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How do I test barrel plug polarity on USB Adaptors?


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I purchased 2 x 5v 3000mA USB Adaptors and a USB to 5.5 mm/2.1 mm 5 Volt DC Barrel Jack Power Cables.


EDIT: the power supplies from one vendor and cables from a different one. Both from China.


One set for my nanoPEB and one set for my 32k Side Cart. The barrel fits perfectly.

However; the USB to Barrel Jack does not make note of the polarity anywhere. So I'm reluctant to use it.

I have a pocket multimeter. Can I use this to verify polarity?


If yes, how? It's a generic HDM350.

Edited by Sinphaltimus
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You most certainly can use your DMM to figure out polarity. Stick the red lead in the barrel and black lead on the outer edge. If you see negative voltage indicated by a minus sign (-) just to the left of your reading, your center tip/inside of barrel is negative. No minus sign indicates positive of course.

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BTW, you/we want tip-positive, so inside of the barrel should be about +5V. This is most common.


You can also do continuity testing with info from a page like this: https://www.moddiy.com/pages/USB-2.0-%7B47%7D-3.0-%7B47%7D-3.1-Connectors-%26-Pinouts.html

In this case, you want continuity between VCC and the inside of the barrel, and continuity between GND and the outside of the barrel.



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