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1 members (Scott35),
235
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Key:
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Global Mod,
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Joined: Jul 2004
Posts: 9,931 Likes: 34
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I think you are right about LEDs in coolers. The outrageous cost of cold start ballasts will push this along.
Greg Fretwell
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Joined: Mar 2007
Posts: 404
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Walmart and other grocery chains have used LEDs as lighting in new refrigerators for well over a year now...
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Joined: Dec 2005
Posts: 869 Likes: 4
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Biggest issue is reliability of the led driver circuit.
These are usually SMPS and will not last the time.
Led's have claims of 100k hours + but when driven hard by the PSU the colour will fade over time and brigtness is reduced.
For cold environments they are excellent provided they are fed from a low voltage supply and the SMPS is not required.
Of course the unit has to be properly sealed agains water ingress, otherwise the led terminals will corrode and an ealry faillure is iminent.
I have built quite a few LED night lights around my house and they run at 10 - 20 mA current at mains voltages with a simple series resistor to control the current.
The reliability is excellent.
The product of rotation, excitation and flux produces electricty.
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Joined: Jun 2004
Posts: 1,273
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I don't see where Switched Mode Power Supplies make much sense for LEDs.
Their limited power draw would seem to indicate that a simple low pass filter with a hefty cap would be sufficient. A tiny transformer, embedded in epoxy, would be able to kick out the joules. If this power supply is properly configured to tolerate plenty of heat... you'd be good to go.
Tesla
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Joined: Jul 2004
Posts: 9,931 Likes: 34
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Since a LED drops 2 - 2.5v across its junction I would think you could string 55 or so in series with a small value resistor to scrub off the rest and limit the current although I bet there is a chip that would do a better job of current regulation for a nickel a unit or less in the quantity.
I am not sure what the new white LEDs need to get to max illumination but I am guessing it is in the 20ma range.
(~24 watts)
Greg Fretwell
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Joined: Feb 2002
Posts: 183
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LEDs should be operated at a constant current, not at a constant voltage. The IV curve is exponential, so a resistor, especially off an unregulated source, is a poor choice.
I just used Supertex's CL2N8-G as a 20mA constant current source in some backlit signs I just made. For higher current, you can use something like an LM317 but power dissipation will start to add up.
For higher power (350mA to 1A LEDs), I have used switching designs.
/mike
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Posts: 57
Joined: August 2003
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