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I was working on a PCB where there was a single DC input with two traces +ve and -ve. At one end there was a connection to a motor which requires 40A. The traces of the DC input were 100mil and 1oz. But the point where the motor was attached, a large polygon power pour was there. My question is that my input trace cant provide this current due to lower width and copper thickness, but due to polygon is it possible that the motor gets enough current due to the spread of current???

enter image description here enter image description here

Here the image on the left is the input to the PCB. The then connects to the power layer which is polygon. The output to the motor is shown in the right image that shows the terminal lie on the power pour from the FET.

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    \$\begingroup\$ It's unclear what you're asking. Could you add a diagram or screenshot? \$\endgroup\$ Commented Jul 8, 2023 at 11:14

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I'm not 100% sure I've understood what you're describing, but see if this is on the right track. If not, I'll edit.

A polygon (depending on size and shape) can typically carry a lot more current than a track, even a 100mil 1oz microstrip track which can carry 5.48A@+30°C. 40A is really pushing it on a single 1oz layer. Are you sure there aren't more internal layers aiding the power path? You need a 40mm width to carry 28A@+30°C but the wider the track, the less current density is considered and the less accurate the calculation. My 90A battery has several layers forming the power path and it manages only +10°C.

It could be that the 100mil track is for sensing or something indirectly related to the motor.

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  • \$\begingroup\$ Ive added abit more clarity to the question. You are right there is a seperate layer for the power. but this layer isnt directly connected to that DC input. Two traces are intitally drawn seperatly which passes through a resistor and a diode and then connects through the power polygon in the other layer. \$\endgroup\$
    – user340506
    Commented Jul 9, 2023 at 13:29
  • \$\begingroup\$ My question is, how could the small traces of 100mil initially provide the large current. could it be damaged? or the motor just works on less current due to more spread...is it this thing or not?? \$\endgroup\$
    – user340506
    Commented Jul 9, 2023 at 13:31
  • \$\begingroup\$ @Dan I haven't checked your math but a polygon and a track have no differences. They both are copper. One way, you get to easily define longer more thin connections (tracks) another is wider and more unique shapes (sometimes). \$\endgroup\$ Commented Jul 13, 2023 at 20:46
  • \$\begingroup\$ Yeh, they are both copper. If they are both the exact same size then yes, they will carry the same current. But an Altium polygon is capable of pouring around vias and behaving in ways an Altium track can't which allows you to make Altium polygons bigger, depending on the layout. You would need no vias covering some amount of board area for a track to compete and my calculations are based on copper width. \$\endgroup\$
    – Dan
    Commented Jul 16, 2023 at 8:31
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I have a few questions: 1-Is your motor running continuously with 40 amps or is it able to give an inrush of 40Amps then run at 4 amps or so? 2-Is the input voltage/current the same as the voltage/current of the motor? 3-Is it your design or someone else (that is known to work)

Why I'm asking those questions is to figure if it is simply a bad design or a mistake of the past. But, on a short distance, the voltage drop won't be to severe on a small trace. That's how they manage to get inside dies.

But 40 amps in a 100 mil trace 1oz seems a bit much. I would definitely use polygon to minimize the heat on that trace.

From your comments, I think, the current can reach up to 40 amp in some scenarios but it is short lived. If so, it's probably fine. The current rating on many motors can vary between their idle current and some load scenarios. It also depend what kind of motor you are using.

What I would suggest you to do is to check the motor datasheet and talk with your mechanical team to figure the current you are expecting to see. If you can modify the design and have the place for a polygon, why not! But that space might be needed for other purpose. If you want more help, can you post a schematic of your electrical circuit? and a better and bigger screenshot of your layout (3D doesn't really help)

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