Dynamo to charge battery using electromagnet.

[horizon79]

Homework Statement

A team on The Apprentice have to come up with a new electrical device. They propose a hand cranked dynamo to charge a battery which initially uses the residual charge in the battery to power the electromagnet, instead of a permanent magnet (the idea being that this reduces the weight of the device by removing the need for an iron core). Once current is flowing this is then used to power the electromagnet as well as charging the battery. A sketch of the circuit is shown in the attachment. Making reasonable assumptions about its size, the number of turns in the induction coil and in the dynamo coil, discuss the feasibility of the device. (I can't upload the sketch here, but basically it has the dynamo coil, the dynamo and the circuit resistance all in series)

Homework Equations

The Attempt at a Solution

 

[member 553083]

The device should be feasible, assuming that the size and the number of turns in the induction coil and the dynamo coil are chosen appropriately. The battery will act as a source of electrical energy, which will power the electromagnet. When current is flowing, it can be used to power the electromagnet as well as charging the battery. In order for the device to be efficient, the size and number of turns in the induction coil and the dynamo coil should be chosen such that the voltage output of the dynamo is greater than the voltage input required by the electromagnet. This will ensure that the device is capable of generating enough power to charge the battery. Furthermore, the circuit resistance should be chosen such that it is low enough to allow for a sufficient amount of current to flow, but high enough to prevent the device from overloading. Overall, the proposed device should be feasible if the size and number of turns in the induction coil and the dynamo coil are chosen appropriately.