Electrics Connecting LEDs directly to battery? - Civinfo
 
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post #1 of 18 (permalink) Old 23rd April 2011, 11:55 Thread Starter
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Connecting LEDs directly to battery?

I want to do something to my car which involves LEDs and I dont want to run the cable through the gromment at the back of the engine bay as its a pain in the arse to do.

Can I connect directly to the pos on the battery or will I need something inbetween the battery and LED because of the amps? Not sure if the ampage will blow the LEDs.
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post #2 of 18 (permalink) Old 23rd April 2011, 17:22
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Items will draw the current required depending on their resistance.
Its the voltage you need to worry about.... it will draw the specified current from the battery @ the specified voltage

Unfortunately, the battery is shared with lots of other circuits that can affect the current/ voltage going through the LEDs.
Resistance in parallel an stuff.
So you need an inline fuse at the very least....possibly a diode to force one way only.
You can always check the the current going though one of the fuses in the fuse box...find one with plenty ampage spare.. maybe interior lights... and run a cable form there
Dont use a feed from something mission critical.... wouldnt want to short anything important while you are tinkering around.




Last edited by Relic; 23rd April 2011 at 17:25.
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post #3 of 18 (permalink) Old 23rd April 2011, 18:44
 
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As far as I know LEDs operate at 5V not at 12V.
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post #4 of 18 (permalink) Old 23rd April 2011, 19:12
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post #5 of 18 (permalink) Old 23rd April 2011, 19:13
 
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Without a serial resistor you must not connect a single LED directly to a battery!

Actually, a LED consumes 10-20mA (sometimes more, but usually less then 1A), so it can behave as a fuse, when it is overloaded accidentally...

When a LED is used normally, it has 1,5-3V between its connectors (depends on type, brightness, etc...), so you should apply an appropriate resistor to decrease 12V of battery. (E.g.: 1kOhm)
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post #6 of 18 (permalink) Old 23rd April 2011, 20:00
 
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Thatīs right!
The existence of a series resistor is absolutely vital for a LED.
Itīs required for each branch containing one or more LEDīs connected together serially.

Maybe, these following words are of any use, too.

If you buy LEDīs, ask the dealer about their voltage and current (or see the according data sheet), because thatīs what you need to calculate the resistor.

This resistor is calculated like this:

1.)
Voltage of resistor = 12V - Usum

...whereas "Usum" is the summary of voltage of LEDīs, if connected together serially. (Btw., if thereīs another voltage in a branch, you will have to replace the 12V by the total voltage of that branch)
Letīs call this voltage of the resistor "Ures".


2.)
Total current = same than a single LED needs, if connected serially.
Letīs call this "Itot"

3.)
Now, the value of the resistor "R" in Ohm is...
R = Ures / Itot

If thereīs no such a resistor available, just take the next one above the calculated value.
A 1/4 Watt type should do, usually.

Donīt forget to add a switch to whatever you want to build.
Your battery will be very grateful to you.

Last edited by Centauri39; 23rd April 2011 at 20:05.
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post #7 of 18 (permalink) Old 24th April 2011, 11:50 Thread Starter
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Thanks guys =)

I think I'll have more piece of mind doing it right if I just use the gromment and connect to the wires to the already connected footwell lights

For those interrested I'm adding a few LEDs to the front bumper. Pics will follow once i'm done
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post #8 of 18 (permalink) Old 24th April 2011, 12:17
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post #9 of 18 (permalink) Old 24th April 2011, 12:39
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post #10 of 18 (permalink) Old 24th April 2011, 12:59 Thread Starter
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Thanks relic... now I gotta do it in the next few days seeing as you are waiting results -.-

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post #11 of 18 (permalink) Old 25th April 2011, 05:25
 
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Quote:
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Thanks guys =)

I think I'll have more piece of mind doing it right if I just use the gromment and connect to the wires to the already connected footwell lights

For those interrested I'm adding a few LEDs to the front bumper. Pics will follow once i'm done
Sounds like sort of "Knightrider 2011"...
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post #12 of 18 (permalink) Old 25th April 2011, 08:35
 
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The leds your looking at are marked up at 12 volt so they Will be fine to conect to the battery as they have been designed ro run that voltage. I have an led strip behind the front bumper to give a subtle glow and i wired that difect to the sidelight.

Sent from my GT-I9000 using Tapatalk
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post #13 of 18 (permalink) Old 25th April 2011, 10:13
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Quote:
Originally Posted by Nick F View Post
The leds your looking at are marked up at 12 volt so they Will be fine to conect to the battery as they have been designed ro run that voltage. I have an led strip behind the front bumper to give a subtle glow and i wired that difect to the sidelight.

Sent from my GT-I9000 using Tapatalk
Any pics
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post #14 of 18 (permalink) Old 26th April 2011, 15:01
 
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Any pics
The pics make it look brighter than it actually is. All i used was a 60 cm strip off ebay for a couple of quid. and cable tied it to the top of the grille
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post #15 of 18 (permalink) Old 26th April 2011, 16:14
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You will need to install a fuse in the wiring for the LEDs otherwise if you have a fault and its connected directly to the battery the wire will melt and could cause a fire, a small 7.5a or 10a fuse will be a little big for the LEDs but will work fine and give the required protection needed. Now if you wire the LEDs to the side lights no fuse will be required as this is will be protected by the sidelight circuit fuse.
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post #16 of 18 (permalink) Old 27th April 2011, 12:25 Thread Starter
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Quote:
Originally Posted by RickHondaR View Post
You will need to install a fuse in the wiring for the LEDs otherwise if you have a fault and its connected directly to the battery the wire will melt and could cause a fire, a small 7.5a or 10a fuse will be a little big for the LEDs but will work fine and give the required protection needed. Now if you wire the LEDs to the side lights no fuse will be required as this is will be protected by the sidelight circuit fuse.
Thanks Rick.

Will still wire the lights into the car as I need a switch. Cant have them running all the time :/
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post #17 of 18 (permalink) Old 27th April 2011, 15:01
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Quote:
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Thanks Rick.

Will still wire the lights into the car as I need a switch. Cant have them running all the time :/

why not just wire them from the permanent supply or ignition supply on the cd player, this way it is fused and you just run the wire through a switch and to your lights and dont have to run a wire from the battery to the switch.
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post #18 of 18 (permalink) Old 28th April 2011, 11:53 Thread Starter
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Quote:
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why not just wire them from the permanent supply or ignition supply on the cd player, this way it is fused and you just run the wire through a switch and to your lights and dont have to run a wire from the battery to the switch.
I may just run them from the very front 12v socket. That way I can locate a switch around the center console somewhere. Gonna go out soon to grap all the goodies I need and then start wiring it all up. Doubt i'll get it done today as I need a drill something I use to have until my dad nicked it -.-

Will post pictures while I go along but will make a new thread for it.
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