How much current through a PCB track?

[andy257]

Hi all,

Trying to calculate how much current a particular track will handle. From what ive read its all about how much temperature rise the design can tolerate. My design uses 8A DC through the trace and the temperature range of the device will prob work between ambient (23C) and 85C.

Ive used some calculators and it gives a recommended track size but this is based heavily on how much temperature rise i can allow within the design Usually (10C). All i really care about is that the 1Oz copper track will not go open circuit. Changing from 10C temp change to 20 or 30 seriously changes the track width so i have no idea what to do.

If i knew how much current would burn out a track?

What do you guys use to prevent your copper tracks from burning out?

 

[dknguyen]

You don't burn tracks so much as you delaminate them (or maybe burn them, I dunno). But you'd probably want to keep the temperature below 60C. When a component is rated up to "85C" that does not mean it can operate when the ambient temperature is 85C. It means that the maximum temperature rise plus the ambient temperature can't exceed 85C. Your ambient is probably not going to go above 35C unless it's next a car engine, in direct sunlight, in a greenhouse effect type area, or a desert, or something like that.

If your ambient actually is 85C well most components aren't going to work anyways since they're already at their maximum temperature even when they dissipate no power. Suppose that wasn't a problem, FR-4 has a maximum temperature of 120-140C. Let's say 120C just to be safe, and probably even more since you don't want to be anywhere near that temperature (and much more if any heat transfer along the board pushes other components past their maximum temperature). You're trying to hold off a 35C temperature at most which is typical for many power components. Large traces, no way around that.

But your ambient probably isn't that high anyways so you're probably fine.

 

[Dean Huster]

Check this out and see how you like it.

PCB Track Width Calculator