Date: Tue, 18 Sep 2007 19:17:23 -0700
Reply-To: David Kao <dtkao0205@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: David Kao <dtkao0205@YAHOO.COM>
Subject: Re: 2 LEDs
In-Reply-To: <20070919014920.EC21D1165C3@hamburg.alientech.net>
Content-Type: text/plain; charset=iso-8859-1
That's just like your words saying I was displaying extreme ignorance.
In fact I fell into the same mistake a few years back in connecting some
LEDs in serial. I tasted the mistake myself. I thought of it a while before
I responded to this thread. I knew someone will jump out and argue about it.
You did. I don't care if you don't believe it. Just keep in mind PN junction
resistance and voltage will drift when temperature changes. You can connect
two resistors (light bulbs) without the problem but not two PN junctions.
LEDs are mass produced and are rarely uniform. They will try to kill each other
when connected in serial with one simple current limiting resistor.
I am sure they won't die instantly but they won't last 20,000 hours.
You do not know how exactly manufacturers design their LED modules. Without
knowing much about them I can not comment anything. The LEDs could be in serial
but you don't know how they are connected in serial. I doubt it is a simple
resistor with LEDs in serial. That's not much value to be added to the product.
I won't invest in a manufacturing plant in USA to make products like that.
David
--- Mike S <mikes@FLATSURFACE.COM> wrote:
> At 08:59 PM 9/18/2007, David Kao wrote...
> >Your example of LEDs in serial is regular signal LEDs not for lighting
> >applications. Regular LED runs at 10 - 50 ma small current. Luxeon
> >LEDs are working at 0.5 - 0.7 amp. Your serial resistor is 390 ohm.
> >The one for two Lexeon in serial with 12 volt supply will be less than
> >5 ohm. Try to short one out and see the smoke yourself.
>
> So when you said "If you don't have LEDs to play with come to grab from
> my bench. I have at least a couple hundreds of them now," you were
> talking about 3W Luxeon's? I'm impressed. I notice you totally ignored
> both the comment about current drivers and the manufacturer's
> statements.
>
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