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Author Topic: Permanent magnet assisted motor coil designs  (Read 19193 times)

Offline gyulasun

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Re: Permanent magnet assisted motor coil designs
« Reply #165 on: April 17, 2022, 08:00:58 PM »

Is there a puffer capacitor right across the supply rail of the coils + the MOSFET switch, which may be able to maintain the supply voltage for a few moments the rotor spins down? Maybe the internal puffer cap of the power supply? (unless you unplug one of its DC output connections)  EDIT check with a separate DC voltmeter across the DC rails of the circuit whether there is some supply voltage remaining after the switch off.

IF there is no such cap, then something may trigger on the MOSFET switch? (the spikes occur at the falling side of the induced voltage just like in the powered case)   
To check this, after you switch off the power supply, get ready with a piece of wire to short circuit the gate and source pins of the MOSFET, to prevent any unwanted drive for the MOSFET. 

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #166 on: April 17, 2022, 08:50:16 PM »
Is there a puffer capacitor right across the supply rail of the coils + the MOSFET switch, which may be able to maintain the supply voltage for a few moments the rotor spins down? Maybe the internal puffer cap of the power supply? (unless you unplug one of its DC output connections)  EDIT check with a separate DC voltmeter across the DC rails of the circuit whether there is some supply voltage remaining after the switch off.

IF there is no such cap, then something may trigger on the MOSFET switch? (the spikes occur at the falling side of the induced voltage just like in the powered case)   
To check this, after you switch off the power supply, get ready with a piece of wire to short circuit the gate and source pins of the MOSFET, to prevent any unwanted drive for the MOSFET.


The power supply I am using does use those huge caps. So what I did this time was run it up. And then completely disconnect it from the circuit. And I got the same results. Here is a quick jot down of the circuit. I will make one showing the mosfet connections instead of just a switch. But basically, I am triggering the gate using a reed switch for each one. There are no other power sources or capacitors in the circuit yet. I haven't added the recovery circuit yet either. I have the coils on the source side of the n channel mosfets instead of on the drain side? Something is causing that spike with only spinning magnets in the circuit? You think the mosfet gate could be triggering? And if so, what would cause the spike? There should be no way for a short coil situation I don't think? After looking at the mosfets, I cam probably get by with just 1 resistor, but shouldn't matter I don't think here.

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #167 on: April 17, 2022, 09:21:03 PM »
I am trying to understand this. Again, this is after power is off to circuit and rotor is still spinning. It looks to me like because the magnets are opposite they are attracting on the way in so the wave looks normal. Maybe it is even pulling the magnetic field from the inner PM outside of the core. But just after the peak it begins to decline. This decline seems to cause that internal magnetic field to flutter and something happens. Maybe this is where it flips it back inside the core causing a negative spike? But it's technically an open coil situation? Thoughts?

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #168 on: April 17, 2022, 09:36:23 PM »
This is wierd, so I dicided to spin it up. The probes are across the coils still. But this time I have BOTH the positive and negative disconnected so there is no way a gate should trigger on a mosfet. It's still happening. I went ahead checked with a test signal to make sure something isn't just interfering with stuff randomly I can't think of. And the square wave is perfect with no spike. Very interesting.


I went ahead and shot a quick video to show what's happening.
https://youtu.be/tCHc9wYdwsE

Offline gyulasun

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Re: Permanent magnet assisted motor coil designs
« Reply #169 on: April 17, 2022, 10:26:14 PM »

Thanks for the circuit drawings.  Considering 2 coils in series with the source of the MOSFET and the 10 k resistor towards the gate of the MOSFET,  the induced voltage appears across the gate-source I suppose. And the reed switches still operate from the small control magnets and they short the drain of the MOSFET to the gate, right?   And there is the body diode between the drain and the source, which may start rectifying the induced coil voltage and the horizontal line you indicate with a questionmark in the scopeshot above may be the indication of a DC component, what may be the supply voltage for a moment?  maybe this is what is happening.

You could use one scope probe across the gate-source when the other scope probe would remain across the same two coils and see the waveforms. (Both scope channel ground clips should be on the common negative of the circuit.) 
Temporarily you could remove the wire coming from the reed switch to the gate the moment you switch off the supply voltage and the rotor starts decelerating from the earlier full speed, to see if the spike disappears. I am watching the video now.

Edit: for the time being, no more comment, try to check the above things.

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #170 on: April 17, 2022, 10:58:46 PM »
Thanks for the circuit drawings.  Considering 2 coils in series with the source of the MOSFET and the 10 k resistor towards the gate of the MOSFET,  the induced voltage appears across the gate-source I suppose. And the reed switches still operate from the small control magnets and they short the drain of the MOSFET to the gate, right?   And there is the body diode between the drain and the source, which may start rectifying the induced coil voltage and the horizontal line you indicate with a questionmark in the scopeshot above may be the indication of a DC component, what may be the supply voltage for a moment?  maybe this is what is happening.

You could use one scope probe across the gate-source when the other scope probe would remain across the same two coils and see the waveforms. (Both scope channel ground clips should be on the common negative of the circuit.) 
Temporarily you could remove the wire coming from the reed switch to the gate the moment you switch off the supply voltage and the rotor starts decelerating from the earlier full speed, to see if the spike disappears. I am watching the video now.

Edit: for the time being, no more comment, try to check the above things.
Thanks for all yout help so far. Okay, I still haven't wrapped my mind around it completely, but you are correct. I was doing some different things to try your suggestions, I noticed it disasappears when I disconnect all other coils from the ground except for the one I have probed. So it is an induced current from one of the other coils gating that transistor. I placed an extra wire to allow me to disconnect the probed coil from the transistors completely and go coil only as soon as power supply is switched off. I get a normal sign wave as it slows down then. Now that I know for sure how to replicate it as well as make it go away, maybe I can fully understand it. Thank you.

EDIT:.. Now, since I have 2 channels on this scope, I think I will figure out which is tripping the gate of this pair of coils and see if I can see it happen and understand why.

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #171 on: April 18, 2022, 08:59:37 AM »
I am now working on the best way to recover the fly back ONLY. The way these coils work with an embedded magnet, helps boost during a drive pulse, but the opposite side is they are terrible for generator coils. So much Lenz drag with that inner genie field popping out. Just using the normal recovery circuits are usually really a half wave rectifier of sorts grabbing the whole negative half wave. I just want the extra spike so it won't drag down the rotor. I plan on generating from this on a different side of it and let these coils only drive.
I found something that seems to work, and does not slow the rotor at all. I dont know if this is the most effective or efficient way, but it's working. I simply hooked a capacitor in parallel with the charge battery, an 18650 at the moment with a resistance between them. The recovery circuit is dumping into the Capacitor which in turn dumps to the battery. I adjusted resistance between the cap and battery to find a balance where the cap stays at about the same voltage of the waveform, but still dumping any extra to the battery. This appears to be very effective. This is kind of like a smoothing capacitor I guess. It seems to do the trick and help me snip that extra out without using the drive coils as generator coils for a half wave, and doesn't change rotor speed at all. I'm trying to learn more as I go. Here is the difference in the circuit as I connect it.

Offline gyulasun

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Re: Permanent magnet assisted motor coil designs
« Reply #172 on: April 18, 2022, 02:12:32 PM »
Just for clarity: the coils you use now and recover their flyback energy have no embedded magnets? or they do?   

Whether the method your using a resistor between the puffer cap and the battery is efficient (or not) can be estimated by hooking up a scope probe across this resistor and read the Mean voltage value of the waveform (it will be kinda saw tooth like).   And knowing the resistor value and the Mean voltage across it the dissipated power comes out. And you would learn about the mean amplitude of charge current the charge battery receives. 
In this test you mention did you use the power supply or a 'run' battery to feed the setup? 
Avoid ground issues if there would be any when estimating the voltage drop across the resistor. 

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #173 on: April 18, 2022, 04:44:24 PM »
Thank you for the response. Yes, they do have the embedded magnet. And I am posting a quick view of the circuit. The switches are n channel mosfets but you get the basic idea of the circuit here. I will do what you suggested when I get home tonight. I think I understand it. I am thinking to help with the collapsing field, maybe i should use 3 more diodes and pull it down from each coil instead of a coil pair? Also, when using a puffer coil like this, doesn't the energy higher than the caps voltage just flow right over it per say? So it's not actually even touching the cap is it, just the loss through the resistor? Or am I thinking of this wrong, or is it actually charging and discharging that extra voltage over the top?


I really appreciate the suggestions everyone makes. I'm trying to follow them and learn from you guys as best I can. Thanks again.

Offline gyulasun

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Re: Permanent magnet assisted motor coil designs
« Reply #174 on: April 18, 2022, 09:51:51 PM »

Well, you can attempt using 3 more diodes as you describe I never tested whether there is a small or significant difference between letting the flyback pulses add up on 2 or more series coils or collecting them individually. 
In theory, the two flyback spikes of the two series coils should add up as if you connect two batteries in series but this could be checked with scope probes, checking individually the amplitudes of spikes across each coil, one at a time while the setup is running.  (care for any scope ground issue)
IT is worth considering that in the present circuit drawing each flyback current of a coil (out of the two in series) goes through the other coil's copper resistance. With the extra 3 diodes this would not happen. Which causes higher loss: the 3 extra diodes or the copper losses?  checking can tell this.

You showed around 80 v peak for the unloaded flyback pulses across two series coils and if the flyback pulses indeed had around 40 V peaks from each coil, this still sounds a little low amplitude. 
This may be due to a slower switch-off speed of the MOSFET concerned or maybe due to some asymmetry between the coils (I suspect the first, not the latter.)   
The slower switch-off speed can come from your using 10 kOhm gate-source resistors for the MOSFETs, replace them with say 2.2 k resistors (or less) to discharge the gate-source capacitance more rapidly, the reed switches should work well with the 7 mA current instead of the previous 1.4 mA or so.  But then you would have about an extra 20 mA draw from the input (for the 3 reeds) 
If you use MOSFET driver circuits, the switching speeds will increase significantly versus the reed switches + the gate-source discharge resistor,  though these circuits also need some (small) input power to function.   

I assume you do not wish to connect the 2 coils in parallel that are in series now, to avoid the higher input current draw involved with this.

Please clarify what you mean on "using a puffer coil like this" ? you wrote it in your last but one sentence.

If you meant puffer capacitor, then the answer is no, all the energy coming from the flyback pulse goes into the capacitor as long as the cap voltage is lower than the spike's peak amplitude. Of course, some part of the flyback pulse will go towards the resistor + the charge battery and how much part is involved depends on the series impedance of the resistor+battery and how this is related to the (normally lower) capacitor impedance.

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #175 on: April 18, 2022, 11:32:33 PM »
Very good response, thank you. A lot of info in there. I will read it over a few times when I get done working for the day and get home.
I have no idea why I said puffer coil, I just mistyped. I meant puffer capacitor. What I was asking is how it worked for sure. Let's say the peak voltage of the wave without the spike is 12v, once the cap fills to 12v, and I have adjusted the resistance for the cap to hold at that voltage, then wouldn't that 40v spike roll right past the Capacitor to the resistor or does it just seem that way? I just want to understand the physics behind it.
As for the other questions, it's entirely possible I have some setting wrong on the scope as well. But I have been leaning on the auto functions before the minor adjustments I do. As far as the gate resistance, that is a very good idea and easy for me to test.
As far as a mosfet driver, are you referring to a simple motor driver circuit instead of just a reed switch on the gate? I was thinking this would use the least amount of energy but of course maybe I'm off base there. I tried hall sensors but I simply have bad parts so until I get more I can't really even do that.
If I missed anything, I'll catch it later when I get time to read more closely and follow point by point. Thank you.


One more thing, is there a better way to get only that spoke collected than what I'm doing? I just found something that seemed to work, I'm open to more options for sure. Thank you so much.


Edit... also, I wired each coil separately in a terminal block so I can test parallel as well. Tests so far have shown series being more efficient, but the trade off is higher voltage of course. But i will test everything!

Offline gyulasun

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Re: Permanent magnet assisted motor coil designs
« Reply #176 on: April 19, 2022, 01:36:52 AM »
Quote
Let's say the peak voltage of the wave without the spike is 12v, once the cap fills to 12v, and I have adjusted the resistance for the cap to hold at that voltage, then wouldn't that 40v spike roll right past the Capacitor to the resistor or does it just seem that way? I just want to understand the physics behind it.
As I mentioned, it is a question of the (frequency dependent) impedances of the puffer cap and that of the series resistor + charge battery, these are connected in parallel so the 40V spike appears across both.  Suppose the frequency of the spikes is 40Hz and the puffer cap is say a 100 uF electrolytic, so it has roughly 40 Ohm capacitive impedance. Suppose you find the best resistor value to charge the battery is higher than 40 Ohm, then the 40V spike will cause higher current towards the cap and less current towards the resistor+battery.  Of course the charge current in the cap will be exponentially decreasing as the voltage increases across the cap, so the battery charge current will be increased accordingly by the current the remaining spike amplitude is able to provide via the series resistor which limits it too of course. This is the dynamics of the process. 
IF the cap is say 470 uF, its reactance would be around 8.5 Ohm at 40 Hz, hence more energy will be captured by the cap if the series resistor value is likely way higher than this (the charge battery has very low internal resistance of course).   
 
Yes the reed switch with the 10 kOhm gate-source resistor uses the least amount of energy for the operation. A 1 kOhm would use 10 times as much and a dedicated gate driver IC would use roughly in-between. A motor driver circuit sounds good if its output has max a few Ohm resistance (say < 2 - 3 Ohm). The input of this driver circuit could still receive the reed switch because the switching speed is always governed by the output speed of the driver circuit.  (rise and fall time of the driver)
The way you collect the flyback spikes is basically good I think.   
Regarding the parallel or series connection of the coils: the series connection reduces input power by the higher series coils impedance but as you find you have to increase supply voltage which works against input reduction. However the still lower currents involved versus the parallel connections give less overall losses, this explains the higher efficiency you find.


Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #177 on: April 19, 2022, 02:54:10 AM »
Very good clear response. That makes perfect sense. Thank you! I'll go over everything you said carefully and try some things.

Offline floodrod

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Re: Permanent magnet assisted motor coil designs
« Reply #178 on: April 19, 2022, 03:41:05 AM »
@ Seychelles
This is a coaxial transformer I put together a few years back. Since I tested with 60 hertz I was only able to apply around 3 vac before core started to saturate. I used 1/8” tubing with 23 gauge center conductor. Don’t remember much results other than coupling between primary and secondary unloaded was near perfect.

Edit: A simple experiment would be wrap some TV coax cable on a core which is what I did at first.

Interesting!  I have access to truckloads of free coaxial daily. Literally..

Offline captainpecan

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Re: Permanent magnet assisted motor coil designs
« Reply #179 on: April 21, 2022, 05:51:19 AM »
Well, I made a change to the motor that did not go well at all. I had a huge gap between the rotors and coils because the rotors were not as straight as needed. I decided to back them with steel and straighten them up so I can decrease the gap. Big mistake. It barely runs at all now. Guess I will be changing back. I expected an increase in rpms and power. But clearly it changed the magnetic fields so much, nothing works right anymore. Really wierd. Maybe its because they are all like poles? Ill keep playing with it a bit to make sure I didnt just do something stupid i havent caught yet before i switch back. Lesson learned I guess.