LED Polarity

[turnitup]

Hi all,

Hope that this an easy one. I bought a LED light panel that requires a 120 AC to 12V DC converter...no big deal, got one. The correct polarity is critical for LEDs, how do I determine which lead is the positive? I’ve got a meter, just don’t know what to test for. Stupid question, I know, but here I am!

Thanks!

 

[avionic]

Positive voltage wire connects to the anode of the diode.

 

[avionic]

I bought a LED light panel

Post a photo..

 

[turnitup]

Thanks for the information Avionic, guess my real question is how do I know which of the 2 wires coming out of the 12v dc converter, is the positive (I.e. a converter like that used for a laptop, if the final connector to the PC has been cut off, leaving just the 2 unmarked wires.)

This is what I will be connecting to my LED lamps (and the +/- IS marked on this unit). If I get it wrong, I’m going to ruin the LEDs...

Thanks!

 

[PE9ZZ]

Obviously you have to use a multimeter to verify polarity of your unmarked wires. Usually, if it's coaxial (center conductor and braid around it) the center conductor is positive. Note that these LED panels typically have three LEDs and one or more current limiting resistors in series. Applying the wrong polarity to such a string is not fatal. LEDs can withstand reverse polarity of more than 5 V so in case of a three LED string this would be 15 V at least. You are not going to ruin your LEDs.

 

[dB happy]

Most multimeters have a polarity indicator. As long as the positive and negative leads are in the proper holes on the meter, it will show you the polarity. If it's hooked up correctly, most multimeters will show just a voltage on the screen. If the polarity is backwards, it will show a - in the corner or off to the side, as well as the voltage.

 

[Catmanboo]

Bottom line, if it doesn't light up first try, reverse polarity, then it will. Case closed. Nothing''s gonna go up in smoke or tits up unless you really try.

 

[fred soop]

If you are really concerned, add a 1N4xxx diode in series and connect the power supply. The diode will protect against reverse voltage. If it's the LEDs you are concerned with, connect a 470 ohm resistor in series with a 9 volt battery and test.