How do I tell which wire is positive and which is negative?

viewsonix

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How do I tell which wire is positive and which is negative?

I have to connect a ac adapter to a battery operated game system. I have an adapter that is the right voltage (6v) and I know I will have to cut off the end of the adapter power cord and splice/connect the wires to the game, but I don't know how to tell which of the two wires coming from the adapter is positive and which is negative.
How do I test this? Both wires will be black so color coding is out obviously.
 
The wire with the white stripe should be the positive wire with the negative wire being the one that's all black.
 
I was waiting for someone to say this. I don't have a multimeter, but that can be fixed with a quick trip to Lowes/HomeDepot. How do I test it with a multimeter?

Set your meter for low DC voltage (20 on mine) -- yours might auto detect.
Put the red lead on one wire and the black lead on the other

If the voltage reads positive, you have the red lead on the positive wire and the black on the negative.

If the voltage reads negative, you have the red lead on the negative wire and the black on the positive.
 
The wire with the white stripe should be the positive wire with the negative wire being the one that's all black.

I've had a number of wall-warts that had the white-striped side as negative. So testing is generally a good idea.

-Jim
 
Would this type of multimeter be ok to test something like this?

http://cgi.ebay.com/LCD-DIGITAL-VOL...828?pt=LH_DefaultDomain_0&hash=item43a031c7e4

Yeah, that should be fine. As a tool, it's a cheap piece of garbage - but for the purposes here, it'll work just fine. I think Harbor Freight even has that same one for even cheaper.

For simply checking what's positive and what is negative, ANY multimeter will do. Heck, you can do it with an LED and a resistor.

If you intend to do a little more with it, I'd go for a slightly better model, but for arcade use, absolute precision isn't usually necessary. I've used one of these meters before (a friend keeps one in his trunk "just in case" with some other basic tools.) It's cheap. It's flimsy. The leads fall out. But it works just fine.

-Ian
 
Oh, I got the multimeter from that guy. It's cheap, no doubt. The fun part is there is one small sheet of instructions with it, and of course it's all in chinese!

Ok, any thoughts as to which jacks I plug the black and red probes into? there are 3 ports on the multimeter.
 
Set your meter for low DC voltage (20 on mine) -- yours might auto detect.
Put the red lead on one wire and the black lead on the other

If the voltage reads positive, you have the red lead on the positive wire and the black on the negative.

If the voltage reads negative, you have the red lead on the negative wire and the black on the positive.

This is a smart man. I suggest everybody bookmark this thread, and ever few days, come back and check MikeyDee's post history to read all the other smart things he has to say, lol.
 
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