Calculate cable losses
In cable losses occur depending on the wire cross-section, length and current. These losses lead to a loss of voltage. In case of a large voltage loss, under certain circumstances the solar module could no longer fully charge the battery. Therefore, it is important to select fitting cable diameters.
The voltage drop can be calculated as follows:
|2 x cable length x current x spec. resistance of the conductor / cross-section|
|Units: [m x A x (Ohm xmm²/m) / mm²]|
|Spec. resistance of copper = 0,0177 [Ohm x mm²/m]|
|Module cable:||2 x 3m x 3A x 0,0177 / 1,5mm² = 0,21V|
|Extension to the controller:||2 x 8m x 3A x 0,0177 / 1,5mm² = 0,57V|
|Cable from controller to battery:||2 x 1m x 3A x 0,0177 / 1,5mm² = 0,07V|
The example shows that you used for the extension cable a thicker cable with 2.5 mm² or 4mm² cross-section if possible. When several modules are connected in parallel then an extension cord should be chosen with large cross section in any case.