Date:         Mon, 17 Sep 2007 12:45:27 -0700
Reply-To:     Robyn Lundstrom <robyn@TRAINWIRE.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Robyn Lundstrom <robyn@TRAINWIRE.COM>
Subject:      Re: LVC adding LED interior lighting
In-Reply-To:  A<091720071937.12252.46EED76D0008B10700002FDC2207001641979A09019B0E0D9A9D@comcast.net>
Content-Type: text/plain; charset="us-ascii"

Hi Todd,

  The device he's using should (will) already have resistors for current
limiting; one per LED or some other number/value for the whole string in
series or parallel, depending on the whim of the engineer who designed
it.

  AAA cells are more than capable of causing thermal runaway in an
un-resistored (is that a word?) LED.

  Since the current limiting is already taken care of, all you need is
an appropriate voltage and (of course) a fuse.

Robyn

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of Todd Last
Sent: Monday, September 17, 2007 12:37 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: LVC adding LED interior lighting

I thought that current was the important factor in LEDs.
Does the LM7805 have a current range?

I would guess that the battery device is limited by the current from the
AAA batteries - which may not be so for the 12V car system.

This may be a moot point, but as they say, a little knowledge is a
dangerous thing. And my electronics knowledge is definately rusty.

Todd

 -------------- Original message ----------------------
From: vanagonvw <ac.vanagon@GMAIL.COM>
> Ed Duntz wrote:
> >
> > Is there an easy way to run 4.5 or 6 volt LEDs on 12 volts?
> Yep. Piece o' cake. :-)
>
> LM7805 is the base number for the part at Radio Shack. It can deliver
up
> to 1 amp out, so depending on what you are doing, you need more than
> one, or a different device with more output capability.
>
> An LM317 is much the same, only it allows you to adjust the voltage
out
> with a few resistors, if you want to be dead on 4.5V or 6V, but 5V
will
> work fine in most cases.
>
> digikey.com or mouser.com have online data sheets that will show how
to
> wire it up if you search for the part number. Calculate the max
current,
> and make sure you use a heat sink if necessary, by the data sheet.
>
> Basically, you will just wire 12V to one pin, ground the gnd pin, and
> take the 5V off the third pin. May want to use filter caps on the
input
> and the output, but its all in the data sheet.
>
> Lots of people around who can help. If you need more, just ask.
>
> John