Identifying + and - on DC power supply

I am getting together the parts for a Son of Fermentation chiller. I found most of what I need around my workshop. I only need a sheet of 2" foam.

My question is how do I determine which wire on the DC power supply is the + one and which is the negative one. The cord has one side which is smooth and the other side is ribbed. Which is which?

I have beem unsing a swamp cooler but if I can put together a SOF for cheap then I want to give it a try.

"Usually", ribbed is red. And red is hot. Black is not.

could always use an automotive light bulb to test the leads.

what kind of power supply? by general rule the + is the marked one (ribbed)

pete

certaut said:

what kind of power supply? by general rule the + is the marked one (ribbed)

pete

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Not sure what kind. I found it in a box of old stuff I had around. Not sure what it was from 120V to 12 VDC.

I will try it and see if it works when I hook it up. Should be a couple of days.I am going to pick up the foam tomorrow.

The only way to really tell is to hook it up to a multi meter and take a reading. If the voltage has a negative sign in front of it, reverse the polarity of the probes. The red probe will tell you which is the positive side.

You should do this to not only figure out what the polarity is, but what the actual voltage is.

If you're just hooking it up to a 6 or 12v computer fan it will either run in reverse if the wires are switched or it won't run at all. This is what happened with me. I take no responsibility if you burn your fan though.... Low enough voltage to just give it a try IMO.

I have hooked up 4 fans to DC power supplies, and have always just used good ol' trial-and-error. It's not going to ruin the fans. None of the fans I've used have run in reverse either, but since the fan blades are designed for pushing air in a specific direction, it makes no sense that they'd include a reversible motor anyways.