Sorry, this may be a stupid question... I have limited electrical knowledge...

I realize that some LED bulbs are sold without having an effect on polarity. superbrightleds.com claims that some of their bulbs will work either way. However, I have bulbs which do require the proper polarity setting so my question is, can I just switch the + and - wire in the plug?

For example, for my map light, I found wide-angle BA9S LEDs which I want to install but the polarity in my map light differs from the bulb's. I know the bulb works b/c I've tested it numerous times, however, when I install it, it does not (I've spun it around, etc...). Therefore, can I just switch the black and red wires in the plug right before the light holder to "re-polarize" it?

Thanks,

 

yes, you can "switch" it back. LED's come with 2 ends for you to attach wires onto. you'll notice a longer end and a slightly shorter end. the longer end is always your positive, and shorter is your negative.

If you attach the wrong polarity, it will not work because LED's aren't your ordinary electronic devices. They are transistors, in a way, they are like valves for mechanical setup. Basic LED's only allow electricity to flow in "only one" direction. This unique feature can help in a circuit to prevent burning the circuitry if power supplies may experience surges and "back flows". Therefore, if you have it placed in the wrong polarity, it will not allow the circuit to run in the active loop.

 

Thank you, I'm sort of understanding it... However, what if I switched the wires in the plug the LED bulb plugs into. I can't switch the 2 ends coming from the LED bulb itself since the bulb is already fitted into a base. Also since it is a bayonet base, the negative is always on the sides and the positive at the tip, so turning the bulb 'around' won't reverse any polarities. If it were a 194 then I'd be able to spin the bulb around but not a bayonet bulb.
So can I just switch the wires?

 

Alright, it's getting a little confusing here. What exactly you are doing? I am not getting the picture here. Are you wiring one power wire to one LED? or did you run several LED's per power wire? If you are just doing one LED per power wire, then yes, you can just switch the wires and it'll work. The main thing is, LED's shouldn't burn up if you have it routed on the wrong polarity. However, if you routed on the correct polarity, but the power source has an overwhelming voltage, it'll possibly burn your LED.

If you experience LED getting burned up, you should put a resistor before the LED, that way you can drop the voltage for LED's normal operating range. LED's typically take only little power supply to work.

 

Well, that works in theory, but only if the resistor is such that it is calculated to withstand 14.4V, not 12.

Dude, you're looking way too deep into this. The very term diode means that the electron flow will only go one way. SO, if you plug your bulb in, and it does not light, remove it and put the ends in the other way. If it does not light again, the bulbs is dead.

 

Sorry, it's hard to explain w/o pix.

This is the bulb that goes into our map lights. It is a bulb: http://autolumination.com/images/aut...a9s_matrix.jpg

The one in the pic is an LED bulb from autolumination.com.

However, when I install it in my map light, it does not work. But when I test it at home using my simple 12v power supply from radio shack it does work.

In the pic, the bottom/tip/base/nipple of the bulb is positive and the sides are negative. However, in our cars, the fixture where the bulb is inserted it is reversed - the sides are positive and the end is negative - that's why the bulb won't work in my car.

If any of you took your map light out you'll notice there is a black and red wire leading to the map light.

What I'm trying to ask is, can I cut those wires and reverse them - make the black connect w/ red and the red connect w/ black.

In my mind that would change the polarity and the bulb should work.

 

yes aaap2, you can switch the neg and pos wire. But be careful on how much voltage those guys can handle. Too much and u'll blow them out. But they usually turn on at around 2-4 V depending on what color and kind they are. I don't knw when they blow because i don't know what type you have.

 

These are automotive bulbs, they're made to work in your car w/o a problem... I've gotten LED bulbs from here before and never had a problem. I don't understand how voltage would be affected by switching wires?
If a 194 bulb doesn't work inserted one way, you take it out, spin it 180 degrees, plug it in, and now you've reversed the polarity and it should work. Since you can't do that with this or any other bayonet based bulb, all I needed to know was if switchng the wires was OK.

It would be the same thing as using a 1156 LED bulb in your blinker. If you insert it and it doesn't work, you can't spin it around because the + will ALWAYS be on the bottom so spinning it won't help. (Unlike the 194 I mentioned above which has the + and - NEXT to each other so spinning it WOULD help).

You said it is OK but to be careful of voltage and now I'm lost...

$h!t, I'm just confusing myself now... Maybe I'll get some pics later tonight and explain that way...

 

aapp81 ... yes you can just swap the wires around, and you will switch the polarity of the socket. What ImmaSquashYou was saying is just in general be careful w/ puting LEDs in a car b/c too high of a voltage will burn them up (if you want a detail explanation, let me know ... i can provide one). However, someone else mentioned that the bulbs from the place that you ordered them will work in a car, i.e. they probably already have the resistor built into the package.

Anyway ... yes switching the wires will switch your polarity and will make your bulb light up. Of course switching polarity will not change the voltage, it will still be 12V (if this bulbs works at 12V this isn't a problem)!

 

Yes, they do have a resistor.

Thank you and everyone else for the help.

 

yup, thats exactly what i mean..heh...thanks for clearing up for me.