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Thread: PCB trace width for high current application

  1. #1
    Senior Member
    Join Date
    Apr 2017

    PCB trace width for high current application


    I've been making my own PCB boards with great success and my next project is a batter tester. I'm looking at testing 12 vdc lead acid batteries (like a motor cycle battery) where my tester will draw around 18 amps for 90 minutes. I have prototype working well, but time to tidy things up.

    I figured traces to carry 18 amps would be large and according an on-line trace calculator, it says my traces must be 112 mm wide (for the 1.4 mil copper thickness boards i'm getting off Amazon). Dang...

    Does this sound right?

    Thanks in advance.

  2. #2
    Senior Member
    Join Date
    Apr 2013
    That's probably reasonable if close to zero voltage drop is the aim, though from the sounds of it losing energy as heat in the track would be a feature not a bug in your application so depending on what is going on you could probably use a smaller trace as long as you are not trying to make measurments along it and you don't actually vaporise anything.

    Looks like there is a fair bit of variety in the online caluclators - see responses

    Edit - some back of the envelope calculations from some found tables suggest 4mm wide will have your tracks at 100 degrees C. Am not in any way endorsing 4mm, but does mean you have some room to come down in size at least a bit.
    Last edited by GremlinWrangler; 11-19-2017 at 11:01 AM.

  3. #3
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Trace width all about how much temperature rise you can allow. Remember, the rise is roughly constant, so the final temperature depends on whatever the ambient temperature happens to be.

    If you have a fan or a vented enclosure (and well defined mounting orientation) that allows for natural convection cooling, then airflow can also help quite a lot with the temperature rise.

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