[RE-wrenches] DC power for LED lighting

[Darryl Thayer]

I have not worked with seperate LEDs for several years, and I am working with an old brain, but it seems that a LED needs about 3.0 to 3.5 volts mimimum to turn on and somewhere about 4.5 volts or 5 volts to fail.  So if you do not have a voltage limiting system or a voltage regulator you must stay within the operating voltage.  If you for example have a 12 volt system, where the max voltage is 16 volts and the minimum is 10.5 volts you should provide about 4 volts to each LED you can onlyt put two in series and must have a voltage regulator.of 8 to 9 volts.    
 
There are single chip voltage regulators, that can work from 25 to 12. volts and give regulated power output of 9 volts. It is simple for Hugh  and others that work with these chips to design and build a VR to work with these LEDs.   If the chip gives 9 volts, and you connect a string of two leds.  One trick is to add the leds in series to a voltage just below the low voltage point of the source.  for example if you have 4 volt leds and a twenty four volt system you would want to put 5 inseres and have the regulator or 20 volts.  
 
Wattage of VR chip, many have wattages 0f 5 to 25 watts, and for a 12 volt system when at 16 volts with the two at 9 volts, the series regulator will be droping almost twice as much power as the LED, a one watt LED shoud be protected with a 2 watt series regulator.  
 
This is straight forward stuff for electronic people, Perole like JJJarvis, who has built many many custome circuits for me or Brand electronics.  If you want several simple circuits, JJ will make a board and use the correct heat sink, for both the LEDs and the VR.  JJ also makes or at least sells a multivoltage LED fixture.        .  
 
, .   three oltage,  
 

________________________________
 From: Hugh Piggott <hugh at scoraigwind.co.uk>
To: danbob at otherpower.com; RE-wrenches <re-wrenches at lists.re-wrenches.org> 
Sent: Saturday, December 17, 2011 12:03 AM
Subject: Re: [RE-wrenches] DC power for LED lighting
 
H Dan,

On 17 Dec 2011, at 00:02, Dan Fink wrote:

>  parallel connections are BAD with LEDs, and the string with the most voltage will eventually fail first, so best practice is regulate every string.

This statement puzzles me so I wonder if you could clarify it for me?  If you connect two strings of LEDs (or batteries) together in parallel then their voltage will be the same.  So how come you are talking about one having more voltage? 

If the answer is that it's absolutely impossible to make the connections and leads have the same resistance then this same logic applies to two strings that are connected each to its own regulated supply.  If a tiny difference in voltage matters (which I doubt) then you will have the same issues with a single string.

What am I missing?

thanks

Hugh

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