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Probably a simple question

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P0wderkeg

New Member
I just got into electronics recently. Is there a way to reduce current? I hooked up a circuit of two AA batteries and two 10K resistors on a breadboard, but the amperage isn't being knocked down, only the voltage. I want to hook up some LEDs, but the amperage in the circuit is way above the limit of the LEDs. Thanks.
 

EN0

Member
I just got into electronics recently. Is there a way to reduce current? I hooked up a circuit of two AA batteries and two 10K resistors on a breadboard, but the amperage isn't being knocked down, only the voltage. I want to hook up some LEDs, but the amperage in the circuit is way above the limit of the LEDs. Thanks.
A resistor will lower the current. It sounds like you might have made a voltage divider shown in my attachment. You should understand the concepts of parallel and series circuitry. For resistors if you connect two 100Ω resistors in parallel it will reduce the resistance to 50Ω. But if you had it in series it would make it 200Ω. If you have two LED's connected in parallel and they each take 10mA, you need to supply the circuit with 20mA. If you kept 10mA, each LED would take 5mA! Or if you have two LED's configured in series you have to double the voltage, so if one LED takes 3V and if you want two LED's, you have to have a supply of 6V (3V x 2 LED's). You should also look at the forward voltage of the LED's in the specs. A typical value will be 2.2V or something. So if a single LED takes 20mA, and you have a 3V supply, then 3V - 2.2V = 0.8V then according to Ohms Law, R=E/I so R= 0.8V/ 20mA which equals a resistor value of 40Ω.
 

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P0wderkeg

New Member
Thanks for the reply! Yeah, I guess I need to read up more about series and parallel circuitry. I don't understand everything from the post but I'll read more, and soon enough I will. Thanks again, it's really appreciated.
 

EN0

Member
No problem. All LED's have internal resistance, and that is what this Forward voltage is about. It will say Fv of 2.2V IF 20mA. So you know that if you have 20mA you'll have a forward voltage of 2.2V. Again, this is the LED's internal resistance, and since you want the LED to get as bright as it possible can, you subtract that from the supply voltage. You can't have a supply that is equal to or lower than 2.2V, it has to be higher than that. So you simply subtract the forward voltage from your supply voltage and divide that into whatever current you have (our example: 20mA).

I'll show you how to calculate the resistor needed for this LED:

http://www.electro-tech-online.com/custompdfs/2009/07/XLBBA12W.pdf

Now, the first thing we need to do is go look at the Forward voltage on the table to the right of the first page. This LED is an UltraBright one so we'll usually have a higher value forward voltage. It says that the forward voltage is 3.2V, so if we have a voltage supply of 4.5V we'll have a 65Ω resistor (4.5V-3.2V = 1.3V/20mA = 65Ω). If we have a 9V supply, we'll have a 290Ω resistor (9-3.2 = 5.8/20mA = 290Ω). See my diagrams.
 

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audioguru

Well-Known Member
Most Helpful Member
All LED's have internal resistance, and that is what this Forward voltage is about.
No.
All LEDs are a diode that has a certain voltage depending on its colour.

It will say Fv of 2.2V IF 20mA. So you know that if you have 20mA you'll have a forward voltage of 2.2V.
No.
LEDs are not perfect so the voltage is a range of voltages. It might be 2.0V to 2.4V if most of them are typically 2.2V.

This LED is an UltraBright one so we'll usually have a higher value forward voltage.
No.
It is ultraBright because its lens focusses and concentrates the light into a very narrow beam. Its voltage is high because it is blue. A red ultra-Bright LED has a lower voltage of about 1.8V to 2.0V.

God this and god that??
Please leave religion at your church.
 
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EN0

Member
No.
All LEDs are a diode that has a certain voltage depending on its colour.


No.
LEDs are not perfect so the voltage is a range of voltages. It might be 2.0V to 2.4V if most of them are typically 2.2V.


No.
It is ultraBright because its lens focusses and concentrates the light into a very narrow beam. Its voltage is high because it is blue. A red ultra-Bright LED has a lower voltage of about 1.8V to 2.0V.


Please leave religion at your church.

Of course LED's have a varying degree of Forward voltage, I didn't say that all have 2.2V for forward voltage! Ultrabright LED's look like anyother LED, I dont see any reflector like on a flashlight or anything. As for the religion thing...I'm not sure where you got that quote...but I'll go ahead and take it off my signature. Hope your satisfied.
 

audioguru

Well-Known Member
Most Helpful Member
A cheap LED doesn't use a reflector to be bright because it does not shine all around like a light bulb. Instead it uses its plastic case as a lens to focus and concentrate its beam into a narrow angle.
 

AlainB

Member
Austin, If you really need to put something, "Good luck" is quite enough.

Alain
 
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EN0

Member
A cheap LED doesn't use a reflector to be bright because it does not shine all around like a light bulb. Instead it uses its plastic case as a lens to focus and concentrate its beam into a narrow angle.
Interesting, well those 5mm round LED's all look like the same to me. All the LED's I've seen have a focused intensity. I'll have to research that...;)
 

audioguru

Well-Known Member
Most Helpful Member
The viewing angle of cheap but bright Chinese LEDs is very narrow due to the focussing. The datasheet for the LED that you posted says that its total angle is only 16 degrees.

A half-decent LED has a viewing angle of 30 degrees or 40 degrees.

Shine the LED on the ground or on a wall to see the viewing angle.
 

EN0

Member
The viewing angle of cheap but bright Chinese LEDs is very narrow due to the focussing. The datasheet for the LED that you posted says that its total angle is only 16 degrees.

A half-decent LED has a viewing angle of 30 degrees or 40 degrees.

Shine the LED on the ground or on a wall to see the viewing angle.
Thanks Audioguru, I'll do that. You certainly have had more experience than me so I'll listen to your advice.

Thanks!
 

Mark68

New Member
God Bless and Good Luck
I would keep the God Bless right where it's at....just get rid of the Good luck part. It's an oxymoron statement. Luck is random chance, blessing is deliberate. Whatever you do...don't keep your religion in church, wear it like a garment everywhere you go.

The man with the experience is never at mercy to the one with the argument

Blessing in the Lord!
 

audioguru

Well-Known Member
Most Helpful Member
I would keep the God Bless right where it's at....just get rid of the Good luck part.
Please do the opposite.

Whatever you do...don't keep your religion in church, wear it like a garment everywhere you go.
But please don't preach here.
We talk about electronics here, not religion.
Go bless and pray somewhere else.
 

Mark68

New Member
I would keep the God Bless right where it's at....just get rid of the Good luck part.
But please don't preach here.
We talk about electronics here, not religion.
Go bless and pray somewhere else.
Saying God Bless is not preaching Audioguru....your being extremely picky. One might tell you to change your name....since a guru is infact a religious teacher..but then they would be just as non sensical.
 

audioguru

Well-Known Member
Most Helpful Member
Most normal people don't go around blessing other people.

If for some reason you want to pray all the time then go ahead and do so. But please don't be obvious.

My name and my avatar were given to me.
I am not Indian and I don't quack.
I also do not pray all the time like some people do.
 

Mark68

New Member
Audio I have nothing personal against you bro.......and it's nothing personal, but come on let's be real. The guy was not praying or preaching or soliciting anything. It was a salutaion, nothing more nothing less. If God bless bothers you that much, you got deeper issues to deal with as far as I am concerned. People should have a right to express their signature anyway they choose, that's why it's called 'signature'. Obviously hatred, racism, etc... cannot be tolerated, but God Bless? Come on chill
 

3v0

Coop Build Coordinator
Forum Supporter
In keeping with the global nature of this forum a more appropriate phrase would be.

If you choose to believe in god(s), goddess(es), or lady luck; may they/he/she/it bless you.

I rather like it. The phase even covers atheists and agnostics.

3v0 ;)
 

audioguru

Well-Known Member
Most Helpful Member
Let's keep religion out of the forums.
What about the weirdo's who worship the devil??
 
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