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]

To determine the total voltage loss, added to the losses incurred on the individual subregions.

An example

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
Sum:	0,85V

The total loss should be in any case smaller than 2V, if possible just 1V. As lower the voltage drop, the better.

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.

Calculation of the voltage losses

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