How to calculate PCB trace sizes based on amperage? - Page 1
Forum section: electronics / projects

author: EasyGoing1
author_rank: Regular Contributor
timestamp: August 08, 2024, 11:45:14 pm
content: If I have a PCB that has a trace on it that needs to handle 6 amps, how do I know how much metal should be given to that lead?

author: rsjsouza
author_rank: Super Contributor
timestamp: August 08, 2024, 11:50:09 pm
content: Many variables are involved in such calculations. Check the utility from Saturn PCB (Kicad also has some built-in utilities) and a few of tens (or hundreds) articles around on the net.https://saturnpcb.com/saturn-pcb-toolkit/https://resources.pcb.cadence.com/blog/2024-high-current-pcb-design-guidelines-for-reliabilityhttps://resources.pcb.cadence.com/blog/2024-optimizing-for-pcb-trace-thickness-vs-current-capacity

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 08, 2024, 11:51:34 pm
content: Quote from: EasyGoing1 on August 08, 2024, 11:45:14 pmPlenty of PCB web calculators out there.Thicker copper means the trace can be narrower.That said, it is rare to use the calculator values, as they have some temperature rise assumed, and the copper is free on your board.More common is to use as much copper as physically practical, and keep traces short, so the trace contribution to temperature rise is kept very low.

author: Smokey
author_rank: Super Contributor
timestamp: August 09, 2024, 12:03:24 am
content: https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-pcb-trace-widthIf you have to neck it down narrower than the given number, make sure there is more width besides the neck down. Think of it as a heatsink.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2024, 04:10:44 am
content: How long is it? How hot can it get? How thick is the board? Inner layers (planes)?A common gotcha for young players is worrying about trace width, when the length is shorter than the calculated width anyway -- example, making a switching supply, motor controller, etc. where the transistors are butted up together with minimal length inbetween. Trace width is meaningless in this regime.Trace width is most meaningful for long traces stretching across large boards, where no heatsinking out the ends occurs: the middle heats up all by itself. It's fairly rare that one needs such routes, but it does happen from time to time.Tim

author: EasyGoing1
author_rank: Regular Contributor
timestamp: August 09, 2024, 06:34:35 am
content: Quote from: T3sl4co1l on August 09, 2024, 04:10:44 amThis is the board that I just got:Where I highlighted in orange, it's too hot to touch. I ran some calcs and decided to re-design the board into a 4 layer board, bumping the top and bottom layers to 2oz copper and making the entire layer solid copper. Top layer is +12, bottom is +5 and the two in the middle are ground but are 1oz thick copper each. Here's the re-design:

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2024, 04:20:21 pm
content: Doing that with four pours, two top and bottom, having an interdigitated shape, should be more than fine for 2 layers. 4 layers works as well.Tim

author: tooki
author_rank: Super Contributor
timestamp: August 09, 2024, 05:17:19 pm
content: Quote from: EasyGoing1 on August 09, 2024, 06:34:35 amWhat happened to the connectors? What are you using now?Where are the grounds for the input?Also, on your outputs, two of the grounds seem to have a different hole size than the others.

author: EasyGoing1
author_rank: Regular Contributor
timestamp: August 10, 2024, 12:08:09 am
content: Quote from: tooki on August 09, 2024, 05:17:19 pmThe first circuit board was intended to be used with these spring clip connectors, but I found that just soldering to the board was best so I just basically converted all of the connectors into consolidated groups.Quote from: tooki on August 09, 2024, 05:17:19 pmAll grounds are electrically equivalent so I just threw them all over to a group.Quote from: tooki on August 09, 2024, 05:17:19 pmGOOD CALL on that one, I might have missed that when placing the order. I'll correct them before the order.My main issue now is getting confirmation that this should work fine given the parameters stated in my opening post.

author: EasyGoing1
author_rank: Regular Contributor
timestamp: August 10, 2024, 12:26:14 am
content: I even added the extra ground for the PSU input for general consistency

author: tooki
author_rank: Super Contributor
timestamp: August 10, 2024, 01:38:25 pm
content: Quote from: EasyGoing1 on August 10, 2024, 12:08:09 amAh. I don’t know what your application is, but it’s almost always better to have some kind of connector or terminal so you can easily disconnect it if need be. Also, wires soldered in directly are much less resistant to vibration or flexing. You’d want to provide robust strain relief. But I would use terminals or connectors. I like the spring or lever ones from WAGO and Phoenix Contact.Quote from: EasyGoing1 on August 10, 2024, 12:08:09 amSure, but consider how much messier this makes the wiring. You want to be able to bundle wires for routing them around, so if possible, you want their PCB pads/terminals to be next to each other. Also consider troubleshooting: this is far easier when each load’s wires are together.Quote from: EasyGoing1 on August 10, 2024, 12:08:09 amIt’ll be fine.Something to consider, since you’re making a power distribution PCB anyway: add fuses. If you use socketed fuses, this also gives you a way to isolate a particular load for troubleshooting purposes.Also a thought: do you even need a PCB? Or would you be better served with some power distribution terminal blocks like thePTFIX seriesfrom Phoenix Contact? (Or possibly even a short DIN rail with terminal blocks.) I’ve used these in a few projects now, and like them enough that I ordered an assortment of them at work to have in stock, along with an assortment of DIN rail terminal blocks from WAGO and Phoenix.

author: EasyGoing1
author_rank: Regular Contributor
timestamp: September 22, 2024, 03:09:29 am
content: Quote from: tooki on August 10, 2024, 01:38:25 pmThe application is a somewhat old but very interesting LED lighting system for fish tanks. It uses LEDs that I am not familiar with and cannot seem to locate replacements for either. And some people who have experience with this unit over on a fish forum have sourced replacements but at $10 per LED, the three that I have that are not working (though they are wired in series and I suspect the center LED is the bad one) I can live with three of them not working. There are three sets of LED arrays. So 5 PCBs each containing 5 LEDs mounted to very large heat sinks which are then mounted to the housing. So 75 LEDs in total, I can live without three.The unit originally was powered by TWO AT-style external power supplies rated at 500 watts each. The company customized the power supplies so that each had a wire harness that connected to the housing unit. Both power supplies had to be on of course for the system to work.The unit belongs to a friend of mine and he brought it to me to fix because when the power supplies were turned on, the unit would light up for less than a second and then just power down.What I discovered was that the wiring harnesses were hard-wired inside the housing using splice and heat shrink method, though that was done very professionally and the wiring was properly fastened inside the housing etc.However, the main circuit board which is just a microcontroller with a LCD user interface that seems to store the user settings inside a battery-backed clock (M48T12-150PC1) that keeps its settings via an internal battery only rated to last 10 years. The MC controls voltage levels to four fans (two on each end of the housing) and it has connections to each of the three LED arrays where it controls - from what I can tell - brightness and possibly color variation ... or perhaps just brightness for each LED circuit on the array PCBs ... not sure yet on that ...The main board was powered from one of the LED array blocks where they had a wire soldered to the board and connected to the main board that drives a simple L7805 which then powers the entire board (I would have used a buck converter myself, but its not my board and this board was designed around 2004-ish so not sure what was available then in terms of PCB buck converters).The wire that powers the board was cooked pretty good and the circuit board had clear burn marks around the 7805 and along the ground strip. Best I can figure, is that the fans failed (they had much what looks like salt buildup around them and only one was working) and I think condensation caused a short that ended up causing the damage to the wire and ultimately - I think one of the PSUs. After doing some testing, the entire unit still works perfectly, so whatever caused the damage only damaged the 7805 and nothing else (although one of the transistors for the fans failed but there was no damage around it or to it that was visible).I replaced the damaged components and re-enforced the ground strip with some wire and this is where my custom PCB comes in...I didn't like the way they distributed power and I didn't like the use of two PSUs. So I replaced them with a single 1,000 watt AT style PSU, and created my own wiring harness where I give each voltage two wires (I use a smaller gauge than they use but I doubled up each feed), and instead of splicing wire inside the unit with solder and heat shrink, it seemed more obvious to me to have a PCB distribute the power.The reason why I say this lighting system is interesting is for two reasons: ONE is the history of the design. The unit was manufactured by a small company in southern California and best I can tell, they designed it themselves. However, an aerospace company up in Oregon or Washington ... not sure ... secured a patent on that design (not sure what about the design is so unique) and they then sent demand letters to this small company insisting on royalties for use of "their design" - mind you, this small company had been selling these units before the patent existed and the aerospace company had significantly more financial resources than this smaller company so they took them to court and ultimately put them out of business.The second reason why I say this unit is interesting is that within the settings of the unit, besides being able to tell it what the date, time and time zone is, are settings for lunar phases ... why a lighting system for fish would need to know lunar cycles is beyond me, but I find it interesting that it wants that information and I'm not sure yet what it does with that info.So you mentioned using spring-loaded connectors and my first PCB design actually did just that ... here are screenshots of the first design the second being a 3D render with the connectors I was going to use:You can see that one trace in the 12V feed in this first image ... that was the trace that was getting hot and started to smoke. The pins on that were for a jumper where I could remove the jumper and read the current through each voltage source. I left that out of the new board design.After implementing it and using the connectors, it was kind of cumbersome to work with, and The original design had all of those wires permanently soldered so I just decided to go with a straight soldered board instead of using the connectors. Though those connectors in particular are the strongest I've ever used. I've often thought that if I could actually mount one on the ceiling, I could probably hang from a wire that is secured by it without it ripping out ... those things are amazing.Here is a partial view of the light fixture with its cover off:And these two show the new six-layer board:Soldering the wires onto the board wasn't a problem at all and I like it better than using the connectors.Quote from: tooki on August 10, 2024, 01:38:25 pmThe wiring in this thing is messy either way. It was messy when I first got it apart and the factory did an OK job at zip tying the wires but they were still all over the place. It's just got a lot of wiring in it and they all need to source to the PSU and some to the MC board so they're just everywhere. Not a problem when the cover is on as you don't see any wires.Quote from: tooki on August 10, 2024, 01:38:25 pmYES, I could not be happier with this outcome. Nothing gets hot in this thing anymore with this six-layer board. Not even warm. I'm very pleased with this design.Quote from: tooki on August 10, 2024, 01:38:25 pmI suppose I could fuse the 5 and 12-volt feed to each of the three LED blocks, but those never were in the original design. Also, the original design used TWO AT-style power supplies at 500W each. I consolidated that nightmare down to a single 1kW PSU and the unit only draws a couple of amps when the lights are on full brightness. Well under what the PSU can handle, so I'm also happy about that. The PSU isn't working hard at all which means it should last quite a while.Quote from: tooki on August 10, 2024, 01:38:25 pmI thought about terminal blocks but there just isn't any room in this thing to mount them. Thats why I decided on a PCB because it did have enough space for that since I was able to make it long enough to fasten to the enclosure with screws.The unit works great now. A resurrected relic from the mid 2000's ...