Calculating wire size and voltage drop
I'm in the process of adding a second battery bank. The bank is two 6v GC2 @220 AH. I've finally nailed down some exacting measurements and have totalled the two runs from the bank to the distribution...
Forum Discussion
When I was adding a second battery that was going to be 10' from the first I did some calculations for voltage drop based on a 20' combined DC run from the charge controller to the battery.
2ga - drop of .53% 14.49 volts to 2nd battery
4ga - drop of .85% 14.38 volts to 2nd battery
6ga - drop of 1.36% 14.3 volts to 2nd battery
8ga - drop of 2.15% 14.2 volts to the 2nd battery
Usually systems are wired to avoid a drop greater than 3% loss. Current capacity is a function of the cross section of the wire or its area and not its diameter. This is why the change is not linear with the diameter of the wire.
Whether you use 2/4/6 gauge wire is not going to make a noticeable difference in performance. Thicker wire is much harder to run and more difficult to properly attach the connectors. I do recommend solder slugs and connectors made for them over using a crimp connection for anything heavier than 8ga. Delcity.com is a good source for these. The solder connector is mechanically stronger and keeps out moisture far better than a mechanical crimp. For ultimate long term performance marine grade wire will greatly reduce corrosion problems with a crimped connector and Jamestown Distributors and West Marine are good sources.
2ga - drop of .53% 14.49 volts to 2nd battery
4ga - drop of .85% 14.38 volts to 2nd battery
6ga - drop of 1.36% 14.3 volts to 2nd battery
8ga - drop of 2.15% 14.2 volts to the 2nd battery
Usually systems are wired to avoid a drop greater than 3% loss. Current capacity is a function of the cross section of the wire or its area and not its diameter. This is why the change is not linear with the diameter of the wire.
Whether you use 2/4/6 gauge wire is not going to make a noticeable difference in performance. Thicker wire is much harder to run and more difficult to properly attach the connectors. I do recommend solder slugs and connectors made for them over using a crimp connection for anything heavier than 8ga. Delcity.com is a good source for these. The solder connector is mechanically stronger and keeps out moisture far better than a mechanical crimp. For ultimate long term performance marine grade wire will greatly reduce corrosion problems with a crimped connector and Jamestown Distributors and West Marine are good sources.
