Re: Considering a change from 37 to 61 am due to added Underdash AC
When I'm installing car amplifier's I'm adding to the load the alternator on the vehicle needs to keep up with and I hate to sell a customer or have him change the alternator if not needed so what I do is get everything installed and working and then turn it up to how loud the customer listens to it and then monitor the battery voltage. If the voltage stays steady at let's say 13.5V and does not slowly drop and drop, then there was enough reserve in the alternator to keep up with the addition of the amplifier BUT if I then see the battery voltage slowly going down from let's say 13.5V and then it slowly drops to 13.0V, and then slowly drops to 12.5V, and continues downward to let's say 10V, then the alternator is not keeping up.
Another thing with alternators is that a 37A model will have an output curve as well as a 61A will but at low idle speeds the 61 will probably keep up better if the total draw is let's say 35A and the motor is at a low RPM. A 35A rated alternator at idle might only put out 20A while a 61A at the same RPM might be able to output 35A.
Something I have not seen and I think is correct is GM used one main harness whether the car was equipped with a 37A or an optional 40's something amp or the even larger 60's something alternator to where if the car has a 37A originally, you can upgrade and not have to do wiring upgrades to those optional installed sizes BUT if you ever find yourself putting in a 90A, 100A, 150A, or larger, then wiring upgrades will probably need to be done as the original wiring was only sized to handle so much.