Picking the correct gauge wire for my project - Page 1
Forum section: electronics / beginners

author: Youkai
author_rank: Regular Contributor
timestamp: July 30, 2022, 09:50:49 pm
content: I'm working on a project that's going to use a micro controller (or two), some dotstars (probably a couple hundred in a chain), and some servos.I want to get some wires that will be flexible enough to make the tight-ish corners and bends I'll probably need. Also a couple of the parts will move 20-30 cm and have LED attached to the moving parts so the wires need to not impede the movement (assuming I leave appropriate slack).Right now I have a bunch of stranded 22 gauge wire but it's not as flexible as I'd like. I'm sure I could get that wire to work but I'm wondering if I switched to 24 gauge if that would help. Also would getting silicone sheathed wire affect the flexibility of short lengths?How do I calculate if I'm going to be hitting the limits of the wire gauge in terms of power through it? i.e. if I have my long chain of Dotstars is that going to be an issue?

author: abquke
author_rank: Regular Contributor
timestamp: July 30, 2022, 10:02:07 pm
content: There's gauge number, but also strands. For instance 22AWG can be found in 7/30 (seven strands of 30AWG) or 19/34 (19 strands of 34AWG). More strands of thinner wire will have the wire be more bendy and supple, but it'll be more expensive.A bit of wire will have a bit of resistance, so plug that into P=R*I^2 and see what manner of power dissipation is going on per length and see if it's a scary-type number.Alternately, the series resistance will cause a bit of voltage drop and the application will have an amount that is tolerable and don't go beyond that.Alternately-alternately, try things out with what you have on hand and see what happens.

author: tooki
author_rank: Super Contributor
timestamp: August 01, 2022, 03:02:12 pm
content: In fact, 19/34 is the “standard” stuff, but much, much finer is available. For example, Kabeltronik LiFY 20AWG (0.5mm2) has 256 strands of 0.05mm diameter, which is about 44AWG.Fine-stranded silicone wire will be much, much more flexible than standard PVC. The downside is that silicone is not as abrasion resistant, so you have to keep that in mind with your mechanical design.Also bear in mind that even within PVC with the same stranding there are big differences in flexibility. For example, the Chinese 24AWG I have is substantially less flexible than the European-made stuff ordered locally. But even that varies brand to brand.As for your dotstar chain: you have to calculate your current draw and size the wire accordingly. At maximum brightness (full white) the current draw is 60mA per LED. That adds upfast. Just 100 LEDs is already 6A. The thin foil conductors in LED strips are no good for long strips like that — the voltage drop is so severe that a) you get visible color shift towards the end of the chain, and b) the voltage drop reduces current flow in the LEDs, making them visibly dimmer. It’s imperative to feed power in at multiple points throughout the chain. Now, if your application means that only a few LEDs will ever be lit at once, or if you’re running them at lower brightness, you can scale down the current linearly. (Some driver libraries even let you program a current limit.) At maximum brightness, I’d feed in power at least every 100 LEDs, but ideally a lot more, like every 30-50. Note that the length matters too, since voltage drop cares about distance. So I’d also say to feed in power every 3 feet at most.

author: Youkai
author_rank: Regular Contributor
timestamp: August 02, 2022, 02:03:34 am
content: There's probably going to be about 100-150 total LED and they are going to be chopped into sections of 10-ish LED at a section. So I'll have plenty of opportunity for power injection. I just want to make sure I'm not going to melt my wires if I pick thinner gauge.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 02, 2022, 02:25:50 am
content: Come up with something wireless. IR or radio. There's some dirt cheap ways to do this. You could flash an IR signal to each array of LEDs. There are some cheap radio modules that can be found on Ebay.Both options might be cheaper than wires.Also consider ribbon cables. Double up on a couple wires if you need more current.You don't want a bundle of wires though. They are just too difficult to manage.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 02, 2022, 02:28:12 am
content: Also, there are plenty of tools on the Internet and, like Electrodoc, you can download that will have calculators that can solve your math part of the program.

author: wizard69
author_rank: Super Contributor
timestamp: August 02, 2022, 04:32:51 am
content: Quote from: Youkai on August 02, 2022, 02:03:34 amYou can't determine wire size without knowing the current to be run through the wire. Now if you know that, you may be able to get test lead wire in the right gauge. I mention test lead wire because it is readily available and often a cheap solution, however it might not be the right solution here.If this is going to be part of an electrical instillation, of any sort, you need to make sure you are safe!!! That can mean fusing that is properly sized and meeting any applicable laws. Your posts are rather opaque so I don't know exactly what you are doing. I could be wrong but it sounds like you are dealing with non trivial currents, so at the very least be careful.

author: tooki
author_rank: Super Contributor
timestamp: August 02, 2022, 08:45:56 am
content: Quote from: JustMeHere on August 02, 2022, 02:25:50 amHow is any of this relevant or useful? You can’t just send the LED power wirelessly, and the LED control lines are no trouble at all.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 02, 2022, 02:45:03 pm
content: You can get more flex with two wires (or more) that give the equivalent CSA of the 22 AWG. This wire size isn't a good choice for more than an amp or so.There are plenty of tables out there to help you calculate the correct size.

author: Ian.M
author_rank: Super Contributor
timestamp: August 02, 2022, 03:33:45 pm
content: The one useful thing 'JustMeHere' said was "Also consider ribbon cables. Double up on a couple wires if you need more current. "Ribbon cables 'play well' with motion along a single axis, especially if you can arrange for the motion to be accommodated by a rolling loop, and protect them from being sharply flexed at or near their terminations. You can parallel as many individual wires as you need to get the copper CSA you need to handle the current without excessive temperature rise, and run control signals down the same cable.