Date: Sun, 23 Sep 2012 22:31:20 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Alternator continuous-duty rating?
In-Reply-To: <505F8CFA.5090400@gmail.com>
Content-Type: text/plain; charset="US-ASCII"
The Vanagon compartment really does not get all that warm. The open bottom
and some air coming down the rear pillars keeps the air exchanged. Rarley
does the stock alternator fail from heat so you are looking to solve a
problem that doesn't need solving.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Rocket J Squirrel
Sent: Sunday, September 23, 2012 6:28 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Alternator continuous-duty rating?
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_cu
> rve.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
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