Electric Motor Secrets

[gyula]

Hi Robert,

Thanks for the further details. Sorry I do not get what you mean on counter emf? For me it means just the (unwanted) induced voltage in the stator coils whenever the rotor magnets are in motion. And if the induced voltage is 80 Vpp, then is not it just the counter emf? I may misunderstand something.

Can you recall when you loaded the shaft of the motor, the input current went up accordingly?

Well, 100 W output is very good indeed when the input is also 100 W. Can you recall the DC input voltage amplitude you gave to the motor and how you measured the output power?

Thanks, Gyula
PS: From tomorrow I will be away for 3 days.

[Robert49]

Hi Robert,

Thanks for the further details. Sorry I do not get what you mean on counter emf? For me it means just the (unwanted) induced voltage in the stator coils whenever the rotor magnets are in motion. And if the induced voltage is 80 Vpp, then is not it just the counter emf? I may misunderstand something.

Can you recall when you loaded the shaft of the motor, the input current went up accordingly?

Well, 100 W output is very good indeed when the input is also 100 W. Can you recall the DC input voltage amplitude you gave to the motor and how you measured the output power?

Thanks, Gyula
PS: From tomorrow I will be away for 3 days.

Gyula, you are right about the counter emf being a generator effect but in this motor it is desired.When the magnets pass through the coils they first generate voltage in one direction until they are dead center where the voltage is at zero. Then the voltage rises in the opposite direction. I pulse the coils in repulsion mode at the zero voltage position or very close to it which eliminates almost all the effect of cemf .At least that's my theory.

As far as loading the shaft and the effect on input power, it is minimal and due to the pulses being longer as speed decreases and on this motor measuredin milliamps. At 100 volts input, the motor uses 490ma and when loaded to half speed it uses 690ma.

I recall putting 100 volts 1amp in and I had a 200 watt light bulb connected on the output.Then I measured the amps and voltage on the bulb.

Hope this clears up things for you

[Robert49]

Update

Hi
I made more precise measurements.
The motor ran at 166volt 740milliamps 3417rpm no load.(122.84 watts)
Loading the shaft 166volt 900milliamps 2500rpm.(149.4 watts)
It takes quite a bit of pressure to slow it down.
I have to capture the spikes from the collapsing fields which are not that high since there is no iron core, otherwise the motor jams. But by doing that, i'm also capturing one phase of the generator voltage and both are dissipated in a 40watt light bulb fully lit.



Robert

[Robert49]

Hi Mbrown.

I decided to ignore the collapsing spikes and am no longer collecting the generator function.
I ran the motor at 140volts and it went to 3362 rpm with only 0.18 amp
or 25.2 watts. It does have a lot of torque.(not measured, just felt)
Look at the position of the driving pulse.
Here are some scope shots.

Robert

[mbrownn]

Those scope shots look exactly like what the friend of mine is getting. Im sure he will be interested. I call that the mwm wave, very similar to the kromray converter.

[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

[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.

[Blargus]

Thanks a lot for the update. Robert!

[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

[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]

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

[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]

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]

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]

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