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Need help with small flashlight...

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fettmaster5

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I just started getting into electronics, and as my second project, I have decided to make a bright blue LED flashlight. (my first was a green LED that lit up with a toggle switch, 2 AAA batterys, and enclosed in a small project box)


my dilemma...

i am using 3 AAA batteries... = 4.0 volts

my lights are high brightness blue = 3.7, 4.0 volts MAX...

after hooking it all up, it shone quite brightly, but has a green tint to it...

so, i was told to get a resister. what type do i need?

i still have trouble converting my units, and am not sure the amps (m amps)

btw, i am using 22-gauge wires, and have access to larger and smaller gauge, but am sure it is not the issue...
 
Whats the max current the led can handle?

3 AAA batterys is a 4.5v supply. Not 4v. With new batterys and a full 4.5v supply-
an 18 ohm resistor will give you about 28mA and a 10 ohm will give you 50mA. Once your batterys drain a bit, the LED won't light up anymore.

The wire gauge shouldn't be an issue unless you are using miles of it.
 
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Since the blue LEDs turned green, I think you fried them and they are ruined.
You forgot to limit the current so they got too hot.
 
As Andy1845c said.3 AAA batteries' max voltage is 4.5V.But the rate voltage is 3.6V.And your LED's working voltage is from 3.0V-3.7V.Because the batteries' voltage may higher than 3.6V,so you should design a constant-current and voltage limitation circuit.
 
As Andy1845c said.3 AAA batteries' max voltage is 4.5V.But the rate voltage is 3.6V.And your LED's working voltage is from 3.0V-3.7V.Because the batteries' voltage may higher than 3.6V,so you should design a constant-current and voltage limitation circuit.

um... how do i do that?

lol, I'm just getting into this stuff, and taking it slow... but your advise has been most helpful, and i understand almost everything you have told me...
 
You don't need to limit the voltage to LEDs because you don't know what is their individual voltage. Instead you limit their current and the LEDs limit their own voltage.

Who said that the LEDs are 3.7V? No they aren't, they have a range of voltages. A few might have a voltage of 3.7V. Some might be 3.4V and others might be 4.0V.

A battery made with three 1.5V AAA alkaline cells is 4.5V or 4.8V only when it is brand new. The voltage quickly drops to 3.6V when some of the LEDs won't work. You will probably see them dim all the short time.
 
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You don't need to limit the voltage to LEDs because you don't know what is their individual voltage. Instead you limit their current and the LEDs limit their own voltage.

Who said that the LEDs are 3.7V? No they aren't, they have a range of voltages. A few might have a voltage of 3.7V. Some might be 3.4V and others might be 4.0V.

A battery made with three 1.5V AAA alkaline cells is 4.5V or 4.8V only when it is brand new. The voltage quickly drops to 3.6V when some of the LEDs won't work. You will probably see them dim all the short time.


LED has a range of voltage.If the voltage is above it's rang,it will be damaged.So you can learn the voltage range of led you are using from it's datasheet.You must assure your supply voltage not to exceed it's top voltage limitation.
 
um... how do i do that?

lol, I'm just getting into this stuff, and taking it slow... but your advise has been most helpful, and i understand almost everything you have told me...


You can build a constant-current circuit.And you can also build a voltage cutoff circuit.This circuit will cut off battery supply when the battery's voltage is below some voltage such as 3v.Because when the battery's voltage is below 3v,it's capacity is almost null and at this time led will be dim.

please email me at ghx420[at]gmail dot com.and i'll send a constant-current diagram to you.
 
LED has a range of voltage.If the voltage is above it's rang,it will be damaged.So you can learn the voltage range of led you are using from it's datasheet.You must assure your supply voltage not to exceed it's top voltage limitation.

Nope, that's wrong.

LEDs does not have "voltage ratings". The foward voltage is the minimum voltage to polarize/bias the junction, so that the LED can conduct current.

LED DOES have current ratings. If you exceed the maximum forward current of a LED, it will heat up until it burns and smells bad.
 
LED has a range of voltage.If the voltage is above it's rang,it will be damaged.So you can learn the voltage range of led you are using from it's datasheet.You must assure your supply voltage not to exceed it's top voltage limitation.
The voltage of an LED doesn't matter. An LED can have a supply of thousands of volts if its current is limited to be less than its max rating.
Limit the current, not the voltage. An LED limits its own voltage.
 
The voltage of an LED doesn't matter. An LED can have a supply of thousands of volts if its current is limited to be less than its max rating.
Limit the current, not the voltage. An LED limits its own voltage.


Yes.You're right.I mean in the application of LED,if the voltage is too high,the current will higher and LED will warm up.
 
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