Rotating Magnetic Field's and Inductors.

[gotoluc]

I made an error in the above circuit.

Please find the correct scope shots below. First is with the rotor then the next is without and below is the same but with math.

Luc

[tinman]

OK,after many attempts to get to the workshop to get this done,here are the result's.

MH
If this is not how you wanted it done,let me know.

The video is unlisted,and no adds,so you must use the link below to view.


Brad


https://www.youtube.com/watch?v=vL6uBgDoVaY

[MileHigh]

Brad:

Great first clip.  On the measurement side the percentage efficiencies without the rotor are clearly not that great and I am wondering why that is.  Some possible candidates include 1) there are major losses due to the core material, 2) the measurements are off because you are not using non-inductive CVRs.  There may be some others that I am not thinking of.

I can't believe that I didn't mention the use of non-inductive CVRs because that has been drilled into my head over the years and it especially applies to cases like this where when the transistor shuts off and you have an instant switch-on of current. If you have an analog scope you should take a look at the waveform across the power-out CVR.  Crank up the brightness and see  if you can see any leading and trailing spikes on the output current pulse from the coil.  There are also simple filtering circuits that give your multimeter an assist for making the average current measurement but I don't know if you really need them.

Please see the attached diagram compliments of Verpies that shows you the energizing efficiency for a coil when you are pulsing it.  If you measure the resistance of the coil wire and the inductance of the coil, then you can calculate the Tau for the coil itself.  If you are pulsing the coil for a fraction of the Tau time then your efficiency should get very good.  For example, at 0.25 Tau the ratio is 6:1 for energy stored vs. energy dissipated when energizing the coil which translates into 85.7% efficiency in energizing the coil. Then that energy is pumped into a 12.6 volt battery with a relatively short pulse of current.  So let's say for the sake of argument the discharge efficiency is 80%.  That means the overall efficiency should be about 68% and you are nowhere near that.

MileHigh

[MileHigh]

Carroll:

Quoting myself:

Fantastic work like usual Itsu.

For you scope traces, this time after taking a one-minute look, I cannot see any appreciable differences between the two waveforms.  However, your multimeter is showing slightly higher voltage across the capacitor which is telling us that slightly more current is being drawn by the drive coil when the rotor is stopped.  This is to be expected because there is no influence from any counter-EMF in the drive coil from the moving magnets in the spinning rotor.

With respect to attempting to measure the added power that has to be pumped into the drive coil to make the rotor spin, that could be done.  However, that would require some thought and careful preparation and developing the right measurement regime to detect it.  Right now what is happening is that when the rotor is in place and spinning, the reduced current draw due to the counter-EMF induced into the drive coil is overshadowing the extra power that is added to make the rotor spin.  In other words, the preliminary analysis is that more current draw is reduced due to the counter-EMF than the extra current draw that is required to make the rotor spin.  There are two opposite effects that are happening at the same time with respect to the current draw and it is not necessarily that easy to separate them from each other.

Then you said this:

MH,

Did you read what you wrote?  You just posted that the magnets are generating more power back into the coil than the extra power it takes to turn the rotor.  That has to mean the system is more efficient with the rotor than without.  I am amazed you can't see that.  Every single person that has done this test for you has shown you that either the rotor made no difference (only one as I recall) or in all other cases the input power went down.  I just don't understand how you can keep saying adding a rotor is not making these systems more efficient.

And by the way you never did comment about why so many industrial motors now have permanent magnets in them since you claim magnets can't do any work.

Respectfully,
Carroll

>>>>

Okay, let's take a look at what I said and your follow-up comments.

I am suggesting that there are two effects happening on the current draw at the same time and one is masking the other.  You, on the other hand are suggesting that, "magnets are generating more power back into the coil than the extra power it takes to turn the rotor."

The magnets are not "generating power back into the coil."  The moving magnets are inducing a counter-EMF in the coil and that's a completely different thing.  All the counter-EMF is doing is reducing the current draw of the coil.  That's it, there is no power generation.  Here is an equivalent effect:  Imagine as a thought experiment where the rotor is turning but there is only power provided by the coil to make it turn, but there is no counter-EMF from the moving rotor magnets.  Instead, we have "replaced" the counter-EMF with a small DC battery placed inside the coil that produces a DC counter-EMF that is equivalent to the moving magnet counter-EMF. We run the test and we get exactly the same results.  Can you imagine that?

So that suggests an interesting test, a test that should be able to measure the "masked" power required to make the rotor turn.  Again, the assumption is this:  We can't directly measure the power required to make the rotor turn because two effects are happening at the same time that counteract each other:  1) counter-EMF due to the moving rotor magnets is reducing the current draw of the coil and doing nothing else, and 2) the power required to make the rotor turn is increasing the current draw of the coil.

The simple test is this:

1)  Run the pulse motor with the rotor spinning with a narrow and efficient pulse and measure the average power draw of the coil and the average power in the back spike as accurately as possible.

2)  Now, keeping the exact same pulse width pulse the coil without the rotor in place.  For starters, we will expect to see an increased average power draw from the coil, and also an increased average power in the back spike.

3) Here is the step where we should (finally) be able to measure how much power it takes to make the rotor spin:  With the setup unchanged from step 2) above, we will now slowly reduce the voltage that we drive the coil with.  By slowly reducing the drive voltage on the coil, we are in effect emulating the counter-EMF from the (now not present) moving rotor magnets.  Here is the key point:  We slowly reduce the drive voltage to the coil until the average back spike power is identical to the average back spike power in step 1).

Finally, you compare the coil average input power in step 1) with the coil input power in step 3).   Note that in both cases we have the identical average back spike power.  All that we did was lower the drive voltage in step 3).

If you do this carefully, you should see that the average coil input power in step 1) (rotor turning), is higher than the average coil input power in step 2) (no rotor).

The difference in the two input powers will effectively be the power required to make the rotor spin.  Note that it takes very little power to make the rotor spin so it will be a tricky measurement to make.

Please anyone that wants to comment on this test let me know what you think.

MileHigh

[MileHigh]

Carroll:

And by the way you never did comment about why so many industrial motors now have permanent magnets in them since you claim magnets can't do any work.

There is really nothing significant to say for this.  Perhaps older-generation industrial motors used the mains power flowing through windings to emulate the needed magnets to make the motor work.  I forget what the name for that kind of motor is.  That made for a cheap and inefficient motor, and perhaps magnets were much more expensive to manufacture back then.

Nowadays we are more concerned with motor efficiency and will get that efficiency with better motors built with permanent magnets.  It has nothing to do with "magnets doing work."  The work is done back at the power plant.

MileHigh