Saturday, November 21, 2020

26 AWG solid copper wire: the perfect choice for hand-soldered Arduino projects

This post is my little token of appreciation for the 26 AWG solid core copper wire. Perfect for creating permanent version of Arduino projects, or if not perfect, then at least much simpler than wire wrapping and much, much more practical than using solder traces. Man, I love 26 AWG solid core.

When I started my journey with small electronics and (inevitably) soldering, I wanted to make sure I'm following the established best practices, and I assumed that there must be a single best way of doing something as fundamental as soldering. I quickly realized this wasn't necessarily the case. There appear to be at least three techniques folks commonly use:

  • Solder traces i.e. using solder to create bridges between pads. I find this method to be tedious, inflexible, wasteful, and error-prone both initially and during any re-work. The traces look kind of cool when done properly, but I ain't doing it for the looks.
  • Wire wrapping. Not bad, but requires special tooling. Due to the thin wire gauge (28-30 AWG) this method might not be ideal if you intend to support larger currents.
  • Soldering regular wires, either taped/tacked down or using "helping hands" to prevent the wire from moving during work.

None of these options sounded particularly appealing, so I decided to take a closer look at the problem/requirement itself and search for solutions as if there were no existing suggestions out there.

The requirements are simple:

  • I want to use solid core wires and common tools only. No specialized tools.
  • I want to attach wires to the device pins before soldering, including in tight spots.
  • The wire needs to stay attached during soldering and can't be easily shaken off or accidentally knocked out of position.
  • The wire must be able to carry 2 amps of current with ease. I only really need 1 A, but derating can't hurt.

There's really only one characteristic the wire must have to meet all these requirements: proper thickness. The thickness of the wire defines its ampacity as well as how easy it is to form it into the required shape (e.g. a hook around a pin). Just find one that's thick and thin enough at the same time.

Meet the 26 gauge solid core copper wire!

Here it is next to its 22 gauge counterpart:

Not surprisingly, it's quite a bit thinner than 22 gauge breadboarding wire:

Here's why I love it and use it for all my permanent or semi-permanent installations:

  • The wire can be shaped quickly and easily using nothing but a pair of tweezers, to create almost any layout you may need to use on your prototyping board.
  • The same pair of tweezers is enough to form the bare ends of the wire into a loop or hook-like shape, tight enough to fit firmly around any through-hole device pin. With that, wires can be securely attached to device pins or other components before soldering.
  • Except for the bare ends, wires are insulated. This allows wires to be routed close to other components (or touch them) without issues.
  • Despite what most gauge tables may indicate, it's capable of carrying low single-digit amp currents without breaking a sweat.
  • It's thin enough that the wire won't stick out of solder blobs formed around IC pins, so there's no risk of the adjacent pins shorting out.

Below are some close-ups to show what I mean:

Now, there's one aspect that may need further clarification, and it's the ampacity i.e. the the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating (Wikipedia).

Sources indicate that 26 AWG should support up to ~2.2 A without getting excessively hot (examples: source 1source 2). For the purposes of this blog, I define excessively hot as 80 degrees Celsius (176 °F), which is a common temperature rating hobbyist-grade wire insulation. At 80 degrees, it's also hot enough that you could probably tell that the wire is perhaps a bit too busy just by touching it.

Anyway, it might appear that 26 gauge wire is only suitable for very low currents, and 2.2 A is already too much to ask of it. However, as the source 2 above is kind enough to point out, the ampacity ratings are very conservative, and you shouldn't let them intimidate you.

Enough with the theory though. Below are thermal camera shots from a 26 AWG wire (5.6 mΩ) and a 22 AWG wire (13.5 mΩ) for comparison.

  • Wires were placed under load for 2 minutes before taking temperature measurements.
  • I know that this is not a perfect way to measure wire temperature. Insulation material is somewhat reflective and doesn't yield itself to accurate infrared measurements
  • I know that the wire is substantially hotter than the insulation.

  • Left side: 26 AWG (top), 22 AWG (bottom) at 5 V / 2 A.
  • Right side: 26 AWG (top), 22 AWG (bottom) at 5 V / 6 A.

You can make up your own mind, but as far as I can tell, 26 gauge is plenty enough for <5 A or thereabout.

That's it. Thank you for reading!

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