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Car Alternator Capacity

1/25/2004 6:02 PM
Rob Mercure
Car Alternator Capacity
I've got a friend I'm trying to advise on installing a far-too-loud car "stereo" for his teenage son. So far we've figures out the size of the farad range capacitor that he needs but when he checked on the output of the car alternator the parts store told him that the 2001 Grand Am - 4 cyl - had an 102 amp alternator! Somehow I just don't believe that such a small car would have such a large alternator - I remember when 60-70 watt alternators were used in police cars. Can anyone provide me with some info on this?  
1/26/2004 12:34 AM

Boy,I hope you mean 60-70 amp.
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1/26/2004 11:11 AM
Rob Mercure

Hey Enzo,  
Yer right - I did mean 60-70 amp. So I'm kinda worried that my friend is getting bad advice from the auto parts store 'cuz I just can't believe that a 100 amp + alternator would be put into a smaller car. Unless I'm mistaken alternator technology is "mature" and there really isn't much more room to tweak characteristics such as size - it's based on how much copper wire of a certain gauge you can cram into a specific space and I just don't see small car alternators - 2/3 the size of the old Delco/Autolite police units - putting out 1/3 again the output of the police units.  
1/26/2004 5:17 PM
A search of the AC Delco site pops up an alternator p/n 321-1782 for your car (with a few assumptions).  
This alternator is spec'd at 102 Amps.  
This is reasonable.  
Consider that an auto electrical system is low voltage dc. In order to get reasonable power (watts), an alternator is required to deliver moderately high current.  
If you add up the wattage rating of headlights, running lights, radio, heater fan, defrost elements, perhaps an electric cooling fan, electric fuel pump, battery trickle charging requirements, instrument panel, a factor of safety, etc. - all of which may be running at once, 102 amps is simply adequate.
1/27/2004 1:17 AM

Cars are a lot more electronic than they used to be. More lights, more bells and whistles, computers. ANy time you add 12 watts of something electric, you add another amp to the total. AS mentioned, the wires have become the limiting factor. The latest trend is the move to 42 volt systems in cars. Triple the voltage, third the current, triple what each wire can do.  
AS to size, the technology has moved along, and higher output units can easily be smaller than older units with less power capability.
1/27/2004 2:10 AM
But that's a damn big battery!
1/27/2004 5:43 AM
102 amps sounds perfectly reasonable. Modern cars have really hot ignitions, computers, pumps, actuators, solenoids, and the occasional huge stereo. Also, those big batteries that new cars have tend to eat a lot of current while charging...
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