Good point Alister, just wanted to add-

When calculating the output it is best not assume 14 volts, there is
voltage drop and other reasons why you hardly ever actually _see_ 14.5 volts.

Even so, if you calculate out (12v*90A)*.667 = 720.36 watts. Still a bunch.

The other thing to consider is it takes mechanical energy to 'generate'
the electricity. This means you will loose more HP to the Alt the higher
amperage you choose.

I also think if you RELAY all those lights and make the travel of
electrons efficient around the car you will be fine with the 90A unit.

hth,
TBerk

Alistair Bell wrote:
>
> A couple more points...
>
> Alternator output is listed on the alternator, for example my 90A Bosch has
> this bit of code: N1-> 14V 34/90, which translates to 14 volts at 3400 rpm
> (alternator speed, faster than crankshaft speed due to pulley size), and 90
> Amps.
>
> But it is commonly assumed (i love that phrase) that maximum continious
> alternator output is at best only 2/3 of their max rating.
>
> So with that in mind:
>
> - Dave C. will have 460W of light producing apparatus up front
> - A 90 A alternator will continiously produce 0.667(90A*14W) = 840W
>
> Leaving 380W "spare"!
>
> (the 55A alternator will be able to produce 0.667(55A*14V) = 514W)
>
> Also remember that this doesn't take into consideration losses due to wiring
> resistance etc.
>
> BTW Dave C., my alternator is currently (!) handling a 450W light load with
> no
> problems, don't have the killer stereo though.
>
> Alistair
>
> on 26/6/01 7:08 PM, David Marshall at vanagon@VOLKSWAGEN.ORG wrote:
>
> > Making things a worse case scenario...
> >
> > P   = I x V
> > 460 = I x 12
> > I   = 460 / 12
> > I   = 38 Amps
> >
> > Unless you have a killer stereo a 90A alternator should be fine.  If you
> > have a 55 Amp alternator maybe you should upgrade.
> >
> > David Marshall
> >
> > -----Original Message-----
> > From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf
> > Of Dave C.
> > Sent: June 26, 2001 6:59 PM
> > To: vanagon@GERRY.VANAGON.COM
> > Subject: 130Amp alternator upgrade?
> >
> >
> > I think I remember someone saying that there was a Jetta alternator that
> > would bolt in to provide 130 amps. Anyone remember the particulars?
> >
> > My ride is an 85 GL Westy with soon to be 460 watts of light up front (260w
> > now).
> >
> > Cheers,
> > Dave C..