Author Topic: LED polarity question?  (Read 1959 times)

Offline PP

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LED polarity question?
« on: August 31, 2012, 07:07:48 PM »
This will seem like a simple question to more than one of you smart guys out there, so here goes. What happens to an LED light if I hook it up backwards? You know, reverse polarity? Will it burn it out? Or will it still work? I'm serious about this. Thanks in advance for any and all responses, Will :)

Offline Ralph7

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Re: LED polarity question?
« Reply #1 on: August 31, 2012, 07:59:18 PM »
 Just redo and mine worked, I have nearly 40 LED's in/on my bus. I prefer the flat not the bubble type LEDs, also I get mine from SuperBrightLEDS. But I got some red LED stop/tail lights from wallyworld (WM).
  Hookem up if not workin reverse, I never hurt any of mine if I hooked them wrong.

Offline Sean

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Re: LED polarity question?
« Reply #2 on: September 01, 2012, 04:30:24 AM »
Will it burn it out?
No.

Quote
Or will it still work?
No.

The "D" in LED stands for "Diode."  A diode only passes current in one direction.  If you connect a diode into a circuit backwards, it passes no current and the circuit does not work.

"LED lamps" or replacement LED bulbs may have integral bridge rectifiers so that the actual LEDs inside the lamp always get the correct polarity.  That's how LED lamps designed for 120 VAC work.  Bridge rectifiers cost money, rob energy, and generate heat, so they are generally not used in LED lamps intended for 12 or 24 VDC.

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Offline PCC

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Re: LED polarity question?
« Reply #3 on: September 01, 2012, 05:48:16 AM »
Will it burn it out?
No.

Quote
Or will it still work?
No.

The "D" in LED stands for "Diode."  A diode only passes current in one direction.  If you connect a diode into a circuit backwards, it passes no current and the circuit does not work.

"LED lamps" or replacement LED bulbs may have integral bridge rectifiers so that the actual LEDs inside the lamp always get the correct polarity.  That's how LED lamps designed for 120 VAC work.  Bridge rectifiers cost money, rob energy, and generate heat, so they are generally not used in LED lamps intended for 12 or 24 VDC.

-Sean
http://OurOdyssey.BlogSpot.com


Awesome answer Sean.

After hooking them up backwards, and not working, when you re-connect them correctly, they will almost always work.

I do like those LED lights.
For some, patience is a virtue.
Dealing with me, it is required.
Thank God - He is always patient.

Offline PP

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Re: LED polarity question?
« Reply #4 on: September 01, 2012, 05:41:44 PM »
Thanks for the wonderful answers! I purchased a couple of LED replacement lights for the wife's MINI and one worked fine and the other didn't. I was careful to install correctly even double checking the polarity. Then I began to wonder if I screwed up and still managed to connect one backwards and burn it out, even though I was certain that I hadn't. So now I am 100% positive that I got a defective unit. I connected directly to a 12V battery and still nothing.
Thank you, Will

Offline Scott & Heather

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Re: LED polarity question?
« Reply #5 on: September 01, 2012, 08:21:24 PM »
some LEDs were made to light up
Different colors when you reversed polarity. Cool stuff :-)


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Offline PCC

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Re: LED polarity question?
« Reply #6 on: September 02, 2012, 05:03:33 AM »
some LEDs were made to light up
Different colors when you reversed polarity. Cool stuff!

Now that's something I hadn't thought about.

Brake lights that are green when I am driving, and red when I am stopping. May I confuse you more? Could substitute the green for ANOTHER color - like blue? Then I might have to carry donuts and coffee? Kidding
For some, patience is a virtue.
Dealing with me, it is required.
Thank God - He is always patient.

Offline Scott & Heather

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Re: LED polarity question?
« Reply #7 on: September 02, 2012, 05:44:12 AM »
When I was a kid, my dad (an electronics guru who marketed and sold electronic components for automotive applications as well as fighter jets) gave me a bunch of LEDs and some resistors and some 9 bolt batteries an taught me how to solder and I went to town! I built
LEDs into my Lego creations, I put them  in my R/C cars, I even put them in my pinewood derby cars and won blue ribbons for it :-) this was before LEDs were even a big item. Blue were rare back then and white didn't even exist on the consumer market.


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Scott & Heather
1984 MCI 9 6V92-turbo with 9 inch roof raise (SOLD)
1992 MCI 102C3 8v92-turbo with 8 inch roof raise CURRENT HOME
Click link for 900 photos of our 1st bus conversion:
https://goo.gl/photos/GVtNRniG2RBXPuXW9