Electronics > Beginners
Hookup wire
DBecker:
--- Quote from: bob91343 on June 07, 2019, 06:04:04 am ---If you really want to get scientific, use a wire size such that the current density in the wire is low.
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Ampacity is primarily based on heat dissipation, not current density. You have to get to nm scale before current density and electromigration becomes an issue.
Circuit boards can support high current density compared to round wires because of the large surface area. Small wires are similar -- there is still lots of surface area to shed the heat.
I wonder how much wire wrapping is still done today. 30+ years ago I wire-wrapped my own prototype boards. The large ones had thousands of connections. The only way to do those with reliability and few enough errors was to use an X-Y position machine and a wire-wrap gun. It's easy to forget how literally painful and tedious that was, for only mediocre (10-50MHz) performance. The only benefit was how easily fixes and enhancements were made.
I'm pretty sure that 99% of "wire wrap" wire used now is soldered board patches.
KL27x:
I have done my own informal tests on 30AWG kynar wire. With a 1 foot section, touching nothing but room temp air, the wire overheats enough to melt insulation at something around 6A. The copper starts to glow somewhere between 6-10A. Obviously, if ambient temp is higher (crammed in a box of electronics) these figures would be lower. And if bundled in a cable with other high current wires, etc.
But if you are doing only very short jumpers to a circuit board, the circuit board will sink heat, too.
The current you can pass depends on the situation. I don't even blink using 30AWG for up to 3A on things for my own use, where airflow/temp isn't an issue, even though the charts I've seen suggest the max is closer to half an A. Obviously, you have to consider all factors when doing this, including voltage drop due to the resistance of the wire (which increases a bit with temp).
David Hess:
--- Quote from: KL27x on June 07, 2019, 04:15:51 am ---I also use 30AWG single/solid conductor "wrapping wire" more than just about anything else for circuit board-level work, whether pcb rework or for use with protoboards. It looks "wrong" because the holes in the protoboard are so large. But as long as the wires are kept short, they can pass a lot of current with minimal voltage drop and heat.
There are multiple reasons to use wire this thin besides cost. It is very easy to strip. The small cross section means that the insulation doesn't have time to melt while soldering the connection. And the very thin insulation and conductor make for high density connections without building a mess, and small enough to fit to the pins of almost any IC.
You would think it is too thin to be reliable, mechanically, but IME it works great once you get the hang of getting the wires the right length and placement. Getting the jumpers where they won't be disturbed works a lot better than trying to use wire so thick that it can handle abuse.
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I also use 30 gauge silver plated Kynar insulated wire wrap wire for point to point work but solid wire like this is not suitable for high vibration environments unless secured. With the Kynar insulation, it is available in all of the standard colors.
But 30 gauge magnet wire with the insulation which burns off at soldering iron temperatures is even better if you do not require color coding and even this is available in a few different colors and it is less expensive. Since no wire strippers are needed, there is no issue with nicking the wire and it is faster to use.
maginnovision:
When you are looking for reliability you can always "glue" it down with some solder-able conformal coat removes issues with vibration.
David Hess:
--- Quote from: maginnovision on June 08, 2019, 04:45:20 am ---When you are looking for reliability you can always "glue" it down with some solder-able conformal coat removes issues with vibration.
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Super glue works well for this.
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