MNRon wrote:
10ga wire is approximately 1 ohm/1000ft. So if the panels try to push 7A, that would be a ~0.5v drop from panel to battery (70ft x 0.001ohm/ft x 7A). The 40ft cable will be ~0.3v drop at 7A. As others have said, sun position will be more important than the difference between these.
This would be all well and good IF the OPs charge controller was at the battery end.
But, it is not the case for the OPs setup.
The OPs charge controller is integrated into the portable solar panel. The output voltage of the controller is fixed 13.5V.
Drop .3V and the battery sees only 13.2V which is nothing more than a trickle charge.
However, your assumption of .5V drop is not correct as it is only taking into account for 1 wire, to complete the circuit there is two wires involved.. So the actual length of wire is 140ft for the 70ft run and 80ft for the 40ft run..
Now that turns out to be 1V drop for 70ft (140ft total length of pos and negative) run at 7A and .6V drop for 40ft (80ft total length of pos and negative)run at 7A..
Now things would be better if the OP could separate the controller from the panel and mount the controller at the battery..
This would mean the input of the controller gets full panel voltage (17V or more)- the voltage lost from the wire and the battery now gets the max voltage output of the controller (13.5V) instead of 13.5V - the voltage lost from the wire run = 13.1V..
You can't make "amps" if you don't have the "volts"..
