PCB Design Consideration for 25A current - Page 1
Forum section: electronics / beginners

author: mys_721tx
author_rank: Contributor
timestamp: September 19, 2020, 03:46:17 am
content: Hello all,I am trying to make a 4-Pin DIN to Anderson PowerPole adapter so that I can replace four wall-warts with a single CUI SDI200G-12U-51 power supply. Based on its data sheet, two pins are positive and two are negative.Based on the supply on DigiKey, I have two options:Use Female 4-pin DIN jack KPJX-CM-4S and spice the wires together and then clamp the other end with a PP15/30 connectorUse a PCB mounted 4-pin DIN jack PD-40S and solder 1377G12 on the other end of PCBFor the PCB, I am aware that to carry 25A current, the trace needs to be either extra wide or use denser copper. What other considerations are there to design such PCB? For example, should I worry about the temperature raise at the solder joint? Should I expose more copper at the pad so that more solder can come into contact with the pins?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 19, 2020, 04:55:23 am
content: If you don't need any EMI considerations (parallel planes, filtering..), and don't have any crossings, you can double up top and bottom copper in parallel.I would use 2oz copper, and leave thermal spokes in. The annoyance of soldering a solid pad outweighs the minuscule voltage drop / temp rise of thermal relief I say. Use pours, nice and wide (fill the available board area between connections, if you like), minimum maybe half an inch (13mm) wide but don't worry too much about short bends or necks.Can also do it entirely as a wiring harness, with crimp or solder-pot terminals and connectors/housings. I'm sure something is available for parts like that. Downside: if it means you need a special crimp tool, well, that might not be great for a one-off.Tim

author: mys_721tx
author_rank: Contributor
timestamp: September 19, 2020, 04:11:13 pm
content: The top and bottom copper is genius! I was thinking about using some obscenely dense copper, but that seems to be a much better idea.Since I don't have my own iron yet and the 4-pin jack has solder-pot terminals, there will be a one-time investment anyway. If there is a butt crimp connectors to splice three wires, I might just roll with it.

author: bob91343
author_rank: Super Contributor
timestamp: September 19, 2020, 04:27:38 pm
content: I warn against high currents on PC traces. The traces may be able to handle it but the interface with the rest of the circuit is suspect. It holds major traps regarding current distribution and dissimilar metals. Nearly all the high current traces I have encountered have had problems. Eyelets loosen, solder doesn't spread widely enough, corrosion sets in, vias crack. Temperature coefficients of expansion cause stresses.In beginning electricity class in engineering college we were required to draw current distributions across surfaces and got to understand how currents tend to concentrate in narrow places.

author: tkamiya
author_rank: Super Contributor
timestamp: October 03, 2020, 07:29:56 pm
content: I would make the traces as wide as practical. Then, solder #12 wire or so over the traces. That way, you don't have to invest so much money for PCB. Thicker copper PCB tend to cost more money.I've taken apart many UPS units. They all look to use regular PCB, but high current traces are wide and flooded with thick layer of solder. I'd think wire over trace approach will give you more predictable result.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 03, 2020, 09:53:33 pm
content: Consider leaving the mask off of your traces and globbing them up with solder. Dave has done a video or two on this.

author: bill_c
author_rank: Regular Contributor
timestamp: October 04, 2020, 12:18:45 am
content: Dave has a video where he compares a normal trace and a trace covered with solder.

author: free_electron
author_rank: Super Contributor
timestamp: October 04, 2020, 01:48:24 am
content: Quote from: bob91343 on September 19, 2020, 04:27:38 pmit can be done without problems. it's a matter of creating via farms as reinforcement and current spreaders. i have boards that handle 400 to 500 ampere without problems. pressift pins , SON style power mosfets. but you need to know a few things and pay attention for pinch-points.

author: jnz
author_rank: Frequent Contributor
timestamp: October 04, 2020, 03:22:29 am
content: Quote from: free_electron on October 04, 2020, 01:48:24 amGreat video post by BillC, but overall this thread needs more pics.Do you have examples of via farms as reinforcement?

author: bob91343
author_rank: Super Contributor
timestamp: October 04, 2020, 04:56:33 am
content: As I mentioned, it's not so much the traces but the way they connect to the outside world. Those interfaces will haunt you unless you get creative. And what's the point of globbing solder over a trace when a bus bar is more predictable?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 04, 2020, 06:54:21 am
content: Quote from: bob91343 on October 04, 2020, 04:56:33 amIt's way cheaper, the solder costs some $0.01 and comes in the standard reflow or wave solder process without any extra steps. In one-off lab environment, it doesn't make sense, but in mass production, yes. Adding a bus bar could cost easily some $1.Adding solder obviously doesn't do wonders, maybe it's some 20-40% increase in current capability, but it's good bang-for-buck.You need to know what you are doing; the same applies to circuit design in general. The factyouare having issues designing things doesn't mean anyone else couldn't do them either. For example, I design high-current PCBs (not 400-500A like free_electron, though, but some 50A is quite usual) all the time without any of the problems you are seeing, and I'm not considering myself an exceptional genius."Unless you get creative", well, I always think that as a designer, I'm doing creative work!

author: free_electron
author_rank: Super Contributor
timestamp: October 05, 2020, 02:30:52 pm
content: Quote from: jnz on October 04, 2020, 03:22:29 amhttp://www.irf.com/technical-info/appnotes/an-1029.pdfThere is a few things to think about- the current carrying ability of a via is given by the plating thickness x circumference ( diameter x pi )- plating is typically half of the finished copper thickness. so for a 1oz copper board ( 35 micron ) you only have 17 micron in the via !- current flows from source to target. it does not make sense to add a via on the 'backside' of a pad. it DOES make sense to add to the frontside of the pad if you are using mulitple layers to spread the current.