An alternator on steroids

The first generators we developed within the Parker project were permanent magnet devices with sophisticated three-phase controllers. These approached 90 percent efficiency in terms of converting mechanical input energy from the engine into electrical output energy. We added a seawater cooling circuit with a small pump. We could run the generators all day at full continuous output, but they were expensive to build and install. As with so many systems derived from automotive hybrid technology, the cumulative cost looked to be prohibitive.

And then we came across a modified form of alternator technology that combined permanent magnet technology with a conventional alternator rotor, which required a much simpler controller that would be cheaper to build. This considerably reduced the cost — for the sacrifice of a few percentage points in efficiency. We experimented with four different construction configurations before determining an optimum version for our application. We know there are additional ways we could boost alternator efficiency, such as hairpin stator windings, but have not explored them as we believe we are at a point of rapidly diminishing returns from a cost/benefit perspective.

As with an alternator, our alternator-based devices are air-cooled. This makes installation really simple. However, even at 85 percent efficiency, if a device is running at 8 kW, it will be generating over a kilowatt of heat. That’s a lot of heat to have to remove, especially from the typical cramped and well-insulated engine compartment on a recreational boat. To prevent overheating, we ramp down the output if a temperature threshold is crossed. The engine compartment on my boat Nada is particularly tight. In a warm climate, at full output the temperature threshold can be reached in as little as 10 minutes, but thereafter the output stabilizes between 6 kW and 7 kW.

To put this in perspective, that is two to three times the maximum output I have seen out of any previous high-output alternator. With AGM batteries, the charge acceptance rate of the batteries rapidly becomes more of a limiting factor than generator heat. With lithium-ion, the additional engine run time to fully recharge a battery pack will be minutes rather than hours.

By Ocean Navigator