What should the trace width on a 1oz. copper Board be for 5 volts, no more than 200ma, at normal operating temperatures?
Your answer, I believe, assumes I have not googled this. I have but am not sure I am doing it right and came here for confirmation and prehaps some helpful tips. For example, I see no entry on the calculator for voltage.
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jack0987:
Your answer, I believe, assumes I have not googled this. I have but am not sure I am doing it right and came here for confirmation and prehaps some helpful tips. For example, I see no entry on the calculator for voltage.
You didn’t specify any of this in your original post. We are not here to do the math for you. And you still haven’t gave us any info as to why you think you’re doing it wrong.
Thanks for your reply.
Using this calulator and entering 0.2 amp with a trace length of 5:
http://www.circuitcalculator.com/wordpr … alculator/
I come up with 1.28 mils.
Do you come up with the same thing? What if the voltage was 500 volts instead of the 5 volts I intend to use?
i think you need to Google the difference between voltage and current. You may also need to read the rest of the calculator page…
For DC, voltage is not a limiting factor (except for arcing to adjacent traces/ground plane/through the dielectric). You’re only concerned with cross section of the trace. If you’re concerned about the result, calculate the cross section of the trace, and compare it to a similar sized single copper wire, and then see what current the copper wire is rated for.
Voltage is a limiting factor, because it affects the total power, which is the true limiting factor. There’s a reason resistors are rated in watts not amps. That being said, as long as you’re not worried about high-frequency signals (at which point you’re dealing with an entirely new set of nightmares in terms of PCB design), the minimum trace width necessary for 5V/200mA is going to be well below the minimum width allowable by manufacturing tolerances, which are typically in the ballpark of 6mil. If you’re etching your own, chances are you’re going to need much wider traces in order to get them to come out right. So basically, at those specs it’s a non-issue, because your board manufacturer won’t be able to make traces small enough to be incapable of handling it. I typically work at 8 or 10 mil width for boards with similar specs.
You don’t need voltage to specify the required trace width. The voltage across the trace will depend on the cross sectional area, the per unit resistance, the length of the trace and how much current you run through it. If you’re talking about high voltage applications, it still doesn’t matter, trace spacing is another story. High frequency applications require additional consideration but still don’t need voltage to specify them.
Power can be calculated using two of the ohm’s law parameters which in this case is current and resistance. Voltage just comes as a result of those other two parameters.
P = I^2 * R
V = I * R
qwertymodo:
Voltage is a limiting factor, because it affects the total power, which is the true limiting factor.
Typically conductor heating is referred to as I^2xR losses, voltage really isn’t used as a factor.
Thank you Dave, rrpilot, and qwertymodo for your considered responses.
Perhaps, at the present time, some of what you talk about is beyond my level of understanding. In any case, when I tried to use the calculator and came up with 1.28 mils it just did not seem right.
I will use 5 volts. The amps will be not more than 200 ma which is double what I figure I will really need. Doing the calculation of 0.2 times 5, I come up with 1 watt max.
I like the suggestion of calculating the equivalent wire size and applying that to a minimum trace width. Being a hobbyist, using a trace width less than 10 mils may be a challenge as stated above and I doubt I would need to go that small anyway. I think, in my case here for this little project, I will use 20 mils. I have been using 27 mils successfully as far as etching goes.
I will reread what you have written and see if I can get a better understanding to apply to future projects.
You also need to take trace inductance into account. For supply rails (5V@200mA sounds like the Vcc rail for the board), you want nice wide low inductance traces (or better yet, pours or planes) to reduce dips and ground bounce.