6 replies to this topic

[mighty mini jack]

Right then....

Ive got a few questions and need some advise...

We're going to make a few L.E.D lights inc plastic casings and such for rc mini shell (tamiya, mardave)

Weve got the casings all sorted its just the leds to deal with now, i havent got a tamiya mini ATM and wont for a while, im going to put white leds in the plastic casing and somehow sort it so it can be wired to the car with an in-line slide switch, will i need to put anything else inline like a transistor or something?

[mighty mini jack]

Bump

[alexcrosse]

resistor

[mighty mini jack]

resistor

what type? honesly i know nothing about it really just know the basics

[MiNi FiZ]

Find out what voltage is coming off the source,

e.g 12v, if you've got a 12 volt source, the easiest way is to find an LED that can do 12V then just wire them straight into the + feed.


HOWEVER

say for instance you went for this LED

http://www.maplin.co...p;doy=11m6#spec

which has a Max. voltage of 5v you will need to put a resistor in series with the LED to lower the current going through so it doesn't pop.

to work out what resistor value you need to

( 12 - 5 ) / 0.03

the 12v Source, the Led Voltage and the LED forward current.

this then gives

233.33 ohms, now just find the next closest resistor value, 230 ohms or 250 ohms? i dunno, but you get the idea, if you go for a higher value resistor, the only thing that will happen is the LED wont be as bright as it normally would be.

hope this helps dude!

also, when you come to wire it in the longer leg on the LED is the + wire the Resistor to longer leg, then the other side of your resistor to the source, the shorter leg which is the - just goes directly onto your ground

Edited by MiNi FiZ, 11 June 2008 - 10:50 PM.

[Jupitus]

Actually, the LED in the link has a reverse voltage of 5V... further down the page is the forward voltage which is 3.2-3.6 V.

The rest of Mini Fiz's stuff is right, so the calculation is:

(source voltage - forwardvoltage)/current rating of LED

so (12V-3.5V)/.03 (That LED is rated at 30milliamps)

Gives about 280 ohms resistor required. The LED lifspan is seriously reduced without the resistor - in the case of one during my recent tests it shortened to about .25 seconds

If you plan to do several in series then you need to add up the total voltage drop, so using the ones in the link for example:

(12-(3x3.5))/0.03 = 50 ohms or so

[joe_m]

bumpety bump !

we'll hav it sorted mate,
came home for dinner
the casts are ace
put some grovess in
il try n take some piccs when i get back !
gota go or il b late !

cya dude !