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Discussion Starter #1
Trying to understand the myriad of LED dash light products out there. Hoping an electronics guru can weigh in. If Ed P is watching, I'm sure he will jump right in.

There are a wide variety of them out there. There are 6mm - 14mm mounting holes. There are colors. There are bezels, chrome or black, etc. But it's the voltage ratings that are confusing me. There are 2V, 6V, 12V, 24V, and 30V. I've always known that an LED diode drops about 0.7 volts. So how do these voltage ratings work.

I know one might be tempted to say just use the 12V ones on our dash boards since our cars are 12V. I have in fact recently used a 12V one in my car and it's great. I do want to know the answers though as I see some pretty cool ones that I want to use for other things. A dash indicator light can have the full car battery voltage across it, like when a pressure or level switch opens. So does that mean that a 2V one will burn up, and a 24V one will only shine half as bright? Would you have to drop some voltage to use a 2 or 6V one, eg. add a resistor to the circuit?

Thanks,
 

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But Mad North-Northwest
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Just decide what size bulb you want, buy an appropriate socket and 12v automotive LED bulb, and wire it up like you’d wire up any other light. These can handle full voltage in indicator applications or whatever.

I generally buy from these guys:

Car and Pick-Up Truck | Vehicle Lighting | Super Bright LEDs
 

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Discussion Starter #3 (Edited)
Again, that is not my question. I would like to know about the different voltage ratings in the LED indicator lights.

Here is an example of some of the ones I am looking at, but there are many varieties of these.

Thanks,
Screenshot 2021-03-09 165340.jpg
 

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But Mad North-Northwest
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Okay, I'm not sure what you're asking, and you may not be either :LOL:

If you're asking about what voltage rating you want for an LED to use on a car, it's 12V. If you're asking when you'd use a 2V or 24V LED on a car, the answer is pretty much "never". You brought up voltage drop which really doesn't enter into the whole thing, so I think you may not be thinking about this properly.

A 12V LED will work properly if hooked up to a switch type indicator like a low oil pressure switch or something. A 24V one won't light and a 2V one will blow.
 

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Discussion Starter #5
That's right. I am not asking which one I should use. I am asking how the non-12V ones would perform in a car.

If a 24V one will truly not light up, why?

If a 2V one will blow, will it not blow if a proper voltage divider were used?

How do these two variants differ internally?
 

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But Mad North-Northwest
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So generally LEDs will take ballpark 2-3V to light. They're semiconductor devices, and the exact voltage depends on the specific semiconductor used, which generally depends on what color it produces. You give them too much voltage and they blow: basically you overwhelm the "semi" portion of semiconductor and just short right through it. So higher voltage rated LEDs will typically have a resistor in series to drop the voltage across the LED to the range the LED can handle. This looks like a pretty good write up:


In practice, with cars none of this really matters since everything is 12-14V. You just buy automotive 12V LEDs and wire them up the same way you'd wire up an incandescent bulb. They'll work the same, just pull a lot less current.
 

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Discussion Starter #8
Here are the lights I was looking at. They are not for replacement, but for adding a light in a new hole in the dash. There are others on Amazon and Ebay.


I did purchase a 12V, of course. And previously I have a 12V single color for my oil light. As mentioned it works fine and very bright. So there seems to be internal resistors associated with the higher voltage ones. I do remember some of my circuit classes, but we always had diodes alone in the circuit and were accompanied by resistors in series. Always used 0.7 volts as diode drop. This was non-LED diode of course. It seems that 2.2 is the drop across LED.

Thanks,
 

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Here are the lights I was looking at. They are not for replacement, but for adding a light in a new hole in the dash. There are others on Amazon and Ebay.


I did purchase a 12V, of course. And previously I have a 12V single color for my oil light. As mentioned it works fine and very bright. So there seems to be internal resistors associated with the higher voltage ones. I do remember some of my circuit classes, but we always had diodes alone in the circuit and were accompanied by resistors in series. Always used 0.7 volts as diode drop. This was non-LED diode of course. It seems that 2.2 is the drop across LED.

Thanks,
Powering an led is very simple you just need to use the correct resistor for the voltage you have .Here is an online calculator to get you in the ballpark. LED Calculator - Current limiting resistor calculator for LED arrays
If you have an led to e used with 6 volts 12v 24 v it already had a resistor attached . You can easily measure this with a $6 meter from harbor freight. Most small leds like 20 ma. Is the current going through them. This is very small. A 24 v led might be bright enough for you with 12v . A 6v led will be too bright or probably burn out at 12v. This is easy to fix just add the correct resistor to the 6v led snd you are good to go at 12v. Resistors just add their values together for a single led . So if the 6v led measures 220 ohms ad the calculator tells you you need 480 to use it with 12v just attach a 260 ohm resistor yo the 6v led. ( going from 24 to 12v is harder because you will need to open the led package and change the resistor to a smaller value.
You can buy a resistor assortment on Amazon for less than $10:
Cutequeen 31 Values 1% 775 pcs,RoHS Compliant Res... Cutequeen 31 Values 1% 775 pcs, RoHS Compliant Resistor Kit x 25pcs =775 pcs (0 Ohm - 1M Ohm) 1/4W Metal Film Resistors Assortment: Amazon.com: Industrial & Scientific

One last thing all leds are not equal and some are much brighter than others with the same voltage and resistor.
The calculator will give you a value that might me too brite for the dashboard. So experiment with higher value resistors until you like what you see Guimarães the led you have
 

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Discussion Starter #10
This is a very helpful website. Thanks Larry. I have received my LED in the mail this morning and will be working on my panel soon.

Thanks,
 
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