GM Alternator

I have a new GM car and am interested in the way the alternator seems to work i.e. when starting it goes to 14+ volts which I assume is replacing the current drawn due to starting. It then returns to 14 volts for some time. However after a period of time it fluctuates from what I am guessing is 13.2 volts and 14. I have had little time to explore this but it seems to me that the if the speed is high enough it stays at 14 but if it is slow it drops to 13.2 (this may not be true) I am told this fluctuation is normal but would like to know more about how this works. Not been able to find anything on web.

Put black tape over that gauge and stop watching it. It will drive you crazy. You don’t know the accuracy of the gauge. It may be reasonably accurate, and it may be ballpark accurate. Ignore it and enjoy your new car. The charging system will do what it needs to do. Don’t worry about the numbers, they are meaningless.

Sort of agree with mcparadise. This gauge doesn’t deserve that much attention. Occasionally glance at it and only be concerned when it indicates less than 10. The voltage regulator is the cause of the fluctuations you’ve observed, and it appears to be working fine.

Sorry guys but I want to learn about the operation and not stick my head in sand. I was hoping some one on here had technical knowledge to help. I guess I’ll have to look elsewhere.

Initially, you’re looking at the result of the topping charge being applied to the battery. The battery is used to start the engine. Once the alternator is turning, it supplies all of the current needs of the electrical systems and replenishes the charge lost in the service battery. Once the battery is fully charged, the charging system simply responds to the current demands of the vehicle electronics. The faster you rev the engine, the more energy is being consumed per unit of time. The alternator output is ramped up to meet that demand.

The alternator needs to be spinning at a pretty high RPM in order to generate the full ouput power it is capable of. At idle speeds the unit may not be able to produce all power that is being drawn by the load on the battery so the voltage level drops down to the charge level of the battery. There is a voltage regulator also in the system that keeps the voltage produced by the alternator at a specified range, between 13 to 15 volts roughly. As long as the battery voltage stays in that range things should be ok.

There should be a lot of info available on the web that talks about this subject in better detail.