What is the ideal Cable cable thickness on a Solar MD battery installation?

DC cabling is used in places when self-generation power takes place like photo-voltaic installations or a battery. When designing a system cable sizing is imperative, especially in Low-Voltage systems.

Resistance describes how difficult it is to make electrical current flow through a material. It is a measure of how much voltage an element needs in order to increase electrical current. Cable thickness is particularly important for low voltage applications with voltage drops or loss being the most common problem for low voltage system faults.

Undersized cables waste energy(energy converter to heat), with oversized cables resulting in a waste of money due to an overspend on copper. Thickness and insulation determine the maximum voltage for the application. The amount of current determines the thickness and the type of material that the cable is made from.

Factors such as electrical resistance of the material, the length of the cable and the diameter of the cable determine cable resistance. When current passes through a cable, the cable resistance is responsible for a voltage drop over the length of a cable as well as the cable heating up. An increase in current will have a worse effect with an undersized cable that heats up and can cause fires.

It is important to keep the voltage drop(losses) to a minimum with the obvious way to increase the thickness of a cable or to keep the length of a cable as short as possible. Another option to avoid losses is to increase the voltage of a system.

Additional resistance is created by items such as:

• Fuses

• Bad cable lug crimps

• Loose connections

• Dirty/Corroded contacts

There are various ways to avoid losses between batteries in a parallel circuit including a diagonal connection, a common busbar or with a positive and negative post with the requirement of cable to be exactly the same length.

Cable thickness on Low-Voltage applications for Solar MD LiFePO4 batteries are as follow:

• SS4037(100A) - 35mm

• SS4074(100A) - 35mm

• SS4143(200A) - 50mm

Further self-education on cable sizing for systems can be found in Victron Energy’s Wiring Unlimited document - https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf

This document shows the maximum current for a number of standard cables - https://www.victronenergy.com/upload/documents/BatteryCables.pdf