Re: [T3] 42 Volts (a bit long)

["Jim Adney" <jadney@vwtype3.org>]

On 6 Jun 00, at 11:59, Jaranson, John (J.W.) wrote:

> The second one first.  Plus it is a simpler answer.  42 volts is three
> times the current system output.  Yes, that's right. You have a 14
> volt system in your T3.  The battery is 12 volt, but the alternator
> puts out 14 volts. Similarily, the 42 volt system will have a 36 volt
> battery.  So it is just multiplying the current system by 3.  Why not
> a higher voltage?  The peak output of the 42 volt ssytem would be 58
> volts.  60 volts is the established upper limit for automotive
> applications considering all safety aspects including electric shock. 
> That's the easy answer as to why 42.

Okay, you've answered my first question of whether this is the real 
or the nominal voltage. Apparently they decided to switch to the 
"real" and get away from that confusion. Still, it's going to be hard 
to convince some people that it is okay for their new battery to 
measure just ~36-38V when it is just sitting there.

I don't get where the 58V comes from. By my calculations the max 
voltage should be ~43-44V. I don't see how you could get 58 
except under some very unusual fault condition. Once you allow for 
that, couldn't it go much higher? I think I can get 25 out of a type 3 
gen if I full-field it at high RPM with no load.

I think I recall that you can get a real knee-weakening shock from a 
45V battery, so this is already into a different realm, shockwise.

> Now the bigger question of why change at all.  Well, partly for the
> same reasons that cars went from 6 volt to 12 volt.  The electrical
> power demand of the car is overwhelming the system.  Modern cars have
> microprocessors all over the place, power everything, high intensity
> lights and tons of courtesy lighting. Modern cars use over 2 KILOWATTS
> of power and have over 2 kilometers of wiring.  As the power demand
> approaches 3 kilowatts, the upgrade to the alternator to meet this
> makes it too noisy and too difficult to cool.  There are already
> liquid cooled alternators in production.  Also, the wiring has to get
> progressively larger in diameter to handle the extra power
> requirements.  2 kilometers of wiring getting bigger around adds
> weight which hurts fuel economy.  It also make the wiring more
> expensive and harder to package.

2kW? Now? Really?  Well, maybe so; that only comes out to 139 
Amps. I suppose there must be 150A alternators out there. What 
is the largest OE alternator put on any of today's vehicles?

> Many of the advantages of a 42 volt system go directly to fuel economy
> improvements.  With gas prices hovering around $2/gal these days, we
> can probably all appreciate that.

I saw premium at $2.10 last week near Chicago. If that doubles 
we'll then be paying just about what the rest of the world has been 
paying for decades. I know it'll be painful, but it will be a good thing 
in the long run.

-
Jim Adney
jadney@vwtype3.org
Madison, WI 53711-3054

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