Hi there,

I am a student that has little background in electronics. I am trying to build a project using a battery powered device, arduino and relay. I am connecting the battery powered device to the relay using a cable that contains two wires inside, but I am unsure how to determine which of the wires are positive or negative. The wires do not follow a colour convention for some reason. The wires are low voltage. Would greatly appreciate any insight or ideas that people may have! Thanks!

 

Welcome to AAC!

It depends on your region. Center positive is most common in my area.

If there's only the white wire and the shield, the shield would typically be ground.

 

Hi there,

I am a student that has little background in electronics. I am trying to build a project using a battery powered device, arduino and relay. I am connecting the battery powered device to the relay using a cable that contains two wires inside, but I am unsure how to determine which of the wires are positive or negative. The wires do not follow a colour convention for some reason. The wires are low voltage. Would greatly appreciate any insight or ideas that people may have! Thanks!
View attachment 284867

Do you have and know how to use a Digital MultiMeter?

Set it to measure voltage. Use the appropriate scale unless it is auto-ranging. Place the leads on the two (powered) wires. If the voltage is negative, reverse the leads.

Then the leads will indicate which is negative (the common or COM lead) and which is positive (+).

 

In the absence of a meter you could use a LED with suitable resistor, it is polarized. see https://www.instructables.com/LED-Polarity-Tester/

 

The picture you show is a shielded cable, probably from a microphone.

What are you plugging it in to? What is it for? A wire itself has no positive or negative.

A microphone cable would be carrying an AC signal with the shield connected to ground.

 

The picture you show is a shielded cable, probably from a microphone.

I have a few Wall-Warts that use shielded cable for the LV DC.

 

What you are really trying to determine is which wire, the one inside the the translucent insulator or the braided wire that surrounds it, is connected to the two contacts on the plug, the center post (the tip) or the barrel (the cylinder near the molded body).

The simplest way is with an ohmmeter. Put on probe on something (such as the braided conductor) and then check for the resistance to each of the two contacts at the plug. One should show an open (essentially infinite resistance) and the other should show a short (essentially zero resistance). The one showing the short is the contact connected to that wire. Check the other wire, too, just incase one of the wires is broken inside the cable somewhere.

In most instances (not all, so don't just assume), the tip will go to the center wire and the barrel will go to the braided shield.

If you don't have a multimeter, get one. You only need the cheapest one you can find, which can often be had for under $10 U.S., Some places, like Harbor Freight, will actually give them away from time to time.

 

Is the only thing connected to the cable is the relay coil?
If so is the relay coil polarised or does it not matter which way power is applied?