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No Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Mon, 23 Jun 2003 13:29:27
In Reply to: Re: Alternator upgrade for 88 900 turbo conv, Chuck 88 900 Conv, Mon, 23 Jun 2003 11:57:56 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The size of the battery and alternator have nothing to do with each other.
The purpose of the battery is to provide power to start the car. The measure of a battery is CCA, or Cold Cranking Amps - how much current it can produce cold. The alternator doesn't come into the picture until the engine has started and is running on its own.
Once the engine is running, the alternator provides all the electrical power the car needs. The alternator also charges the battery, to replace the power that the battery used to start the car. As long as the alternator voltage is greater than the battery voltage, the battery charges. As the battery charges, its voltage increases, and once fully charged, takes no more current. So a bigger alternator doesn't require a different battery.
The voltage regulator, well, regulates the voltage. Normally, an alternator's voltage would increase the faster it spins. So you'd get a lot of voltage at high rpm, and lower at idle. The purpose of the voltage regulator is to control the alternator's output so that it puts out pretty much the same voltage at idle as at full rpm. Now, the more the electrical load (more lights, blower on high, etc.), the more current gets pulled from the alternator. This would cause the voltage to drop, so the VR compensates.
But the VR can only do so much. If you have a smaller alternator (say, 80 amps), the most the VR can do is ask the alternator for 80 amps at 13+ volts. If you have a bigger electrical load, the voltage will drop. If you have a 115 amp alternator, the VR has a little more leeway.
Think of it this way - you've got a little Hyundai with a 100 hp engine (80 amp alternator), and a nice 9000 Aero with a 225 hp engine (115 Amp alternator). You are the 'regulator'. If both cars are lightly loaded, and you want to keep the same speed (voltage), you can press more or less on the accelerator as you go up hills. As long as both cars are lightly loaded, and the hills aren't too steep, you can keep the speed up equally - both cars are the same.
Now, fill both cars with people, luggage, and a roof rack full of kayaks. Add a head wind. Going up hill, you can press the gas pedal to the floor of the Hyundai, and it's going to slow down. It can't keep the speed (voltage) and you can press only so far on the pedal. Whereas with the 9000 Aero, you don't have to floor it - you can keep up the speed (voltage).
posted by 192.249....
, Mon, 23 Jun 2003 09:44:36
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