Why does a heavy duty vehicle require a special alternator?

Looking back at commuter cars or SUVs for a second, let’s think again about the electrical load required to be satisfied by their alternators. There are not electrically powered devices beyond the radios, dash and head lights, and heating/air conditioning fans that alternators need to power. In a vehicle such as a fire truck, however, there is an enormous electrical load , especially when the vehicle is operating at idle working at the scene of a fire. The same goes for refuse collection vehicles and utility company bucket trucks – all of these vehicles have one thing in common: a large electrical load that must be satisfied at idle. A simple, run of the mill stock alternator does not handle this well. The most important specification for these types of vehicles is a heavy duty alternator that performs well at low engine RPM and at engine idle.