How do you know what size of DC barrel connector to use for a particular voltage power supply? Unfortunately, in general, there are no well-established standards for DC barrel connectors and intended supply voltage. However, there are a few very common sizes for particular uses.
- 12 V: 5.5 mm outer diameter, either 2.1 mm inner diameter or 2.5 mm inner diameter.
- 5 V: 3.5 mm outer diameter, 1.3(5) mm inner diameter. Please note that I have found the Japanese Standard 5 V to be more common than this dimension.
- Both standards use 9.5 mm length barrels.
- Japanese standard 5 V: “EIAJ-02 for 3.15–6.3 V 4.2 mm OD, 1.7 mm ID.”
- Japanese standard 3 V: “EIAJ-01 for 0–3.15 V 2.5 mm OD, 0.7 mm ID.”
Beyond that, you’ve got to really do guess and check. Digi-Key made a good recommendation on some helpful common gear tools you may have for performing the measurement.
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A toothpick is gemerally manufactured from 2.1 mm to 2.2 mm in diameter, so you can use this to help disambiguate between 2.1 mm and 2.5 mm. Likewise, the tip of a ball-point pen can similarly be used.
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A multimeter test lead is manufactured to 2.0 mm in diameter, so you can also use this with visual analysis to compare diameters.
20181128/https://en.wikipedia.org/wiki/Coaxial_power_connector
20181128/https://en.wikipedia.org/wiki/DC_connector
20181128/https://forum.digikey.com/t/measuring-power-supply-barrel-plug-id-2-1mm-vs-2-5mm/401
Please note! Some barrel connectors are not actually standard barrel connectors, but a proprietary variant of the general barrel connector design. For example, I found a Canon 12 V DC adapter that looked like a barrel adapter, but had a center pin in the middle. In effect, it was like the reverse of standard barrel connectors. Rather than the pin/plug connector on the adapter and the socket connector on the equipment, it had the socket connector on the adapter and the pin/plig connector on the equipment. Yeah, so things can be tricky like that when working with existing equipment. Of course, when designing your own electronics, you’ll want to stick to the standards as much as possible.