Figuring out Polarity of installed wires

[slookabill]

Is there a way to check which wire is + and which is -, without destroying the LED? I was installing some LEDs and now starting to seal up, I realized I screwed up in my marking of 2 wires that are now hidden, to know which end is positive and which was negative.

[Zubie]

Is there a way to check which wire is + and which is -, without destroying the LED? I was installing some LEDs and now starting to seal up, I realized I screwed up in my marking of 2 wires that are now hidden, to know which end is positive and which was negative.

Wiring it up in reverse should not kill the LED, but it won't light up and conceivably kill a series circuit. Diodes (the "D" part in LED) act like gates that only allow current to flow in one direction (very very low impedance one way, very very high the other). It shouldn't burn out assuming the operating current wouldn't have burned it out in the first place whichever way you hooked it up.

From the description, I presumed what happened was that you wired your LED on two separate colored wires, it now sits in the model and all you have is the bare ends sticking out to hook up to the power supply and you can't remember which wire is hooked up to what. If you have a multimeter (V/I/R), measure the resistance on the circuit with the LED. The correct direction should give you a low R rating, the reverse should give you a very, very high value. If it is really a question of measuring the polarity from a power supply wires before you hook up the LED, use the same multimeter to touch the bare ends of the wire to measure the voltage (I'm assuming you are working with low voltages/current, not house lines. Testing voltages with metal probes on house currents is not recommended if you are not a professional).

If you don't have a multimeter, they aren't expensive and handy if you are going to do more wiring.

[slookabill]

Is there a way to check which wire is + and which is -, without destroying the LED? I was installing some LEDs and now starting to seal up, I realized I screwed up in my marking of 2 wires that are now hidden, to know which end is positive and which was negative.

Wiring it up in reverse should not kill the LED, but it won't light up and conceivably kill a series circuit. Diodes (the "D" part in LED) act like gates that only allow current to flow in one direction (very very low impedance one way, very very high the other). It shouldn't burn out assuming the operating current wouldn't have burned it out in the first place whichever way you hooked it up.

From the description, I presumed what happened was that you wired your LED on two separate colored wires, it now sits in the model and all you have is the bare ends sticking out to hook up to the power supply and you can't remember which wire is hooked up to what. If you have a multimeter (V/I/R), measure the resistance on the circuit with the LED. The correct direction should give you a low R rating, the reverse should give you a very, very high value. If it is really a question of measuring the polarity from a power supply wires before you hook up the LED, use the same multimeter to touch the bare ends of the wire to measure the voltage (I'm assuming you are working with low voltages/current, not house lines. Testing voltages with metal probes on house currents is not recommended if you are not a professional).

If you don't have a multimeter, they aren't expensive and handy if you are going to do more wiring.

Thanks, thought I could use a multimeter, now just to find mine and test it out.

[EVApodman]

First determine the polarity of the LED with a DMM by touching it with the leads in the resistance mode. The meter's 1v output will safely light the LED without damaging it. Then with the the meter set to voltage, measure the voltage of the wires referenced to ground ( the neg point of your power supply). The higher voltage wire needs to be connected to the positive lead of the LED and the lower voltage to the negative side. This correctly biases the LED and it should work properly in the circuit.

[battlestar62]

would using tape to either number or mark p and N help? I forget sometimes too because I have so much on my plate trying to make my model the best I can. what I mean because sometimes I am not clear would it help to stop this common mistake? before it happens if you put this where you can see it even if you have put the wire in the model already? I understand what you may be thinking how can I see the tape if I can't see the wire. and wouldn't the tape cause its own problems.

[EVApodman]

If possible use red tape for plus and black for ground (neg). This will give a clear and instant sign of the polarity. Also if possible wire positive side components with red wire and negative with black.