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QUESTION: Sir I want to know that how to install flywheel on alternator
I have 500w 3000rpm 220v single phase alternator
I want to install flywheel on this. But I dont know calculation
that is: what weight of flywheel;what radius;what speed:
sir please provide me formula for this
same for 220v single phase and 220v three phase..

ANSWER: Hello vinu,

I have decided that I need to ask some questions to help me understand what you need the flywheel to do for you.

What is the source of the power to rotate the alternator? Would it provide constant rotation speed or would it fluctuate?

Would the load on the electrical output of the alternator be constant or would it fluctuate?

Is your reason for the flywheel to make the rotation speed more constant than it would be without one? If not, explain what the reason is.

Is there a maximum radius for a flywheel that would fit in your machine?

Here is some information for you to think about:
The energy that the flywheel has stored when rotating at 3000rpm is given by
KE = (1/2)*I*w^2
The parameter I is called rotational inertia. For a flywheel that is a disk,
I = M*R^2 / 2
If you could obtain a flywheel that concentrates the mass at the rim (similar to a bicycle wheel), the formula for I would be double that for a disk:
I = M*R^2
Notice that with either flywheel design, the value of I doubles if you double the mass but quadruples if you double the radius.
The parameter w is angular speed in radians/s. 3000 rpm = 314 radians/s.  

The value of KE is an indication of how much the flywheel could help the speed remain constant. So I need to have an idea of how much help the system will require from the flywheel. If for some reason the source of the power to rotate the alternator falters, I need to know how much energy would need to be drawn from the flywheel.

How much can the alternator velocity be allowed to decrease?

If you can provide information on these points, please send a follow-up.


---------- FOLLOW-UP ----------

QUESTION: Sir I have a ac motor 90w 1440rpm and alternator is 100w 3000rpm and I want to install flywheel in this system and acceleration I want 100sec
[same like in a maruti800 car gravity acceleration( 70sec for 100km/hr) I want that ;in this car torque is 65NM @2500rpm max. 12" wheel and loading capacity is (car weight 650kg;450kg loading capacity ;total 1100kg)]
so, I want calculation to install flywheel on 90w ac motor 1440rpm I want to know,flywheel type, mass of flywheel, radius of flywheel, surface speed of flywheel, inertial constant of flywheel, KE, etc....

Hello vinu,

I still do not have a clear picture the motor and alternator are connected. Here are the 2 possibilities I can see:

The output voltage from the alternator is the power for the motor. If that is the case, what provides the power to rotate the alternator's shaft?

The motor gets its power from an unknown ac power source and provides the rotation for the alternator's shaft. If that is the case, there are 2 questions: what is the unknown ac power source for the motor and what is the alternator's output voltage used for?

I have a fear that you think you can have the motor provide the rotation for the alternator's shaft and have the alternator's output provide the electrical power to the motor. That would violate basic principles of Physics. A flywheel would not help.

Please provide more details.


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Steve Johnson


I would be delighted to help with questions up through the first year of college Physics. Particularly Electricity, Electronics and Newtonian Mechanics (motion, acceleration etc.). I decline questions on relativity and Atomic Physics. I also could discuss the Space Shuttle and space flight in general.


I have a BS in Physics and an MS in Electrical Engineering. I am retired now. My professional career was in Electrical Engineering with considerable time spent working with accelerometers, gyroscopes and flight dynamics (Physics related topics) while working on the Space Shuttle. I gave formal classroom lessons to technical co-workers periodically over a several year period.

BS Physics, North Dakota State University
MS Electrical Engineering, North Dakota State University

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