<VV> MY ALTERNATOR CONVERSIONS
corvairs at pacifier.com
corvairs at pacifier.com
Thu Jul 29 17:15:00 EDT 2010
Well, belt life suffering is the effect. The cause is slippage, which
is, I would think, much greater than simply running the engine at 4800
rpms (which by the way would be pretty severe engine use) LOn
> Let's look at this comparatively. We know from the GM dyno test the fan
> and belt adsorb 14 hp @ 4,800 rpm on a late model. Let's consider that
> to be a 180 degree belt wrap on a 4" dia. sheave. The alternator has a
> 2.5" dia. sheave with a 85 degree belt wrap. The power transmission
> factor of less than a 180 degree wrap is calculated at 0.59 for 85
> degrees. The sheave ratio is 0.62:1 --- Thus 14 x 0.59 x 0.62 = 5.2
> hp. Conversion of HP to watts is 746 watts = 1 hp. Now consider the
> alternator at 60% efficient and the belt drive at 80% efficient so 5.2 x
> 0.60 x 0.80 = 2.50 hp. Converted to electrical terns is watts or in
> terms of amps 1862 watts /13.5 volts = 140 amps.
> Will belt life suffer? Yes, but no more than operating the engine at
> 4,800 rpm.
> One thing to remember -- HP transmitted by a belt is always a function
> of belt speed. The same Corvair fan belt that can deliver 100 amps at
> 6,000 f/s will slip if it tries to deliver 50 amps at 1,500 f/s.
> Fortunately alternator output is proportional to engine speed until the
> alternator reaches 6,000 rpm; then its output is constant until its
> rotor explosion speed of around 18,000 rpm.
> Jim Davis
> corvairs at pacifier.com wrote:
>> Tim - My youngest brother was a commercial custom electrical component
>> rebuilder for nearly 20 years and he said that anything over 75 amps in
>> Corvair alternator was a shaky proposition.
>> The reason is the small contact area on the pulley made by the Corvair
>> belt. You get much above 75 amps and start getting slippage and other
>> As usual, his standards were based on a safe margin, and like many
>> your experiences may vary.
>> Only 2 days left on our motor mount sale!
>>> i am running 100 amp "3 wire?" or more alternators on my rampy and 64
>>> coupe with no issues. the rampy has aircraft landing high beams , 100
>>> ham radio , gas heater , and heated seats. yes i upgraded a few other
>>> things along the way to cope with increased loads .
>>> i had 2 140 amp (real one wire units with the little module plugged
>>> in )
>>> units made at the local auto electrical shop that were the same
>>> for my boat. they also worked well , but we had to go to double pulley/
>>> on those.
>>> i bet the rampy draw gets right up there at times , but so far it works
>>> fine. dimmer switch was my first failure , so added a relay. that was
>>> running a new larger wire for battery feed up front , isolator for
>>> battery to run a marine refrigerator freezer on trips .
>>> i think there were photos posted on the old website
>>> (http://www.corvair.de/corvair_ham/corvair_ham.html) .
>>> i run a voltmeter in my spyder dashes to monitor .
>>> so far , i am very glad i did this upgrade.
>>> got the old 70's 80's gm alternators for $5 each cores at the junkyard
>>> then put new parts and corvair front and fan on them. i think they
>>> costing @$50 each by the time i was done. that was new aftermarket
>>> rotor ,
>>> field , regulator , and brushes .
>>> regards, tim colson
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