# How does RPM and the Number of Coils affect a Generator output?

I’m making a simulation where the user inputs a value of force to apply to turn the generator. This is used to calculate torque and then rpm. The user can also decide how many coils the generator should have so he can adjust for the voltage.

The problem I’m having is that because I accounted for the mass of the coil. So when the user adds more coils the mass he has to turn is increased thus the he turns it slower due but because of the increase in number of coils the voltage stays the same.

Since the force is applied for the same amount of time and it is giving a lower voltage (with more coils) I get a lower output power thus lower current. (I know something is wrong here)

• Increasing the rotor mass should not affect how fast the prime mover is able to turn it. That should only affect how quickly the prime mover can change the rotor's speed. – Solomon Slow Mar 27 '18 at 20:41
• But to get angular acceleration in order to get the rpm, you need to account for the mass @jameslarge – J A Mar 27 '18 at 20:45
• That's my point, exactly. I'm assuming that the torque that the prime mover can exert on the shaft is limited. Increasing the mass of the rotor does not limit the maximum speed that can be attained with the limited torque, but it does limit how quickly the rotor can be brought up to any given speed. – Solomon Slow Mar 27 '18 at 21:15
• Okay, so how would I calculate this? What is do now is 1. Calculate torque 2. Get total mass of coil 3. Calculate angular acceleration a=t/MR^2 using mass of coil. 4. Get rad/s with a x (amount of time force is applied)  then convert to rpm 5. Calc coil area and get emf @jameslarge – J A Mar 27 '18 at 22:01

## 1 Answer

You mix steady state process and transient process. For transient process, the mass (or moment, to be more accurate) is needed. For steady state, it doesn't account.

For a steady state, if you input rpm and number of coil, you can get current and emf. This would give the power output. Energy conservation needs the power input equals to the power output. The power input is the multiplication of torque and rotation speed. If the torque is input, then by this equation, you can get generator's rpm by equating input power and output power.

• How would I calculate rpm of mass is not needed? – J A Mar 28 '18 at 7:20
• To get rpm I have to get the angular acceleration from the force which requires to account for the mass @user115350 – J A Mar 29 '18 at 7:20
• when the generator speed is not the specified rpm, you need to know moment in order to calculate angular acceleration. However, it can be large or small and is a transient simulation. When the generator speed is maintained, you don't need mass as there is no change in speed and no angular acceleration. – user115350 Mar 29 '18 at 14:34
• I do understand that when the generator speed is maintained you don't need the mass as there's no change in speed. In my case the user will apply a fixed amount of force for a fixed amount of time this will cause the generator to have an angular a acceleration regardless of rpm. – J A Mar 31 '18 at 7:25