DC power supply question / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

DC power supply question

1 2 next

Move Thread

LAN_403

magnetomotive

Mon Feb 11 2008, 08:59PM

Registered Member #267 Joined: Mon Feb 27 2006, 09:44PM
Location:
Posts: 46

I have a DC power supply that has the output wires exposed. There is a white wire and a bare copper wire. I need to know for sure which one is ground (negative) and which one is hot (positive), but I do not have a multimeter to test this.

My first thought was that white is the positive wire. Is this correct?

Proud Mary

Mon Feb 11 2008, 10:34PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Assuming this is a relatively low voltage DC supply, then it should be safe to do the following

Extend your unknown wires, bare them at the very ends, and stick them in a glass of strong salt water made with ordinary kitchen salt. Take care you don't let the wires touch together which might damage your supply.[secure them with clothes' pegs etc to stop them wandering about in the glass] In a very short time you will begin to see:

Yellow-Green bubbles of chlorine gas forming at the anode (+) and colourless bubbles of hydrogen rising up from the cathode [-]

Myke

Mon Feb 11 2008, 10:50PM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

If you know the output voltage then you can connect a LED with an appropriate series resistor to see what is positive and what is negitive.

magnetomotive

Mon Feb 11 2008, 11:46PM

Registered Member #267 Joined: Mon Feb 27 2006, 09:44PM
Location:
Posts: 46

Thanks for the suggestions. However, I do not have an LED or a resistor available, and the salt water idea does not sound safe at all.

It is a 12V supply rated at 10W. I was simply wondering if anyone here was familiar with wire color codes for DC supplies. I could not find a definite answer by searching google.

Proud Mary

Tue Feb 12 2008, 12:27AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

On the scale of things in this forum, you're not really likely to come to any great harm putting a pair of electrodes at 12V into some salt water, but you know your own situation better than I do!

rp181

Tue Feb 12 2008, 01:19AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

put the wires in weak salt water and the one with most bubbles is -. Wont produce much chlorine and the chlorine that does come will probably dissolve in the water.

Capper

Tue Feb 12 2008, 01:32AM

Registered Member #914 Joined: Fri Jul 20 2007, 06:22PM
Location: South Bend, IN
Posts: 85

I was simply wondering if anyone here was familiar with wire color codes for DC supplies

There's no such thing. Every shop, every industry, even every country has their own color code standards, and none of them follow them. In the US, {most of the time, or some of the time, or sometimes} red wires are positive and black wires are negative, and bare copper wires are either a neutral, ground, or a shield.

We had a German intern here for a while, and his color code was red for negative, white for positive, and black was something else - caused quite some trouble while we were building test stands.

If you have co-axial cable, and the bare copper is wrapped around the white center wire, then I would assume the white wire to be the positive one. The LED test is a good one I use most of the time myself when I can't get to a volt meter.

Another trick is to use a small DC motor (or PC fan) and hook it to a known voltage like a 9V battery and watch what direction it spins, then put your power supply on it and watch what way it spins.

C@P

Shaun

Tue Feb 12 2008, 02:01AM

Registered Member #690 Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616

The salt water idea is totally safe. The one that bubbles will be negative.

I think that if you are going to work on any type of electronics you should at the very least have a multimeter. It would make this a trivial issue requiring less than 5 seconds of your time. They can be had for $8 or so at places like hardware stores, radioshack, hell I've even seen 'em at Kmart.

HV Enthusiast

Tue Feb 12 2008, 03:19AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

magnetomotive wrote ...

Thanks for the suggestions. However, I do not have an LED or a resistor available, and the salt water idea does not sound safe at all.

It is a 12V supply rated at 10W. I was simply wondering if anyone here was familiar with wire color codes for DC supplies. I could not find a definite answer by searching google.

There are no universal color codes when it comes to supplies like that.

As others have said, you have several suggestions:

1) Get a cheap multimeter - you can get one for about $5.00 at radio shack
2) Get an LED - about $0.10 or you can probably find one

magnetomotive

Tue Feb 12 2008, 03:37AM

Registered Member #267 Joined: Mon Feb 27 2006, 09:44PM
Location:
Posts: 46

Thanks for the help everyone. The wire is a coaxial-type like Capper said. The bare wire was ground.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob