[etrailer]

Question:

I assume the thermal paste is there to take advantage of the aluminum plate as a heat sink. If that is the case, what on that board is creating that much heat? Especially if those LED's are pulsing when "constantly" on, what could create enough heat to warrant thermal paste?

 

[jpark]

The LEDs are only pulsing when the tail circuit is on (on "low" brightness). They're not pulsed on "high", so they generate a lot of heat when the brake circuit is on. Also, when the brakes are on, the car isn't moving, and a heat sink is just another way to help dissipate the heat without the help of extra air circulation.

The circuit board has pads for each LED on both sides of the board. Each pad on the front side is through-plated in several locations to each pad on the back. Osram recommends a 9-square-mm pad for each anode pin (4 anode pins on each LED) for extra heat dissipation. Here's the PDF for these LEDs: http://tinyurl.com/37rkyzf

I've used Osram's 30mA white LEDs at 17mA for various cricuits, and they get a little warm even at that current level, so using an aluminum backplate with thermal paste makes perfect sense. Heat is an LED's worst enemy, next to overcurrent and overvoltage.

 

[etrailer]

The LEDs are only pulsing when the tail circuit is on (on "low" brightness). They're not pulsed on "high", so they generate a lot of heat when the brake circuit is on. Also, when the brakes are on, the car isn't moving, and a heat sink is just another way to help dissipate the heat.

The circuit board has pads for each LED on both sides of the board. Each pad on the front side is through-plated in several locations to each pad on the back. Osram recommends a 9-square-mm pad for each anode pin (4 on each LED) for extra heat dissipation. Here's the PDF for these LEDs: http://tinyurl.com/37rkyzf

I've used Osram's 30mA white LEDs at 17mA for various cricuits, and they get a little warm even at that current level, so using an aluminum backplate with thermal paste makes perfect sense. Heat is an LED's worst enemy, next to overcurrent and overvoltage.

I had no idea the anodes on LED's could get that warm. I always though they created no heat because of their ultra-low draw, but I guess that's just the diode itself. The other components that conduct current still build enough heat that it needs to be managed, even at that small cosumption. Learn something new everyday.

Is it the same kind of paste that you use on computer processors and coolers? Or are automotive/light applications a different compound?

 

[jay_esc]

Question:

I assume the thermal paste is there to take advantage of the aluminum plate as a heat sink. If that is the case, what on that board is creating that much heat? Especially if those LED's are pulsing when "constantly" on, what could create enough heat to warrant thermal paste?

Adding to what jpark said, the voltage regulator can also generate a fair amount of heat and almost always require a heat sink. If you look at the picture of just the circuit board (and if I remember my circuit courses correctly), it appears the voltage regulator is in the lower right hand corner (the biggest black box).

 

[etrailer]

Adding to what jpark said, the voltage regulator can also generate a fair amount of heat and almost always require a heat sink. If you look at the picture of just the circuit board (and if I remember my circuit courses correctly), it appears the voltage regulator is in the lower right hand corner (the biggest black box).

That was my first reaction too. Of all the components he listed, I figured that would be the one that created the most heat. I take it we have a couple electrical engineers on the board.

 

[jpark]

You could say that.



I have to look up the part number on that part. It probably is the voltage regulator, although it could also be a transistor using a lower-current zener diode as the regulator. Since the regulator only needs to pass around 350mA through it, that's not enough current to generate much heat in a voltage regulator, especially since it's really only there to protect against spikes higher than 14V.

And yes, it's the same kind of thermal paste used on computers, although I'd never use something like Arctic Silver in this application, because the board may move slightly inside the assembly as things heat up and cool down. Arctic Silver hardens as it ages, and that would lead to a cracked circuit board after a while!

LED technology has also changed over the years. Old-technology (Gallium Arsenide/Gallium Phosphide/Gallium/Arsenide/Phosphide) red, orange, yellow and older green LEDs (the brownish-yellowish "green") have the cathode side of the chip directly mounted to a flat plane, and the anode is connected by a tiny wire betwee the top of the chip and the anode lead. These are still manufactured and used as low-intensity indicators.

Newer LEDs (anything with Indium, Aluminum and/or Silicon), starting with the first blue LED, followed by "true" green, purple, ultraviolet, and white (usually a blue LED with a phosphor that emits white light), use a non-conductive substate, and usually between the anode and the chip. The chip is more of a crystal, and the connections are both done on the top of the chip with wires. Now, that technology is being applied to red, yellow, and orange LEDs as well (such as these Osram LEDs). Some power LEDs actually have heat sinks built into the package.

You can already buy LED yard floodlights, and I've seen a few places around here with LED street lamps. And none of our traffic signals around here are incandescent anymore.

 

[etrailer]

It's pretty exciting technology that has a ton of applications.

We have a bunch of RV/trailer/camper towers that are converting all their lights to LED bulbs or fixtures. Because their amperage draw is so low, they can keep the lights on longer without draining the trailer batteries nearly as quickly as they would without the LEDs. I'm sure you know better than I the consumption reduction that LEDs offer over their incandescent counterparts. All that light at a fraction of the power use is pretty neat.

 

[jpark]

It sure is!

I built my own LED bulbs for the outside of our home. We have 7 fixtures that are mainly for formal lighting, not actual light, and I have them all on at night (with
photocells). I got tired of replacing the 25W bulbs that I was using in them, so...

That's the circuit I metioned above. In each bulb, I use 33 Osram white PLCC4 LEDs (5 on each of 6 sides, and 3 on top) in series with 6 470-ohm, 1W resistors, run off the DC side of a full-wave bridge rectifier and SMD fuse in the base, and each LED draws about 17mA with those parts. That is a picture of the first bulb, but I changed the circuit design to add another resistor after I ran the bulb for 48 hours and thought that the resistors were a little too warm. The sixth resistor made it perfect. I'll grab a picture of a finished bulb later. They flicker at 120Hz, unlike half-wave LED Christmas lights (which light only half the time at 60Hz). The flicker is barely noticeable, though, and I actually like it, or I would have added a capacitor to stop it.

I used 27mm X 72mm medical vials for the bulbs, and empty brass base shells (ebay). I designed, etched, and soldered everything.



They give off about as much light as a 25W bulb. I used the cool white LEDs, because we also have a metal halide light fixture in the back yard (with the same bluish white color).

 

[jay_esc]

Impressive stuff. I've dabbled in a few things since college, but nothing close to making my own light bulbs. I'm just happy I understand everything you are talking about.

 

[etrailer]

We have some ceiling fans at home with uncommon light bulbs. They will be getting an LED bulb treatment. I have a halogen light ceiling fan in my office that has a pretty narrow beam so the room isn't lit up as well as I'd like. They will be replaced with wide angle LED versions.

 

[jpark]

gmpartsdirect.com has the L1230R modules for $30.48 each.

Just thought I'd throw that out there.

 

[tang]

gmpartsdirect.com has the L1230R modules for $30.48 each.

Just thought I'd throw that out there.

Will the connectors/harnesses be different? I don't want to have to cut and re-connect cables.

For a temporary fix, I might try to put a foil ring around the bulb to see if I can get any more light distribution.

 

[jpark]

The connectors are different, but I have other plans.

:calvin:

 

[tang]

The connectors are different, but I have other plans.

:calvin:

That's a surprise.

:tease:

 

[jpark]

Now I have even more plans. And allow me to get really LED-geeky here.

Osram has released two more LEDs that change some of my plans.

RED

The first is the red LR-G5AP, which has an output of 13.8 lumens at 100mA (60 lumens per watt). Osram currently uses the LR-G6SP in the L1224R and L1230R modules, and it has an output of 13.4 lumens at 140mA (46 lumens per watt). So these new red LEDs are more efficient and brighter.

LR-G5AP:
http://catalog.osram-os.com/catalogue/c ... 64000200b6

LR-G6SP:
http://catalog.osram-os.com/catalogue/c ... 0f000100b6

AMBER

The second new amber LED is a piece of engineering genius.

First, some quick background:
1) You may or may not know this, but an LED is not a white light source with a piece of colored plastic over it. It's a tiny piece of metal or crystal that actually emits the color you see, and only that color (except for white LEDs).
2) Yellow LEDs are not as efficient as other LED colors, including red, although engineering improvements have brought up their brightness recently, as well as adding enough orange to the yellow to produce a more amber color. But you may notice that some of the LED traffic signals have caution lamps that aren't as bright as they should be. And pure orange LEDs, which are more efficient, are too orange to be used as traffic signals.
3) You'll see how this is related in a minute. A white LED isn't really white. It's actually a blue LED covered with a phosphor casing (usually yellowish in appearance) that uses the radiation from the narrow blue band of light to generate other colors as well as the blue, making semi-white light. This is why some white LEDs have a blue tint to them, although advances in phosphor technology have brought out other shades of white, like "warm white".

Sooo, Osram began playing around with phosphors, and they've developed a phosphor that generates an almost pure yellow-orange light (around 602nm) when lighted by a blue LED, but at a much higher light level than a regular yellow LED (usually 590nm). Even more amazing is that there's no visible blue in the output. Although this LED is based on the same package as the dimmer of the two red LEDs, this little beastie pumps out 16 lumens at 140mA. And Osram lists only one application for it: exterior automotive turn signals. They're also $3.06 each right now, but I only need eight of them for two lamps.

LCY-G6SP:
http://catalog.osram-os.com/catalogue/c ... bc000200b6

So I have to make a few changes to the circuits I'm going to use for the front lamps, since blue LEDs draw 3.6V versus the 2.15V drawn by red LEDs.

If any of this doesn't make sense, don't worry. I'll have pictures when I pick some of these parts up next week, along with a pair of L1230R modules, just for their light pipes. My plan is to make LED modules equal to or brighter than the current Osram modules, but able to fit into the Ford lamp assemblies, front and back, with no modifications to the lamp housings.

 

[tang]

I get it. And I have my checkbook ready.

 

[jonas1022]

Now that's some interesting statistics about the new LEDs. If this keeps up, I might make a mod to the wife's Tribute. :shock: :angel:

 

[jpark]

Ironically, an '08+ Tribute would be MUCH easier to modify, since it seems to have a bowl-shaped reflector with no obstructions around the socket, unlike the Escape, which has a reflector with interior ribbing on outer side that interferes with anything larger than the standard socket. For a Tribute, I wouldn't even need to disassemble the Osram modules, just add a Ford socket sleeve around the collar. I'm not sure about the front lamps, though.

And while '08+ Tribute tail lamps will fit on an '08+ Escape, there's no rear reflector in the housing, since the Tribute has reflectors on the rear bumper cover.

So my life is never easy.

:wall:

I get it. And I have my checkbook ready.

 

[tang]

I wonder if this assembly would have any purpose as a fog light bulb....?

 

[jpark]

With white LEDs, it could.

Maybe we should start a company. You become the idea guy, and I'll do the engineering.



BTW, here are my module circuits, although I'm still changing minor things.

Pulsed tail lamps:

Solid-on tail lamps: