Dennis writes to say, "[...] if you have 90 amps with a drop of 12 volts
you are dissipating 1,080 watts [in the alternator] as heat."

Has anyone looked at ducting cool air to the fan intake on the
alternator? Probably not. Am I boldly going where no man has gone before?

--
Jack "Rocket j Squirrel" Elliott
1984 Westfalia, auto trans,
Bend, Ore.

On 09/23/2012 02:19 PM, Dennis Haynes wrote:
> Get bit complicated but the limiting factor for an alternator is the
> internal resistance of the windings. Since it is really in series with
> everything if you have 90 amps with a drop of 12 volts you are dissipating
> 1,080 watts as heat. At 750 watts/HP you have 1.44 HP right there. For the
> alternator rpm it is the ratio of the circumference of the pulleys. You'd be
> surprised how fast that thing spins at 4000 engine rpm.
>
> Dennis
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> David Beierl
> Sent: Sunday, September 23, 2012 2:27 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Re: Alternator continuous-duty rating?
>
>> Just some context - with 90 amps at 13.6 volts, assuming 85% efficiency
>> the alternator will be sucking down about two horsepower from the belt
>> and dissipating about 225 watts as heat.
>
> Hmmm...Leece-Neville show this 90-A alternator using almost four horsepower
> at full output:
> http://www.prestolite.com/productinfo/alternators/8AR2112T/8AR2112T_curve.jp
> g
>
> I guess 85% is a bit optimistic.
>
> I've also been seeing alternators rated full output at 6,000 rpm, with max
> rpm of 6,500.  Our alternator spins a lot faster than that - just measured
> the sheaves, and alternator runs twice engine rpm or a bit more.
>
> And you're right, the big three-groove crank pulley is tapered, at least on
> the engine I just looked at (random 2.1l core).  I've been looking at that
> thing for twenty years now...in the engine bay, mostly.  Not that that's an
> excuse.<shakes head>
>
> Yrs,
> d