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Author Topic: Self accelerating reed switch magnet spinner.  (Read 220186 times)

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #75 on: October 06, 2013, 10:22:27 PM »
A little extra comment:  Looking again at your last scope shot, you can clearly see that the rotor magnet responsible for the third "zero cross" waveform is stronger than the previous two magnets.

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Re: Self accelerating reed switch magnet spinner.
« Reply #75 on: October 06, 2013, 10:22:27 PM »

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #76 on: October 06, 2013, 10:39:19 PM »
TK:

The angular adjustment for the sensor coil looks great!

How can I tell it's operating in attraction mode from the scope shot?  In looking at the sensor coil waveform I can see the "zero cross" is the center of the steep negative slope between the positive and negative humps.  That's also top-dead-center for the rotor magnet fly-by.

In looking at the drive coil waveform I can see that the switching is ON BEFORE the "zero cross" and it switches OFF at the "zero cross."  Hence the motor is running in attraction mode.

If I saw the drive coil being switched ON at the moment of the "zero cross" and it then switched OFF a certain amount of time AFTER the "zero cross" then I would know the motor was running in repulsion mode.

You can also see the switching angle of course.  To be more precise, you can clearly see that your actual switching threshold is actually set below the "zero cross" of approximately six volts.  Your switching threshold is set to let's say rougly five volts.  i.e.; negative one volt relative to the "zero cross."  Again, this is impossible to do with a conventional Bedini motor.

MileHigh

Yes, you are right all the way, I think. Actually the switching voltage level is about 5 1/2 volts, the sense trace is at 1 V/div and AC coupled, the "baseline" or "zero" is the 6 volt level.
(Since the coil's "reference" voltage is half the opamp supply because of the 22k dividing resistors, no matter what the opamp supply is, the thing is stable and switches at the same point even if the supply voltage changes. I tested it and it's good from 8 1/2 volts to 15 volts supply.)

Thanks for the clear description of how to tell repulsion from attraction. It is all coming back to me now, these are things I explained back in 2011 during the Orbette core effect motor days, when I was showing the difference between the three basic types of PMs: attractive, repulsive, and core effect. (My Marinov slab works on a fourth principle, repultraction.) Hopefully I'll be able to demonstrate the scope trace differences you describe, a bit later today or this evening.

I want to thank you again for your ideas, your help and your advice. This certainly is turning out to be a neat project. The controlled starting and the LED strobe just tickle me silly whenever I look at it. Yep, it is Way More Fun than the Bedini SGM. But it does like long duty cycles for max RPM. I wonder if it's possible to reproduce any of the effects or claims of Bedini with this driver/motor configuration. Any ideas on that?

I'm also wondering about the optimum mosfet to use. I've got the IRFP360 in there now. I just received some IRF3205  but they are low voltage high current units. Looking at the data sheets and what I have on hand, I might have chosen the best one already, by accident.


Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #77 on: October 06, 2013, 10:45:53 PM »
A little extra comment:  Looking again at your last scope shot, you can clearly see that the rotor magnet responsible for the third "zero cross" waveform is stronger than the previous two magnets.
Yes, that's right, you'd be surprised at the rotor magnet arrangement. I don't want to take it apart right now, but glued to the inside of the rotor edge there are two round ceramic disks and two little ceramic flat bars, and then each has a tiny NdBFe button on top of it. So the rotor magnet fields are ... not all that well equalized, nor is the rotor very well mass-balanced. But it works anyhow!

Good catch on the scope traces. You can also see some little differences in the slopes of the individual magnets too. This is actually the reason for the four separate tape markings over the magnets: I was using a phototransistor to look at the reflective tape on one scope channel, and the Bedini pulses on the other channel. So I would see one, two, three, or four little pips and I could tell which magnet position was making which drive coil pulse.

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Re: Self accelerating reed switch magnet spinner.
« Reply #77 on: October 06, 2013, 10:45:53 PM »
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Offline Pirate88179

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Re: Self accelerating reed switch magnet spinner.
« Reply #78 on: October 06, 2013, 11:03:48 PM »

 But it does like long duty cycles for max RPM. I wonder if it's possible to reproduce any of the effects or claims of Bedini with this driver/motor configuration. Any ideas on that?




TK:

Can you change the duty cycle on the fly on the op-amp while the rotor is running?  In other words, at max rpm can you then begin to shorten the duty cycle?  Sort of like the timing advance on the older cars of my youth.  My best Bedini set-up hit what I called second gear when the pots were all the way open, and then I began to add resistance again and it continued to accelerate ending up at 2 times the max rpm than if I just had the pots in that position from the start.

Just wondering.

Bill

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #79 on: October 06, 2013, 11:34:45 PM »

TK:

Can you change the duty cycle on the fly on the op-amp while the rotor is running?  In other words, at max rpm can you then begin to shorten the duty cycle?  Sort of like the timing advance on the older cars of my youth.  My best Bedini set-up hit what I called second gear when the pots were all the way open, and then I began to add resistance again and it continued to accelerate ending up at 2 times the max rpm than if I just had the pots in that position from the start.

Just wondering.

Bill
Yes, the current setup allows complete control of timing (by varying the position of the sense coil) and duty cycle (the setpoint control) while running "live". You can vary the timing so far you can even change magnets you are triggering on, and you can vary the duty cycle from 0 to 100 percent. It is fully controllable. The strobe will show the exact sweet spot, and the brightness of the neon does too, but is less precise.
The scope traces allow instant determination of RPM increasing or decreasing, by showing the frequency changing. More pulses = faster, and v.v.

Here's an annotated scopetrace with the Drain trace lowered and superimposed on the Sense coil trace. This clearly shows the switching points that MH pointed out above, and it shows a little hysteresis, which surprises me, but it's not too much. This is with the NE-2 from coil to Batt positive.

The Drain spike peaks are at a bit over 400 volts, off screen at the top. They would go even higher if I disconnected the neon.

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Re: Self accelerating reed switch magnet spinner.
« Reply #79 on: October 06, 2013, 11:34:45 PM »
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Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #80 on: October 06, 2013, 11:46:03 PM »
TK:

Quote
I wonder if it's possible to reproduce any of the effects or claims of Bedini with this driver/motor configuration. Any ideas on that?

You probably know that I have never been impressed with any of the claims made about a Bedini motor.  I have often bitched and moaned that measuring source and charging battery voltages for before and after test runs is meaningless data.  What I have seen from eyeballing many Bedini motor clips on YouTube is that the power out into the charging battery compared to the power draw from the source battery is pretty miserable.  I am pretty sure that for a typical Bedini motor that only about 30% of the source battery power makes it to the charging battery, and of course 70% of the source battery power is lost in heat production in the drive coil and elsewhere.

Certainly the cleaner switching with the op-amp design should give you a slightly more efficiency in transferring power from the source battery to the charging battery.  However, "slightly more efficiency" might mean you go from 30% efficient to 32% efficient, not too much to get excited about.

If you assume that resistive losses in the drive coil are a big part of the problem, then you could investigate that.  You could start by measuring the drive coil resistance and then looking at the drive coil current waveform.  And then estimating how much power is lost inside the drive coil.  Just eyeballing 10 sampling points and crunching the numbers would be easy, and it's something that you have done many times before.

Supposing that you conclude that there is indeed too much power being dissipated in the drive coil itself.  Let's assume for the sake of argument that you actually want to do something about it.  One means to have "shallow current depth" when powering the drive coil might be that 555 and AND gate technique I mentioned before to modulate the energizing of the drive coil.  You will get more spikes going into the charging battery - but the motor will also slow down.

I am not getting a sense that you would want to do that, at least for the short to medium term.  How about something more basic, like to explore the power out vs. power in ratio for the motor as you play with the parameters that you already have at your disposal right now?

Of course you have a beautiful regulated power supply, or your battery stack, to act as the source battery.  All that you have to do is put a current meter in series with the supply voltage and you measure the power consumption of the motor.  All that you have to do for the real batteries is scope the battery voltage to make sure it is not dipping too much when powering the drive coil.

You could put a charging battery in place and then measure the average current into the charging battery with another multimeter in series.  You can even scope the charging battery voltage to make sure it itself is steady to ensure that your output power calculation is legit.

Many times I have mentioned emulating the charging battery with a very large capacitor with a rheostat + series resistor across the large cap.  You can emulate a charging battery like that and it could be a very useful tool for your kit whenever you want to make an average power measurement when the output is coming from a Bedini-type pulse power output section.  The output power is just the cap voltage squared over the resistance!

I am not sure if you meant some other type of Bedini testing, I just discussed power out vs. power in.

As far as MOSFETs go, I don't really see that as a critical component in this setup and just about any MOSFET should do.  I am assuming that in all cases the drain-source resistance will be much lower than the DC resistance of the drive coil so it doesn't really matter.

MileHigh

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #81 on: October 07, 2013, 12:01:39 AM »
TK:

Quote
The Drain spike peaks are at a bit over 400 volts, off screen at the top. They would go even higher if I disconnected the neon.

That's really interesting.  Is it possible that the switching off is so fast that you get a very short high voltage spike before the neon has a chance to kick in?   Are you not concerned about damaging your MOSFET?

Indeed you are getting higher speed with greater than 45 degrees of conduction angle.  That's because there is another factor at play.  Some of you brainiacs out there may have answered the question for why 45 degrees of conduction angle is the theoretical max for getting max RPM out of the rotor.

The other factor at play is the L/R time constant of the drive coil.  For maximum push on the rotor you need maximum current through the drive coil.  Therefore, you may need to start energizing the coil before top-dead-center to "get some good push current going" before you get to the "push sweet spot" in the rotation of the rotor.  However, the 45 degree conduction angle factor is still there, but having the extra time to build up "good push current" is a more important factor.

MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #81 on: October 07, 2013, 12:01:39 AM »
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Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #82 on: October 07, 2013, 01:10:39 AM »
TK:

That's really interesting.  Is it possible that the switching off is so fast that you get a very short high voltage spike before the neon has a chance to kick in?   Are you not concerned about damaging your MOSFET?
Yes, I think that's right.
I'm concerned about a lot of things; blowing mosfets isn't usually one of them...   ;)    but in this case it's the only P360 I have on hand, and all mosfets aren't created equal, this one has a fairly low Rdss and a fairly high voltage rating.
Quote
Indeed you are getting higher speed with greater than 45 degrees of conduction angle.  That's because there is another factor at play.  Some of you brainiacs out there may have answered the question for why 45 degrees of conduction angle is the theoretical max for getting max RPM out of the rotor.

Just to be clear for the observers, you are calling "conduction angle" what I am calling "dwell", corresponding to Duty Cycle, and a 45 degree conduction angle corresponds to a dwell time or duty cycle of 50 percent of the total period. Indeed, this system appears to like around 65-70 percent On, which is more like 60 degrees of conduction angle.
Quote
The other factor at play is the L/R time constant of the drive coil.  For maximum push on the rotor you need maximum current through the drive coil.  Therefore, you may need to start energizing the coil before top-dead-center to "get some good push current going" before you get to the "push sweet spot" in the rotation of the rotor.  However, the 45 degree conduction angle factor is still there, but having the extra time to build up "good push current" is a more important factor.

MileHigh
I haven't run the numbers but we are operating at under 200 Hz... even the ringing that you see in the waveform after the spike is only 4 kHz about. So maybe the time constant is important, I dunno at this point.

There is yet another factor and that is the spacing of the rotor magnets. Note the trace from the sense coil: it's not sinusoidal, it has intervals between the sinus segments. This represents the space between the magnets on the rotor. Would it be better to have them closer (or stronger) so that the Sense signal was more perfectly sinusoidal, without the spaces, or would it be better to go the other way, with more flat spots between the sinus portions?

Offline synchro1

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Re: Self accelerating reed switch magnet spinner.
« Reply #83 on: October 07, 2013, 01:52:15 AM »

Quote from MileHigh:

"I am pretty sure that for a typical Bedini motor that only about 30% of the source battery power makes it to the charging battery, and of course 70% of the source battery power is lost in heat production in the drive coil and elsewhere."


I lit a 120 volt LED bulb to about 2/3 the brightness directly from my SSG Bedini output leads, measured by a LUX  meter. I then calculated the output in watts and compared that figure to the input as measured by an analog amp meter. The best recovery ratio I recorded was around half your 30% estimate at 17%. Measuring rise in charge battery voltage is extremely deceptive.  


Also, running that kind of low ripple AC current into a DC battery kills it. That's why Bedini is practicaly broke from consumer litigation.

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Re: Self accelerating reed switch magnet spinner.
« Reply #83 on: October 07, 2013, 01:52:15 AM »
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Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #84 on: October 07, 2013, 02:16:51 AM »
TK:

Yes what I call "conduction angle" is what you are calling "dwell."  In my mind I change my frame of reference to the angle of the spinning rotor and the "conduction angle" is the angle the rotor turns through while the MOSFET is ON.   So let's say that TDC is zero degrees.  Therefore the conduction angle might be from zero degrees to 45 degrees which would translate into a 50% duty cycle.  Without scrutinizing your scope shot for maximum RPM it might be that your conduction angle subtends 60 degrees total, switching on at minus ten degrees and switching off at plus 50 degrees.

For the spacing of the rotor magnets and the size and waveform of the sense coil, there are indeed some issues to ponder.  Certainly there is no compelling reason to add rotor magnets and make the rotor more "crowded" with magnets.  Once the drive coil is half way between two rotor magnets you have reached a "point of no return" of sorts.  If you energize the drive coil past the "point of no return" the drive coil is working to slow down the rotor, not to speed it up.

For the sense coil, you noticed that your smaller relay sense coil gave you a flatter waveform between the double-humps.  However, the waveform is still not flat and it would appear that the comparator will sill give you a nice sharp transition even when the slope of the waveform is not really that steep at all.  In that sense it may be that the size and shape of the sense coil is not that critical.  If you had a larger sense coil then the double-humps would be wider overall, and therefore the "near flat areas" would be greatly reduced or eliminated.  That would in theory make "life easier" for the comparator.

Again, it seems that the comparator is functioning fine and there are no issues.  The net effect of the interaction between the comparator and the sense coil is a means for you to set the duty cycle, a.k.a. conduction angle.  Honestly I think I would prefer a larger sense coil to make life easier for the comparator and to improve the noise immunity of the overall circuit.  Then of course you can change the angle of the sense coil to offset the duty cycle.   The goal is to have full control over the duty cycle (a.k.a. conduction angle) and the starting angle for the duty cycle relative to TDC.  It appears that your hardware does that job perfectly fine right now so you are good to go.

One thing to keep in mind is the overall impedance of the sense coil.  Right now it looks like you have a 6-volt battery connected to an 11K resistor connected to the sense coil connected to the op-amp input.  So you can say that the "external noise immunity impedance" of the sense coil is 11 kohm.  If your resistor divider network was 500k + 500k then the "external noise immunity impedance" of the coil would be 250 kohm, which probably would be way too high and it would "waver in potential" due to external magnetic fields from things like 60 cycle mains power.  If you in your investigations think that you might want to anchor the sense coil to +6 volts more firmly, you might want to change the resistors to 5K + 5K as an example.  Then the "external noise immunity impedance" of the sense coil would drop to 2.5 kohm.  So the sense coil is more securely "anchored" to +6 volts and you pay a very small price in a few extra milliamperes of current consumption.

MileHigh

Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #85 on: October 07, 2013, 02:34:18 AM »
Synchro1:

Quote
I lit a 120 volt LED bulb to about 2/3 the brightness directly from my SSG Bedini output leads, measured by a LUX  meter. I then calculated the output in watts and compared that figure to the input as measured by an analog amp meter. The best recovery ratio I recorded was around half your 30% estimate at 17%. Measuring rise in charge battery voltage is extremely deceptive.

There is a "chicken and egg" issue for Bedini motors.  The average beginner joins the Yahoo Bedini group and uses his source battery to charge the charging battery.  He or she gets all excited when they see the resting voltage go up on the charging battery.  However, they are not aware that the Bedini motor was doing an absolutely miserable job of transferring input power from the source battery to the output power going to the charge battery.  The "radiant spikes" business is all just a psychological deflection scheme to divert your attention away from other things and keep it focused on the "magic spikes."

The "chicken and egg" issue is this:  You get all excited about charging target batteries using your source battery.  But who charges the source battery when it gets depleted?  It's probably usually a battery charger from the mains!  They even tell you to not use one of your recently charged batteries as the source battery.  Something about "you should not use a 'radiantly' charged battery as the source battery."  The real reason is that your "radiantly charged" battery will crap out pretty quickly in its new found role as a source battery - because it only got 30% or less of the energy transferred into it that was in the original source battery.

And the "magic spikes" are not "magic" - in the Yahoo Bedini groups they will not explain to you how a coil works.  Likewise, at the Bedini conferences they will not explain to you how a coil works.  A lot of the people on "Team Bedini" don't even know themselves.  It's just the way it is.

MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #85 on: October 07, 2013, 02:34:18 AM »
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Offline MileHigh

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Re: Self accelerating reed switch magnet spinner.
« Reply #86 on: October 07, 2013, 03:08:10 AM »
I am going to more or less close out the issue of the sense coil with one more example and leave people to ponder some issues.

Let's suppose in TK's rotor the diameter of each of the rotor magnets is one inch.   Let's suppose that we use a sense coil that is large and has the proportions of a large ring.   Suppose the sense coil is three inches inner diameter and 3 1/4 inches outer diameter and and about 1/4 inch deep with lots of turns.

If a sense coil like this is close to the rotor, you will lose that nice steep "zero cross" portion of the waveform at top-dead-center that we have seen in all of TK's screen captures.  There will be a large "dead zone" instead where the waveform is flat or nearly flat.  So you will lose or almost lose your top-dead-center reference, which would not be nice.

Now, with the same ring sense coil, if you moved it a few inches away from the rotor, chances are you would get much better results and you will see a waveform that gives you a very good indication of top-dead-center.

If somebody checked this in real life, my descriptions above might not correspond directly, but they will be close enough.  I am crunching this all in my head.

Anyway, I will leave it to the readers, if they are so inclined, to try to understand why the larger sense coil will act like this.

MileHigh

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #87 on: October 07, 2013, 03:39:28 AM »
I put a 10 pF cap from the op-amp sense coil input, to ground. It helped stabilize the thing, since it went all wonky after I rebuilt it mechanically, moving the drive coil over to where it belongs and mounting the circuit boards better. It suffered from the jitters after that, but now with the 10 pF cap all is stable again.



Offline Magluvin

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Re: Self accelerating reed switch magnet spinner.
« Reply #88 on: October 07, 2013, 03:42:09 AM »


Anyway, I will leave it to the readers, if they are so inclined, to try to understand why the larger sense coil will act like this.

MileHigh

Its simple enough to say. Having a 3in inner diameter coil leaves a lot of space where there is no windings for the 1in mags flux to cut and induce current. So you see a positive hump, dead zone, negative hump. Where a coil with a small inner dia, the transition from pos to neg humps is seamless.

But, thats only if the coil is close to the rotor/mag. ;) The further outward from the rotor, the less of a signal, but the dead zone will shrink with distance. ;) Not sure how much signal is needed to trigger here.

Mags

Offline TinselKoala

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Re: Self accelerating reed switch magnet spinner.
« Reply #89 on: October 07, 2013, 06:48:58 AM »
It runs stably at 14 percent duty cycle, 1110 RPM (74 Hz) and the neon is still lighting, not brilliantly but nicely lit. This is as slow as I can get it at the moment. And the Max RPM sweet spot is about 2310 RPM, brilliant neon, and a duty cycle of about 77 percent. The timing varies a bit over the range, it needs to be adjusted for the min and max RPM zones. Easy to do with this setup and the scope!

 

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