Even a uniform rotor magnet configuration, that has all the magnets with the same polarity,  still has an alternating pattern of N - S, because there are VIRTUAL magnet poles of opposite polarity between those of the magnets.

This is really a question of  whether we have  16 or 8, N-S alternations.

Quote
B.t.w. the 1 waveform indication should be 1/2 waveform, since is shows only half the period.

I'll let you think about that one some more.   

EM

PS  You do have a point about the opposite polarity, but forget about Peter's waveform, it's really about the periodicity of that rotor modulation.

Quote from: EMdevices on June 24, 2011, 11:52:37 AM
Even a uniform rotor magnet configuration, that has all the magnets with the same polarity,  still has an alternating pattern of N - S, because there are VIRTUAL magnet poles of opposite polarity between those of the magnets.

This is really a question of  whether we have  16 or 8, N-S alternations.


I'll let you think about that one some more.   

EM

PS  You do have a point about the opposite polarity, but forget about Peter's waveform, it's really about the periodicity of that rotor modulation.

Im going to throw this out there one more time...

As the rotor magnet approaches the gen coil, the side of the coil that the magnet is approaching produces 1 half of the wave form. As the rotor magnet is leaving tdc of the coil, the magnets field drags through the other side of the winding producing the other half of the wave form.

If someone had an optical wheel on the rotor to track the rotors position in fine increments, then you could associate when and where the rotor magnet is along with the wave form and be able to see what im saying is true.

The field lines need to cross the windings to induce current.  When the mag is tdc, some field lines are on both sides of the coil, this cancels out induced current and we see the crossover point from one half of the wave to the other.

Mags

Quote from: chrisC on June 23, 2011, 06:56:12 PM

Thanks. I did see that reference you posted and I believe the resistor limiting base current is not going to affect the TIP42C  emitter current that much. He's running off 12V battery power and that 1N4007 even if at reversed biased charging (the battery) should not have pulled so much extra power.

I think you are right in that the series base resistance would not save the total current consumption significantly, because the two series driving coils (i.e. the load for the transistor) are placed in the emitter.  Any series resistor placed in the base would reduce the base current but then the  collector current would nearly supply the "missing" current to the emitter. 
I would  have been right for saving in the emitter current if the coils were placed in the collector, sorry for this. The advantage of using a series resistor would be to defend the output transistor in the Hall device from possible high peak currents at the lower RPMs of the rotor.

As to the rest of your reasonings, answers can only be had by practical tests.

rgds, Gyula

Quote from: Magluvin on June 24, 2011, 12:43:04 PM
Im going to throw this out there one more time...

As the rotor magnet approaches the gen coil, the side of the coil that the magnet is approaching produces 1 half of the wave form. As the rotor magnet is leaving tdc of the coil, the magnets field drags through the other side of the winding producing the other half of the wave form.

Mags

Mags,

This sounds very plausible to me. So in R_UK 's scopeshot i guess the approaching magnet first induces the negative spike, followed by the positive one (magnet is passed TDC). Is the flat bit in the trace nothing more than waiting for the next magnet to approach?

regards,

Dutchy

Some quote from wikipedia :
"Heins states that the steel rotor and driveshaft had conducted the magnetic resistance away from the coil and back into the electric motor. In effect, the back EMF was boosting the magnetic fields used by the motor to generate electrical energy and cause acceleration. The faster the motor accelerated, the stronger the electromagnetic field it would create on the wire coil, which in turn would make the motor go even faster. Heins seemed to have created a positive feedback loop. To confirm the theory, Heins replaced part of the driveshaft with plastic pipe that wouldn't conduct the magnetic field. There was no acceleration."