I have some non-standard bikes to hook up so rather than ordering the kits with fixed length wires, I want to just order appropriate double strand (or coaxial) wire in bulk, along with the connectors, and get the job done that way. I can't seem to find the standard size used for this job, however. Appears to be about 22 AWG.
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As mattnz suggests, the wire size choice is based more on the strength/stiffness of the wire, and on the ease of working with it.– Daniel R HicksNov 24, 2020 at 23:11
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I will note that there are several places online that sell the Schmidt coax wire in bulk by the foot; it's not that expensive and it is by far the cleaning looking I've worked with if you need double-strand. Everyone who sells it will also have the Schmidt and B&M type connectors; the B&M 2.8mm ones are the same as many other generator lights take.– Nathan KnutsonNov 24, 2020 at 23:56
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2 Answers
Won't matter much, 22AWG is rated at about 1AMP for power transmission and 7AMP maximum current (i.e. that is around the current insulation starts to melt), is plenty large enough to carry the current from a dynamo (a few hundred milliamp's) and provides a strong enough wire that it won't break easily when in use. A size or two smaller or larger won't hurt.
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1I've used 22AWG stranded ethernet cable as a proof of concept, and a year later its still working fine so haven't replaced it.– Criggie ♦Nov 25, 2020 at 1:07
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1Probably good to emphasize that stranded wire (not solid) should be used, as the wire may flex and solid wire's metal conductor will eventually break after repeated bending.– ArmandNov 25, 2020 at 1:12
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@Craggie - Ethernet cable, the #8 wire of DIY electronics and electrical. :)– mattnzNov 25, 2020 at 2:07
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Not a bad idea. I've got a lot of cat 5e sitting around. I've got some salvaged charger cable that's 22 x 2 strand and nice and sturdy that'll work for some of this too. Nov 25, 2020 at 2:37
The "official" answer is AWG 20.
According to SON (hub dynamo manufacturer), their coaxial cable (and it really is coax, not just 2x conductors inside a round, foam-filled housing) corresponds to:
2 x 0.5 mm^2 conductor wires.
That corresponds, according to conversion tables like this one, to an AWG 20.
As noted above, 22 should already be overkill for the current carried, but in terms of durability of the wire and maybe the crimping at the spade connectors, 20 may be the better bet.
I'm not finding a bulk SON coax seller in the US for < $1 / foot, which isn't terrible, unless you want to do 4 long bikes (as I do) and need about 50 feet, given that bulk auto / electronics 2-strand can be had for a fraction of that price, though it may be a lot uglier.
One more tip if you're going this route, there are spade connector + crimper kits available online (here's an example on Amazon) that give you dozens of the 2.8mm and 4.8mm connectors you need, plus housings for them, as well as a crimper, all for <$30.