AC generators produce a different type of electric energy from DC generators, and both are best suited for specific applications. Alternating Current (AC) is typically found in the home and Direct Current (DC) is typically found in mobile or off-grid applications where batteries are used.

When a DC current is needed, people unfamiliar with DC generators will often use AC generators with complex electrical equipment when a DC generator could have provided a more efficient, reliable power generating platform.

There are, however, specific reasons when a DC generator should be used versus an AC generator. For example, the use of a DC generator is often more appropriate when charging banks of batteries, like those used with renewable energy systems, uninterruptible power systems (UPS) or backup power systems (BPS). DC generators provide a seamless energy supply directly into batteries without expensive switch gear and transfer schemes required with AC generators.

Some DC generators can monitor the state of charge (SOC) in battery banks to automatically start and stop battery charging. Intermittent battery charging combined with Grid power and/or renewable energy power is considered a hybrid power platform and the amount of fossil fuel burned is minimized. A hybrid energy platform provides an efficient and reliable power platform, with the added bonus of enhanced energy security from backup power in the event any natural or man-made disasters.
Often, renewable energy systems tend to be oversized to bridge any energy shortfalls during cloudy or non-windy days. The additional capital required to purchase and install the oversized solar panels, wind turbines and related hardware would cover the cost of a small DC generator, many times over. In this case it makes more sense to burn a few gallons of fossil fuel intermittently (typically over a few weeks) in a highly efficient small DC generator to see a greater number of affordable, smaller sized renewable energy systems installed.

A DC generator can be sized smaller than an AC generator for the same application and need only run intermittently to charge batteries. An AC generator must be sized to power the largest connected AC load at any one time and must run constantly, burning more fuel than a DC generator. As a result, the AC generator requires considerably more maintenance and would have a shorter life cycle. If the AC generator is not manufactured by a well known company like Honda, that product's expected life cycle and overall reliability may be reduced further.

DC power systems used in heavy industrial equipment, marine applications, or the telecommunications industry can be located in remote areas far away from the Grid. This typically means that service calls are very costly and time consuming. Internet-based communication packages are available on some DC generators and can allow owners or operators the ability to monitor and control a generators performance from anywhere in the world.

The following is a summary of what are considered the most significant differences between AC and DC generators.

 

  AC Generators DC Generators
System Connectivity Require a high degree of engineering and equipment costs to transfer power onto an isolated section of the electrical network. Do not require a transfer switch, energy flows seamlessly into a DC power system safely.
Expandability Cannot be connected in parallel without expensive phase synchronizing equipment. Can be easily connected in parallel to add capacity without special equipment. Polarity is the only concern.
Energy Quality and Stability Any change is RPM significantly affects power output quality. Speed control devices such as governors need regular service. Are not affected by engine speed variations and produce a constant and stable DC voltage.
Safety and Regulation Are normally 120 volts and above and require special certification for safety reasons. Alternating current can be deadly and cause serious injury. Low voltage DC generators less than 50 volts require minimal permitting and inspection by safety and regulatory authorities.
Sizing and Efficiency Must be sized to power the greatest combined loads that may be connected at one time. Smaller loads may be connected a majority of the time, but the larger generator still has to run at full speed the entire time. When charging batteries, can be sized much smaller to provide a steady charge current. Surge currents are supplied through the battery bank and act as a buffer.