PCB Track Width Question

Hi All,

I am designing a PCB which has got some fuse holders on it for power distribution. I am unsure about the track width I should be using.

There is a single power in connector and 10 fuse holders. Each fuse holder will contain a 2 Amp fuse. Therefore the power track supplying the fuse holders will have a maximum of 20A @ 12V. The PCB manufacturer I am using uses 35µm Cu thick metal.

I have used the circuitcalculator.com website to calculate the track width and it says it should be 18.7mm. It doesn't use voltage in this calculation, so could someone confirm that this is correct?

If anyone has a simple method they use to calculate track widths could they let me have it.

Many thanks in advance!

Voltage is not important to determine the trace width. It's the current and the resisistance of the trace which are important.

E.g. a trace of 15mm width and 50mm length has a resistance of 0.0018Ω at 30deg/C. Multiplying the resistance with the current flow (20A) the result is voltage drop across the trace, being 36mV.

To calculate for power dissipation multiply the voltage drop with the current: 0.036V*20A=0.72W (720mW)

Design your circuit board the way to have shortest possible connections between power in and out.

15mm trace width won't be easy to achieve using screw terminals with 7.5mm pin spacing.

Boncuk

Voltage is not important to determine the trace width. It's the current and the resisistance of the trace which are important.

E.g. a trace of 15mm width and 50mm length has a resistance of 0.0018Ω at 30deg/C. Multiplying the resistance with the current flow (20A) the result is voltage drop across the trace, being 36mV.

To calculate for power dissipation multiply the voltage drop with the current: 0.036V*20A=0.72W (720mW)

Design your circuit board the way to have shortest possible connections between power in and out.

15mm trace width won't be easy to achieve using screw terminals with 7.5mm pin spacing.

Boncuk

I use a neat little freeware program called PCBTemp made by ultracad.com.
It will show you the track resistance per inch, and the temperature rise of the track at any given current. I like to use it to design track resistors (for crude current sense resistors etc), or just to see what resistance a track will be.



Notes on using pcbtemp and download

hi,
If you want more detail regarding pcb tracking, this is a good tutorial
Page 7 is the current/width/thickness data.