HyundaiKitCoupe

Lighting up my F2 Gauges. Took the cluster all apart. We've got:

-21 5mm 5500mcd 12V Blue LED's.
-11 3mm 4500mcd 12V Red LED's.
-5 ft 22 gauge wire.

Are those good to go behind the plastic?

Also Resistors. 470ohm for the Blue ones? And what resistors to use for the red ones?

Thanks guys for the help, I hope we got this right. Don't want to blow sh*t up.

DTN

The important values that you need to post in order to figure out what resistance values are required is the Foreward Bias (FV) and the Foreward Current in miliamps mA (sometimes called fC, FI, Iv).

The way you can determine the correct resistance value is to subtract max battery charging voltage (14.6 rounded to 15V) from the combined total foreward bias of a LED (usually blue is 3.2-3.6) so 15-3.2V = 11.8V needs to be dropped across the resistor.

Now typically a LED runs on 20mA or .020A of current, so we'll calculate using ohm's law of E=IR, or in this case V/I=R

11.8V / .020A = 590 ohms

for 2 blue LEDs, 430 ohms, for 3 blue LEDs, 280 ohms

You need to post the FV and mA values for each type of LED.

HyundaiKitCoupe

holy crap dtn you know a lot off the top of your head. you and t01 are always here to help me out. 14.6V's is what the battery voltage of our cars runs at so that's where you got that from?

here are the given:
blue leds

red leds

i want to wire one resistor per led, so the more led's the smaller ohm per resistor?

DTN

you posted both red LEDs.

HyundaiKitCoupe

shennanegans.
pat.gif
Blue LEDs

DTN

620 ohm 1/4W resistor minimum for 1 red LED or you will burn it out prematurely. This type of LED will run .24W. Wattage goes down with the more LEDs you put on a resistor.

to calculate for red LEDs
(14.6V-(2.2 times the number of LEDs on the resistor))/.02 = resistor values











For the blue LEDs, you'll need at least a 555ohm 1/4W resistor. This LED/resistor is .222 watts.

(14.6-(3.5xnumber of LEDs in series))/.02 = resistor value

radu_rd2

Make sure you really test if you like the color first. I bought some blue leds from ebay (topbright88), and I love their color. I also bought some blue led bulbs from superbrightleds, and I hate the color, it's more towards light blue/cyan. The ebay led specs showed dominant wavelength of 465 Typical, 475 Max; the superbright specs showed dominant wavelength of 470. I thought they would be the same color, but I guess one of the specs was wrong (or 5nm makes such a big difference?). I just looked it up and it seems pure blue is somewhere closer to 450.. anyway, just test them first smile.gif

DTN

Don't trust the ratings on ebay... I've bought alot of blue LEDs some were blue, some were almost purple, some were kind of green.... I tend to like the green kind best because they seem to be able to hold up to more. My only advice is to buy more then you need, label them "for use in my tiburon" then put them away in a drawer in case one or two go out. Then you don't have to buy more and guess the color.

HyundaiKitCoupe

adam, thanks so much for the diagram. my good friend from poland is helping me do this, tested your figure over and over on paper and said it's correct. fing02.gif he's studying engineering.

so we've plugged in the numbers and they work out to 555ohm for the 21 blue and 625ohm's for the 11 red. one resistor per LED and into a the 12v bulb socket. he said the resistors will release more heat but at least the LED's won't burn. excellent work!

does this sound right? and where can we buy resistors anywhere near our ohm ratings? radioshack? because surely they don't have any exact ohm rated ones.

i didn't know LED's were so complicated. i don't trust the ones from Hong Kong hehehe. the color looks good, it will have to depend on the resistors from now on.

radu_rd2

A nice site with electronic stuff is www.partsexpress.com You can find all sorts of resistors there. I just checked and they have 1/2Watt 560 and 620 resistors, for 50 cents a 10 pack. Although they don't really say the size of the resistor, I hope they're not too big (not the resistance, the actual size)