A dynamo is an electrical generator. It works on the principle of using rotating coils to convert mechanical rotations into direct electric current. Dynamo generators were the first large-scale generators available to deliver large amounts of power to an industrial complex. It was the forerunner to present day electrical generators such as the electric motor and the alternator. Dynamos are obsolete today because of the widespread use of alternating current, the simplicity of converting alternating current to direct current and the proliferation of small solid state devices that require small scale, more efficient power sources. Regardless of the size and make-up, dynamo generators obey ohms law where current equals voltage divided by resistance.
Locate the specifications for the rotating coil. Find the manufactured measure resistance level. Resistance decrease is proportional to the cross-sectional area of the rotating coil assembly. For this reason, resistance tend to be low for dynamo generators. As an example, assume 0.005 ohms or 5 milliohms.
Determine the voltage rating of the coil from the specification. Because of the low resistance, the amount of voltage produced across the rotating coil assembly will be low. As an example, assume 2 volts.
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Determine the current by dividing the voltage by the resistance. Using the examples above, the current flowing through the rotating coil is 400 amps (2/0.005).