Electric Motor Secrets

[gyula]

Hi Robert,

Very interesting measurement data for sure...

I wonder what may cause to measure 61V at 0.28A load current on you input DC voltage while you measure 63.8V at 0.302A load current? (on load current here I mean the current taken out from the DC supply by your pulse motor setup of course)

It seems a bit strange that a DC supply drops its output voltage by a larger amount when its load current is less (behaves just in a reverse way: 'normal' DC supplies drop output voltage the higher, the more load current you take out).

I would suggest using an LC low pass filter between the DC output of your power supply and the pulse motor. Perhaps such LC filter could also be useful at the DC output of the diode bridge even if you do have a very high value puffer capacitor. Here is a link to a two-stage low pass filter:

https://rdl.train.army.mil/catalog-ws/view/100.ATSC/C3A71302-9C9F-4523-8F5B-6FA417E004ED-1274309231310/9-62/chap4.htm#fig4-51

For L1 and L2 you could use the classic air gapped core choke coils of the past electric valve era but these are a rarity nowadays so if you happen to have any mains transformer designed for at least 30-40VA power, with 6 or 12 or 15 or 24V secondary windings, you could use the secondary as a choke (leaving the primary coil floating and isolated). So you would need two such transformers, in case you have any coil with some 10mH self inductance which does not saturate for a 300-400mA DC current, you could use them of course. For the C1 and C2 capacitors try to use some hundred uF or higher electrolytic type.

IF you feel like using such two stage low pass filter between the DC supply and the pulse motor supply input, try to check the input current taken by your motor at numbered points 6 or 7 and 8 as labeled in Figure 4-51 in the link.

Regarding your DC output after the diode bridge, a single stage LC filter could also be considered there. So the 200W lamp load would connect via a choke to the big puffer cap and a filter cap across the lamp would also ease the ripple if there is still some left. Checking these things by an oscilloscope can reveal the validity of measured values received by the DMMs.

Gyula

[voltan]

hi robert.nice outside of the box concept and nice build.just a thought.i'm not sure if your switching devices are fets or igbts or something else,but if they have a built in diode then a portion of the collapsing field energy might be pulsing back to the power source via one or both devices,(not a bad thing but it may affect meter readings and/or reduce the output at the fwbr).cheers.

[Robert49]

O.U.

Hi

I just realized that I never measured the output power.

input: 63.8v x 0.302a =19.26w

input with cap and 200w light bulb in parallel staying connected on output: 63.8v x 0.05a =3.19w for a brief moment

Then when stabilized, input: 61v 0.28a =17.08w
Measuring the power on light bulb, I get: 40v x 0.83a= 33.2w
COP > 1.94
Slight decrease on rotational speed.

Maybe I'm dreaming!

Robert

[Robert49]

a lot to think about

Gyula,

We seem to understand all this the same way so I think we're getting somewhere.
I have three different timing wheels that I can use. One at 5% ,the present one at about 12% and one at about 50% ( which is too much).
My next drive circuit will have 555 timers to control the duty cycle and timing of the drive pulses.(for delaying the pulse)

When I put the bridge ac input between the two drains of the mosfet instead of between the plus and the blue drain, the effect was not there and the input current rose about 50%.
I already thought of using a second bridge on the other coil also. And I will.
For now, I'll be working on a new circuit which will be able to delay the start of the switching-on and the duration of the capture to the cap, and also switch the cap to some load.I think that timing is critical on this thing.

I'll get back as soon as it is done.

Robert

[gyula]

Hi Robert,

Well, one of the differences I did not consider in the placement of the switch is that the direct connection of the puffer cap to the diode bridge would make the cap to be seen by the input current draw all the time (the cap would always be in parallel with the half coils via the diode bridge) while in your schematic the cap is present only when you activate the switching at the diode bridge output and the two input MOSFET switches are also off.

Now I wonder what may cause the "effect"? You wrote that it disappears when the cap is not fully disharged: this means that for the effect to occur, a nearly zero capacitive reactance should suddenly appear across the coils (one half of the coils in this case) and the reactance of a cap is the closest to a short circuit when the cap is fully discharged. And it must be the current (what this cap starts to take from all the half coils from the moment of the cap switch-on) which may make magnetic fields in the half coils that may add / help positively to the normal fields the input current creates. And of course the capacitive current is driven by the instanteneous AC voltage difference across the series half coils (when the input current is off and the AC voltage across the half coils comes from the induction and from the remains of the collapsing fields spikes).
When you connect the resistor, the effect is less pronounced, probably because there isn't an instanteneous short across the coil like in case of the empty cap, and when both the cap and the resistor are present across the diode bridge output, then the instanteneous load is even more like a short (paralell RC impedance is at the smallest value). Obviously, the rise time depends on the load impedance (RC time constant of the charging cap) as you found.

Would like to ask whether you have the possibility to change the duty cycle for the input pulses? Their duty cycle now is less than 50% I guess. Also, you drive the two input MOSFET switches in push pull? when one of them is on, the other is off and vice versa, right?

You mentioned a possible similarity with Jim Murray reactive power experiment: while it is not known yet how Jim does 'his tricks' I think what I wrote above can fairly well explain the effect? You have a DC voltage source at the input and the input current is reduced from it when the load is switched across the half coils via the diode bridge, and it is at the output where the current is instantly high and the voltage is lagging, right? While in Jim's case the input voltage source is AC and (I assume) the lag-lead situation exists for the input voltage and current I guess.

Greetings, Gyula

PS: When you wrote "I put a bridge rectifier on just one half of the coils for this test and only capture the output between the drive pulses. If I try with the two halves, I get the usual drag with a 50% rise in amps." did you mean with "the two halves" that you placed the red coloured AC input of the bridge to the drain of the red MOSFET?
I ask because if the answer is yes, then what if you try a second diode bridge across the red half coils too? and also switch the diode output like for the first bridge (but perhaps with different timing)?

[Robert49]

Yes, it explains, thanks for the drawing.

Now on your switching at the output of the full wave bridge: I had thought that the puffer capacitor would connect directly to the diode bridge output and the switching would take place only between the actual load and the capacitor in the desired and controlled time.
PErhaps there is no meaningful difference between the two?

Gyula

Well I believe there is a big difference because I have noticed that the effect disappears when the cap is not fully discharged but I will nevertheless try both setups to confirm .
I'm wondering if this has a similarity with Jim Murray's "reactive power experiment"? since the voltage is lagging or delayed and the current is instantly high. They are out of phase. ( Just a thought )


Robert

[gyula]

Yes, it explains, thanks for the drawing.

Now on your switching at the output of the full wave bridge: I had thought that the puffer capacitor would connect directly to the diode bridge output and the switching would take place only between the actual load and the capacitor in the desired and controlled time.
PErhaps there is no meaningful difference between the two?

Gyula

[Robert49]

Hi Robert,

Thanks for the further details on your interestingly shaped coil setup. I ask how you mean using "the half of the coils" for the test:

1) out of each bifilar coils, you used only the single wire coil halves for driving and the other single wire coil halves for generating? (i.e your bifilar coils acted as a 1:1 turns ratio air core transformer, right?)

OR

2) you used only 4 bifilar coils for driving and the remaining 4 bifilars for generating, using the bifilars in series aiding phase for both?

I guess your answer is the first possibility?


Now on your question: I think you are correct when assuming you could switch the capacitor to discharge it to a load and the best moment of time and its duration should be found for this switching action, as you suggest during the rise of the voltage on the capacitor. To find it, this definitely needs tinkering and I do not think you are wrong on that.

Greetings, Gyula

Hi Gyula

Here is a drawing of what I mean.
Hope this explains it clearly.

Thanks

Robert

[gyula]

Hi Robert,

Thanks for the further details on your interestingly shaped coil setup. I ask how you mean using "the half of the coils" for the test:

1) out of each bifilar coils, you used only the single wire coil halves for driving and the other single wire coil halves for generating? (i.e your bifilar coils acted as a 1:1 turns ratio air core transformer, right?)

OR

2) you used only 4 bifilar coils for driving and the remaining 4 bifilars for generating, using the bifilars in series aiding phase for both?

I guess your answer is the first possibility?


Now on your question: I think you are correct when assuming you could switch the capacitor to discharge it to a load and the best moment of time and its duration should be found for this switching action, as you suggest during the rise of the voltage on the capacitor. To find it, this definitely needs tinkering and I do not think you are wrong on that.

Greetings, Gyula

[Robert49]

New tests

Hi.

If you look at my motor-generators on posts #1618 and especially #1629 which is the new one I'm working on now.The "twisted" coils are bi-filar #23awg and are pulsed one after the other in opposite polarity. The magnets are ns-sn-ns-sn etc...
I put a bridge rectifier on just one half of the coils for this test and only capture the output between the drive pulses. If I try with the two halves, I get the usual drag with a 50% rise in amps.But with only one, here's what happens.

70v .325a= 22.75 watts input

When I switch on a resistive load of 25 ohms on the rectifier,there is a quick drop to 18.7 watts input and then a slower rise to over 22.75w.

With a 96000uf capacitor as a load, the drop was even greater and the rise time longer.( lost the numbers but about 10 watts)

With the cap and resistor in parallel, the input dropped to 6.45 watts (from 0.325a to 0.1a) and rose back very slowly to higher than 22.75w

In either case the motor slows down and the amps should rise as it does when I simply put a load on the shaft while not collecting anything, and that is due to the timing pulses getting longer, not to counter emf.

I shorted the output and a sudden jump to 0.00a 0.00w for a brief moment and blew up a 17amp 500v 250watt mosfet. Not a good idea...$$

As a result, I'm guessing if I capture the output just for that brief moment during the rise of voltage on the cap to about 50volts, where it's about to draw over 22.75 watts, I could switch the cap to discharge on a load and not raise the input power at all. Of course, I could also be wrong??
That is the next step for me.



Robert

[ren]

The missus had a thermomix demonstration the other day at our house. So I looked it up and it has a variable reluctance motor in it. Should have seen her face when I said I was going to pull it apart.

Damn thing minced raw sugar granules into powdered (icing) sugar in 5 seconds flat. Is a beast. The "demonstrator" then went on to tell everybody that it has no contacting OR moving parts. Had to leave the room.

lol.

[Robert49]

Prototype2...

My pleasure Blargus.

I just made another one of the same crazy design with a clear view of the design. Really don't know where I'm going with this but it's fun to experiment.
The magnets are too small and I'll need to make a new wheel and put
stronger magnets.
Nevertheless it works great and has quite a bit of torque.
If you look at the first scope shot on post 1624, you'll see that the drive pulse is applied at the zero voltage of the generator wave.
I can vary the pulse position easily while running which is good for finding the most effective setting.

Thanks

Robert

[Blargus]

Thanks a lot for the update. Robert!

[voltan]

hi all.after reading this from page 1 to here, and looking around the internet it would appear that this thread was ahead of it's time.for the average home builder, the challenges of engineering a variable reluctance motor,either from scratch or by stripping and machining rotors in conventional designs,are formidable.an image search for variable or switched reluctance motors shows examples of commercially available motors that are ready to go.no stripping or machining required.presumably this is a recent development and was not the case for most of the time that this thread has been going.
the V.R motor concept is notable for dating back to the 1840s.it has laid dormant,mostly ignored and forgotten about for a staggering 150+ years,considered impractical due to difficulties with switching coils reliably and accurately in a brushless motor.in recent times advances in IC's,sensors and PLC's etc.have made them practical.now that it works properly,the inherent advantages of the design make it the motor of choice for a growing number of applications,domestic,commercial and industrial.

[gyula]

Hi Robert,

Have come back from traveling. Re on your Reply #1622 above, yes it would be very good to have a counter emf waveform which has a zero or near zero value where an appropiate input pulse can be fired to repel (or attract, as wished) the rotor magnets. The relatively smaller than 'usual' increase in input current for a shaft load indicates that you have found such "sweet" positions for the driving pulse.
Your latest tests (25.2 W input power only) when ignoring the collapsing spikes and not collecting the 'juice' from the generator function indicate that conventional induction from the rotating magnets makes you "pay" in input power as usual.
Some tinkerers with motors say that if the captured and collected power in a puffer capacitor is also pulsed by a correctly controlled (and separate) switch into a load (like a light bulb), then this method would make such load almost "invisible" to the motor input power. I think this can be true only at the expense of simply not utilizing all the captured and stored energy from the capacitor versus the case when you have a direct connection and no controlled switch for such light bulb load.

Thanks, Gyula