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Subject: Re: Parallel LEDs calculation
References: <3D7B8B88.4ED5A338@bellatlantic.net> <3D7D580B.7DBE070D@bellatlantic.net> <3D7EB60D.B730482F@bellatlantic.net>
Date: Wed, 11 Sep 2002 15:49:32 GMT
NNTP-Posting-Date: Wed, 11 Sep 2002 11:49:32 EDT
Martin Riddle wrote:
> wrote in message
> > I see your numbers as a problem: how realistic do you
> > think 112c is? That's 233f. How realistic is your 302f
> > (150c)? Even the 85c - that's 185 f - you mentioned in
> > your prior post is higher than what you'll ever find in
> > the passenger compartment. To get the temperatures you
> > mention, you'll have to get near the engine. Do you
> > think he's going to mount these resistors on the exhaust
> > manifold??
> Sorry, your original post rolled off the news server.
> But the auto enviroment is a harsh one. How hot does it get, I really dont
> But if this is a high mount stop lite, then the chances of 'getting very
> hot' is real. In an uncooled space that is being heated by thermal radiation
> (the sun) it is quite possible for the temperature to reach the limit of the
> component ratings.
> So, using derating as a guide line a 1 w resistor would be the proper
> choice. This makes a difference in reliability.
OK! We agree. That is what I said in my original post which
rolled off your server. I told him he should use at 220 ohms
at at least 1/2 watt, and for better reliability, two 1/2 watt
470 ohm resistors in parallel. And I mentioned the need to
increase resistor value over the computed wattage because of
the hostile environment. I wondered what I was missing when
I saw your post.
Plus you dont want to pick a
> resistor larger than you need, expecially if your making 100,000 units.
> But for the hobbiest all this really dosent matter, there are mechanical
> problems that are hard for the hobbiest to fix properly. And the device will
> most likely fail after a year or two and get thrown out.
> BTW, exhaust manifold temperatures run around 800f at WOT.