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12v 3w led project Answered

I am trying to build a "knight rider" light for my car using 3w led's.
I know enough that I want 2 per section (8 sections total) and to wire the led's in series.
They will be mounted to an aluminum bar, so I might not need heatsinks.
They will be controlled by a "chaser light" sequential controller.
The specs are:
yellow 3w led
forward voltage:  2.9v - 3.3v
forward current: 750 mA
I have researched and found led drivers but they are a bit more expensive than I would like to pay, since I would need
8 of them.
Can anyone help me with what I need for this to work on my 12v dc automobile?
Do I need transistors, diodes?
What resistors do I need (value, wattage, etc)?
I need major help from the electronics gurus.

How do I do this???
I posted this in the workshop section mistakenly yesterday.

6 Replies

user
gizmo13 (author)2013-04-16

Thanks. Just waiting for parts to arrive to test it.

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user
gizmo13 (author)gizmo132013-04-26

So do I NOT need a led driver????
I can just hook up these 2, 3w led's in series with the two 3.3, 3w
resistors with the controller with no problems????

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user
gizmo13 (author)2013-04-15

Here is a link to the schematic and what it says about hooking up
high powered led's.
It looks like it is already set up to accept them but you can tell me
better as I know very little about this stuff. I can read a schematic
and assemble kits but not design and/or alter them.

Link:
http://picprojects.org.uk/projects/480/pro483/483ledcon.jpg

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jduffy54 (author)gizmo132013-04-15

Yes, that will work just fine. In fact, you could probably run up to 9 LEDs per channel.

So yes, the resistors I pointed out will work with two LEDs arranged in series on each output. Also, as current is pretty low, you can attach the + directly to the v+ on the terminal, and do NOT need to go the the voltage directly on the PSU.

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user
jduffy54 (author)2013-04-14

The first thing is, can the "chaser light" sink 750mA?
if so, then all you need is ohm's law.
If the controller drops the voltage at all (measure it before you connect anything), then it would probably be about 11V, and as you have 2x3V LEDs, then that leaves 5V (11V-6V). put that into ohms law (V=IR), so 5=0.75*R. therefore the resistor would be 6.6666666666 ohms, the closest resistor to that is two 3.3ohm resistors. I would use two 3W resistors, to avoid heat problems.


Most important part is, do you have a schematic or link to the controller portion?

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jduffy54 (author)jduffy542013-04-14

such resistors are avaliable cheap at mouser, such as
http://www.mouser.com/ProductDetail/Xicon/283-33-RC/?qs=sGAEpiMZZMtlubZbdhIBIJCTAEmJkxCPDI1gn34Hhc0%3d

and
http://www.mouser.com/ProductDetail/Vishay-Sfernice/RWM04103R30JR15E1/?qs=sGAEpiMZZMtlubZbdhIBIFkmiS0T8atJdwdUoEh7Dm0%3d

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