Y branch or Junction Box for 4P (24V 200W ea)

[2BZ2Ranch]

I’m mounting an array on my Truck Camper consisting of 200W, Voc = 44V and Isc = 5.75A panels wired 4P; total Isc of 23A (EDIT Amps not Watts)
Is it okay to use 4x1 50A ”Y” connectors (photo) an all MC4 run,,, or should I wire the panels through a roof-mounted junction box with minimal (if any) MC-4 connections?
I could pull new cables through the roof-gland down to the controller and possibly run new cables from the panels to the J box (while hoping not compromising H2O seals). This would cost more in time and money than using the MC4 configuration.

Thanks for your input.
Dave

 

[2BZ2Ranch]

Forgot the photo

 

[Rednecktek]

Any reason you're running 4p instead of 2s2p or 4s?

Sounds like you need a combiner box since you're going to need fuses for it all.

 

[2BZ2Ranch]

Thanks for the reply.
Running 4P mainly to ameliorate the effects of shading. Shade is inevitable at some point during the day when boondocking in the forests (typically Arizona and Utah). I do winter in the desert for a while but mainly spring through autumn travels.
Going 4S would exceed the Voc limits of my controller. Wouldn’t shading one panel shut down the entire string?
2S2P is certainly doable but if one panel of each series string is shaded it would impact the entire system (yes?). I did run 2S2P on a previous camper but they were 12 volt panels. Since I am using 24 volt panels I thought 4P would work.

I thought fusing (30A breaker) between the controller and arrays would be sufficient. I didn’t realize I would need to fuse each individual panel. Why is that necessary?
My concern was the number of MC4 connectors used vs straight wire runs to a combiner box then a straight run to the controller. I would think straight wire runs would be better but everyone‘s RV setup I’ve seen just use connectors.

Dave

 

[Rocketman]

If more than 3p you need to fuse each “p” - so definitely need fuses for 4p.

They have mc4 connectors that have a fuse in them and then use the 4 in 1 MC4 connector or just do the combiner box (with fuses inside it).

Or go 2s2p - really all of these are good choices - the thing that probably matters most is what fits the best for your rig!!!

On 2s2p, if one panel is shaded you will lose the power from the two panels connected in series - but the other two will produce just fine. So you will get more power from a 4p arraignment- but the 2s2p - will have lower amps (so slightly less voltage loss) and a higher voltage in the morning- so charging starts earlier (but both these effects are small). But then having only one panel shaded - overall that will probably be a smaller effect too.

Good Luck!

 

[Dooug]

I'm going to run two charge controllers in my truck camper to minimize shading effect. Worked great in my last trailer and two 20 amp controllers where not any more expensive than the 50 amp I would have had to run with them in parallel.

 

[Rednecktek]

Running 4P mainly to ameliorate the effects of shading.

Gotcha! ?

I didn’t realize I would need to fuse each individual panel. Why is that necessary?

In the event of a short in one of your pannels, the other 3 will want to follow the path of least resistance, so now you'll have 300w of panel sending all the voltage and amperage into the shorted panel.

My concern was the number of MC4 connectors used vs straight wire runs to a combiner box then a straight run to the controller. I would think straight wire runs would be better but everyone‘s RV setup I’ve seen just use connectors.

Yes, but with the fuses required you'll be adding 3 more points of failure into each panel. Instead of a single connection you'll have MC4 -> MC4 fuse male -> fuse end -> other fuse end -> MC4 female.

Wouldn’t shading one panel shut down the entire string?

Yes, so 4p works out well for you.

 

[HarryN]

In general I agree with the idea of fusing on the roof - but technically isn't this limit driven by the max series fuse rating of the specific panel ?

For instance a lot of panels have a 15 amp rating, so if they are wired 2S2P then ( I think) that officially no fuse is needed. Comments?

 

[Rednecktek]

In general I agree with the idea of fusing on the roof - but technically isn't this limit driven by the max series fuse rating of the specific panel ?

For instance a lot of panels have a 15 amp rating, so if they are wired 2S2P then ( I think) that officially no fuse is needed. Comments?

Correct, 2 strings/panels you can use wire nuts if you really wanted to (not recommended but it works), it's only 3+ where you need fuses on each string/panel.

 

[2BZ2Ranch]

I'm going to run two charge controllers in my truck camper to minimize shading effect. Worked great in my last trailer and two 20 amp controllers where not any more expensive than the 50 amp I would have had to run with them in parallel.

I have a second controller (Morningstar 15A mppt) from my old camper that I put in the battery compartment. I made a 24V 120W portable panel (2P 60W). I went with the higher voltage so I could use smaller gauge extension cables. Since Watts are Watts and I don’t need to worry about shade I might change my “portable” to 2S and get it REALLY OUT THERE from under the trees.

Dave

 

[2BZ2Ranch]

I don’t participate much on here but just about everything I learned about solar comes from diysolarforum. Thank you @Rednecktek and @Rocketman for sharing your knowledge and @HarryN for asking such a pertinent question.

D

 

[Tomthumb62]

On 2s2p, if one panel is shaded you will lose the power from the two panels connected in series - but the other two will produce just fine.

In theory. Have you seen Will’s latest thread on “effects of shading explained in 4 photos”? He claims that the bypass diodes don’t work like they’re advertised to do in shading situations.

 

[HarryN]

Correct, 2 strings/panels you can use wire nuts if you really wanted to (not recommended but it works), it's only 3+ where you need fuses on each string/panel.

So 4 panels in parallel drives this requirement no matter the panel amps or max series fuse rating or is just likely to?

 

[Rednecktek]

So 4 panels in parallel drives this requirement no matter the panel amps or max series fuse rating or is just likely to?

Yup. It would be the same issue if you had 3 or 30 in parallel.

 

[featherlite]

If more than 3p you need to fuse each “p”

I think you meant to say "if more than 2p"

 

[2BZ2Ranch]

Since my controller can easily handle a Voc of 88 volts (and I already have everything I need) I’m going to try 2S2P for a while. If that doesn’t work for me then “it only costs a little bit more to go first class.”

Thanks everyone,
Dave

 

[HRTKD]

I think you'll be fine with 2s2p. My experience with shading is that if one panel is shaded, then so is the other one. If that's the case then I break out my two ground deployed panels and place them so they aren't in the shade.

I do mostly boondocking in the Rocky Mountains so I can pick whatever sunny spots works for me. On those occasions that I'm forced into a campground, I'll use Google Maps to find a site that has minimal shading.

 

[2BZ2Ranch]

In theory. Have you seen Will’s latest thread on “effects of shading explained in 4 photos”? He claims that the bypass diodes don’t work like they’re advertised to do in shading situations.

My search skills are not very good. I tried different iterations of: effects, shading explained, etc., and couldn’t find it. Will is a pretty sharp fella and I would like to read up on the discussion.
Could you provide a link to that thread?
Thanks
Dave

 

[2BZ2Ranch]

I think you'll be fine with 2s2p. My experience with shading is that if one panel is shaded, then so is the other one. If that's the case then I break out my two ground deployed panels and place them so they aren't in the shade.

I do mostly boondocking in the Rocky Mountains so I can pick whatever sunny spots works for me. On those occasions that I'm forced into a campground, I'll use Google Maps to find a site that has minimal shading.

I had a narrow and short Lance 1575 TT before. I put 2S strings on either side of the AC specifically for the reason you mention and it worked fine. I also had a portable setup for the same purpose and kept it.
Thanks,
D

 

[Tomthumb62]

My search skills are not very good. I tried different iterations of: effects, shading explained, etc., and couldn’t find it. Will is a pretty sharp fella and I would like to read up on the discussion.
Could you provide a link to that thread?
Thanks
Dave

I can’t find it now. The forum search feature is broken at the moment and looking through Will’s threads I don’t see it.