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??
Linear Mode
