Date:         Fri, 12 May 2000 16:24:39 -0500
Reply-To:     Marshall Ruskin <mruskin@PANGEA.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Marshall Ruskin <mruskin@PANGEA.CA>
Subject:      Re: What is the simplest way to get 12V in a 24V VW electrical
              system?
Comments: To: David Marshall <vanagon@VOLKSWAGEN.ORG>
Content-Type: text/plain; charset="iso-8859-1"

<snip>
>Take two 12V lights and wire them in series (12+12=24).  Use these at
>daytime running lights or something simular.  Attach a 12V device in
>parallel to one of the lights as the difference across one of the lights
>would be 12V.  I guess the flaw in my logic might be that if they were two
>IDENTICAL 12V lights then they would take 12V each... if one light, or one
>light and the 12V accessory attached to it take more current than the
>other, the voltage will be different... am I right or am I wrong?
>
>Thanks!

Hi David:

Sorry, but you're wrong. ;>)

(I have a feeling a lot of people are going to say that.)

As soon as you tap off the 12 volts across one of your lights using your
load, it no longer is 12V anymore.

VNew_Load= 24(Light2 ||(new_load))/(light1 +(light2||new load))

The symbol "||" means the parallel equivalent of. A new value of resistance,
in other words.

To solve your problem you have two options (at least):

1.    convert 24VDC to 24VAC, using a switching circuit, a filter, and then
use a tranformer to step the ac voltage down - then convert it to a DC with
a bridge circuit and some filters.

2.    connect a voltage regulator circuit that will output 12 V. You're
gonna need a hefty heat sink, I'm afraid. You may experiment and see if the
voltage regulator off of an alternator will work for you. Gonna need a big
heat sink - depending on how much current your load will draw.

Make sure that you fuse the source and load sides of the circuit, K?

Do not kill yourself, please.

Marshall Ruskin
84 Westy "Iron Igloo"