Cars don't use generators because the batery is already generating energy. They use alternators in order to convert the energy generated into a usable form.
Direct current can be generated by a generator. Generators are not as efficient as alternators ( that generated AC power ). Vehicles use direct current but come equipped with alternators. The AC power is rectified ( changed to DC ) for use.
Multiple generators are when you use several smaller generators instead of one larger one. For example, you might use multiple 10Kw generators instead of one 30Kw generator.
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That depends on where it is used. As a general rule an "alternator" produces AC and a "generator" produces DC. Car Alternators have diode assemblies that make them generators by the time of 'output' so the terms are synonymous with each other. On cars they are normally connected to the engine by a belt or gear and spun by the crankshaft of the engine. Some cars tie this to the wheel or drive shaft (very rare). On Bicycles (yes some use alternators instead of generators) they are tied to the chain, or wheel. On Lawnmowers (and other garden equipment) they are fixed placements and the flywheel of the engine contain the magnetics - although not a true alternator, they are still termed as such. On some planes a separate smaller jet engine is used to generate electricity. Your home has several alternators (believe it or not) - Computer power supplies for instance are actually alternators in function (though not by mechanical means). Fan's will also produce 'voltage' if you spin them fast enough (not suggested).
The generator charges the battery! In an automobile, the battery produces the electricity to start the car. Starting the car takes electricity out of the battery. The car needs to replace the electricity so it will start again the next time. The generator produces the electricity to recharge the battery so the car will start the next time. Cars today use Alternators not Generators. Generators have not been used in autos since the mid 60s. Alternators unlike a generator can still charge a battery even with the engine idling. Alternators are more complex but much better at handling todays high demands for current on modern cars with all the associated electronics.
Wind
Depends on what type of generator you are talking about. A Generator in an older car uses energy from the engine to produce electricity. New cars use alternators. A generator for a house can use Natural Gas, Propane, Diesel, Gasoline, or just about any combustible fluid. There are also wind and hydro electric powered generators.
you can use electric cars instead of regular cars that use gas.
The main alternators use electromagnetic windings "excited" by auxiliary generators whose own magnetic fields are of permanent-magnets.
A "generator" usually produces DC current. An "alternator" usually produces AC current. Older cars up to the 1960's used generators. Newer cars use alternators (simpler design) with diode rectifiers to convert the AC to DC. Batteries are DC. Some electronic circuitry (inverters) can change DC to AC.
Some information about standby generators can be found here. http://www.generatorjoe.net/html/stepxstepgenerator.html According to this article, standby generators are for emergency use only. You should use a prime generator instead if you are lighting up your patio lights daily.
Venice, Italy has canals instead of roads, so they use boats instead of cars.