Solar pre-wire location

[rodsterinfl]

Great thread. I have some questions as well.

I have already ordered my components and have gone aftermarket; however, I am looking at using the Airstream prewiring for solar. From what I understand, the Yellow (+) and Green (-) lead wires from the battery bus (under my sofa) terminate at the refrigerator outside access- I have located these wires. Although there is some dispute on this matter, I will stick with the AWG wire gauge chart to conclude that the provided 10 gauge wiring is three gauge sizes larger than what I need and therefore large enough using the power transfer ratings.

Supposedly there is a cat5 wire running from the tank monitor (not connected but bundled behind it) to the battery bus. This determines the location, by wire convergence, of the controller to be under the sofa.

Has anyone else used the prewired system on aftermarket?

I am thinking about adding the remote solar monitor next to the tank monitor as the wire is there (logical) but would like to hear any thoughts on sawing a hole in the aluminum and doing such. In my camper, it is on the kitchen wall. The roof panel installation seems straightforward- mount panels to roof using Z brackets, seal the area, run the wiring to the refrigerator vent and attach to the yellow and green wires.

Without having looked at the battery bus area yet, I am hoping to find the cat5, the yellow and green wires easily. I understand as well that I will need to include a fuse on the positive connection to the battery bus. Any other thoughts?

Finally, is the temperature sensor wire critical to operation? I understand what I would need to do for this but do not know if it is REALLY important or just an additional thing one can do. I remember reading about charge converters with and without temperature monitoring and some write ups that made it sound as if it were something that made little difference. I do not know if solar is more critical. BTW, I am using a 25 amp morning star SunSaver Duo that came highly recommended. It allows for adding additional batteries if desired separate from the original bank and comes WITH the monitor. The cool thing is that it is fully programmable and you can shut off the 2nd battery bank option or even create priority charging. So, you can use it with one bank too.

[rodsterinfl]

Additional:

Alano, I am wondering, they must have changed the wiring scheme from my vintage to the newer model. Did you have Yellow and Green terminal wires in your fridge area? My manual mentions only those wires and the Cat5 as prewire. Just checking. My roof panel arrives tomorrow. I am installing a roof system with wiring for two portable systems. I need to change one question in post #21 to add using the Airstream prewire with the same wiring scheme.

BTW, what is the wattage of the factory installed option now? Looking at Paceman's roof photo and the panel size, I would guess 300 watt.

[idroba]

Factory is still two 50 watt panels.

[kenen42]

Originally Posted by alano

I was also able to reuse the existing CAT5 cable that was pre-installed. The Blue Sky IPN remote requires a 4-pin RJ-11 connector (telephone), while the current shunt from the battery to the remote requires a twisted pair. Well, if you cut the CAT5 connectors off you'll find (4) twisted pairs! So simply splice back on a 4-pin telephone connector to connect the Solar Boost converter to the IPN remote and connect one of the unused twisted pairs from the current shunt. The CAT5 cable is already pre-run and terminates next to the Inverter on/off switch. It was easy to cut a hole just below the Seelevel controller using a Dremel tool and mount the IPN remote.

How did reusing the CAT5 cable go? I'm planning on doing the same thing and wasn't sure if the CAT5 twisted pair was heavy enough for the shunt monitor.

[alano]

The pre-wiring was found near the inside ceiling light just in front of the rear skylight. The pre-wiring terminated just in back of the sofa, not far from the outside battery box. The CAT5 cable was also found in back of the sofa on the 2015 Classic.

I used the existing CAT5 cable for connecting both the current shunt and the control signals for the IPN remote. The actual current shunt is located in the battery compartment. The sense wires connected to the shunt do no carry current, so one of the twisted pairs in the CAT5 cable can be used for this signal. The only requirement when running wires for a current shunt a fair distance is that they are a twisted pair. The twisting prevents external electromagnetic coupling which can affect the current measurement. Fortunately the CAT5 cable includes four twisted pairs!

The system is working perfectly. I'm very happy with the result having reused as much wiring as possible.

[rodsterinfl]

The system is working perfectly. I'm very happy with the result having reused as much wiring as possible.

That is good to hear. Hopefully I will be able to do the same. The difference though is in the location of the wiring- I guess.

Factory is still two 50 watt panels.

They look big on that roof for 50 watt panels but that makes sense. They are about 25x20 or so. The one I ordered is 40x39 - should fit. I did not measure as I knew the AC was 30ish wide and there is quite a bit of open space on my rear roof area behind the AC. The bath and fridge vents are on the side of the AC.

[rodsterinfl]

I posted this already in another thread but I finished my solar wiring tonight using the prewiring. I used the Cat 5 cable as well for my monitor now mounted under my tanks monitor. My father came by and we had a discussion about the wiring. (He is a senior electrician that sells and services generator systems all over FL- he's the one they call often when the others cannot get it to work). I shared with him about the forum discussion on wiring and solar and gauge, etc., he laughed and said,

"amperage is amperage DC or AC. Wire has a rating and 10 gauge is use quite often on generators and used in particular 30 amp circuits. The wire can handle up to that amperage but usually you want to follow the guideline related to continual current (power transfer rate), 15-20 amps, so the wire doesn't heat up too much. Your trailer is wired here with 10 so you easily pump around 12 amps without any issue and still have room to spare. If people are telling you that you need great big large wires for amperage like that they are wire salesmen. On this trailer you shouldn't have a resistance run issue either."

I just wanted to share this about the prewire and his assessment of it when he looked at it tonight. While it's true about needing larger wire for greater power or decreasing resistance, it is not going to matter with a roof system using the prewiring up to about 200 watts or 12 amps.

[lewster]

Rod,

The amperage is not really the issue, but the voltage drop certainly IS. No disrespect to your Dad, but in the world of DC solar, where one is trying to squeeze every drop of charge capacity from a given system, even the slightest bit of voltage drop is to be considered.

The systems that I install all have minimal voltage drop due to the over sized cables that we use. The chart that I posted from Blue Sky Energy clearly shows the realtionship between voltage drop and acceptable wire lengths for 12VDC & 24VDC cable runs.

These folks have specific requirements to assure that their systems will operate at peak efficiency. Their recommendations are made after extensive research and testing of their systems.

Will a system work with smaller wire......... sure! Is it as efficient as it should be.......... probably not.

I always find it interesting when certain folks on these Forums always seem to have better answers and solutions than those that engineer these systems and earn their living in doing so.

I'm done arguing the point! Use whatever wire floats your boat. Enjoy your system and enjoy your trailer and don't sweat the small stuff ........ that's what folks pay ME to do !


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center
Lifeline Batteries**Magnum Inverters
541-490-6357

[rodsterinfl]

I do not mean to argue with you. Your advice has been very helpful. I became concerned while planning this project as it was a point of issue to be reviewed. What I hear you saying is to tweak every ounce of power from those panels go with larger wire. No issues. There were a few though that were telling me that DC was totally different from AC power, I had to use 00 wire, etc for my one panel! I just try to glean info from those that know and deal with conflicting info. I appreciate you and your knowledge on this stuff. No worries.

Here is my wire setup on the single panel- max 8.84 amps, 10 gauge wire with 16.5' run to controller with 1'- 10awg cable run from controller to batt terminal (bus) wired with large battery cables- length within 1.5' of battery.

[lewster]

Originally Posted by rodsterinfl

I do not mean to argue with you. Your advice has been very helpful. I became concerned while planning this project as it was a point of issue to be reviewed. What I hear you saying is to tweak every ounce of power from those panels go with larger wire. No issues. There were a few though that were telling me that DC was totally different from AC power, I had to use 00 wire, etc for my one panel! I just try to glean info from those that know and deal with conflicting info. I appreciate you and your knowledge on this stuff. No worries.

Rod, No offense taken. Everyone knows that whatever information that is placed on the Web is to be taken as gospel, regardless of the source!

You take what works best for you and live with the results.

[mikebee]

Originally Posted by rodsterinfl

I just wanted to share this about the prewire and his assessment of it when he looked at it tonight. While it's true about needing larger wire for greater power or decreasing resistance, it is not going to matter with a roof system using the prewiring up to about 200 watts or 12 amps.

Rodster -- can you please ask him whether he thinks 300 watts or 18 amps would be safe with the prewire? Curious minds want to know!

[alano]

Hope you don't mind me sticking my two cents in here but when using #10 AWG wire, the maximum carrying currrent for power transmission is 15 A. These are very very conservative guidelines. Could you get away with pushing 18 A through #10 wire, sure. But let's look at your losses.

I've been thinking about how to discuss losses with regard to solar installations and I think the best way is to represent losses is in terms of power. Why, because in a solar configuration you're goal is to convert the sun's solar energy into power at the solar cells, and then convert this power again to charger your batteries.

So if you intend on using #10 AWG wire and let's say you have a total of 40 feet of wire. Your resistance will be 40 ft * .001 ohm/ft = .04 ohms. Your power losses, just due to the #10 AWG pre-wire (neglecting all other losses) will be P = I*I*R = 18 * 18 * .04 = 13 W. Since your total power is 300 W, the losses to the pre-wire are (13/300)*100 = 4.3%. This isn't an outrageous loss, but considering there are other losses in the system you might not want to throw away 4.3%.

So here's the beauty of an MPPT system... If you connect your two panels (I'm guessing you're considering two 150W panels) in series, then the current stays the same, 9 A, but the voltage doubles. So now your power losses in the pre-wires are 9 * 9 * .04 = 3.24 W, which is only (3.24/300)*100 = 1.08% of the total. By connecting your panels in series you've reduced your pre-wire losses by a factor of 4!

This assumes you're using an MPPT solar charger that can handle the voltage of two panels in series.

Hope this is helpful.

[BAB]

Found it interesting that at the annual session with the Airstream execs (Alumapalooza, last month), they admitted that it was time for them to get serious about the solar package that they are installing. It really is pretty puny given the demands of the 12V system of some of the trailers -- like the '15 Classic. You need 12V for a LOT of stuff, including the power awning, power stabilizers, power recliners, etc. I found after 3 weeks with my 600W AM solar package and my Magnum MSH inverter, 4 Lifeline 6V batteries, my batteries never fell below 45%. Really only needed my generator for the A/C. Solar easily covered everything else.

[rodsterinfl]

Rodster -- can you please ask him whether he thinks 300 watts or 18 amps would be safe with the prewire? Curious minds want to know!

I just asked him and he said that the power source will probably not be continuously producing the extra three amps (above spec) and he wouldn't worry about it on the length of run in "those trailers".

He started telling me again how 10 awg is used in large generator circuits to carry up to 30 amps, usually short runs but nonetheless.

So there you have it. His Father's Day opinion.

@BABS:

Really only needed my generator for the A/C. Solar easily covered everything else.

That is my goal, though my needs are much lighter. In a lengthy phone meeting with Renogy I spelled out my projected daily need and they came up with a solar requirement of 236 watts. Naturally this did not include AC or toaster use. They recommended a system of 300 watts to slightly overkill the need. I will use the generator for higher wattage items like AC or alternative toast making methods! In your case, that's the problem with having a Cadillac with all the options, all that power requires more more more!

It all depends on what kind of system someone wants to build out. I wanted to maximize my use of the current battery system without adding more batteries. I have the ability with my system to add more in the future but for now it is enough. My 70 amps usage is 80% of the current batteries' available capacity so I am good. The system follows the 8-10 times rule- 18 amp solar capacity/184 amp storage/110 amps available for use.

[BAB]

Rod, you do an amazing job with the science of electrons! It is very easy to get spoiled with the goodies, but there is definitely seems to be some infinite loop associated with power stuff. Add a goody, figure out how to power it! My buddy Gary finished upgrading his electrical system with solar AND lithiums. That will be my next step, hopefully the 6V Lifelines will last long enough for lithium prices to drop out of the stratosphere.

[switz]

Another tidbit concerning solar is that the battery system amp hours rating should be at least 75% of the total solar panel wattage. Thus we have a 600 amp hour lithium battery with 800 watts of solar on the roof. The wire size coming down from the solar panel roof junction box is #2 copper. The wire size between the battery and the Magnum, a distance of less than two feet, is 4-0.

[alano]

Ok, let's do the math again. 10 AWG wire has a resistance of 1 ohm / 1000 ft. Four Renology panels configured as two in series paralleled with another two in series result in an optimal current of 10.6 A and voltage of 37.8 V.

In my 30' Classic I conservatively estimate the pre-wire length to be 35 ft per conductor. So 70 ft equals 70 milliohms and this results in a voltage drop of 10.6 A * 0.07 ohms = 0.742 V. So the voltage loss due to the pre-wiring is .742/37.8 = 1.96%

You'll probably also hear that series connected panels are not as good as parallel connected panels. Another wives tale where there's no field data that's reliable.

Conclusion: if you can DIY a system go ahead and reuse the existing wiring in a series connected configuration with an MPPT controller.

[lewster]

I prefer to use the stated requirements of the manufacturers of the equipment that I'm using. This specifically includes solar charge controllers and inverter/chargers.

You might find this table of interest; taken from Pg. 8 of the Blue Sky Energy 3024iL manual: (slightly mis-aligned, but you get the picture!). Perhaps some folks think that they have better answers than the equipment manufacturers that they use. Maybe they should offer their services to the OEMs!

12VDC System 24VDC System
Feet/Meters
12AWG 4.0/1.2 10.7/3.3
10AWG 6.4/2.0 16.9/5.2
8AWG 10.1/3.1 26.9/8.2
6AWG 16.1/4.9 42.8/13.0
4AWG 25.5/7.8 68.1/20.7
2AWG 40.6/12.4 108.2/33.0
1/0AWG 64.6/19.7 172.2/52.5

Pay particular attention to the line in red, which is for the 10AWG that Airstream uses as their solar pre-wire. For a 12VDC parallel connected solar array, you need 6.4' maximum run or less to achieve 3% voltage drop. For a 24VDC series/parallel array, you need 16.9' or less for 3% voltage drop or less. Still thinking of using the solar pre-wire????

And BTW, parallel connections vs. series is no "wives tail"! If you even partially shade one of a series connected pair of panels on an RV roof, you loose the output of the majority of that string. Loose a single panel in a parallel connection and you only miss the output of that single panel. Series connections might be great for free-stanging residential solar arrays, but almost every RV installation will be subject to some shading over the course of a day, unless you have a 40' motor home or huge 5th wheel with a veritable dance floor of available space.

The folks at AM Solar, with 28 years of specific experience in the RV solar business and thousands of RV solar installations have tested this extensively. Their conclusions are that more usable wattage is recovered from parallel connected panels.

Folks, of course, are free to use what ever systems they want. I would rather defer to proven experience.

[rmkrum]

Which is exactly why we didn't bother looking for the 'top end' of the dinky factory pre-wire when I installed solar on our AS. We used the nice heavy wire that came with the AM Solar kit. Bigger wire is better, period. And yes, I am an electrical engineering type person...


Sent from my pocket Internet using Airstream Forums

[acstokes]

Maybe someone can answer this question that's been puzzling me:

I'm no solar guru, but I've installed 2 systems of my own, one was 360 watts and the other 600 watts. The inverters were 1000 watts and the batteries used were 2-Lifeline 6v totaling 300ah. I would've added two more batteries if I had had more room in the front of my trailer near the inverter and DC breaker panel. I wired all panels in parallel and used #4 AWG for the run from my combiner to the MPPT controller. Once I used a Blue Sky controller and the second time a MidNite Solar controller...both American brands. I know some will say I should have used a Magnum controller, but I didn't want to pay the additional expense and I only needed a 1000 watt inverter.

I was puzzled by the fact that both the Blue Sky and MidNite Solar controllers would only accept wire size of up to 10 AWG for both input and output wires. After the expense of buying marine-grade #4 wire I had to downsize to #10 to connect to these controllers. Why aren't these controllers designed to accept up to at least #4 or #6 wire? Am I missing something here?

By the way, what size wire will Magnum controllers accept?

Thanks for your suggestions.