kosienutter

hi guys. i fitted a secs monitor a few weeks ago and as you know you get a green led to put somewhere in your dash.

now i put a 8mm led just above my boost gauge as you can see in one of the pics in my photo album on here.

i ran it in-line/paralell with the secs one. it worked a few times then blew. i was told it could be that the secs monitor led has a resistor in it, which i think it does, but i dont want to pull of the insulation on it to find out and possibly break that one too.

anyway i was also told that the led is 5 volts and it needs a resistor to run with 12 volts, but which one.

they have colour codes don't they?.

does anyone know which one i should buy so i can solder in on.

cheeRS

ram

iTrader: (4)

id too like to know this. i bought a pack of various resistors for a 6v intake temps gauge im wiring up to a 12v supply but at the mo ive only got it working using 4 different resistors at the same time lol, knowing what the right colour code for one would be nice!

tabetha

R = (Vs - Vf)/if is the formula to use!!
In english this is, V is voltage supply(use 13.5 volt) Vf is the forward voltage drop across the LED, If is the forward current through the led.
You should get this info with the led when you buy them.
EG,
LED if = 20mA and Vf = 2.5V,
To operate from a 12V DC supply R =(12-2.5) /0.02= 475ohm anywhere within 10% resistor value will be fine, so that is 12-2.5 = 9.5/0.02(of an amp) 475 ohm.
In short unless you know the forward voltage drop and forward current you cannot work it out only guess, but most led around 20-60ma, if you err on the side of caution it will still work, just not as brightly.
It looks a lot harder than it is, I would suggest Maplin or similar for led's to ensure you get this data, I use this all the time for overpowering and sinking CREE led's(bright white ones for torches).
tabetha

kosienutter

i got it from maplin and the staff there didnt have a clue what resistor i needed.

so i guess from my v low electrical resistor knowledge that any resistor will do the job?

pa_sjo

Do you know the maplin part number? The Vf and If values are in the catalogue.

kosienutter

i think a value thing is in the catalogue but i could not understand itr at the time. with the info here now i might try tomorrow

tabetha

As said quite easy, some maplin staff are better than others!!
If still stuck just give me page number and item number and I'll pm you the values, or post them on here.
On DC circuits you can get away with a bit more intolerance than AC so that helps, but most led are quite okay with a little overdrive, apart from Gallium Arsenide ones, plus a few exotic ones the forces use.
tabetha

kosienutter

ok will try and get them tomorrow. agree with you there though forces stuff is cack lol

tabetha

The forces(certain ones) are using a LED that is 1 million lumen, or around 500 times brighter than a car headlight, from a little 7mm chip!!
They are used as a disabling manner to cause 10 minute total blindness with no after effects.
tabetha

kosienutter

shit, cool as fook then!! might try and get one from stores lol.