Self accelerating reed switch magnet spinner.

[MileHigh]

TK:

I am getting stuck on the signal coupling transformer part of the design.  I think it's because it's more difficult to couple lower frequencies though the transformer than I thought.   Note that in the AC-coupling with the capacitor, it's fairly easy to have a very long time constant.  So although the signal is "corrupted" because of the voltage droop associated with the RC time constant, you can easily make the time constant long enough so that you don't notice it at all when you look at your pulsing current waveform.

Then when I switched to the signal coupling transformer, I realized that if you had a half-ideal transformer with no resistance in the primary winding, and the op-amp could source or sink enough current, then you in theory get perfect signal integrity from input to output.   However, how long you can maintain that perfect signal integrity depends on how much current you can source or sink at your maximum output voltage.

Let's just do some number without major limits on the parameters.

Let's assume that we can source or sink 200 mlilliamperes and we want one-half second of perfect signal integrity and the resistance of the primary is zero.  We will keep the max output voltage at +/-0.25 volts.

L = vt/i

L = (0.25 x 0.5)/0.2 = 0.625 Henries.

That seems more reasonable, but then we have to factor in the resistance of the primary winding.  That will cause an L/R time constant for the current flow.

If the resistance of the primary coil is 2 ohms, then L/R = 0.625/2 = 0.3125 seconds.  So that is shorter then 0.5 seconds but that all seems to be in the right ball park.  There is not that much "droop" over 1.5 time constants so it's a reasonable compromise.

If the current waveform is pulsing at 10 Hz and the duty cycle is 50% then the pulse is active for 50 miliseconds.  Let's use that as a baseline.  Let's say we want good signal integrity and very little perceptible L/R voltage droop for 100 miliseconds.

Initial parameters:  0.25 maximum voltage onput, very good signal integrity for 100 milliseconds, 200 milliamperes maximum current sourcing or sinking, and an L/R time constant of 150 milliseconds.

L = vt/i

L = (0.25 x 0.1)/0.2 = 0.125 Henries.

L/R = time_constant,

Therefore R = L/time_constant

R = 0.125/0.150 = 0.83 ohms

So, to meet the "10 Hertz" threshold for good isolated signal integrity on your scope display, you need the following:

Max voltage drive to the transformer of +/-0.25 volts
Op-amp that can source or sink 200 milliamperes of current
Transformer primary of 0.125 Henries
Transformer primary resistance of 0.83 ohms or less

I suppose the above or something similar where you play with the parameters would give you what you want - isolated coupling on a current sensor probe.  It's just that it's a more involved project that requires a beefier op-amp that has higher output current capabilities.  The transformer might be hard to reproduce, I'm not sure.  The low primary resistance worries me.

Oh well, perhaps this will remain a paper napkin design.  If somebody was hard core, this would all be doable.  You can shop around for an integrated amplifier power module, or perhaps even use an old car stereo amplifier.  If you can source or sink a lot more current that 200 milliamperes then you can get a break on the transformer specification and then find the transformer more easily, as an example.

Anyway, I haven't crunched timing parameters for pulse circuits in a looong time.  If I made any mistakes perhaps someone will let me know.  I am reasonably confident that I am in the right ballpark at least.

MileHigh

P.S.:  I forgot to check what the current limit would be as imposed by the coil resistance and the max voltage drive.

Max current = 0.25/0.83 = 301 milliamperes.  It's above the 200 milliampere limit of the op-amp output so it appears that it might be okay.

[synchro1]

@Tinselkoala,


       Run a ferrite rod with a magnet attached to the end of it into the air core of the power coil from behind.
This will cause the rotor to speed up at a certain distance into the air core. The rotor will stabilize. Now, re-time the circuit and repeat the process, by running the ferrite rod a little further into the core. This should speed the rotor up a second time, wait again for it to stabilize a second time and re-time the pulse again. This should cause constant acceleration with a decrease in input power until the ferrite core is nearly adjacent to the rotor.!  

[synchro1]

@Tinselkoala,

Please take another look at this video:

http://www.youtube.com/watch?v=mzNjAs3-9LA

[TinselKoala]

@Tinselkoala,

Please take another look at this video:

http://www.youtube.com/watch?v=mzNjAs3-9LA

Why? I find it boring and the music very obnoxious. Why don't you take a look at this video, and compare the dates.

http://www.youtube.com/watch?v=W8S02SB-ENA

Most of my Orbette videos seem to be missing. I have several where I demonstrate and explain the effect of biasing magnets on the drive coils. But even in this video, where I am talking about the effect of the ferrite core on the _generating_ coil,  you can see that I am using biasing magnets on the drive coil, for example at 3:58 you can see the two NdBFe button magnets on the right side of the frame, stuck to the core of the toroidally wound "bead" drive coil.

You may note that I am actually _generating power_ here, from a separate coil system, not extracting it from interacting drive-sense-pickup coils wound on the same core.

You may also note that none of my videos are "monetized"... you don't have to watch ads to see them, and I get _no revenue_ when people watch them.

[synchro1]

@Tinselkoala,

Here's a quote from your "Orbette" youtube comment:

"Change the inductance of the coil by placing a small magnet near it. Now again compare the rotor's equilibrium speeds with and without the diode in circuit. The speeds will be different with the extra magnet than without it, and the exact amount of work that it takes to move the inductance from its former value to its new value will be seen in the change in momentum of the rotor".

You had no way to narrow the pulse width with your old "Orbette" circuit as the new inductance value changed the momentum of the rotor. Your new MHOP circuit allows you this flexability, right? How better to miser your input?