How many watts brighter is Mike S than Mike E and how does it relate to MPG
increasing?

:)

Brendan

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf Of
Michael Elliott
Sent: Tuesday, November 13, 2007 3:12 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Hid AUX lamps GoWesty's headlight upgrade kit

Coolness. I knew all I had to do was to make an amateurish stab at the
math and someone who knows a lot more than I would provide the real
numbers. Thanks, Mike!

--
Mike "Rocket J Squirrel" Elliott
71 Type 2: the Wonderbus
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Utility Trailer. Ladybug Trailer, Inc., San Juan Capistrano
KG6RCR

On 11/13/2007 3:06 PM Mike S wrote:

> At 05:32 PM 11/13/2007, Michael Elliott wrote...
>> So, how important is the difference between 160 or 300 Watts of power
>> going to the headlights when compared to 100,000 watts moving the van?
>
> The point is valid, but some math is missing.
>
> The useful BTU capacity of gasoline is reduced by the fact that engines
> are very much less than 100% efficient, and there are also drivetrain
> losses before any energy is used to move the car.
>
> 20% efficiency is in the ballpark, so we're talking about 20K Watts
> actually being used. An A/C Vanagon has a maximum output of 67 HP, or 49
> KW, and would  cruise at some fraction of that (1/3?) , so all of those
> figures seem to be reasonable.
>
> 140 Watts of 12V power from the alternator is more than that from the
> engine, because alternators, too, are not 100% efficient. 55% is a
> reasonable ballpark, to that 140 W of DC takes ~250W of engine power.
>
> 250W / 20KW = 1.25%
>
> If a Vanagon gets 20 MPG, then the savings would be about the same as
> getting an extra 1/4 MPG.
>