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+-- Thread: 12V LED polarity? (/showthread.php?tid=7329611)
12V LED polarity? - Foggy - 04-19-2017
I'm putting new 12 volt lights on a trailer. Are LED lights fussy about polarity?
RE: 12V LED polarity? - Cecil - 04-19-2017
Very !
RE: 12V LED polarity? - WoodCzech - 04-20-2017
The D in LED stands for diode. The definition of that is it only allows current to flow in one direction. So if connected correctly, the current will flow and the LED will light up, otherwise, it won't.
RE: 12V LED polarity? - TDKPE - 04-20-2017
(04-19-2017, 03:28 PM)Foggy Wrote: I'm putting new 12 volt lights on a trailer. Are LED lights fussy about polarity?
Being that it's a trailer, following the standard color scheme for trailer wiring should result in the correct polarity. Assuming, of course, that the vehicle end is wired correctly.
RE: 12V LED polarity? - Foggy - 04-20-2017
License plate light has a white and a black wire. No markings. Will it just not light if connected backwards, or will the factory smoke come out?
RE: 12V LED polarity? - WoodCzech - 04-20-2017
Connect it one way, if it doesn't light up, connect it the other way. If it still doesn't light up, there are other problems. It won't burn up, smoke nor explode when connected backwards.
At least that's how I have always done it....
RE: 12V LED polarity? - geek2me - 04-20-2017
(04-20-2017, 09:53 AM)WoodCzech Wrote: The D in LED stands for diode. The definition of that is it only allows current to flow in one direction. So if connected correctly, the current will flow and the LED will light up, otherwise, it won't.
Sort of. A diode allows current to flow in both directions, it just allows a lot more current to flow in one direction than the other. LEDs are diodes and light up when forward biased, while zeners regulate while connected "backwards".
Probably more EE than you wanted to know lol...
RE: 12V LED polarity? - WoodCzech - 04-20-2017
(04-20-2017, 12:24 PM)geek2me Wrote: Sort of. A diode allows current to flow in both directions, it just allows a lot more current to flow in one direction than the other. LEDs are diodes, but they light up when reverse biased - connected backwards, essentially.
Probably more EE than you wanted to know lol...
Ok, I knew about the current flow in both directions, but kept it simple for this scenario. I didn't know that LED's light up when connected backwards. I certainly don't mind learning more EE stuff nor being corrected
. I briefly studied EE before switching to IT.
RE: 12V LED polarity? - Robert Adams - 04-20-2017
(04-20-2017, 12:39 PM)Roly Wrote: Black +, white - Most auto systems are negative (-) ground. Roly
Black is always the ground in automotive EXCEPT on trailers. For some strange and odd reason trailers use white for the ground. It had to be a ford electrical engineer that came up with it. They never had any sort of wiring standard and often changed in production if they ran out of one color of wire they just used what they had on hand. (used to be an ase master tech)
RE: 12V LED polarity? - Robert Adams - 04-20-2017
(04-20-2017, 12:55 PM)WoodCzech Wrote: Ok, I knew about the current flow in both directions, but kept it simple for this scenario. I didn't know that LED's light up when connected backwards. I certainly don't mind learning more EE stuff nor being corrected
They don't light up when hooked up backwards unless there is enough ac ripple from the alternator ie dying rectifier diodes. Diodes will flow current in the opposite direction if enough voltage is shoved through them. Zener and and a few others have goofy characteristics when it comes to that.
Now with replacement bulbs and most add on stuff for automotive they have a rectifier bridge (4 more diodes) that will allow the bulb to be inserted either way and work