How are dc generators able to generate constant dc voltage if the coil with constant velocity rotates in a uniform magnetic field

 

As the rotor revolves the commutator reverses the connections to keep the output polarity constant.
https://en.wikipedia.org/wiki/Commutator_(electric)

 

If you are talking a generator and not an alternator, the field is not a "uniform magnetic field". It is a variable magnetic field, controlled by the voltage regulator. This is also true for an alternator, except that an alternator puts out AC that is then rectified into DC.

 

And the voltage varies with time.

 

If you are talking a generator and not an alternator, the field is not a "uniform magnetic field". It is a variable magnetic field, controlled by the voltage regulator. This is also true for an alternator, except that an alternator puts out AC that is then rectified into DC.

So are u saying a dc generator actually produces ac then a rectifier comes up..?..yeah I think I kinda experienced that from my gasoline generator *key series..i put my hand on the terminal of the batteries after putting the generator on..to my suprise I received a shock which was definitely from the alternator charging the battery..#please Is there a rectifier in conjunction with the alternator charging the lead acid battery or it uses ac to charge which I dont think is possible

 

So are u saying a dc generator actually produces ac then a rectifier comes up..?

The commutator produces the same result as rectifier.
Car alternators include a rectifier, usually inside the alternator casing.

 

No, a car with a generator puts out DC. A car with an alternator puts out AC that is then rectified to DC. Generators and alternators are NOT the same thing. https://sciencing.com/dc-generator-vs-alternator-6164381.html