REVscene - Vancouver Automotive Forum

illicitstylz · 06-25-2009, 01:39 AM

Powersource: cigarette lighter (12v)

Add-ons: 2x DC 12v Applications

Basically I'll be hooking up 4 LED's (2 LED's per application).
Would it be too much to handle if i use both applications through that one power source?

slammer111 · 06-25-2009, 01:44 AM

No problem. LEDs draw MILLIAMPS. You can probably run 100 strings without a single hitch.

1) Make sure you have a resistor in line with each string of LEDs. So you'll need 2.
2) Make sure the LEDs in question can handle 6VDC. I thought most handed 3-4V, so doublecheck.

illicitstylz · 06-25-2009, 02:03 AM

I'll have to double check the packaging to see what the specific numbers are, i don't recall seeing 6vdc etc though.

where do i buy resistors? I honestly have no clue to what they even look like lol

edit: these are the two items i plan on wiring up

http://www.dealextreme.com/details.dx/sku.16975

http://www.dealextreme.com/details.dx/sku.5164

slammer111 · 06-25-2009, 02:07 AM

Resistors can be picked up at The Source. Just get like 100 for $8, a wide assortment. Then learn how to read resistor codes, and use a LED calculator to figure out which resistor to slap on each string.

I got 6VDC because if you are putting 2 in line, 12VDC / 2 = 6VDC. I'd say you're probably better off using 3-4 LEDs per string (which makes it 3-4VDC), though it does depend on the specific LED model you're using. Generally they take 3-4VDC though that's a generic statement.

http://en.wikipedia.org/wiki/Resistor

JdmProbe · 06-25-2009, 03:31 AM

Hey, do not add any resistors!
They are already in the internal circuitry of the products you want to install.

goo3 · 06-25-2009, 03:31 AM

wouldn't you want to run those 2 in parallel? I've never touched those leds before so i don't know what's typical. It looks like they're both designed for the 12V out.

I guess you'll be splicing the cigarette adapters then?

Great68 · 06-25-2009, 06:52 AM

For an LED, it is more important to look at maximum current rating than voltage rating.

The more current you pass through it, the brighter it will be. How bright you want it to be, and the current rating of the LED are what dictate what resistor you need to choose.

If you are putting LED's in series you need to add the forward bias voltages of the LEDs to figure out your voltage drop across the LED's.

Soundy · 06-25-2009, 07:43 AM

Quote:

Originally Posted by Great68

For an LED, it is more important to look at maximum current rating than voltage rating.

The more current you pass through it, the brighter it will be. How bright you want it to be, and the current rating of the LED are what dictate what resistor you need to choose.

If you are putting LED's in series you need to add the forward bias voltages of the LEDs to figure out your voltage drop across the LED's.

Wow, finally, someone with a clue.

LEDs don't have "voltage ratings" per se. Their forward voltage drop will always be the same - usually about 1.7V, more than that for some types. The only time this comes into play is if you want to figure out how many you can hook in series... and to a small degree, what value limiting resistor to use.

If an LED drops (for the sake of calculation) 2V, you can put *up to* three of them in series with a 6V supply... *up to* six on a 12V supply... and so on. You still have to limit the current.

Some really great, useful stuff on all this here: http://www.kpsec.freeuk.com/components/led.htm

All that aside... those units the OP is looking at will already have all that compensated for; you just supply 12VDC to the unit. And no, there should be NO problem running multiple units in parallel off the cigarette lighter.

Just make sure you don't have the running (at least not in a visible position) while you're on the roads - the cops will be all over you for illegal lighting.

trip · 06-25-2009, 11:49 AM

run them in parallel because if they are in series .. if one goes out so does the other

illicitstylz · 06-25-2009, 12:52 PM

Wow, thanks for all the great information guys.

Last question would be how do I run them in parallel compared to in series?

If i take all the positives and attach them to positive, and all negatives to the ground, that would be in.. series?

Selanne_200 · 06-25-2009, 01:04 PM

That would be parallel. Runnin them in series would be something like

(+)(-)(+)(-)(+)(-)

Soundy · 06-25-2009, 01:13 PM

Parallel vs. series only applies if you're wiring up bare LEDs. These lighting units you're getting are designed and built to simply be fed 12V, no extra components needed. Parallel is the ONLY way to wire them. They won't operate if you wire them in series.

And yes, you'll wire them all with their positives to power and negatives to ground... that's parallel.