip that changes shape when it heats up and pulls apart a pair of contacts to open the breaker. The voltage limitations are the contacts, arching and life. If we are not relying on the breaker to open or having it engage frequently then there should be no problem operating at higher voltage. He did inform me that we need to de-rate maximum current based on temperature and sent me some tables. My estimate is de-rating to 20A the breaker should not trip on even the hottest of days.

I still like series/parallel though I conceded it is not as good as all parallel with adequate wire and panel voltage. I am concerned about the voltage delta with low light with my current panels. I experimented with some indirect daylight and found my panels will get to 18V but not much more without some direct light. 5V below that (MPPT turn on) is only 13V which is pretty low for BattleBorn LiFePo4. So based on all this my go forward plan is to go back with series/parallel (2x2 100 watt panels plugged into Zamp combiner) in which I am going to pair the front two and back two in series. Last time I kept series strings on same side, logic being they would get similar radiance. In reality I found that the farther apart the series panels are the more likely one with get shaded. In addition, I also found that the MPPT would hunt a bit when it had one string operating with a significantly different radiance. So I did not end up with more solar on the roof, but I agree with gator.bigfoot that ultimately the roof of an RV is a lousy place for solar panels for many reasons. Instead I am going to add a 200 watt Renogy suitcase w/o controller which is basically 2xEclipse/SP100 panels wired in series. I plan to control it with a Victron BlueSolar inside wired through a switch to the Zamp port on the front of the trailer. That gives me a 3rd identical 200 watt string with it's own MPPT that I can move around to seek sun.

ohhh - and no fuses

p.s. - The Zamp Obsidien is a good 4+V higher than Renogy/Am Solar 32 cell SunPower panels. Pricey but no concern running them all parallel with MPPT and LiFePo4 batteries.

[jranck]

Originally Posted by OrangeCrush

... So I did not end up with more solar on the roof, but I agree with gator.bigfoot that ultimately the roof of an RV is a lousy place for solar panels for many reasons. Instead I am going to add a 200 watt Renogy suitcase w/o controller which is basically 2xEclipse/SP100 panels wired in series. I plan to control it with a Victron BlueSolar inside wired through a switch to the Zamp port on the front of the trailer. That gives me a 3rd identical 200 watt string with it's own MPPT that I can move around to seek sun.

ohhh - and no fuses

p.s. - The Zamp Obsidien is a good 4+V higher than Renogy/Am Solar 32 cell SunPower panels. Pricey but no concern running them all parallel with MPPT and LiFePo4 batteries.

I am also thinking of some sort of a suitcase panel. However, I'm not exactly sure how I want to wire the front connection into the rest of the system. If you connect it directly to the battery bank and use a regulated panel, you always have voltage on the connector unless I install some cutoff switch.

I've not thought about wiring it to the Victron Smartsolar MPPT 150/70 charger that I have and using an unregulated panel.

How are you wiring your front connector to your charger and your existing strings of pannels?

[OrangeCrush]

Originally Posted by jranck

I am also thinking of some sort of a suitcase panel. However, I'm not exactly sure how I want to wire the front connection into the rest of the system. If you connect it directly to the battery bank and use a regulated panel, you always have voltage on the connector unless I install some cutoff switch.

I've not thought about wiring it to the Victron Smartsolar MPPT 150/70 charger that I have and using an unregulated panel.

How are you wiring your front connector to your charger and your existing strings of pannels?

First of all, I do not recommend wiring a portable panel to your rooftop controller for multiple reasons (panel mismatch, operating point differences, etc). A separate Victron 75/15 Smartsolar charge controller is only $120 and will work fine.

My system consist of 3 solar charge controllers, all Victron. One for the roof solar (Bluesolar 100/30 with dongle), a DC-DC converter for TV charging (Orion 12/12-18), and one for an external panel (Smartsolar 75/15). All 3 can be networked together so that they coordinate effort and not fight each other. This may not be totally necessary but I think it makes sense. All 3 controllers will be installed with the rest of the electronics inside the trailer. In addition to coordinated charging the other attribute is with 2x100 watt panels in series you don't have to worry about exceeding the current rating through that SAE connector or length of extension cable (within reason). The reason I chose the Renogy 200 watt w/o controller is it has the same panels as my roof so it can be used for backup or roof mounted. I am working on my schematic now and will post it once complete.

[jranck]

Originally Posted by OrangeCrush

First of all, I do not recommend wiring a portable panel to your rooftop controller for multiple reasons (panel mismatch, operating point differences, etc). A separate Victron 75/15 Smartsolar charge controller is only $120 and will work fine.

My system consist of 3 solar charge controllers, all Victron. One for the roof solar (Bluesolar 100/30 with dongle), a DC-DC converter for TV charging (Orion 12/12-18), and one for an external panel (Smartsolar 75/15). All 3 can be networked together so that they coordinate effort and not fight each other. This may not be totally necessary but I think it makes sense. All 3 controllers will be installed with the rest of the electronics inside the trailer. In addition to coordinated charging the other attribute is with 2x100 watt panels in series you don't have to worry about exceeding the current rating through that SAE connector or length of extension cable (within reason). The reason I chose the Renogy 200 watt w/o controller is it has the same panels as my roof so it can be used for backup or roof mounted. I am working on my schematic now and will post it once complete.

All that makes sense. Thanks for posting the schematic.

Jeff.