how to convert 12V to 3V for LED light in car !

[limandy]

All Sifu,

Can teach me how to do.

 

[kruger]

All Sifu,

Can teach me how to do.

i tought this topic has already been discussed. try search it lar... :) btw if you put 1k resistor is enough already at your led...

 

[khguan]

yep.. just use a 1K resistor.. kau tim...

 

[sam1741]

ya... use 1k
very cheap also
few cent only... :D

 

[kage2099]

guys... the 1K Ohm resistor got many many different watts... got 1/2W, 1W...........etc... last time i wana put LED on my VS i ask the electronic shop for 1K resistor and they asked me wat watt u wan... i duno wat to answer...

so... sifoo sifoo sekalian... which watt is ideal to be used lehh??

 

[khguan]

for LED... 1/4W is more than enough..

 

[jswong]

Wa lau eh! Put 1k resistor is good enough? Hmmm.. so that means the resistor will soak up all the rest of the voltage? (3 volts for LED, 9 volts for resistor).

I think we can also make a 5-volt regulator using a single 7805 IC.. safer that way. Besides, direct 12 volt in car wiring can run high currents also.

 

[jaywat]

like that not really cost effective...some more add up complexity...being using 1k resister on my LED in VS so long already ...now still as bright as ever.

 

[khguan]

jswong,
no prob lar dude... dun worry... LED taking very little current onli.. therefore the current that pass tru de resistor also very little.... go n learn more about basic electronics then u know y...

 

[sam1741]

if u wan regulator...
got one for 3.3v also..
but forgot what code...
something like 7829 or something

 

[lcchong]

jswong,
no prob lar dude... dun worry... LED taking very little current onli.. therefore the current that pass tru de resistor also very little.... go n learn more about basic electronics then u know y...

the resistor will heat up or not?

 

[sam1741]

wow... such an old thread
anyway, since that time (4 years ago) until now
there is a better solution

using LM317 regulator
(the sample circuit is inside the data sheet)

u can limit the current for the LED (normal one, 20mA is more than enough, i have high power LED running at 300mA which is very hungry beast)
or , can limit the voltage (e.g. 3v for normal LED)

and best thing about LM317 is u just set the limit
no matter the input voltage goes until how much (but there is a limit, i think 37volt)
the limit u set will be the same

 

[lcchong]

instead of the LM317, can we connect 4 pcs of LED (3v) in series?

----(+)LED(-)--(+)LED(-)--(+)LED(-)--(+)LED(-)---(+)LED(-)----

then can directly connect to car (+) power????

Bump: find the suitable resistor for your LED...........

using this online calculator.....!

http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

http://www.theledlight.com/ledcircuits.html

Bump: find the suitable resistor for your LED...........

using this online calculator.....!

http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

http://www.theledlight.com/ledcircuits.html

 

[khguan]

if 1 LED kaput.. then all wont light up...

 

[lcchong]

aiya.........

 

[cybtech]

1k for each LED oklo.... y so ma fan...?
+12V batt ----|>|----[1K]---- GND
if wan more LED just connect parallel from + and also to the GND (-); --|>|-- (LED)
*----|>|----[1K]----*
|----|>|----[1K]----|
|----|>|----[1K]----|
+12V
this one in form 2 Kemahiran Hidup got ma, go dig-up and study back...

 

[lcchong]

if 1 LED kaput.. then all wont light up...

bro, i read that resistor will heat up laa..... will melt the plastic arr?

Bump:

if 1 LED kaput.. then all wont light up...

bro, i read that resistor will heat up laa..... will melt the plastic arr?

 

[khguan]

if u use LED no prob la....

if u worry use a higher wattage resistor.

 

[lcchong]

if u use LED no prob la....

if u worry use a higher wattage resistor.

already install HU Compartment with 4 blue LED......

sifu ar.... hav some problem laa.... i got 1 xtra screw....

another 2 screw already back to their original place....

forgotten the location for the last screw......


btw, i broken 1 of the panel clips......

 

[donCityZ]

guys guys guys...

dont make simple thing become difficult.

use 1K resistor is OK edi. u must consider when engine running, so that is 14V.
LED always arnd 3V, so remaining 11V will be across resistor. for current, since 1k
resistor, i=v/r=11/1000=11mA. since it is connected in series, current thru resistor=current thru led. normal 3V led will have rating of 25mA~30mA max current. so u are safe. for resistor power, similarly, use ohm law, p=vi=11x0.011=0.12W. so use 0.25W is safe (0.25W=1/4W).

use regulator also can. but, u need to consider heat dissipation. coz regulator uses more energy than just to supply current, it also uses energy to maintain that voltage. so, it will be bulky AND unnecessary.

my 1 sen nia.. hope clear about LED cct in car.
but do remember though, pls use 1 resistor for each LED.. i can explain y.. but lazy.. juz trust me can ar?