Self accelerating reed switch magnet spinner.

[MileHigh]

TK:

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

[MileHigh]

TK:

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

[TinselKoala]

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.

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.

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?

[synchro1]

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.

[MileHigh]

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