Calculating wire size in a solar system
The current flowing in the wires of a solar system depends on the power that is being transferred. The relevant formula is Watts = Volts x Amps. When calculating wiring sizes there are two separate circuits operating at different voltages and so they each get calculated separately, The goal in the wiring is 1) to make sure the wire is capable of carrying the current and 2) to minimiize voltage drop while still keeping the wire to a reasonable size.
The wiring between the charge controller and the battery will be at battery voltage. In a 12 volt battery system you can it would be fair to assume that it will be around 13.3 - 13.5 volts for much of the charge cycle. Because the voltage is low the current will be high. With 500 Watts of solar panel the formula Watts = Volts x Amps gives you about 37 Amps of current.
You can use the voltage drop tables
to calculate the wire size based on the round trip distance between the batteries and the controller. You are aiming to be between 3% and 10% voltage drop, preferrably nearer the 3% end. Its usually becomes very impractical to do better than 3% drop.
You can do the same calculation at the solar end of the circuit. The distance will be longer, the voltage will be higher and the current will be less. The voltage depends on the voltage of the panels, I would go with the "maximum output" voltage figure. Then it depends on if you put the panels in series or parallel.
How to calculate wire size
For DC wires there are two things to consider, the ampacity of the wire and the voltage drop. In low voltage DC circuits the voltage drop tables will give you the larger result in most if not all cases. Here is a link to the tables: Voltage Drop ...
Solar System for a Catamaran
When planning a solar installation on a catamaran you first need to consider shading. If all the panels are shaded equally then you can group them together with a single charge controller. If however you end up with panels that are Port, Starboard ...
Solar panel size for powerboat
This is the table showing what charge controller goes with what panels. It depends on your system voltage, for example if you have a 12 volt boat the 100/50 can accommodate 700 watts of panels but if you have a 24 volt boat the same controller can ...
Fuse and DC cables for MultiPlus 12/3000
The normal fuse you would install with the 12 volt MultiPlus 12/3000 is at least 350 Amps. This is because it has a surge capability and because as the battery voltage varies so does the current. A 350 amp fuse will avoid nuisance tripping caused ...
Index to technical writing
Our Technical Pages has an index to the technical articles on our website. This index includes all our blog posts. In addition our Blog is divided up into sections as follows: Alternators System Integration Battery Chargers Battery Combiners ...