Wire Gauge Required Question
For some reason I just can't understand the various wire gauge tables, and I have tried to, so I am hoping somebody will take pity and do all the work! :) One table that I can follow says that for...
Forum Discussion
BFL13 wrote:
Ok , I have very fat wires ( I have the mohms at 20a/12v if anyone cares--from tests last winter using Salvo's methods) from controller to battery so that whole side is not an "issue." ( I hope) My question is all about the run from controller to array.
It was not an "issue" there either until I went from 12v to 24v panel and MPPT. ( I knew I hated all this MPPT business! :) ) Now I don't know what gauge wire to use to the 230w panel 30ft from the 20a MPPT controller and I don't even know what amps to use, 8 or 16.
OK, for voltage drop calculations from the panel to the controller, use the Isc or more correctly Imp of the panel. That is the max current that will be delivered FROM the panel TO the MPPT controller when the controller sets itself for max power outpu.
I can do some calculations for you for various wire sizes of what to expect in the output of the MPPT controller for various wire losses, but can't get to it till tomorrow.
A quick one though is to do an I2R loss for power loss from the panel to the controller. eg. if Imp is 8A and R is 0.1ohms, the power loss is 8*8*0.1= 6.4Watts. OK, so MPPT output will go down by about 6.4W. so at say 13V MPPT output 6.4/13 = 0.5A so in that case I'd expect about a 0.5A decrease in current to the battery from the theoretical maximum. This assumes 100% conversion efficency. And the current loss will drop as panel output current drops.
