AC generator vs DC generator

It will mainly depend on the application. The automotive industry went from generators to altenators in about 1965 because by using an alternating current they were able to use electric mangets for the field coils instead of permanent magnets.

The effect was a stronger magnetic field which meant a stronger charge (more amps and volts).

The downside is that you can not charge a dead battery with an alternator. There has to power for the electric magnets to work. A generator does not not care.

Now, for elevators, they use an ac motor to drive a generator to drive a dc motor. They give off a lot of heat and wasted energy by doing that, but it is less than for a rectifier. But fairly recently, Montgomery-Kone developed a rectifier and a small motor system that attaches to the side of an elevator. It is good for smaller buildings and does not have the the reach a normal cable elevator has. But it has a greater range than a hydraulic elevator.

I hope this helps some.

Most D.C. Generators are not as efficient as an alternator like is on your automobile.

An alternator has the pickup coils in the stator and is 3 phase rectified to make D.C. The rotor has the excitation windings and more magnetic lines pass thru the stator. The strength of the magnetic field can be varied to get more output at the same rpm. Generators , however, must be increase the rpm to increase the voltage and amperage available.

Older cars with D.C. generators could hardly keep up with headlights, radio, and air conditions. Alternators (properly sized) will increase output up to the point of destroying the rectifiers. Many people make the mistake of running their engines while trying to start another car with a dead battery. Hence, the alternator increases output and fries the diodes. Turning off the car after letting the other battery charge a while will avoid this. (Experience Speaking!)

Main reason in the auto industry was the alternator ability to generate voltage at slower rpm thus, keep charging the battery even at at idle.

Wangito

With alternator (AC generator) it is easy to get Constant voltage. As one commented at low RPM also you get the voltage. Also you can avoid Corbon Brushes.

is it the case for charging a small battery too ... which one is the best for the purpose. Since the battery is DC , we must use a AC generator requires the use of a rectifier.

The original post caught my attention, and thought I'd reply. Yes, as another stated: "depends on the application". Within that, what is the input requirement? Output requirement: Volts/Amps/Watts or KVA?

As one possible: today's AC-DC power supplies can provide over 90% efficiency and with PFC, relatively HV and in the multiple KW range! But maybe this is not at all in the ballbark of what the Guest is looking for. Maybe he is only seeking something in the mW arena?

Meanwhile, the inputs seemed to migrate toward and automotive application. I didn't see where the Guest cited that.

Most people related to automobiles because that is where the most common example of alternators replacing DC generator.

However one contributor is wrong as the alternator still has carbon brushes in its slip rings, in fact the most common failure of automobile alternators is the carbon brushes.

Speed, positioning and creep controls is better done by DC and as said, a lot of lifts use DC motors powered by rotary inverters from A.C.

In real terms you get more electrical energy for your input from alternator.

At the other end of the spectrum DC current was used for power distribution from early power stations. Obvious it could not be transformed and volt drop was a serious matter - limiting the distance of transmission.

AC solved this problem by transforming the alternator output to high voltage transmission and reverting back to low voltage at the point of use.

Not all alternators have slip rings. Self-exciting synchronous alternators don't have them, instead relying on residual magnetism to get started. At least the 50KW ones we had on our container cranes didn't. These were used to provide lighting, receptacle, and power for 3-phase motors, power for the control circuitry, and excitation for the DC generators and motor fields for the DC motors. Motor armature current was provided by one each 100 and 300KW DC generators. DC motors and generators always have carbon dust to cause grounds and commutators to maintain. AC generators are usually cleaner and easier to maintain.

I am looking for the power only in mW to charge a battery and use the stored electricity for use in different applications

all rotary mechanical generators are AC generators, RIGHT, the ones they call DC used brushes & copper commutator to pick off the half cycle of the AC at the right time to give you the pos & neg for the DC voltages for your battery or what ever others needs or uses Leece--Nee ville manufactured alternators for police cars and other high use power in Mobile machines, these used selenium or copper oxide rectifiers that were large & bulky what made the difference was the silicone rectifiers which were small & efficient perry

Across the board Generators lose out in efficiency and maintenance costs to Alternators. Mobile traction applications (Locomotives and Off Highway Vehicles) superceded generators in the 1970s. Draglines on the other hand kept Motor Generator sets for much longer. The motors and Generators in this application have been compound wound for the specific application and use a modified Ward Leonard control system. Even in this specialised application AC traction is taking over gradually.