I'm using a 120V AC to 12V DC power converted I scavenged off of an old router. So now that I have the 12V DC I need for my project;
Now what about ground?

Can I use the wire with "-" signs all over it as a ground for all the pieces in my project or?

 

yes, that would be your DC ground...

 

Yep. The 12 volt supply will have two output wires. One of them is positive with respect to the other and one of them is negative with respect to the other. You can call either one of them "ground" and it will work.

 

Thanks guys

 

Sorry for the double post but I didn't want to start a new topic.

I tested the adapter with my multimeter;
I secured the wire with the -'s on it to the black tester, and the other wire was secured to the red tester. I got -12v DC. So does this mean the side with the -'s down it is actually positive? Thanks;
Josh

 

Sorry for the double post but I didn't want to start a new topic.

I tested the adapter with my multimeter;
I secured the wire with the -'s on it to the black tester, and the other wire was secured to the red tester. I got -12v DC. So does this mean the side with the -'s down it is actually positive? Thanks;
Josh

Probably, but to be certain, you can connect your tester to a battery; even a AAA, AA, or 9V cell would work. Connect the black tester lead to the negative (-) side of the battery and the red tester lead to the positive (+) side of the battery. If the tester shows + voltage, you will know for sure which way around to connect the tester; then connect it the same way to your unknown power supply. When you get the + reading on the tester, you will know which is the positive and negative lead on the unknown power supply.

 

Its really simple..You just need to pay attention to which wire the black lead is connected to. A meter will tell you polarity with respect to the black lead.

If you want to work with positive voltages and your meter is showing -12VDC then the wire attached to the red meter lead is your ground (you have the wires switched). If your meter is showing 12VDC then the wire hooked to the black meter lead is ground. (you have the wires correct)

The opposite is true when working with negative voltages.

 

Another thing to point out is to make certain that the test leads are plugged into the correct places on the meter. I have, on occasion, goofed that up. Reading a negative voltage when I know it should be positive.

 

Another thing to point out is to make certain that the test leads are plugged into the correct places on the meter. I have, on occasion, goofed that up. Reading a negative voltage when I know it should be positive.

No ! That could never happen

I thought about making that comment...

 

Yeah they're correctly in place, as when I tested a AAA battery I got +1.48V with the red tester on the + end, and the black tester on the flat - end.