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How to find polarity of a power supply that's lacking the customary markings

How to find polarity of a power supply that's lacking the customary markings

If I have a power supply (not a computer power supply, just a battery-replacing wall wart) and it doesn't have the usual polarity marking, how to I know if the tip is positive or negative?

Asked by: Guest | Views: 58
Total answers/comments: 1
Guest [Entry]

"I have a simple voltage probe that has a bi-color LED, instead of a light bulb. It's wired so that if the point is positive relative to the ground clip, it's green. So I normally clip the ground clip to the outside of the connector, and put the point inside. That tells me at glance the polarity.

I also have used it for debugging RS232 signals, it's surprisingly fun to watch the LED flash red and green.

I would also, after determining the polarity, use the point to etch the polarity symbol into the case, or label. I mean it has a hardened tip already, why not use it?"