Backlighting Gauges

SeeMe

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:anyone: I am designing custom gauges for my car and want to backlight them using LEDs. I think that a COB LED module will work, but I really know very little about this technology. I want to hear what you think about my idea or if you have a better way to do this. Here's a drawing of what I plan. The gauge face will of course go between the pointer and the COB. One question I have is if I can drill a hole through the COB to allow the motor shaft to go through it. And another is if heat will be a problem. The gauge will be be nearly fully enclosed so as to keep out dirt and dust.
 
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Lynx_Arc

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Why do you need a cob LED won't that blind you looking at the guage? most gauges use low output bulbs you could probably light it up with a single 5mm LED depending on the way the gauge is designed.
 

Alaric Darconville

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Here's a drawing of what I plan

A drawing we don't see.

I do see the site owner edited your post-- did you by any chance hotlink an image, in violation of Rule #3?

You plan on drilling THROUGH the LED itself? Not its bezel, but through the LED panel itself? Sounds like recipe for not working anymore.
 

SeeMe

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I think the image must have been too large but it probably would not help anyway. There are two gauges in one housing. The illuminated portion of each face is 1 3/4 X 1 1/1/4 inches. The stepper motor is 1 1/8" diameter. Without extending the shaft, there's less than 1/4" (5-7 mm) between the motor and face. A COB panel will nicely fit in the space between motor and face and that's the reason I posted this thread.

Because the gauge is back lit, much of the light is attenuated by the gauge face. Multiple LEDs are needed but their light is spotty and they are too tall to fit in the space. I've experimented with several LED types. The COB strips that are sold as running lights work great except they must be cut to fit. When placed side by side to illuminate the full face, light is not evenly spread because of the void between strips. Since the strips work fine after being cut I am pretty sure that a small (1/16" or less) hole will not damage the COB. For example, the common conductive strip between individual rows of LEDs is almost 3/16" wide so the hole for the motor shaft could be through this strip.

Couldn't the brightness be adjusted with a simple rheostat or potentiometer?

So what about heat? There is always talk about the heat that LEDs and COBs generate and how the COBs have a conductive base to dissipate heat. The COB strips I have get warm (in open air) but they feel cooler than a single instrument bulb when touched. If sealed into an instrument housing with some ventilation holes, will a COB get too hot? If so, what can be done to cool them?
 

Lynx_Arc

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I think the image must have been too large but it probably would not help anyway. There are two gauges in one housing. The illuminated portion of each face is 1 3/4 X 1 1/1/4 inches. The stepper motor is 1 1/8" diameter. Without extending the shaft, there's less than 1/4" (5-7 mm) between the motor and face. A COB panel will nicely fit in the space between motor and face and that's the reason I posted this thread.
Without seeing the gauge I couldn't easily recommend an alternative but they do make 3mm LEDs and I have some flat LEDs for displays although I'm not sure if the light coming out on the sides of them is enough.
Because the gauge is back lit, much of the light is attenuated by the gauge face. Multiple LEDs are needed but their light is spotty and they are too tall to fit in the space. I've experimented with several LED types. The COB strips that are sold as running lights work great except they must be cut to fit. When placed side by side to illuminate the full face, light is not evenly spread because of the void between strips. Since the strips work fine after being cut I am pretty sure that a small (1/16" or less) hole will not damage the COB. For example, the common conductive strip between individual rows of LEDs is almost 3/16" wide so the hole for the motor shaft could be through this strip.

Couldn't the brightness be adjusted with a simple rheostat or potentiometer?
You could use one but my experience with using one is that too often you end up with most of the adjustment in only 10% of the range of the control if even that.
So what about heat? There is always talk about the heat that LEDs and COBs generate and how the COBs have a conductive base to dissipate heat. The COB strips I have get warm (in open air) but they feel cooler than a single instrument bulb when touched. If sealed into an instrument housing with some ventilation holes, will a COB get too hot? If so, what can be done to cool them?
Light bulbs and LEDs are completely different in the way they both handle and get rid of heat. Light bulbs radiate most of the heat from them via infrared and can handle heat very well unless they get extreme heat it rarely is an issue for the bulb itself. With LEDs the heat is mostly radiated through a heat sink connected on the back side of it some of it can be radiated through the air but the percentage of that is pretty much negligible for the sake of protecting it from damage. When you are using heatsinks with LEDs you either need a larger mass to wick the heat away from the LED in an enclosed area or the area ends up actually fighting with the LED for heat dissipation. COB LEDs do get hot and IMO the board that comes with them isn't adequate to cool some of them alone running them at full output but should be ok perhaps at half rated output. I would suggest if you have room getting a thin piece of aluminum to wick the heat from the COB if you run it at full output.
 
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