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Constant Current and Constant Voltage Regardless of Load

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neomag

Sun Jan 03 2010, 08:22AM

Registered Member #2595 Joined: Sun Jan 03 2010, 08:17AM
Location:
Posts: 4

What is a good explanation for how a brushless DC motor can run with a constant current and voltage regardless of load?

For example, how can this motor do so?

Sulaiman

Sun Jan 03 2010, 10:02AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

A simple explanation is that the motor is so inefficient
Efficiency = (mechanical Watts out) / (electrical Watts in)
that changes in mechanical load are not easily seen as electrical input changes.

Conventional electric motors range in efficiency up to about 95%
I doubt that the motor shown can do even 50%. I guess much much less.

It appears that they are using a toroid - that's a new one for me
can't see any benefit other than the 'novelty' may attract optimistic investors !

If increasing the load TRULY did not increase input then as you increase the load you would (presumably) get to a point where the mechanical power output is greater than the electrical power input - free energy - which we all know is not possible with ANY of the marvelous electro-mechanical inventions floating around on the

The clamped ringing at the end of the current pulse is enough to show that energy is being wasted.

Avalanche

Sun Jan 03 2010, 12:28PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Using toroids is hilarious - surely this will ensure absolute minimum flux linkage because the toroid is containing it all?

unless they are using powder toroids and relying on the leakage. Still I don't get it

Dr. Slack

Sun Jan 03 2010, 01:02PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

This is not a convtional brushless DC motor. This is an M&S (UK joke, other nationalities please ignore) useless exotic demo motor, about as useful as the thermo-ball-bearing motors that also appear to defy explanation, but work nevertheless.

At 7:00 to 7:30 into the linked clip, he asserts that "all the input energy is disspated as heat, yet we still have rotary output". I stopped watching at that point. It sounds but a short step from there to proclaiming that this motor delivers phree n-ur-gee (speeling mistakes intentional to avoid attracting the wrong kind of search). I wonder if he's trying to attract funds for its further development. The motor is so inefficnet, there would be no way to do calorimetry on the setup he has there to confirm or disprove his assertion within measurement error bounds.

<edit> yup, I was right, see

<edit>

Don't try to learn about real brushless motors from these quacks.

The motor works as a reluctance motor. An unpowered toroid will attract the rotor magnets because of its relative permeability of hundreds. It takes very little current to saturate the toroid, and then the rotor magnet will no longer be attracted. Alternately saturating and not the toroids at the correct instants causes motor rotation to continue once it has been started.

He makes a big deal of it spinning in the same direction, reegardless of input polarity, but it doesn't switch on until it's spun, and he spins it the same way each time. As the stator pitch is the same as the rotor pitch, it will spin in either direction once started. However, it would be trivial to make a three phase, or N phase for that matter, version which could self start.

You may rest assured that not all of the large amount of input energy to this very inefficient motor gets dissipated as heat, a tiny fraction ends up as mechanical energy in the output. I presume that magnetising the toroid when the field is strong due to the rotor magnet proximity, then demagnetising it when the external field is weaker is akin to taking a volume of gas round a compress, heat, expand, cool cycle that does work. A cookie for anyone who fills in the details of this suggested energy transfer mechanism, or comes up with the correct one.

I'm sure that his next round of funding will be to replace the copper by superconductor to eliminate all of the electrical losses, to be left with just the output of the rotor for free.

Avalanche

Sun Jan 03 2010, 02:10PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Something to do with the speed being necessary to achieve any torque whatsoever?

I'm probably totally incorrectly trying to compare this thing to conventional motor, but it sounds to me like a motor that converts 99% of it's input energy into heat and 1% into torque is a conventional motor running in the worst possible condition (all the current on the wasteful 'd' axis, rather than the 'q' axis where the torque is). Conventionally, as a motor speeds up, current appears on the 'd' axis due to an armature reaction type effect, so a control loop is set up to compensate by shifting the field. It looks like this thing is doing the opposite, and relying on the armature reaction to create the torque - and so the thing accelerates because the optical trigger is 'fixed' and doesn't compensate for speed. All this assumes there *is* some back EMF and therefore flux-linkage, I don't see how there can't be a small amount otherwise what would be limiting the speed to a constant RPM, other than mechanical losses? In this case though, the EMF would be able to exceed the supply voltage, yet the supply voltage would still limit maximum speed - due to conventional field weakening (running the motor inefficiently as above, so that a greater EMF and therefore speed can be achieved).

That's my take on it, but I'm not sure if any of that stuff applies on this slightly nuts thing

Dr. Slack

Sun Jan 03 2010, 02:56PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

The motor is a switched reluctance motor, and a very inefficient one at that, not a "brushless DC" motor, in the useful energy transforming sense of the phrase.

This is the icon from the Steorn site

against the "how the orbo motor works" page

1262530358 72 FT1630 Sect Validation

like, duh!

Avalanche

Sun Jan 03 2010, 03:54PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

lol, I dunno

I didn't think switched reluctance motors had permanent magnets and electrical switches, the 'switched' meaning the alignment of pole pieces in the motor. Closest thing I could compare this to would be a very poor permanent magnet synchronous motor..?

Anyway I'm off to put a 0.5ohm shunt across the filament in my room light, because all the electrical energy will go into heating my room, and the light will be free!!!

Steve Conner

Sun Jan 03 2010, 06:09PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I refuse to watch this! But I do know that Tesla used a toroid made of coiled iron wire as the stator for his "Egg Of Columbus", and maybe his first induction motor too.

It's all in how the coils are wound. If you have three coils wound in lumps 120 degrees apart on the toroidal core, connected to a three-phase supply, then the flux contained in the toroid always sums to zero, because the voltage vectors in a three-phase system sum to zero. Therefore, the magnetizing flux is forced to pass out of the toroid at the unwound spots in between the coils, and across the hole in the middle, which is where you put the rotor.

It doesn't work as well as the modern form of stator with its salient poles and distributed windings, but it does work.

neomag

Tue Jan 05 2010, 08:07AM

Registered Member #2595 Joined: Sun Jan 03 2010, 08:17AM
Location:
Posts: 4

I'm going to be watching the demo today as it starts back up. I will also be watching the new experiment they will perform on Friday.

Carbon_Rod

Tue Jan 05 2010, 08:49AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Steve McConner wrote ...

I refuse to watch this!

I must agree... as its excruciating to watch a con...
the local corporate relations officer actually asked if some research projects were related to those crank's contraptions.

The publicity the Steorn group has received is the only real innovation they've made.

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