making a small ciurcuit with 20 led´s

[theelectronicsfan]

sorry i dont get it
do u mean i should change the 560Ohm res
to a 1/4w res?

Added after 5 minutes:

but another BIG prob is that i allready soldered the led´s

 

[Audioguru]

560 ohms is the value of a resistor.
1/4W is how much power the resistor can survive.

The resistor value is calculated for the amount of current you want.
The resistor power rating is calculated so it doesn't get too hot and so that it isn't too big.

Your 560 ohm resistor is good for limiting the current in one 2V LED to 17.7mA. The resistor will dissipate 0.179W when the supply is 12V. A 1/4W resistor will be pretty warm but not too hot.

Your problems are that you connected the LEDs wrong and used the wrong value resistor. All the LEDs will be dim and will have different brightnesses. But the current is so low that an LED will not burn out.

 

[theelectronicsfan]

any idea what i can change resistor to?
this is what the calc says



Added after 33 seconds:

oh btw i gonna eat soon brb

 

[Audioguru]

The calculator is WRONG. You should NEVER connect LEDs in parallel.

The circuit is stupid because it wastes such a high amount of power by heating the huge resistor.

Red LEDs are probably 1.8V to 2.0V. Their max voltage might be 2.2V.
Their max allowed current is probably 30mA and they usually operate and are spec'd at 20mA.

 

[theelectronicsfan]

but it works fine can i useit anyway the resistor getting hot?

Added after 1 hours 2 minutes:

can i still use it? or is it dangerous that the resistor getting hot?ΛΛ

 

[Audioguru]

Do you have all 20 LEDs in parallel?
Do you have a 560 ohm or an 18 ohm resistor?
What is the rower rating of your resistor?
Do you have a 12V supply?

 

[dmk]

Just use 0.25W resistor of 560 Ohms, or connect two of 0.125W, 270 Ohms in series.

 

[theelectronicsfan]

Do you have all 20 LEDs in parallel?-Yes
Do you have a 560 ohm or an 18 ohm resistor?-560Ω
What is the power rating of your resistor?-Idk
Do you have a 12V supply?-Yes

Added after 1 minutes:

ok gonna try to find 0.125W, 270 Ohms resistors on monday

Added after 2 hours 10 minutes:

how do i know what wattage rating my res is?

 

[hameeds01]

hey y u r connecting all of them in parallel ??
whatz the specification of the LED that u r using??
V? I?

 

[theelectronicsfan]

specification?
and yea im connecting all of them in parallel

Added after 3 minutes:

v? i?

Added after 21 minutes:

oh specs is 2.2v
30 mA

Added after 36 seconds:

sorry i mean 20 mA

 

[Audioguru]

With a 560 ohm resistor feeding 2.2V LEDs from a 12V supply, the current in the resistor (and the total current in the LEDs) is (12V - 2.2V)/560= 17.5mA. Since you have 20 LEDs in parallel then each one has a current of only 17.5mA/20= 0.875mA and they will be very dim.

The 560 ohm resistor dissipates (12V - 2.2V) x 17.5mA= 0.172W so a 1/4W resistor will be very warm.

The physical size of a resistor determines its power rating. At its power rating a resistor is hot enough to melt plastic or burn you.

 

[theelectronicsfan]

oh shit do you know if 27Ω would be good?

 

[hameeds01]

use R = 25Ω , >5W

 

[theelectronicsfan]

Yea the calculator told me to use a 24.5Ωresistor
and the closest one was 27Ω

sorr about the quality (had to save it i a GIF )

 

[hameeds01]

p = (12 - 2)² / 25 = 4w
use a resistance greater than 5w

 

[Audioguru]

LEDs have a range of voltages. Your "2.2V" ones might be 2.0V or might be 2.4V.

The 2.0V ones will be very bright and might burn out and the 2.4V ones will be dim or will not light.
That is the problem with connecting LEDs in parallel.

 

[hameeds01]

The 2.0V ones will be very bright and might burn out and the 2.4V ones will be dim or will not light.
That is the problem with connecting LEDs in parallel.

i don't know y "theelectronicsfan" is willing to connect them in parallel

 

[theelectronicsfan]

The 2.0V ones will be very bright and might burn out and the 2.4V ones will be dim or will not light.
That is the problem with connecting LEDs in parallel.

i don't know y "theelectronicsfan" is willing to connect them in parallel

i conncted them in parallel allready

 

[Audioguru]

Try your 20 paralleled LEDs with a 560 ohm resistor and a 12V power supply. Look at the LEDs in a dark room because they will be dim. If they have different brightnesses then the brightest ones might burn out if you use 27 ohms.

 

[theelectronicsfan]

Yea they got different brightnesses
as you can see on the drawing i make they should make a big E and a B (the B is the brightest)
the leds is bought in different stores
so i should "swap" the leds making the B ??
so all of them are the same type?
and i will be able to use a 27 ohm resistor?right?