Grand Design Reflection

[rob2020]

I have searched high and low. I posted a few month or more ago now. I have a bumper pull Reflection 300 RBTS with the prewire on the roof for solar. It has a 10ga wire I have been trying to find out can you put a larger wire in the tube or how ever they did it.
I have four batteries on the way and want to but 1200 watts of solar. I am undecided whether to go in series or parallel. I think heavier gauge wire would be better. I would preferer to use the route Grand Design used for the 10ga if at all possible rather than drilling holes.
I have read of guys using 1250 watts with 10ga but coming from automotive back ground we always used a little heavier wire in most cases. In searching the web I find so many different opinions and lots of them don't know what they are talking about.
I think someone in this group will have the proper answer. Thanks all for your time.

Rob

[Butcher]

I'm in the same boat as you, but with the MPPT I have chosen, I'm limited with a 25v solar panel voltage. I have not run larger wiring, but I will be by spring. The other issue you may have is the current capabilities of the connectors. Most MC4 connectors are rated around 20A. They do make some rated at 60A but they are difficult to find. I will be running 4ga welding cable from the roof to the MPPT. I will eventually be running two MPPT's so that mean I need to run two pairs of cables.

If you are not limited by your MPPT, then most people are running series and therefore the voltage goes up but the amperage goes down. That is probably the best way to go for most people. I'm certainly not a specialist of any kind but all the questions I have found are just under your fingertips. Google is your friend.

[Second Chance]

Moved to Solar Systems and Generators.
@rob2020, you can create a signature block with your RV and tow vehicle information (see mine below). That way you won't have to repeat that information whenever you post or ask a question - and others won't have to ask. You can create a signature by going to:

Forum Actions (on menu bar) -> Edit Profile -> Edit Signature (under My Settings on the left)
@SolarPoweredRV is one of our resident experts on this topic - perhaps he'll chime in here with some advice.

Rob

[SolarPoweredRV]

In most cases 10ga wire should be adequate ( I used 6ga only because my coach was not pre-wired and I had a 100' spool of 6ga).

The limiting factor of wiring is the amps being transported, one way to increase the carrying capacity of your wiring is to increase the voltage carried over the wires. This is easy to do when you are talking about Solar panels, you can increase the voltage by stringing your Solar panels together in a series/parallel configuration.

When you string Solar panels together in series, the voltages are added together, when you string Solar panels together in Parallel, the amperages are added together. Consequently, if you increase the voltage being sent down from the roof the smaller 10ga wire can easily handle the output from a 1200 Watt Solar Array by using a combination of Series and Parallel connections.

This concept can be easily seen by looking at the attached wire gauge chart (linked below). The chart shows that (at a 3% loss rate) a 20 foot 10ga wire can handle 15 amps at 12 volts, however, that same 10ga wire can handle 30 amps at 24 volts.

The chart also has the formula to calculate the amperage load for any voltage and wire combination.

[Butcher]

I think I know what you are saying but that certainly does not look right.

If a wire can handle 15a, then it can handle 15a. So, 15a at 24v is more watts than 15a at 12v. You are saying that you can double the amperage on the same wire?

Yes, I'm purposely being non technical.

[SolarPoweredRV]

I think I know what you are saying but that certainly does not look right.

If a wire can handle 15a, then it can handle 15a. So, 15a at 24v is more watts than 15a at 12v. You are saying that you can double the amperage on the same wire?

Yes, I'm purposely being non technical.

In this example it did turn out to be double the amps, however, that is not the case with every instance of increased voltage.

All I did was look at the chart (3% loss) for a 20 foot wire run and follow that column down to the last listing for 10ga wire on both the 12v chart and the 24v chart.

Using that same example, if a 10% loss is acceptable in your application then the 12v amperage can be increased to 50 and the 24v amperage is increased to 100 on that same 10ga wire.

This chart brings the concept of "acceptable loss" into your wiring design. How this relates to Solar panels on an RV is...

When your Solar panels capture energy from the Sun, you want as much of that energy to reach your battery bank as possible, therefore, you want to size your wires large enough to minimize your "wire losses", ergo, you want to use the 3% chart. The same concept applies when you are cabling your Inverter, you want as many electrons feeding into your Inverter as possible (again, using the 3% table).

I get that it doesn't make a lot of (logical) sense, however, some of the 4, 6, and 10ga wire is rated for 600 volts, if there was not this inverse correlation between Amps and Volts, how would you ever force 600 volts through a 10ga wire if you can only run 15 amps through it at 12 volts.

FYI: the math would look like this: 600 volts is 50 times larger than 12 volts, therefore, 15 amps divided by 50 would equal .3 amps at 600v, .3 amps at 600v would be useless .

[Butcher]

As I mentioned, it just did not look right the way you first put it. Some people would get confused.

To me it's pretty simple. If you are stuck with a certain gauge wire, If you can, up the voltage so the amperage will go down. That would keep the wire happy.

[rob2020]

Thanks a lot for the info. I have ordered a book by Will Prowse I would like to run all panels in a parallel as where I live in BC Canada we don't always get the most sun. All I read is with series you don't always get max from the panels. Or if I go series/parallel it it not a concern. I guess I am just having a hard time wrapping my head around such a small wire doing the job. I sure don't know why Grand Design can't answer if a larger wire can be run in the tube they used to run the 10ga. They referred me to the dealer which has no clue. I have four Renogy batteries on the way and have all winter to get the solar in place so not a big rush. Thanks again. Rob

[SolarPoweredRV]

Thanks a lot for the info. I have ordered a book by Will Prowse I would like to run all panels in a parallel as where I live in BC Canada we don't always get the most sun. All I read is with series you don't always get max from the panels. Or if I go series/parallel it it not a concern. I guess I am just having a hard time wrapping my head around such a small wire doing the job. I sure don't know why Grand Design can't answer if a larger wire can be run in the tube they used to run the 10ga. They referred me to the dealer which has no clue. I have four Renogy batteries on the way and have all winter to get the solar in place so not a big rush. Thanks again. Rob

While I did not have the pre-wired Solar package on my coach, I did find that GD had installed a 3/4" conduit from the roof into the main hold. This 3/4' Conduit was large enough for me to run 2, 6ga wires down into the hold (10ga would have been sufficient, however I had 100' of 6ga for the project and that is what I used).

I don't know (or remember) which Solar panels you are planning on using, but, I suggest you look into the new Residential Solar panels. Many of the newer Solar panels are designed with circuitry that minimizes panel loss from shading. I recently saw a video that demonstrated shading on Solar panels and they discovered that there was almost no loss when the panels were shaded vs not shaded (search YouTube for Solar panel shading).

I also struggled with the Series/Parallel decision, what my decision boiled down to is that mounting Solar panels on an RV roof is never going to give you perfect Sunlight conditions because they are almost flat mounted and your RV is never going to be parked, or rolling, in the ideal direction to avoid shading. So, my solution was to use the latest Solar panel tech available and hope for the best. This is also why I do not concern myself with parking the coach in any particular direction, I mounted the panels on both the right and left side of the coach and one panel up front across the cap, this way I figure I have three directions covered for the sun to hit my panels and at high Noon, in the Desert, I will get my Max Sun, basically, I don't worry about it.

By-the-way, one of the reasons I chose my panels was because they performed 11% better than "Standard" panels in low light, I felt that was an advantage being mounted on an RV that is often under the shade of trees.

With the newer Residential Solar panels (not Renogy, Furrion, Nupowa, etc.) you will be able to Series and Parallel your panels without needing to worry about shading (just assume there is going to be shading at some point in the day).

I felt that having higher voltage available was better than worrying about shading.

Let me explain: a "12v" Solar panel operates at ~ 18 volts to charge your batteries, the charging voltage is 14.4 volts for LiFePo batteries, this only allows you loose 3.6 volts (due to clouds or shading) before your Solar panels are unable to charge your batteries. Now, if you paired two panels in Series you would be charging at ~36 volts which allows you to loose 21.6 volts before you are unable to charge the batteries. This I felt was the advantage of having a Series/Parallel (2s/2p) Solar panel installation.

[Butcher]

. I sure don't know why Grand Design can't answer if a larger wire can be run in the tube they used to run the 10ga. They referred me to the dealer which has no clue.

Many times they can't tell you because the person you are talking to is from a call center. The person who may know is too busy designing other things. The installers are just that, they do as they are told and wonder every day if a robot will be taking over their job.

If they did tell you 'it could' AND it does not, who are you to blame? If they told you 'it can't' and it does, who are you to blame? It's a no win situation and a lot of time lost to work threw your problem that really is not GD's problem. So, it's real simple to pass the buck to the dealer. Of course, the dealer will not know either. Unless they run across this issue all the time [which I do not believe they do].

You bought the product as designed. Anything you do to it, is not designed and therefore you should be on your own. Although you may think it's a simple change, for an engineer, it may not be so simple.

I wish I could help but I will not know how they ran my wire until I convert mine this winter. In the end, 99% of the people just series the panels and call it done. So much easier than changing the cable.