# Ganerator and Alternator

1. Nov 29, 2005

### karim102

Hi ,
How are you? I am a again. I've question about what is diffenent between Ganerator D.C and Alternator. I know the Alternater always give us A.C but we use rectifier when we wanna D.C, but what is the better Generator D.C (it is one Machine) Alternator, when we wanna D.C? because I think the Generator is better when we wanna D.C cuz it is one machine. and it is so cheap then Alternator.

Thanks
I appreciate it :!!)

2. Nov 29, 2005

### ranger

While DC generators work on the same general principle of electromagnetic induction, their construction is not as simple as their AC counterparts.

That is a basic diagram of a alternator. BAsically the switching of the polarities of the voltage and direction of the current are changed because of the chaning magnetic field.

That is a basic diagram of a DC generator. The coils are the key difference. In order for a DC generator to produce constant voltage, rather than brief pulses of voltage once every 1/2 revolution, there are multiple sets of coils making intermittent contact with the brushes.

The relative simplicity of an alternator translates into greater reliability and lower cost of manufacture.

Last edited: Nov 29, 2005
3. Nov 29, 2005

### gschjetne

A rectifier bridge isn't very complicated, nor is it expensive. Possibly even less so than a set of commutators.

Also, my Private Pilot's License textbook offers the very scant explanation that alternators are preferred in light aircraft over generators because they generate a higher voltage at lower RPMs.

But I don't see why. Faraday's law still holds!
$$\varepsilon = -N \frac{d {\Phi}_B}{d t}$$

Besides, the book is full of typos. It's a miracle I passed the exam.

Last edited: Nov 29, 2005