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Overview

I've recently developed an obsession to replace all the lights in my fifth-wheel with something much more efficient. In my past fifth I replaced all the lights with 12V CFLs. Although I was happy with the results I wanted to do something different this time. So I began researching the latest generation of LEDs. This research leads me to a confusing array of products and options on the market.

So first let's begin with a quick and dirty lesson about LEDs.

The latest generation of high power LEDs are mostly manufactured by 3 companies.
1. Phillips Lumiled
2. Cree, Inc
3. Seoul Semiconductor Inc.

The LED industry is very competitive and recently Phillips Lumiled had fallen behind, leaving Cree and Seoul with the brightest LEDs on the market.

So now that we have it narrowed down to 2 companies we can focus in on their LEDs. Unfortunately LEDs come in many powers and colors, so the choice can be very confusing. The manufacturers refer to these color and power groupings as "BINS". I will spare everyone with all the gory details of narrowing down my selection. I will just say that the BINs I selected were based on efficiency and the cleanest light. All the BINs I selected are "Pure White" and comparable to "Daylight" CFLs, NOT COOL WHITE. These LEDs have no blue ting at all.

The next important thing to know about LEDs is that they cannot be run directly from a 12v source. LEDs are a constant current device. This means they expect a set current or milliamps at 4v to be delivered to them. This can be achieved in two ways, one by chaining the correct number of LEDs together and using resistors to limit the current. Second, is to use a LED driver. Since resistors simply waste the excess current as heat, they are very inefficient, and make the use of a driver a "No Brainer". I was able to find the perfect driver. Input can be 6 - 16V, output is 4.0v @ 750ma and its 75% efficient. (Bonus input polarity does not matter)

Testing Images

So without further ado here are my test images. All LEDs are using the exact same driver and hooked to the same batteries.
NOTE I'm still waiting on a Seoul U bin LED. It should be slightly brighter than the T bin.
Incandescent Buld
Regular 12.8W 912 Wedge Style Incandescent
Cree Q2
Cree Q2 WC Bin LED(3.5W)
Z-Power T Bin
Seoul Z-Power T Bin LED(3.5W)
Cree R2
Cree R2 WG Bin LED(3.5W)
Incandescent Buld
Regular 12.8W 912 Wedge Style Incandescent
Cree Q2
Cree Q2 WC Bin LED(3.5W)
Z-Power T Bin
Seoul Z-Power T Bin LED(3.5W)
Cree R2
Cree R2 WG Bin LED(3.5W)
Incandescent Buld
Regular 12.8W 912 Wedge Style Incandescent
Cree Q2
Cree Q2 WC Bin LED(3.5W)
Z-Power T Bin
Seoul Z-Power T Bin LED(3.5W)
Cree R2
Cree R2 WG Bin LED(3.5W)

Test Results

Ok first thing I want to make clear is that my digital camera does not show the true colors. With the incandescent bulb my camera adds a lot of red to the image. Similarly with the LEDs it adds blue to the image. Both of the bulbs have a much different coloring in real life. The incandescent is what you would expect for a normal trailer bulb. Like I said earlier the LEDs are pure snow white and comparable to "Daylight" color fluorescents. NOT COOL WHITE.

So with that out of the way, let's analyze the images. I think it pretty clear in the images that the Seoul T bin emitter is the brightest. I can also verify that it "felt" the brightest in person. Actually I was very surprised by these results. On paper the Cree R2 is the brightest and most efficient. The only explanation I have for my results is that we are not pushing these LEDs to their max current of 1 amp. It possible that the Cree LEDs come alive when they are driven at their max. I didn't think it would be a good idea to run at 1 amp since the RV enclosures are quite small and I was worried about heat build up.

So that really leaves us with the Seoul LEDs. This is actually good, since the Seoul LEDs are over $1 cheaper than the Cree's. My final lights will be built using the Seoul LEDs. I'm just not sure which bin yet. I noted earlier that I'm waiting for a U bin emitter and I suspect it will be the brightest of the bunch.

Putting it Together

Materials:
Seoul Leds (http://www.dealextreme.com/details.dx/sku.1445)
Driver Board (http://www.dealextreme.com/details.dx/sku.13557)
Arctic Silver Thermal Adhesive (Ebay seems cheapest)
Regular Epoxy
2" Wide X 1/8" Thick Aluminum Flat bar
Aluminum Flashing
Wire
Soldering Iron
Solder
Shrink Tube or Electrical Tape

Step 1: Remove the light fixture!


Step 2: Cut or break the old bulbs off the light fixture. I found that simply pulling to right then the left would snap them off cleanly.


Step 3: Use a screw driver to remove the aluminum heat shields.
Note If you are careful, you may be able to remove the shields and use them as a heat sink. This will save you many steps later on. Unfortunately mine were unusable due to the screw the factory put through them.

Step 4: Use a knife, or a Dremel grinder to remove the heat shield stands. They are not required as LEDs are not hot enough to require them.


Step 5: Press a piece of paper tightly into the fixture and trace around the inside. Use scissors to cut out shape you traced (it should match the inside of the fixture perfectly). Now trace the shape onto thicker cardstock that can be used as a template. Use the template to create 4 aluminum heat sinks (for a double fixture, 2 for a single fixture) from the flashing material. Flashing material can be cut easily with scissors

Step 6: Use low grit (80 or 100) sandpaper to rough one side of the heat sinks.


Step 7: Now mix some Epoxy and spread it evenly on the rough side of one of the heat sinks. Clamp the other side of the heat sink (rough side to the Epoxy) to the first heat sink side. (Make a sandwich. Aluminum, Epoxy, Aluminum)


Step 8: Once the Epoxy has cured check the fit in the fixture. Use Scissors to trim as necessary.


Step 9: Use a hacksaw to cut a 1 1/2 inch piece from the aluminum flat bar.
Image Missing
Step 10: Use the Arctic Silver Thermal Adhesive to glue the 1 1/2" X 2" piece of aluminum to the center of the heat sink sandwich. Remember to rough the flashing material with sand paper first.


Step 11: Place the finished heat sink in the fixture. From the bottom use a felt to mark the screw holes. Remove the heat sink from the fixture and drill out the screw holes (TIP: Place a piece of scrap wood under the heat sink for a clean hole)


Step 12: Use a soldering iron to de-solder both the pins and wires from the controller board.


Step 13: Solder the LED and controller board in the configuration below.


Step 14: Again use the Arctic Silver Thermal Adhesive to glue the LED star to the heat sink just like the pictures below.

Step 15: Finally wrap the boards in shrink tube or electrical tape to ensure they are protected.

Step 16: Then reinstall the light fixture.


If you found this article valuable and are in the market for a new generator, please visit our sponsorís site at http://www.campgen.com. Also don't forget to check back for more articles. I will be doing one soon on Hydronic heating using the RV hot water heater.