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Electronics => Electronics => Topic started by: electrofan on July 30, 2010, 02:24:16 PM

Title: Trace width issue
Post by: electrofan on July 30, 2010, 02:24:16 PM

Hi guys. I'm using the L298n H bridge to drive some motors. Assuming I use a 50mil trace width on my power and ground lines (given to me by a calculator), where do I STOP making the widths this large? In other words, do I make all the ground lines on my PCB thick? Or should I just make a thick one from the H bridge to the DC jack port and leave all the others thin?

Thanks guys!

Title: Re: Trace width issue
Post by: SmAsH on July 30, 2010, 04:20:44 PM

Yep, that can work fine.

Title: Re: Trace width issue
Post by: Razor Concepts on July 30, 2010, 08:48:55 PM

You can use the polygon tool to make a big ground plane also.

Title: Re: Trace width issue
Post by: Soeren on July 30, 2010, 08:59:18 PM

Hi,

Quote from: electrofan on July 30, 2010, 02:24:16 PM

Assuming I use a 50mil trace width on my power and ground lines (given to me by a calculator), where do I STOP making the widths this large? In other words, do I make all the ground lines on my PCB thick? Or should I just make a thick one from the H bridge to the DC jack port and leave all the others thin?

No reason to make other lines more narrow, if there's room for it, but what's needed as a minimum for the wide traces on a L298 setup, is the traces that carries the "high" current, i.e. from positive supply to negative supply (probably 0V here) including the L298 and the motor - keep them short and 100 mil won't hurt if room exists, nor will tinning the traces with solder.

Thinner traces means more copper to etch (less life from your etchant in number of PCBs etched), more likely problems with pinholes, hairlines and scratches, less heat sinking and a larger voltage drop on high current lines.

If you look at some of the PCB designs I've posted, you'll see that I usually only etch a very small amount of copper to create the PCB, the rest is ground plane and traces.

Title: Re: Trace width issue
Post by: electrofan on July 31, 2010, 08:18:15 AM

What I'm confused about is where to stop making the power and ground lines (high current) thick. I don't have room to make all of them thick, but I don't know if I can be 100% sure that the current will not randomly travel through the thinner ground traces (since they're the same net in eagle)...

I'm getting the PCBs manufactured this time around. I've done etching in the past, with good results though.

Title: Re: Trace width issue
Post by: SmAsH on July 31, 2010, 09:38:02 AM

Maybe solder over the tracks after etching to help a bit with the current?

Title: Re: Trace width issue
Post by: madsci1016 on July 31, 2010, 10:15:07 AM

Only make the VCC and Ground traces thick from the battery connector, to the hbridge, and from the hbridge to the motor terminals.

Title: Re: Trace width issue
Post by: electrofan on July 31, 2010, 10:37:29 AM

Alright  cool. And what about vias, do they have to be thickened as well for high-current lines?

edit: alright I found a nice via calculator, looks like I'll use 40mil via drillholes for my larger current traces. I'm gonna manually route the high current traces so they're as short as possible, and leave the rest to autoroute.

Calculator here http://www.skottanselektronik.com/ (http://www.skottanselektronik.com/)

Thanks guys.

Title: Re: Trace width issue
Post by: Soeren on July 31, 2010, 01:04:03 PM

If you post the Eagle files, I can route the high current wires for you.