# Dynamo design with regenerative back mmf

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1. May 6, 2017

### Narayanan KR

In the above presented dynamo design, three snapshots taken during three instances during the rotor running.
In fig 1 the approaching magnet builds an induced voltage across the coil, however the circuit is still open, hence no current flows. In fig 2 when the rotor reaches TDC (top dead center) switch is closed leading to the flow of current into the load.
According to lenz law, this induced current flows so as to create north pole on the rotor facing side of the coil, and this will push the rotor away thus adding to the kinetic energy of the flywheel.
I wonder how the back mmf instead of braking the fly wheel, it pushes/propels the fly wheel, I hope you mates share your suggestions and critics on this idea, thank you.

2. May 6, 2017

### Staff: Mentor

Since no current flows in the coil while the switch is open, there is no storage of magnetic energy. Were you hoping that you found a viable Perpetual Motion Machine (PMM)?

Nice avatar, BTW.

3. May 6, 2017

### Narayanan KR

PMM?,I would never claim so. It was just a thought experiment performed within the rules of present physics and i was expecting an scientific explanation whether it works that way or not.
Even when coil is open it develops induced emf because of the changing magnetic flux linked to it, and the moment the load is connected across such emf current has to start flow.

4. May 6, 2017

### Staff: Mentor

How does current flow through an open circuit? Mate in 2...

5. May 6, 2017

### Staff: Mentor

At "TDC" the $\Phi$ is at a maximum so $d\Phi/dt =0$. There is no EMF and no induced current.

6. May 8, 2017

### jim hardy

@Narayan KR
You're approaching a 'magneto ignition'. Study up on that subject and you'll be better able to work your hypothetical machine in your head.

When you can explain its "E-Gap" in a couple concise sentences , please do. It'll both cement the concept in your mind and help other students of magnetics who stumble across this thread.

Did you make those nice drawings ?

old jim

7. May 8, 2017

### cnh1995

As Dale pointed out, there is no emf and no current at TDC. But as the magnet moves away from TDC, there will be an induced emf and current in the coil. The coil mmf should try to "oppose the cause" of the induction i.e. it should try to stop the magnet from going away.
So the coil should attract the magnet and reduce its kinetic energy.

8. May 11, 2017

### Narayanan KR

Yes sir..I did those drawings on MS Paint, and 'magneto ignition'....i believe it will be interesting.