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Old 07-20-2016, 10:44 AM   #15
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Quote:
Originally Posted by Pongo View Post
When I saw the original post, which expressed concern regarding solar hub gauge waiting, I contacted my dealer. (I've a 2017 International Serenity 27FB on order, with 160W solar on the roof and 160W of portable via the front solar connector for use in shade).

An Airstream electrical engineer responded back straight away. It's been a long time since I was a practicing electrical engineer, but I'm comfortable with his response. I've pasted a copy of his response below:
....
It is interesting that, despite his response, if you look at the table in the reference it clearly states that #10 wire in a power transmission application is rated for 15 amps.

His response is based on what is safe for the wire. Ampacity is a term from the National Electrical Code and is predominantly about AC power distribution in homes, businesses and industrial applications. It is essentially the electrical building code.

Lew has it right, as usual. Voltage drop in wires is all about resistance and current. The voltage drop in a wire at a particular wire size and current will be the same in a 12V circuit as a 120V circuit, but proportionally it is 10x larger in the 12V circuit. Depending on the charge controller, the impact can be even greater.

Series connection can help, but makes the shading problem worse. If I install solar, I will be replacing the existing wiring and running panels in parallel.

Al
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Old 07-20-2016, 11:38 AM   #16
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It looks like to me the Airstream engineer above is using 120v values for his conclusion. Does anyone agree that he is correct?
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Old 07-20-2016, 11:40 AM   #17
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One more thought. Does anyone know if Airsteam will install #6 or #4 wire in place of the #10 to the batteries during construction of a new trailer if paid to do so?
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Old 07-20-2016, 01:39 PM   #18
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Airstream doesn't do anything from their build at the factory. I have the factory installed solar and have found it works good for me. I also have 150 watts of portable panels. We always look for shade so having the panels on the roof is somewhat not good. I am looking into a small wind generator and maybe another set of portable panels but only have 2 AGM 12 volt batteries in the trailer so can only use so much at night anyway Boondocking is our way on the road and we know that so if you learn how to conserve and think you don't need a lot of solar to survive
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Old 07-20-2016, 04:37 PM   #19
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Thanks for the info, I read your post and was confused because before starting the post I called both Airstream and Zamp. I talked to Jeff at Zamp in technical services and he was very helpful and provided a wealth of information. He stated as far as he knows no one has contacted them from Airstream for advice on the solar package that airstream has put together. Jeff explained to me that 10 Gage wire is NOT what they recommend for solar installs if you have the ability to add more solar panels to the system. No one knows what the Airstream Engineer is talking about 10 Gage wire being able to handle the amps that the 3 port can be connected to. If you buy 3 160 watt solar panel you'll have 480 watts thats about 27 amps, 10 gage is only rated for about 30 amps you would have a very high resistance with this set up. I'm sure many who view this know alot more than I do about solar install but I'm learning quickly with all your advice and help but one thing I do know Airstream is not doing it right.
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Old 01-03-2017, 03:21 PM   #20
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Quote:
Originally Posted by Pongo View Post
When I saw the original post, which expressed concern regarding solar hub gauge waiting, I contacted my dealer. (I've a 2017 International Serenity 27FB on order, with 160W solar on the roof and 160W of portable via the front solar connector for use in shade).

An Airstream electrical engineer responded back straight away. It's been a long time since I was a practicing electrical engineer, but I'm comfortable with his response. I've pasted a copy of his response below:



The 10 AWG wiring used by Zamp is sized correctly for the application and will support up to 3 x 200W panels running at 100% capacity with a 10% overhead. Note this also assumes that all 3 panels could actually run at 100% capacity, which is rare. While I understand the one forum poster's reasoning behind it, 6 AWG or 4 AWG in this application is not needed.

There are a number of factors that come into play when deciding the correct wire size, these are things like the length of the wire run, insulation size, air flow, ambient temperature range, proximity to other wires, breaker / fuse response time, etc.

In general use applications, like house wiring, the voltage is higher and most of these variables are not fully known or understood by the installer, or can be accounted for over the life of the house, so for a safety margin, the wire is de-rated to a smaller number.

14 Gauge = 15Amp Circuit
12 Gauge = 20 Amp Circuit
10 Gauge = 30 Amp Circuit

In Zamp's case, the application is known, the voltage range is known, and a number of other variables are also known, so it allows more freedom to better utilize the capacity of the wire safely.

Here a couple of links to websites that attempt to explain these ratings and what they mean. This information has been around a long time and is published in Handbook of Electronic Tables and Formulas for American Wire Gauge. 10 Gauge, non-bundled, open air wire is capable of handling 55 Amps for Chassis wiring, which is a conservative rating. 55 Amps in a solar application equates to around 660W, which is 10% more than 3 x 200W Zamp panels operating at 100% capacity.

http://www.coonerwire.com/amp-chart/
http://www.powerstream.com/Wire_Size.htm[/B]
Well Said!...In my previous life i've battled California State Authorities (OSHPD) over voltage drop, also worked closely with U.L. In one instance I even had to bring in actual wiring lengths and end devices on a backboard connected to Power supplies all the way to Sacramento, to prove their voltage drop methods were incorrect. It's a widely misunderstood subject. In Airstream trailers, as in most manufactured products these are not guesses, but engineered systems with life safety in mind.

Note: Belden was an excellent resource.
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Old 01-03-2017, 06:11 PM   #21
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This issue has been discussed at length in numerous other threads. Being an engineer also, I find it incredulous that Airstream is simply using the generally accepted ampacity of ROMEX cabling when used in stationary environments @120VAC without regard to circuit length.

A simple look at the cabling requirements of ANY quality solar charge controller manufacturer will give you a TOTALLY DIFFERENT PICTURE!!!!!

Here is a link to the installation manual for the Blue Sea Systems 3024iL solar charge controller: http://www.blueskyenergyinc.com/uplo...E_SB3024iL.pdf

Specifically listed on page 8, Table 2 is their acceptable length of a DC circuit for solar wiring at 3% voltage drop. For a 12VDC system running at a 32amp capacity, the acceptable length for a 10AWG cable is 6.4 FEET. If you decrease the amperage of the circuit to 16 amps, the cable length only increases to 12.8 FEET.

300 watts of solar will easily provide 16 amps into the batteries with a quality MPPT solar charge controller, so where does the Airstream engineer come up with 600 watts for his 10AWG cable. He also does not state the length of the circuit, which in DC circuits is a measure of BOTH the positive AND negative cable lengths.

In the larger Airstream trailers where the 10AWG solar prewire is located at the rear Fantastic Fan, it runs all the way forward to the DC bus bars......... a distance of 35+ feet in a 27' trailer (including the distance to drop it from the roof to the floor) FOR A SINGLE CONDUCTOR!!!! This circuit path effectively becomes 70+ feet when you include the length of BOTH conductors in the circuit.

Voltage drop CAN be mitigated by using series connections for the solar panels and a solar charge controller that will accept those high voltages (like Victron, up to 150VDC), but the charge voltage coming FROM the solar charge controller IS STILL 12VDC.

It gets better all the time!!!!!

And you wonder why Airstream still used constant voltage converters to charge (actually to destroy) their battery systems??
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