Re: LED's for sandblast cabinet?


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Posted by Sherman in Idaho [72.47.153.24] on Sunday, July 08, 2012 at 12:46:14 :

In Reply to: Re: LED's for sandblast cabinet? posted by Franz [4.157.20.72] on Saturday, July 07, 2012 at 01:35:45 :

You don't just go hooking up bare LEDs to voltages and experimenting to see what happens. What will probably happen is you'll destroy them. LED bulbs of all kinds need some electronics inside them to convert the raw power supply, which is usually a voltage source (ac or dc) to what the LEDs want to see, which is a regulated current (not a voltage). If you put a voltage across them, you can get them to light to some extent, but the current varies wildly as the voltage changes, and they'll likely burn out. Also, the bare LEDs can't take much of a reverse voltage before breaking down.

I won't go into all the details of designing LED power supplies, but basically this is not something to g-job by hooking some raw LEDs out of something to a welder and adjusting the voltage until they light up. Personally, I can't see any reason to mess with trying to use LEDs in a sandblasting cabinet, but if you do, buy pre-packaged assemblies that include the driver electronics. If you open one up, you'll see a circuit board with some electronics on it inside. That's there for a reason, and not because the engineers just wanted to make things complicated.

As for the LED streetlights, cities don't buy them to light up the streets, or even to save electricity. They buy them because there's a certain politically-active constituency that wants the city to "go green". These people have absolutely no idea of the cost of anything or about how anything works. They can't calculate an ROI. They don't know a lumen from a foot-candle or an amp-hour from a kilowatt. All they know is solar is green and they want green streetlights. They have some votes, and so it's easy enough for the city council to throw a million dollars or so at an LED streetlight contract. The lights aren't very bright, so they usually put them in places where lots of people will see them, but they don't have to actually be good, like parks. To the extent that they buy green votes, they're a smart investment. We're just wrong to look at them as a way to light up streets economically. That was never the intent, and if they quit working and get surplussed in 5 years, that's okay because they've already served their only real purpose.

Yeah, Seattle, putting in a bunch of them too -- another place where the sun rarely shines in the winter. But hey, the city that just banned plastic bags has to keep doing more to stay on the greener-than-though cutting edge.



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