Author Topic: 12 Volt light bulb version 2 , and a question  (Read 10675 times)

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Rover

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12 Volt light bulb version 2 , and a question
« on: January 11, 2011, 06:48:10 PM »
I've received my 300 5050 SMD LED strip (this one is flexible), and I am in the process of building a new light. Following my previous one of 56 LEDs, this will have ~ 96.

As a test , I took a section of 96 LEDs and wrapped it barber pole style around a short piece of 2" PVC and turned on the power.  Oh yeah, it is bright, but I kept testing the temp (finger test, I don't have a decent non contact thermometer) of the inner portion of the tube, and it was getting quite warm. It never got untouchable  or too hot to hold, but the temp in my garage is quite cool (50-60F). I'm a little worried about use in the summer when temps will be in the 90s F .

The whole goal is to build this with easily purchased material, hence the PVC. I've thought of using aluminum flashing but the strips have exposed contacts every 3 LEDs that would need to be isolated.

Question is, should I rethink the design?  perforate the tube? or is the insulation effect, (probably not the right term) of PVC , insurmountable?
Rover
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DanG

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Re: 12 Volt light bulb version 2 , and a question
« Reply #1 on: January 11, 2011, 09:10:03 PM »
Can you do a side profile and back shot using macro setting?  Or get as close as focus will allow using maximum pixels and file size and crop the image to show only the assembly?

ghurd

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Re: 12 Volt light bulb version 2 , and a question
« Reply #2 on: January 11, 2011, 09:26:14 PM »
Congrats!
You made it to No Man's Land.
There are a lot of things nobody will tell you past this point, and the Chinees EEs aparently don't know,
like most of the heat in an LED comes out of the cathode, which is why my (not for sale) custom LED boards include that fact in the surface area of both sides of a double sided through hole plated 2oz board.

If you want it to last for decades, they have to stay very cool.
"A little bit Warm" is not an option IMHO.

Heat is wasted power.  Decades of power being wasted.
The solution, IMHO, is to reduce the If to the point it is not warm without a heat sink.
Then heat sink it.

The efficiency goes up a lot (usually), the heat goes down a lot, the service life goes up a lot^2.

I still can't tell exactly how those things are wired, and I tried hard, but I'd add some extra resistance or series them.

I doubt heat sinks are practical for those.

My standard start Rant of the Day Warning-
Besides, heat sinks are almost like poking a hole in a gas tank if too much fuel is coming in?
There is SOOOooo much power being WASTED it requires a pile of 1/8" thick heat sink to get rid of it?
Get rid of the extra power (wasted as heat) for 50 years,
Or spend a few $ extra now for more LEDs to drive more of them but "underpowered" to get more lumens with less power in a bulb that lasts many times longer?
G-
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Bruce S

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Re: 12 Volt light bulb version 2 , and a question
« Reply #3 on: January 12, 2011, 11:52:55 AM »
Rover;
I'm with G- on this one. What are the numbers?
Vf and If? reducing If will reduce the warm to touch a lot and preserve the LEDS far longer without that much of a lumen hit.

I realize you're probably driving this at 12Vdc, but what is the current set at. 12V using 96 LEDs with say 20ma for each one should put you in the ~2A area, try dropping that to about 15ma each or for whole area 1.5A total the viewable light output will probably not be that much different.

BTW: That's a lot of LEDs will be interesting to see it lit up  ;D
Cheers;
Bruce S
A kind word often goes unsaid BUT never goes unheard

DanG

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Re: 12 Volt light bulb version 2 , and a question
« Reply #4 on: January 12, 2011, 01:02:34 PM »
Quote
most of the heat in an LED comes out of the cathode... ...spend a few $ extra now for more LEDs to drive more of them but "underpowered"

Amen.

Independent of the packaging there is the instant heat of the junctions before residual heat has a chance to be wicked away via the conductor(s) or mounting substrate or assembly package. Its like the dome of an 2-stroke engine piston versus the cylinder wall temperature - the spot where the devices work is most concentrated, even running at lower energy levels it is still seeing nearly the same instant heat - so doing both heat management (not accepting as-provided) and lowering current is a double win situation.

I'm still very curious to see a photo expose of them  : )

ghurd

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Re: 12 Volt light bulb version 2 , and a question
« Reply #5 on: January 12, 2011, 01:49:40 PM »
I'm still very curious to see a photo expose of them  : )

Of mine?
I made several versions like that.  There is only one posted here, the large one on the left.
Notice the cathodes all have the same surface area (the inner rings are wider).
The diode or bridge, and a pre-balast resistor, is in the E27 base to get that heat away from the LEDs.
The rest of the resistors are connected to the center 'dot' of the board, with long leads to get the actual resistors back up the pipe a bit.
The potting compound is thermally conductive, and entire pipe at the rear of the board is full.
Very rare to hear of an LED failure in that style bulb.  17.5ma per series string.
Giant 1240x560 pic, but 81K.
http://www.otherpower.com/images/scimages/2050/bulbs.jpg

The others have the LED leads left as long as practicle to give the heat somewhere to go, then hopefully the potting compound carries it to the brass base.
Rare to have a failure in those either, but they are underdriven to about 12 or 15ma max.  Sometimes only 7ma.
G-
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Rover

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Re: 12 Volt light bulb version 2 , and a question
« Reply #6 on: January 12, 2011, 04:10:21 PM »
Ghurd,

Yep I'd like the flexibility to drive them differently , but these are on a prewired strip , each LED in parallel  with a 150 ohm resistor. (pics below)
Figure each LED is 60 mA /3.6 V

In my tests, an strip of 96 @12 volts was right around  22W


Test Assembly


short section of the strip 6 LEDs


Same strip reverse side, notice that the strip can be cut every 3 LEDs, so you can see the solder pads for attaching wires. Also why I can't just stick them on an aluminum backer
Rover
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Rover

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Re: 12 Volt light bulb version 2 , and a question
« Reply #7 on: January 12, 2011, 05:58:20 PM »
NIX that ... must be 20 mA, no idea where I got 60.
Rover
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DanG

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Re: 12 Volt light bulb version 2 , and a question
« Reply #8 on: January 13, 2011, 12:21:44 AM »
- 3 watt high power connector; - Input/output Voltage: 12V;  Current: 300mA

>   http://www.dealextreme.com/details.dx/sku.47354


ghurd

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Re: 12 Volt light bulb version 2 , and a question
« Reply #9 on: January 13, 2011, 01:14:45 PM »
Can you measure the V on a resistor?
And the resistance from the 1st to the 3rd resistor (to see if they share the pos).
I have a feeling they could be used in series. 
Hard to say how they are connected.  They are not a typical LED.

Or could try seriesing 3 like strips, and see if they light up at 12V.
G-
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Rover

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Re: 12 Volt light bulb version 2 , and a question
« Reply #10 on: January 13, 2011, 04:33:13 PM »
A little clarification,

Each SMD is 3 LEDs  (3x20mA) , each of the LEDs on the SMD are  serial connected outside the SMD package (pins connected serial, 6 pin SMD)  , and in series with an external  150 ohm resistor

I'm using 96 SMDs   (think of each SMD  as  3 LEDs in series with a series resistor) . The have made the strip cuttable every 3 SMDs by placing solder tabs and a cut line.

Each of the SMD/resistor arrays is parallel connected across the feed lines (12v +/-)  on the strip (can't see the trace lines assume the are there due to the +/- markings)

It really is 3x96 LEDs   ... on the strip as  (12V+)...(SMD(LED...LED...LED...))...150 ohm... (-)
Rover
<Where did I bury that microcontroller?>

ghurd

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Re: 12 Volt light bulb version 2 , and a question
« Reply #11 on: January 13, 2011, 04:59:30 PM »
"Each SMD is 3 LEDs  (3x20mA) , each of the LEDs on the SMD are  serial connected outside the SMD package (pins connected serial, 6 pin SMD)  , and in series with an external  150 ohm resistor"
THAT is Exactly what I was looking for.   :)
Good to know somebody made a consumer item with a little bit of thought!

If it was mine, I'd still try to get the ma down a bit lower.
The (perceptable with human eyes) output will not be much lower if they only pull 15ma.
G-
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Rover

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Re: 12 Volt light bulb version 2 , and a question
« Reply #12 on: January 13, 2011, 05:18:54 PM »
Since I can't remove the resistors easily (SMD's themselves) , The only thing I can think of doing is reducing the voltage a wee bit. You apply power to the strips themselves. In my case I'm going cut and and  use 8 strips of the LEDs, each with 12 SMD's (can only cut every 3)  , each strip wrapped around the pipe. comes pretty close to the circumference of 2" PVC pipe . I'll then parallel the strips to the power supply

My prime concern I was the total heat given off by the total assembly of the 96 wrapped around the PVC pipe, and temp tolerances of the PVC pipe and the assembly. (heat coming from the SMD LEDs, and the power dissipating resistors).

PVC does not have great heat transfer properties, especially when you are talking about sch 40 , walls are bit thick.

I think I might be OK though, I'm going to perforate the PVC pipe (make it kinda look like a drainage pipe), and top and bottom will be vented.

Rover
<Where did I bury that microcontroller?>

ghurd

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Re: 12 Volt light bulb version 2 , and a question
« Reply #13 on: January 13, 2011, 05:47:58 PM »
I think you will be surprised how little difference there is between 20 and 15ma.

A strip of 12 LEDs will pull about (12 x 20ma) 240ma?

Might try a 10 to 18 ohm 1W in series with each strip to get some idea of how they act.
I might have something in that class here, if you want to try it, shoot me an email.
G-
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commanda

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Re: 12 Volt light bulb version 2 , and a question
« Reply #14 on: January 27, 2011, 08:52:46 AM »
You know the insulators for mounting TO220 devices, the gray plastic sheet thingies, well, you can buy that stuff by the sheet, usually 12 inches square. I've got some at work, which I bought from Farnell, so it wasn't cheap. But, if you had that, you could build your lamp around an aluminium tube.  Or, just use the little TO220 insulators to cover up the exposed pads on the back of your strip.  More fiddly though.

As an aside, I was going to say, if you want something as bright as a CFL, just use a CFL. A couple of years ago, in the user diaries, I described an inverter using an SG3525, and a transformer salvaged from a PC power supply. It outputs 240 volts DC, which our Australian 240 Vac cfl's run just fine on.  I've got half a dozen of them here ready to go, if my builder ever gets my shed up.

Amanda

JamesJackson

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Re: 12 Volt light bulb version 2 , and a question
« Reply #15 on: May 04, 2011, 10:41:50 AM »
Hey Rover! I like your 'lightbulb'!

I purchased some of these peel-n-stick LEDs a while ago... I think I got about 64 (or so) of them.

What I did was to create a 'picture frame' LED light using them. It was/is a proof-of-concept type of thing - that worked.

I took the long roll of LEDs and unsoldered them into 4 strips. I placed these side-by-side onto the cardboard backing of the picture frame that I bought at a used store.

I then used copper tape that I bought at a hobby shop that also has adhesive backing, and 'wired' up the 4 strips. I soldered a 2mm plug onto the LED leads and hot-glued the plug to the back side of the cardboard.

I control (ON/OF) this LED 'lamp' using my IR-LVD controller. Using a TV remote controller we are able to switch it on and off. It is hung on the wall behind our living room couch. For all practical appearances, it looks like a picture, until it is lit up. It then looks like an open window with the sunshine shining in.

I wouldn't worry too much about the heat it is putting off. However, if you are concerned, you might consider getting a slender ceramic coffee mug, and wrap your LEDs around the ceramic. Ceramic can pull the heat from the LEDs a bit, and if the mug gets warm, it won't hurt.

Another option would be to wrap your LEDs with a gap equal to the width of the LED strip - which would look more like a barber pole. This would allow the heat to not build up so much.

Good work! I like it!

Regards,

James Jackson
Oztronics

Rover

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Re: 12 Volt light bulb version 2 , and a question
« Reply #16 on: May 04, 2011, 06:30:32 PM »
Thanks James,

Then you might like this http://fieldlines.com/board/index.php/topic,144841.0.html which followed it

You might also want to check out Wooferhound's FAQ on the subject at :

http://fieldlines.com/board/index.php/topic,143569.0.html

Rover
<Where did I bury that microcontroller?>

JamesJackson

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Re: 12 Volt light bulb version 2 , and a question
« Reply #17 on: May 04, 2011, 08:57:16 PM »
Good light you built.

I got home and counted the LEDs I am using... 120 of them in 4 strips of 30.

I was pretty amazed at how much light these little LEDs create.

Regards,

James Jackson
Oztronics