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Old 04-18-2016, 08:53 PM   #1
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800W, 60A using built in solar wiring capacity

The factory solar pre-wiring consists of:
- solar panel to front-galley-cabinet YELLOW-GREEN wiring #10 THHN 90C.
- front-galley-cabinet to DC wiring area RED-BLACK #10 THHN 90C.

I've decided to use the existing wiring rather than running larger conductors. Perhaps one day when I renovate the trailer I might run larger cables, but it is too hard to access the route now.

Because these two wires are run in wiring bundles with other low voltage wires, telecommunications, etc, NEC 720 seems to govern the installation. Since it is not in Romex or other separated branch circuit wiring, the maximum voltage on the solar pre-wiring must remain < 50 V.

Also, from NEC table 310.15, the maximum current capacity is 35 amps. I will run the wiring to the charge controller located at the main battery bus in the trailer front curb side under the couch, not placing the charge controller in the front-galley-cabinet

Ideally, I want the highest voltage on these wires to minimize the current. A good example would be to have solar generation at 48V and 32A = 1536W.

I using a Morningstar TriStar MPPT 60, which has a 60A maximum battery current ~ 800W for my 12 VDC system. Using 2 ft. of #4 90C wire from TriStar to main battery bus bar through a 60A Blue Sea circuit breaker.

Given what I can buy that will fit, I am considering one panel per string two strings in parallel, each 335W as a reasonable installation. Combined they will output about 18A. So I have plenty of safety margin on the wiring capacity, and I stay below the 50 V limit.

Am working now to make sure they can physically fit on the roof.

Does anyone have experience with paralleling voltage panels on your trailer operating closer to 800W? If so, what panels did you choose, and what string configuration do you recommend?

73/gus
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Old 04-19-2016, 12:19 PM   #2
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I installed a 400 W system, see here. The system included (4) 100 W Renology panels in a series/parallel configuration connected to a BlueSky 3024i MPPT controller. The voltage losses due to the pre-wiring in my 30' classic were just less than 2%.

Since the TriStar is rated for a PV input of 150 V open-circuit, you have quite a bit of flexibility. If you're suggesting to create a string of two 160 W panels in series and then parallel another string to create an array of (4) panels for a total power of 640 W, then you should be fine. At the maximum operating point, the array will have a current of 17.3 A and a voltage of 37. Let's calculate your voltage losses due to the solar pre-wiring assuming 70 feet of solar pre-wiring: Resistance of the pre-wiring is 70 ft * .001 ohm/ft = .07 ohm. Voltage drop is 17.3 A * .07 ohm = 1.2 V. Since the voltage across the string is 37 V, the voltage losses due to the pre-wiring are 100 * 1.2 / 37 = 3.2%. If you could stack three panels in series and parallel another string your losses would be a bit less due to the higher voltage operation.
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Old 04-19-2016, 02:40 PM   #3
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Thanks. Agree on the voltage drop issue, and I would like to keep it less than 1 V. Your systems sounds quite nice.

Actually, my plan is for only two panels, 335W each. Would like to use an even higher voltage with them in series, with ~78 V. Am looking for a configuration that gets me closer to the 800W.

By putting the solar pre-wiring in the big low-voltage cable bundle without being ROMEX-like construction, I read the NEC as requiring me to keep it < 50 V.

Do you know otherwise about this type of combined wiring bundle?

I would really prefer to have #2 run from the panel combiner box to charger wiring. Still trying to figure out a route to take new wiring from the refrigerator access port along the curb side forward to under the front sofa. I am not seeing any straightforward means to install the new wiring without removing the dinette and credenza. (OUCH)

Any suggestions on wire routing to the front curb side?

73/gus
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Old 04-19-2016, 02:46 PM   #4
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Keep in mind that the "codes" are for commercial purposes and recommendations for the rest of us.
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Old 04-19-2016, 03:20 PM   #5
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I agree that the NEC makes recommendations. I work with NFPA 70 (NEC) everyday. The code represents our accumulated knowledge and experience, and it's primary purpose is to protect life and prevent accidents (fires). I like those ideas, and so does the RVIA.

The knowledge accumulation is why I like to follow the recommendations in NFPA 1192: Standard on Recreational Vehicles.

Also, suspect everyone's Airstream trailer insurance includes a clause like this:
"What we do NOT cover…”
C. Faulty, negligent, inadequate, or defective...
(2) Design, specifications, workmanship, repair, or
(3) Materials used in repair or maintenance, or..."
By not following the NEC, and your trailer catches fire or someone is hurt, the insurance company would have a good case to walk away.

I recommend that we use the NEC's recommendations in our practice, especially Article 551 and Article 690 in this solar install case.

73/gus
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Old 04-19-2016, 03:55 PM   #6
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Gus, are you confident in the robustness of a large 335 W panel mounted on the trailer? The smaller 12 V panels, (Grape and Renology being the most popular) at least seem to have a track record with good results.
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Old 04-19-2016, 04:18 PM   #7
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I'd love to see how you intend to mount those big suckers. Friend just installed two of the 160 watt panels on his 1978 and they eat up A LOT of roof space.
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Old 04-19-2016, 04:22 PM   #8
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Gus,

We have a 2014 30' FC with 740w on the roof (4x135w and 2x100w AM Solar pannels) with room for one more 100w pannel. We did not use factory wiring. Ran cable down refrigerator vent and used special lewster airstream conduit to run cables to under the front couch where our batteries, solar controler and inverter/charger are located. Also used same conduit to run data lines for remote dislpays. Will post pictures later.

Benn
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Old 04-20-2016, 12:28 PM   #9
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I am doing a remodel on my trailer and decided to run wiring for my future solar install. I spoke to two different techs at Renogy, and they told me that the screws on their controllers cannot handle any wire larger than 10 AWG. As I have a 32' trailer, my run is about 28' from the panels to where I am putting the controller- in a new cabinet right over my front mounted batteries. ( I have to put the panels near the back of the trailer) .I wanted to run 8 AWG, but they said that was overkill for the 2 -100 watt panels I want to install. How long is your run?
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Old 04-20-2016, 02:00 PM   #10
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I assumed about 70' of #10 AWG for my 30' Classic. However, if you put both panels in parallel, your voltage drop due to the #10 wire alone will be... 10.6 A * .07 ohms = .742 V, and the voltage losses only due to the wiring will be 100 * .742 / 18.9 = 3.9%.

You should be able to find adapter pins that accept #8 AWG wire into a #10 pin.

I like the Renology panels, but I personally would not recommend their controllers. Their design is based on an older PWM technology, not the more efficient MPPT technology, and they do not include a proper battery monitor. I would pay the extra money and look at the Blue Sky MPPT controllers and the IPN Pro remote.
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Old 04-20-2016, 02:44 PM   #11
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We currently (pardon the pun) have eight AM Solar GS-100 panels on the roof of our 2014 Classic. Plan to add another GS-100 and perhaps a second one in May if there is space. Power comes into a TriStar 60 solar charge controller and then to a single 600 amp-hour lithium iron phosphate battery. We are using a Magnum MS-2812 inverter. We have both the TriStar and Magnum ARC-50 remote controls installed. #2 copper wires come from the solar panels to the Tri-Star and 2-0 copper from the battery to the inverter.

The 2014 23D International Serenity roof is fully loaded with five GS-100, panels on the roof and a 300 amp-hour lithium iron phosphate battery inside using a Blue-Sky 3024iL charge controller and a Magnum MSH-3012 converter. The hybrid inverter can augment our propane only converted 2000 watt Honda generator to start and run the air conditioner. We have the ME-ARC control head and the Blue Sky IPN Pro remote control heads.
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Old 04-20-2016, 02:56 PM   #12
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Thanks.

While the Airstream manual drawing says "ALL WIRE TO BE TEW, 105C, UL/CSA LISTED." If that were the case, I could exceed 50 V.

Unfortunately, the same interior body harness includes coaxial and telephone cables, which are not similarly insulated. Besides, higher voltage mixed with < 50V is just plain bad practice.

Wish Airstream had segregated power from all other wiring.

73/gus
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Old 04-20-2016, 03:12 PM   #13
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Wowzers, Switz. That is quite close to what I am installing:
- 2/0 battery to inverter cable (with new breakers)
- Magnum MMS1012 charger/inverter with ME-ARC50 and ME-BMK
- TriStar MPPT 60 with RTS and TS-RM-2
- new bus bars
- custom Blue Sea panel with all the breakers, disconnects, & metering

One solar panel option is 4 SF160 and 2 SF100 for 840W, which is at the TriStar's limit.

Really like your combination. How did you install the #2 wires?

Waiting to hear from Beach Bum about the "special lewster airstream conduit" as a viable option without having to remove the furniture to get it there.

73/gus
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Old 04-20-2016, 05:46 PM   #14
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With our 30' classic, and using the 12V main interior wiring harness drawing in the manual, the YELLOW-GREEN #10 run is 298 in. from refrigerator location to beneath galley sink, and the RED-BLACK #10 run from beneath the galley sink to beneath the front sofa is 299 in., total 49.75 ft. - say 100 ft round trip.

The #10 TEW wire resistance is ~ 0.09 ohm per 100 ft. at 50C. So 800W (max), 36 V, ~23A, results in a 1.9V drop = ~5%. Would like to keep it less than 1V drop. MorningStar states 99% peak efficiency, so I could realize about ~750 W charging

Would ideally like to run #2 TEW in a 1" or #4 in a 3/4" flexible conduit direct from refrigerator access along street side to under front sofa, ~ 50 ft. round trip. An alternative would be to snake in Anchor Duplex Cable, #6/2 AWG (120712 or 120705).

With Anchor #6/2 @ 0.04 ohm per 100 ft. that would be 0.5 V drop, ~ 1.6%. Being in separate insulation, I could up the voltage to the TriStar 150V limit and increase efficiency even more. I like to have options.

73/gus
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