Balling
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Registered: 7th Apr 04
Location: Denmark
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Usually when you fit an LED in a car, you fit a resistor as well.
Say I want to fit quite a lot of LED's to one place, how would I go about it?
Do I connect them in serial or parallel? Do each LED need it's own resistor?
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Steve
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Registered: 30th Mar 02
Location: Worcestershire Drives: Defender
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no expert but id say in parallel each with a resistor
[Edited on 26-09-2012 by Steve]
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Dom
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Registered: 13th Sep 03
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If you do it in parallel then you'll need a resistor per LED, otherwise in series you just have one (can be a number in series to get the required resistance). Either way, make sure the resistor used is sufficient for the current limiting.
There are a handful of calculators out there if you do a search for 'Resistor Current Limiting'.
Edit - Leg work done http://ledcalc.com/; work off the maximum of the source voltage.
[Edited on 26-09-2012 by Dom]
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Balling
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Registered: 7th Apr 04
Location: Denmark
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Yeah... Dom, I don't understand any of that... 
I'd prefer to just solder them in series or perhaps a few series of 3 or 4, but I only have one type of resistor and don't fancy to order more shit...
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Dom
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Registered: 13th Sep 03
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Have you got the specs on the LEDs or know where you ordered them from?
Once you know the specs then using the calculator is a piece of piss, especially with the linked one which will also parallel the circuit when the combined diode/LED voltage is greater than the supply voltage.
However for a 'plain' LED work on the basis of 13-14V supply voltage (typical car iirc), 2.5V forward voltage, 30mA forward current; which will give you 390Ohm (use a .5/1W) per LED.
*note, i'm working off rusty school electronics so some of this could be wrong 
Edit - Another calculator for single LEDs http://led.linear1.org/1led.wiz
[Edited on 26-09-2012 by Dom]
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Ian
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Registered: 28th Aug 99
Location: Liverpool
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quote:
Originally posted by Dom
If you do it in parallel then you'll need a resistor per LED
Not necessarily - you could wire the LEDs in parallel then have a resistor to that.
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Balling
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Registered: 7th Apr 04
Location: Denmark
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I have no clue about the spec on the LEDs. I'm not even sure where I have them from, I've had them forever.
Probably some Hong Kong lot job bought on eBay...
Isn't there some way of determining this from the coloured lines on the resistors? 
Think I'll just do parallel to be sure.
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Dom
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Registered: 13th Sep 03
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quote:
Originally posted by Balling
Isn't there some way of determining this from the coloured lines on the resistors?
That'll be the resistance of the resistor (look up a resistor colour chart) 
Grab 3 or 4 AA batteries (4.5-6V), wire them up in series along with the resistor and LED and if it goes pop (usually it'll blow the top off the LED) then you're going to need a higher resistance resistor
Do you know what colour the LEDs are?
Ian - Wouldn't that essentially be the same as wiring the LEDs in series? You still be having the same 'load' either way.
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ed
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Registered: 10th Sep 03
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As Dom says, calculate the resistance you need. LEDs need voltage and not current, the have no resistance hence the need for a resistor. The you'll see a voltage drop as the electricity passes through the LED. With my clocks I calculated that I could run two LEDs with a 330ohm resistor or three LEDs with a 150ohm (off the top of my head) at 12v. Here's how the backlights looked - think you can see the LEDs and resistors OK:
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Balling
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Registered: 7th Apr 04
Location: Denmark
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I did them in parallel with a resistor each, it worked alright, though looked a bit messy.
Thanks for the help guys!
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