I'm working on an electronics project that'll regulate and offboard solenoid. The leads controlling the solenoid will need to sustain fairly high levels of current. This is the solenoid I'm working with:

Solenoid specifications

This is the schematic I currently have set up, with the solenoid in the top-right connecting via a screw connector. I've set the trace at 48mil.

The schematic

Is this a large enough trace or will it burn up?

  • \$\begingroup\$ That is not a schematic, that is a board layout, can you post the schematic? \$\endgroup\$
    – Tyler
    Mar 30, 2016 at 18:00
  • \$\begingroup\$ To truly answer your question we need more info. Among other things you need to know the copper thickness of your board. You can use this calculator to help you determine the required trace width. 4pcb.com/trace-width-calculator.html \$\endgroup\$
    – Doov
    Mar 30, 2016 at 18:01
  • \$\begingroup\$ You can, on the one hand, sort out the minimum trace width required, based on current and copper wight. You can, on the other hand, take all the space available and use it. Of particular note is that you have a fat trace to one terminal on the transistor, not two - that makes no sense. If there be "high current" to the collector, it passes from the emitter, too. And what Neil says below. And some bypass capacitors on general principles. \$\endgroup\$
    – Ecnerwal
    Mar 30, 2016 at 18:12
  • 1
    \$\begingroup\$ Don't forget the current will flow through the traces from your supply connector as well! \$\endgroup\$
    – Neil_UK
    Mar 30, 2016 at 18:13
  • \$\begingroup\$ With a few layout tweaks this appears to be single-side do-able, FYI. Might take one jumper. \$\endgroup\$
    – Ecnerwal
    Mar 30, 2016 at 18:30

1 Answer 1


7W at 12V comes up to around 0.6A. Round up to 1A for safety, then calculate the required trace width using one of the various calculators.

The first calculator I found on Google gives me 30 mil for inner, and 11 mil for outer layers with 1 oz/ft² copper, so these should be fine.

On a board as simple as this I'd probably go Copper Thieving and create huge zones instead of traces.

  • \$\begingroup\$ Since this is just a simple two layer board will I have any "inner" layers or does that mean both of my layers can be considered "outer"? \$\endgroup\$
    – F Young
    Mar 30, 2016 at 18:22
  • \$\begingroup\$ A trace being "wide enough" is not a yes/no question, but rather a function of how much temperature increase you are willing to accept (within the boundaries of available board space on the lower end, and the point where you get toxic fumes on the upper). The calculator giving a much smaller width for "outer" traces is a result of assumed air circulation around the board, so if you have a tight enclosure, go with larger widths. \$\endgroup\$ Mar 30, 2016 at 19:46

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