The alternator generates all the electrical energy stored and consumed on the vehicle. Today’s alternators use the engine to create electrical power both to recharge batteries as well as to power electrical loads while the engine is running.
Alternators are offered to the market in two efficiency ranges. The standard alternators generally have a maximum efficiency rating somewhere in the 55–60% range and the high-efficiency models are generally in the 68–75% range. These efficiency gains are mostly due to using conductors that allow greater fill of the windings in the alternator.
Versions that operate at higher efficiencies place less load on the engine.
It is important to note that alternators typically consume 0.5–1% of the truck’s fuel to perform their function, so any fuel economy gains from new technology will be modest.
The study team developed a Confidence Matrix, an OEM Availability Matrix and an Engine-driven Accessories Power Use Chart to assist fleets. The Confidence Matrix is designed to inform fleets of the study team’s confidence in the technology being studied vs. the payback the fleet should expect to receive from the technology. Technologies in the top right of the matrix have a short payback, usually thanks to their low upfront cost, and moreover are found to have enough performance data that fleets can be highly confident in those short payback times, usually because the technology is more mature or otherwise has a more substantial track record of results. The OEM Availability Matrix shows the current availability (as of March 2017) of these engine-drive accessories at the various truck builders. The Engine-driven Accessories Power Use Chart shows the various places the energy from fuel is used in a Class 8 truck.