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Old 12-30-2011, 12:45 PM   #1
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LED Strips: Dimming, Transforming and Installing


Want to order some LEDs for my bookcase project (see thread in siggy) and am amazed by the lack of coherent DIY LED strip info out there.

I want to hardwire a 120V AC to 12V DC transformer so that I can put a dimmer on the line side. Load would be approximately 24 watts... would a 2.5 amp (30 watt) transformer be sufficient (derating to 80%)? Like so:



Also, how much access would I need per NEC 2008? I want to hide it the best I possibly can.

Do they make combo 12v DC transformers / light switches? And do I want to use a magnetic or electronic dimmer?

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Old 12-30-2011, 12:57 PM   #2
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LED Strips: Dimming, Transforming and Installing


To answer your question, yes... You'd be fine with that load.

HOWEVER...
Dimming LED's isn't like dimming incandescent bulbs.

If you're going to use that to dim, you'll need a dimmer on your 12V side of that. The best way is to use PWM(pule width modulation). Without getting into too much detail, the way it dims is by applying 12V 50% of the time, then zero bolts 50% of the time. This happens several to several hundreds of times per second.(Frequency depends upon the PWM device)

If you get a dimmable transformer, you'll need a dimmer switch specific to dimming LEDs as well. The type/kind you'll need is usually specified by the manufacture's of said transformer.

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Old 12-30-2011, 01:34 PM   #3
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Ah... ha! I think I get it...

Found a PWM dimmer that would work, but it's ugly as sin. Trying to conceal and much as I can.



Edit: A much less ugly one. I might just have to go AC plug style instead. Only $9.


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Old 12-30-2011, 02:06 PM   #4
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LED Strips: Dimming, Transforming and Installing


If that first one is small enough, you could place it inside a 1-gange device box with a small holed face plate.
You would have to make sure there is no high voltage in there, or you'll be violating alot of codes/common sense.
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Old 12-30-2011, 02:08 PM   #5
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I have five units, which means I'd need 5 1-gang boxes...

...it's a good idea, and it crossed my mind using a coax faceplate or similar, but I don't think it'll work in this situation.
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Old 12-30-2011, 02:16 PM   #6
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LED Strips: Dimming, Transforming and Installing


Quote:
Originally Posted by Thadius856 View Post
I have five units, which means I'd need 5 1-gang boxes...

...it's a good idea, and it crossed my mind using a coax faceplate or similar, but I don't think it'll work in this situation.

Why 5?

The PWM dimmer looks to be 12v 8A

That's more than enough for your whole system.
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Old 12-30-2011, 02:18 PM   #7
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Well, connecting the first one seems obvious. But I don't know how I'd connect the other four strips because they wouldn't easily reach...

...use a couple pieces of 18g THHN and nut them together?

Edit: or maybe connect the strips in series instead?
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Old 12-30-2011, 03:05 PM   #8
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Quote:
Originally Posted by Thadius856 View Post
Well, connecting the first one seems obvious. But I don't know how I'd connect the other four strips because they wouldn't easily reach...

...use a couple pieces of 18g THHN and nut them together?

Edit: or maybe connect the strips in series instead?
Parallel would be best. But yes, using 18awg would be good.
You can run low voltage just about anywhere, as opposed to the 120V romex.
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Old 12-30-2011, 03:23 PM   #9
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LED Strips: Dimming, Transforming and Installing


we bought our under cabinet led lights from this place. they have the dimmers for them also and the lights just daisy chain together. the price was the best we found anywhere.

http://www.inspiredled.com/under_cabinet.html
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Old 12-30-2011, 03:27 PM   #10
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Under cabinet LEDs are attractive, but I'm trying to hide the LEDs behind the lip of the face frame, which leaves me only enough room for an 8mm strip, plus 1/16" of wiggle room.

Their custom cords are attractive. I wonder if they're 5.5mm or something else.
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Old 12-30-2011, 03:35 PM   #11
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they have some that are .38- 3/8 of an inch thick, i guess thats around 9mm.
they have other that are .30 which is less then 9mm.

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Old 12-30-2011, 03:37 PM   #12
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To be clear, I can only take a 8mm wide strip. Thickness I need as thin is I can possibly get, certainly not much thicker than 1/8".
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Old 12-30-2011, 04:07 PM   #13
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Figured out a setup that would work, went to piece it together on Amazon, and then realized that the power adapter didn't get Prime shipping... $9.97 ea plus $5 shipping per item. Ugh.

Stumbled upon a kit of the exact three items that I wanted, in a kit. It's not my first choice, but I'll just hide the power adapters behind the drawers. Plus, the price was pretty darn decent at $37/set.



I did have to compromise on the color. Only available in 3100k and 6000k in the kit. Had originally wanted the 3700k, but this will give the books an old-worldly glow.

Thanks guys!
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Old 12-30-2011, 06:09 PM   #14
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LED Strips: Dimming, Transforming and Installing


A much easier way to dim led stripes is
to use a multi voltage plugpack
Name:  multi voltage.jpg
Views: 87
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This pic should give you an idea !
Check that the current capacity is correct
for your application, cause there are many
different types available.
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Old 12-30-2011, 11:45 PM   #15
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LED Strips: Dimming, Transforming and Installing


Seen those at Radio Shack, and used to own one, but totally forgot they exist. Think I lost all the little connector doo-dads.

Great idea.

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