Alternators

"Your alternator" is not what is causing the overcharging except in rare instances. Might be a grounded brush if it's an isolated field, might be a short to ground in the rotor. That would be rare

MUCH more likely is (in no particular order)

1....Poor ground condition between REGULATOR and BATTERY
2....Voltage drop between REGULATOR and BATTERY in the harness/ bulkhead connector/ ignition switch/ connectors
3....Fairly rare is a defective regulator
4...Sometime a defective battery will cause this.