Join Date: Dec 2002
Location: Saint Louis, Missouri
No such thing as a dumb question. A 140A alternator should put out 140A maximum at and above a certain alternator armature speed (depending on pulley sizes the crank RPM may not be the same as the alternator's RPM). Below that speed it will put out less. How much less depends on the manufacturer. The 140A rating could have been measured at 0 degrees or at a temperature of like 200 degree's. Temperature effects the output also.
An alternator even though rated at 140A output maximum will be allowed to have that amount of output or less depending on the signal it is getting from the voltage regulator. If the car is running down the road the alternator might only be putting out 60A but if the headlights are turned on the output may be increased to 70A to compensate for the increased current demands. If the demands of an electrical system are more than 140A then the remainder is coming off of the battery (if you have a 200A total electrical system load hooked up in a system with an alternator putting out 140A maximum then you will be drawing 60A off of the battery) and eventually, since the battery is does not create electricity, the voltage will go down until the battery has nothing left to give and now the electrical devices are given reduced voltage and things like headlights will become dimmer and electric motors will spin slower as the alternator is trying to supply it all.
1974 Spirit Of America Nova (being restored), 1973 Nova Custom, 1968 Chevy II (Garage Find 2012)
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