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making a small ciurcuit with 20 led´s

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theelectronicsfan

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ok my problem is : im making a small ciurcuit with 20 led´s powerd by 12v with a 560 ohms resistor calculated with a led calc and the resisor is getting really damn hot (if i lick my finger and touch it i hear a fsss sound) what am i doing wrong?
look at cuircuit diagram exactly how i connected the res and led´s
 

Help me wat am i doing wrong?????????

+ and katot of leds mustnt add each other. Why did you so that?

change - with +
 

Help me wat am i doing wrong?????????

change - with +
 

Help me wat am i doing wrong?????????

oh btw i dont know how to draw leds th correct way i draw them wrong right?
 

Help me wat am i doing wrong?????????

46_1258818944.png


it must be ....
 

Help me wat am i doing wrong?????????

i know i just draw it wrong:)
 

Help me wat am i doing wrong?????????

then, I= 12/560 =~0,02 Amper except leds resist. İf there are no short circuit , 560 ohm resist must not hot...
 

Help me wat am i doing wrong?????????

Did you calculate the power, dissipated of your resistor?
(It should use a resistor at least 0.25W: P=(12/560)*(12-1.8)~220mW)
 

Help me wat am i doing wrong?????????

You have all the LEDs in parallel. That is wrong unless you matched their voltages. The one with the lowest voltage will hog most of the current and quickly burn out. Then the next one will burn out then the next and the next.

If the LEDs are 2V red ones then you can connect 5 LEDs in series then use a resistor in series to limit the current. That makes one string. Then make as many strings as you want.

If the LEDs are 3.5V white or blue ones then connect 3 in series and in series with a current-limiting resistor to make one string.
 
its red green and yellow 2v ones (2.2v exactly)

Added after 3 minutes:

oh check this link
**broken link removed**
its the type of cuircuit board i use
 

hi

u can use that connection for led here current for each led abt 0.018a per led
with vf 2volt for led all res 1/4 watt
 

but is it possible to connect ressistors in a row?
like the first restistor changes the volt from 12 to 7
and the seccond from 7to5 and like that?
 

nashwan said:
You can use that connection for led here current for each led about 0.018a per led
with vf 2volt for led all res 1/4 watt
Click to expand...
You are wasting half of the supply voltage heating the resistors.
You are using too many resistors.
If you use 5 LEDs in series then each resistor is 2V/18mA= 111 ohms. Use 110 ohms, 120 ohms or 100 ohms.
 

theelectronicsfan said:
but is it possible to connect ressistors in a row?
Click to expand...
The LEDs are not "in a row". They are in series and their voltages add.
This makes one string.

My LED Christmas tree lights have thirty 2V LEDs in series (120V mains).
I don't see a current-limiting resistor and there must be a little diode somewhere.
 

like can they take fire??

Added after 2 minutes:

not led "in a row" i said resistors:D
 

theelectronicsfan said:
but is there any danger with hot resistors?
Click to expand...
Use arithmatic:
2V squared/100 ohms= 0.04W. A 1/4W resistor will not get warm.
If the 100 ohm resistor is connected directly across a 12V power supply then it will dissipate 1.44W and a little 1/4W resistor will smoke and burn.
 

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