Difference Between Similar Terms and Objects

Difference Between Dynamo and Alternator

Dynamo vs Alternator

The dynamo and alternator are two very similar devices that have the same function; to produce electric power via a mechanical input. Both dynamos and alternators use the same concept of electromagnetic fields to produce power. The main difference between dynamos and alternator is the type of current they produce. Dynamos produce a direct current that flows in the same direction. In comparison, alternators produce an alternating current, which constantly changes directions.

The part that allows the dynamo to produce direct current is the commutator. At its simplest, it is basically a fixed switch connects and disconnects as the shaft turns. The commutator constantly changes the polarity of the output current so that the output is always of the same polarity. Without a commutator, a dynamo would simply produce alternating current just like an alternator. But, the commutator adds another point of possible failure, which lowers the reliability of the device. Even more so since the commutator contacts are constantly moving and wear down quite quickly due to friction.

Direct current is desirable because most of our devices need direct to function. Anything with semiconductors, which includes pretty much all appliances and gadgets, require direct current. Although we need direct current, the power supplied to us via our mains is alternating current provided by alternators. This is because it is easier and more efficient to transmit power via alternating current. Converting AC voltage to thousands of volts for transmission then reduced to usable levels at the receiving end can be easily achieved via transformers. The same is very difficult to do with direct current. The alternating current is then easily converted to DC at the homes by rectification using solid state devices.

Power generation via alternators is the widely accepted practice around the world. Even vehicles like ships, cars, and motorcycles use alternators to charge their batteries and provide power to the accessories. On the other hand, dynamos are rarely if ever used to produce power but are still in widespread use as motors. Devices that use motors but rely on batteries for power use dynamos, since it can be run via DC. Toys, power tools, and other devices are some examples of things that use dynamos.


  1. A dynamo produces direct current while an alternator produces alternating current
  2. A dynamo has a commutator while an alternator doesn’t
  3. A dynamo is less reliable than an alternator
  4. A dynamo based system is less efficient than an alternator based system

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