Automotive Alternator Technical Article

Go With The Flow
Current flow through an automotive electrical system can be compared to the storage and distribution of water. Large lakes and reservoirs are similar to batteries in that they store huge amounts of water for future demand. Holding tanks way up on the hillsides overlooking our homes and on top of towers in our backyards store the smaller amounts of water we use for short-term immediate demands. Capacitors store electrical energy in the same fashion. Pumps send the water through a series of pipes transferring it from the reservoirs to keep the smaller holding tanks full and then finally piping it to the consumer. These pipes must be large enough to prevent resistance, as is the case with power cables. Think of your alternator as the pump that keeps the reservoir filled and supplies all the water for the system. The water volume (i.e. gallons) represents amperage and the pressure from the pump that pushes the water is just like the voltage in an electrical system. The alternator supplies the pressure (i.e voltage) for the system, until the demand is greater than the pump can deliver. When this occurs, the reservoir or battery becomes the source for the pressure.
GLOSSARY:
CURRENT	The rate of transfer of electricity usually expressed in amperes.
AMPERE	The unit used to measure the quantity of an electric current flow.
GAUGE (Gage)	The physical size of a wire, which also encompasses all size ratings.
AWG (American Wire Gauge)	The standard for determining wire size. The larger the AWG number, the smaller the diameter of the wire.
VOLT	A unit of electromotive force.
HOW TO CALCULATE ALTERNATOR RPM
To calculate a vehicle's pulley ratio, the crank pulley diameter is divided by the alternator's pulley diameter. This ratio is then multiplied times the lowest and highest engine RPM. The result will be the vehicle's minimum and maximum alternator RPM.
CRANK SHAFT PULLEY DIAMETER
Alternator Pulley Diameter	= Pulley Ratio
Pulley Ratio x Engine rpm	= Alternator RPM
EXAMPLE:
7" crank pulley
2 3/8" (2.375) alt. pulley	= 2.95:1 ratio
2.95 X 6000 rpm	= 17,700 alternator rpms

SOURCES
Painless Performance 2501 Ludelle St. Fort Worth Te 76105	Autotronic Controls Corp. (MSD Ignition) 1490 Henry Brennan Dr. El Paso TX 79936
Powermaster Motorsports 2401 Dutch Valley Drive Knoxville TN 37918 423-688-5953	Optima Batteries, INC.
March Performance 5820 Hix Rd. Westland MI 48185 734-729-9070 www.marchperformance.com