dumb question about wall-wart power

[novahobbies]

OK, this is going to sound silly, but here it is: I'm finally stepping into the world of LED-lighting for some buildups I have on the bench. I've done my homework, checked out some how-to sites, used the LED calculator, and finally bought the LEDs, resistors, wire-wrap, etc,etc, etc.
I'm going to use a wall-wart to power most of these assemblies when they're done. I know that the (+) and (-) sides are extremely important when wiring up LEDs, so........what s the positive, and what is the negative, on the wall-warts male jack???? I assume that the positive is the INSIDE portion of the jack, while the negative is the outside of the cylinder, but you know what they say about assume!!!! Can anyone help, confirm/deny my assumption? I've looked around and ironically can't find this answer! Any help would be.....helpful!

[jwrjr]

There is no simple answer to your question. The polarity is a matter of the manufacturers' whim. However, the polarity is usually marked on the adapter's case somewhere - usually small, but there somewhere. But when dealing with leds, the matter is no big thing. If the power is hooked up backwards, nothing bad will happen to leds. Just reverse the polarity and they should work fine. (Note:reversed polarity will hurt flashers, strobes, and such. Best to be sure of your polarity before using those.)

[novahobbies]

Many thanks. As it happens, the WW that I'm using is a variable-output variety that even has a polarity switch on it, so I think I'm good to go!

[macfrank]

Many thanks. :D As it happens, the WW that I'm using is a variable-output variety that even has a polarity switch on it, so I think I'm good to go!

You can get a cheap multimeter (a tool that is as important as a soldering iron in electronics - maybe even moreso!) for $5+ shipping. Here's one and here's another. It would solve your problem in no time, plus you can check resistors.

Frank