The next step with the open-source charge controller project is to design the printed circuit board (PCB).

This circuit board has specifications that it will work with up to 20A DC, hence I need to ensure that the thickness of the tracks is able to cope with this current without any problems.

Here I show how I calculated the track width for the PCB.

# Background

Due to the resistance of most conductors, there will always be some power lost within any conductor carrying any current. This is due to P = I2R and that the conductors have resistance (even if it is very small). So any current carrying conductor will dissipate power as heat.

We need to ensure that this track will not get too hot then carrying the maximum current.

The resistance of the the copper track on a PCB is related to the cross-sectional area of the track and its length.

The copper on a PCB is generally rated in terms of volume of copper applied per square foot, or by its thickness. Different thicknesses of copper can be obtained from PCB manufacturers, typically 1oz/ft2 = 35micron thick, 3oz/ft2 = 70micron thick or 3oz/ft2 = 105micron thick.

Knowing this, the current, the maximum temperature rise we allow and the approximate length of the conductor we can use an on-line PCB trace width calculator, such as this one which is great.

There are more details on the PCB process and thickness of copper from a PCB manufacturer, here.

# Calculations

The maximum design current is 20A. The copper thickness available are 1 or 2oz/ft2, which came from my PCB supplier. I will choose the thickest. The length of the track is up to 25mm long. I set the maximum temperature rise to 20C, as the 20A rating is a maximum.

The width of the track must be: 12.3mm wide for 1oz/ft2 or 6.14mm wide for 2oz/ft2. These are wide, but with good PCB layout this should be achievable. I will try and use as wide PCB tracks as I can for all the high current sections.

One other option would be to solder on additional cable to the whole PCB track path to bulk out the tracks. This will allow higher currents. But this would be a hassle to do for every board. I will try to fit wide tracks on the PCB.