Help Repurposing a power supply

[theCougfan97]

So I have a 12V 0.8 amp pump. It came with a black and red wire (no plug). I took a power supply that says output:5Vdc--2.5A / 12Vdc -- 1.5A. My thought being I would chop off one end of my power supply and attached red to red black to black. What I discovered inside my power supply cord was a yellow, red and black wire as well as some bare wire. What do I do with the yellow wire and bare wire?

 

[DaleHair]

Generally the red will be +12, the yellow +5, and the black common to both. Do you have a volt meter? You could just hook it up red nd black and try it briefly to see if it runs OK.

 

[theCougfan97]

What do I do with the yellow? It seems if I have the power supply plugged in, with the red and black going to the pump, the yellow would remain live. Will it be sufficient to just wrap it in electrical tape?

 

[DaleHair]

Wirenut would be better but tape will work.

 

[processhead]

This almost sounds like an old computer power supply.

IIRC

Red 5 volt
Yellow 12 Volt
Black Common

As mentioned, before connecting the pump, you really should confirm voltage and polarity with a voltmeter

 

[DaleHair]

With only three wires I didn't think it was from a computer, I've seen power supplies like it before, don't know what they were from.

As far as which voltage is which color, it really is a crap shoot and you can get a cheap meter for about $10.

 

[rcbishop]

Black is very likely to be the minus side. Red and yellow are probably the 5 and 12V, but which is which could definitely go either way. You do want to be sure you use the right one, because you can actually burn out a motor by using too low a voltage.

If it's a 12V pump, and your supply gives 12V and 5V, why not just try it on each wire (for a couple seconds) and see which one runs the pump faster?

As for what to do with the other wires, maybe trim the shield back as far as you strip off the outer insulation, then let the unused wire go another half inch or so. The two wires you're using can extend out beyond that to the pump, and you can wrap the whole thing with tape. There are better-looking ways to do it, but this will be more than enough for low voltage DC.