Solar pre-wire location

[rodsterinfl]

Figure out your run length and amperage then the actual loss. On a 25' my run was shorter than I expected. By the book up to 5% is acceptable. Consider too that the calculation is assuming maximum or perfect solar conditions.

[alano]

Originally Posted by Burnside Bob

I would like to add solar, so I've been following this discussion. I have been wondering if 200W of solar would be enough so the 10 gauge seems marginal to sketchy.

Since those #10 wires are there, its a shame not to use them. Why not combine them--two strands of #10 tied together are the same ampacity and resistance/foot as one strand of #7 and then run one strand of #6 to complete the solar circuit. Alternately, run two strands of #8 and wire one #8 and one #10 together to get the equivalent ampacity and resistance/foot of a circuit made entirely from #6?

Doing either would result in a circuit that could handle more watts of solar at lower cost with less voltage drop.

10 gauge wire supports 400 W of solar with the loss due to the pre-wiring less than 2%! Just use a MPPT charger like the Solar Boost 3024iL MPPT and configure the panels in a serial/parallel arrangement. If you're only planning on 200 W then configure the panels in series. It's probably not worth your time and money to run additional wires just to save 2%. Better to spend the extra money on a battery monitor like the IPN remote so you can keep track of your energy consumption and battery state.

[Streamer1492]

Has anyone found the Solar Green and Yellow prewires that are suppose to be just "to the rear of the front vent" on 2014 27FB with two AC's (no front vent) and the AC covers about 14-16" of the roof behind where the normal vent would sit. Can't see any marking on roof around the front AC unit but then again can't see under AC. Took off the inside AC cover and didn't see any sign of Green / Yellow wires and also removed three ceiling light between skylight and AC, no luck, and just wondered if anyone has done this before I start removing the AC and/or cutting holes in the roof. Thanks

[alano]

I found mine from inside the trailer by removing the LED light. If you have a light near where AS describes the wires should be I would suggest dropping the light (unscrew the cover, then remove three screws) and feeling around for the wires.

[Streamer1492]

Don't read the manual the pre wired solar on my 2014 27FB International 2 AC units was found under the rear Fantastic Fan Vent cover. So at least check that hiding spot before you look under the FRONT vent or AC unit.

[lewster]

Some common misconceptions about voltage drop in wire sizing:

Based on the ABYC (American Boat and Yacht Council) recommendations for voltage drop in current carrying wires, Blue Sea Systems has generously provided this chart: https://www.bluesea.com/files/resour...on_chartlg.jpg

Example: If your Airstream solar pre-wire is located in the rear vent fan location of a 27FB, they terminate in the front of the trailer under the front bed at the bus bars. For a straight shot run (which it ISN'T), you get approx. 24' run and 8' drop from the ceiling to the floor, or a total of 32 feet.

ABYC electrical standard E-11 requires that you calculate the wire run from the power source AND BACK which effectively is double this length, or 64 feet, and then round up to the next available bracket.

Let's assume that we are looking at a 400 watt solar array, which should be capable of providing your 20 + amps to your charge controller. If your look at the table in the link (sorry, but I couldn't get it to reproduce here) at 3% voltage drop, a distance of 70 feet for a 20 amp load requires 4AWG cables! If you use the 10% voltage drop column for the same parameters (this time at the 65' bracket), you need 8AWG cables for a 20 amp load……..STILL larger than 10AWG.

Major solar charge controller manufacturers like Blue Sky Energy recommend that you use cable sizes from their chart: (taken from there manual for Blue Sky's 2512iX-HV solar charge controller, pg. 7) for specified cable run lengths as described below:

Blue Sky Energy - Solar Boost 2512i-HV and 2512iX-HV
BATTERY AND PV WIRING
A desirable installation will produce a total system wiring voltage drop of 3% or less. The lengths shown in Table 2 are one way from the PV modules to the battery with the 2512 located along the path. Length can be increased inversely proportional to actual PV IMP such that if current was reduced by 1/2 wire lengths could be doubled and still provide the same 3% voltage drop.

WIRE GAUGE AWG 3% VOLTAGE DROP 36 CELL MODULES
@ 20AMPS INPUT FEET / METERS
12 AWG 6.4 / 1.9
10 AWG 10.2 / 3.1
8 AWG 16.2 / 4.9
6 AWG 25.7 / 7.8
4 AWG 40.8 / 12.5

I maintain, (and so do the many people who write ampacity standards for the marine industry and solar industry) that Airstream's use of 10AWG cables for their solar prewire WILL NOT provide you with 3% voltage drop for any solar array above 100 watts (5 amps). The ABYC chart clearly shows a 5 amp load for 10AWG cable and 3% voltage drop to be limited to a circuit length of between 40-60'. This length must be divided by 2 to get the actual lineal length, or 20-30 feet…..just about what you find in most Airstreams today.

The tables cited above SPECIFICALLY address the issue of voltage drop in cable runs of varying amperage ratings and circuit lengths. Choose to believe AND USE what you want. The evidence is clear.

[alano]

Lew, these tables are misleading. They assume solar panels produce 12 V. They don't. Take the Renology 36 cell panel. At maximum power it's producing 18.9 V at 5.29 A.

So, you want to build at 400 W system? Add four panels in a series/parallel configuration. This yields 37.8 V at 10.58 A.

Let's take your 3% voltage drop example. For this series/parallel 400 W system, 3% voltage drop corresponds to 3% * 37.8 V = 1.134 V = 10.58 A * R, therefore R = .107 ohms. Since 10 AWG is 1 milliohm/1000 ft this corresponds to wire length of 107 feet.

I've got no horse in this game except to educate folks and encourage them to DIY their solar systems.

[Tino643]

Hello Alano, I read yours post and I need some clarification. First of all, sory for the english. I am from the french part of Canada, so write in english it is not familiar to me. I have a 30 foot 2015 interna. and want to put like you for solar panel. I am very handy but not for the electricity. Like you i don't want to peut a biger cable. So I no where is the pre wire. And now this cable what do i do whit it???? I supose plug some where in the trailer. If it is possible to explane to me what you did it can be very helpfull for me. Thanks!

[alano]

Salut Tino,

I have a 30' 2015 Classic, so perhaps the solar pre-wires are near the same location. In my trailer I have a rear skylight window. In front of the rear skylight is an interior light. You can unscrew the dome, then remove three screws and drop the light fixture. If you reach up with your hand in the small space in the ceiling you should perhaps find the solar pre-wires. They are #10 AWG yellow and green.

If this doesn't help, I would suggest you contact your dealer and ask them exactly how to access the solar pre-wiring.

[Zybane]

Originally Posted by lewster

Some common misconceptions about voltage drop in wire sizing:

Based on the ABYC (American Boat and Yacht Council) recommendations for voltage drop in current carrying wires, Blue Sea Systems has generously provided this chart: https://www.bluesea.com/files/resour...on_chartlg.jpg

Example: If your Airstream solar pre-wire is located in the rear vent fan location of a 27FB, they terminate in the front of the trailer under the front bed at the bus bars. For a straight shot run (which it ISN'T), you get approx. 24' run and 8' drop from the ceiling to the floor, or a total of 32 feet.

ABYC electrical standard E-11 requires that you calculate the wire run from the power source AND BACK which effectively is double this length, or 64 feet, and then round up to the next available bracket.

Let's assume that we are looking at a 400 watt solar array, which should be capable of providing your 20 + amps to your charge controller. If your look at the table in the link (sorry, but I couldn't get it to reproduce here) at 3% voltage drop, a distance of 70 feet for a 20 amp load requires 4AWG cables! If you use the 10% voltage drop column for the same parameters (this time at the 65' bracket), you need 8AWG cables for a 20 amp load……..STILL larger than 10AWG.

Major solar charge controller manufacturers like Blue Sky Energy recommend that you use cable sizes from their chart: (taken from there manual for Blue Sky's 2512iX-HV solar charge controller, pg. 7) for specified cable run lengths as described below:

Blue Sky Energy - Solar Boost 2512i-HV and 2512iX-HV
BATTERY AND PV WIRING
A desirable installation will produce a total system wiring voltage drop of 3% or less. The lengths shown in Table 2 are one way from the PV modules to the battery with the 2512 located along the path. Length can be increased inversely proportional to actual PV IMP such that if current was reduced by 1/2 wire lengths could be doubled and still provide the same 3% voltage drop.

WIRE GAUGE AWG 3% VOLTAGE DROP 36 CELL MODULES
@ 20AMPS INPUT FEET / METERS
12 AWG 6.4 / 1.9
10 AWG 10.2 / 3.1
8 AWG 16.2 / 4.9
6 AWG 25.7 / 7.8
4 AWG 40.8 / 12.5

I maintain, (and so do the many people who write ampacity standards for the marine industry and solar industry) that Airstream's use of 10AWG cables for their solar prewire WILL NOT provide you with 3% voltage drop for any solar array above 100 watts (5 amps). The ABYC chart clearly shows a 5 amp load for 10AWG cable and 3% voltage drop to be limited to a circuit length of between 40-60'. This length must be divided by 2 to get the actual lineal length, or 20-30 feet…..just about what you find in most Airstreams today.

The tables cited above SPECIFICALLY address the issue of voltage drop in cable runs of varying amperage ratings and circuit lengths. Choose to believe AND USE what you want. The evidence is clear.

You can't talk about wire gauge and amperage without talking about voltage. Voltage is a crucial part of the equation. It really depends on what solar panels you will use, what controller, what voltage, series/parallel.

A perfect example is a 1500 watt space heater I have here. About 8 foot of 16 gauge lamp cord is all it uses, because it's running 110v.

[rmkrum]

Respectfully disagree. Lew is correct in using that table.

Wire size is properly chosen based on amperage, and acceptable voltage drop over the length of the wire, period.

Insulation thickness and type is chosen for voltage and temperature rise caused by the current

A 1500 watt heater in my AS would NOT have a 16 gauge cord. It's too light to be safe. It would be 14 gauge minimum or I would not buy it.

A degree in Electrical Engineering and about 40 years of designing power distribution and grounding systems leads me to this conclusion




Sent from my pocket Internet using Airstream Forums

[Zybane]

We are talking about two different things. In solar, you speak in watts as that is the amount of power.

Take a space heater, 1500 watts of power.

A 12v 1500 watt space heater draws 125 amps! That is some thick wire required.

A 110v 1500 watt space heater draws 13.6 amps. Now the wire doesn't need to be so thick.

Whether you think 16 gauge cord is no good for 110v at 1500 watts (6 foot cord), the device is UL certified. When you increase the voltage of the solar system (to a point), the thinner the gauge wire can be used.

I think the confusion is people are talking about those charts at 12v only. 12v = thick wire needed. Bump your solar array up to say 48v and much thinner wire needed as the AMPs are changed.

600 watts of solar at 12v = 60 AMPS. 20 foot run within 3% voltage drop = 4 gauge wire.
600 watts of solar at 48v = 12.5 AMPS. 20 foot run within 3% voltage drop = 10 gauge wire.

There is a big bonus for increasing the voltage of many electrical systems. Hence why 220v in Europe has less losses than our 110v system in the US.

My favorite chart:




Alano's point was that if you can raise the voltage of the solar panels, you can use the factory pre-wiring at much higher wattage than you could if you kept it at 12v. This is absolutely true.

Now of course every time you change voltage etc you incur a loss, so all of the losses have to be taken into account.

[lewster]

Many other issues exist with higher voltage solar arrays in an RV installation other than being able to simply using thinner wire. After almost 30 years in the RV solar business, AM Solar has effectively been there and done that and has experimented with many different components and wire/panel configurations in real world situations.

While an electrically savvy DIY installer can expect some success in going 'big' with panel output voltage, there are other concerns that we have seen which make the use of higher voltage solar arrays challenging with regard to the expected consistency for commercial installation purposes.

[alano]

I've had very good success stacking modern panels in a series/parallel arrangement to create a 400 W (four 100 W panels) solar array using the existing #10 AWG pre-wiring with wiring losses less than 3%. This is largely made possible with newer technology MPPT solar controllers. All specs are well within limits and after a year I've had no issues whatsoever. I have approximately 200 Ahr of total battery capacity and find that even if I consume 50% of the batteries' capacity, the solar charger is back to 100% even on overcast days. I also store my trailer under a cloth tent and I'm surprised that even with the diffused lighting of the covered tent, the solar system keeps the system at 100%.

For those of you DIYers who have some electrical knowledge, don't be afraid to install a generous solar system for a fraction of the cost of a factory or professionally installed system. There's plenty of folks on this forum who can share their experience!

[Zybane]

I think around 800 watts of solar and 1,000 AH of battery (3000 watt inverter) you can become completely independent of shore power. Unless it's something crazy like 110 degrees outside and you need to run both air conditioners.

[switz]

A 1,500 watt heater is a resistive load so spikes in the power draw. That is approximately 13.6 amps (1500 watts/110 Vac = 13.6 amps). Wire in branch circuits must be derated 20% per the NEC for continuous loads, #14 wire is rated 15 amps. Derated it has a 12 amp continuous load capacity. #16 wire is rated 10 amps or 8 amps for continuous loads. #12 wire is rated 20 amps and must be derated to 16 amps for continuous loads.

The possibility of a short in the #16 wire or the appliance means the wire could melt before the 15 or 20 amp breaker opened.

Just something to be aware of.

[idroba]

NEC defines "continuous loads" as those of 3 hours or more in duration. That usually only means electric heaters, air conditioners, and water heaters. Even water heaters in RV use rarely run for 3 hours at a time. BTW, the de-rating also applies to the circuit breakers used on those same circuits. But to be clear, a 20 amp circuit, can legally cary 20 amps, and will do so just fine. However, if it is supplying a load known to be be "continuous" it must be de-rated to only 80% of capacity. This gets to be a somewhat hard to understand area of the code.

Yes, a smaller wire running to anything like a radio or clock which is not rated for 20 amps could in some strange circumstances become overloaded and fail prior to the typical 20 amp interior circuit breaker opening. But to build things like clocks, TV's and radios with #12 wire to them would make them clunky and very inconvenient, so the UL listings allow for smaller wire to plug in individual devices.

I am not disagreeing with anyone here, only trying to clarify the somewhat difficult to understand National Electrical Code, and some of the UL regulations and real life considerations. As said in the post above, just something to be aware of.

[JeffsTardis]

I am going to add solar to the roof of my pre wired 2015 classic 30. I see the yellow and green wire behind the couch. I am told there is a plug on the roof where I intend to attach 400 watts of solar panels. How do I connect the charge controller to those wires? How do I get power out to the batteries? How do I attach the controller panel? Just wondering if you already worked through these questions

[AirMiles]

Originally Posted by JeffsTardis

I am going to add solar to the roof of my pre wired 2015 classic 30. I see the yellow and green wire behind the couch. I am told there is a plug on the roof where I intend to attach 400 watts of solar panels. How do I connect the charge controller to those wires? How do I get power out to the batteries? How do I attach the controller panel? Just wondering if you already worked through these questions

Welcome to AirForums Jeff.

I think the rooftop box started in 2017. Your 2015 has a yellow and green prewire, but you would need to install a rooftop box. It might be easier to drop a new wire down the refrigerator vent. How to connect wires, there's lots of threads but I attached the pictures of how I connected a solar controller to the prewire in my 2017 FC25FB. You do not need to connect directly to the batteries, you can connect to the positive and negative busbars (see pictures). I attached my solar panels with 3M 4950 VHB tape buried in SikaFlex 221 caulk. You can read through the "Solar Show and Tell" thread to see more installations and read how many installed their systems. https://www.airforums.com/forums/f44...ll-181608.html Here is a post with links to all the parts I used to connect 600W to my 2018 27' Globetrotter using the factory prewire: https://www.airforums.com/forums/f44...ml#post2288472 Here's a post where I described the complete install in two short paragraphs: https://www.airforums.com/forums/f44...ml#post2331527

[Bigventure]

Your solar pre wire is located behind the center light in front of the refrigerator. You will have to feel around for it, as it could be behind the installation batts.

Grab the chrome ring and give it a slight twist to remove. You will see philips screws. Remove those and it drops out.

You will need a rooftop combiner box.