Track width question
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Pablo Carrero Garcia 2 months ago
Good evening mates!. I was considering about how must the track width be. Im using a raspberry pi 3b+, connected with dht22, bh1750, fsr sensor and a mcp3008. I was considering about 0.65mm because RPI 3b+ current max is 1.65A. Thank you very much for your time!
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andyfierman 2 months ago
Which tracks do you mean? Signals? Inputs? Outputs? Power supply? For most circuits except transmission lines requiring a controlled impedance or RF circuits, the track width is determined by the acceptable temperature rise in the track due to the current passing through it. For most signal inputs the currentr is so small that the resistance and theefore the temperature rise of the track is not an issue. For outputs this is often true unless a significant current is being supplied to some sort of load. Power supply tracks should be checked using (11) in: [https://easyeda.com/forum/topic/Extension-User-Extensions-for-EasyEDA-Summary-9e065b68316f4491a3911dc6204be31e](https://easyeda.com/forum/topic/Extension-User-Extensions-for-EasyEDA-Summary-9e065b68316f4491a3911dc6204be31e)<br> <br> or any one of several online tools. For information about PCB trace widths vs. copper thickness, current and temperature rise, there are a number of online calculators available, based on the graphs that @cjohnson kindly uploaded in his reply to this post: [https://easyeda.com/forum/topic/PCB-high-current-thermal-design-562f7a69a7ad41a38b18ea150d6703ed](https://easyeda.com/forum/topic/PCB-high-current-thermal-design-562f7a69a7ad41a38b18ea150d6703ed). For example: [https://www.7pcb.com/trace-width-calculator.php](https://www.7pcb.com/trace-width-calculator.php) [https://www.4pcb.com/trace-width-calculator.html](https://www.4pcb.com/trace-width-calculator.html) [https://www.desmith.net/NMdS/Electronics/TraceWidth.html](https://www.desmith.net/NMdS/Electronics/TraceWidth.html) [https://www.smps.us/pcb-calculator.html](https://www.smps.us/pcb-calculator.html)
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Pablo Carrero Garcia 2 months ago
I am going to share the project looking for help about tracking. I can not know the temperatura i am having troubles. I will need to know power tracs width and in/out data signals ofc. This is a HAT for a RPI 3B+, i can not find the current supply so im in a big trouble. Thank you very much i aprecciate it a lot [https://oshwlab.com/carrerogarciapablo/holaprueba](https://oshwlab.com/carrerogarciapablo/holaprueba)
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andyfierman 2 months ago
"This is a HAT for a RPI 3B+, i can not find the current supply so im in a big trouble." You might like to try using the power of the internet to help you find information. Search "RPI 3B+ power consumption.". Find: [https://www.raspberrypi.org/documentation/hardware/raspberrypi/power/README.md](https://www.raspberrypi.org/documentation/hardware/raspberrypi/power/README.md) You decide how hot (above ambient) you are willing to let your tracks run. 1C? 5C? 10C? For power supply (power and ground) tracks, the basic rule is that you use as much copper as you can. Realise the ground and power supply nets as Copper Areas (a.k.a. copper flood or copper plane).
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Pablo Carrero Garcia 2 months ago
Iv been using the track width simulator using 85C as the maximum operative temperatura and 40C for normal use. Also a maximum current of 2.5A, 50mm as the maximum wire length and a peak voltage of 5V, and i got 0.65mm. Thats what iv used for all traces.
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andyfierman 2 months ago
"...using 85C as the maximum operative temperatura and 40C for normal use." The track temperature in the width calculation is not the ambient temperature of the board. It is the temprature **rise** of the track **above** ambient. "Thats what iv used for all traces." Why? You should use maximum possoble copper for power and ground and then use something between 0.254mm to 0.6mm for signal tracks because they carry very little current and so dissipate negligible power.
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Pablo Carrero Garcia 2 months ago
You have totally the reason. I read what temperature rise is and was the difference between máximum anda operativo temperature, thats why i chose 40C. Taking into account rpi Maxim current id 2.6A, i think 0.65mm os good for allí traces. I should hace selected power and gnd higuer, yo 1.5A for instante, but i chose the other option
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