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Uspring

Mon Sept 07 2015, 05:49PM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Dr. Slack wrote:

c) Assume the rotation rates are identical.

If I can get my head round this properly, I think it makes a rectifier with a controllable output voltage*. If the armature is driven synchronously to the field excitation, then it will output any DC voltage from fully negative to fully positive, controlled by adjusting the phase of the armature with respect to the field excitation.

For a DC voltage output of an inductor a constant dphi/dt is required. That's only possible for a limited duration.

Salvador

Mon Sept 07 2015, 07:03PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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still would love to hear comments about the use if high frequency and having smaller size thing about this generator, or maybe it doesnt work that way but it should?

there is one other idea , already pinned down by one man who even made a patent for it , well this would be even closer to the point but sadly it has to have a sliding contact, because as far as I know the faraday disc phenomena doesnt work otherwise the electricity inducing part always has to be moving.
here is a video about the way it should work.

a while back i had the idea that maybe a faraday disc would work with a spinning AC field and the disc being stationary but i guess that didint work but now i can't remember.
i mean the idea of a few thick loops of faraday type generator with a controllable field is not bad the downside for this is the brushcontacts.

Dr. Slack

Tue Sept 08 2015, 09:17AM

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

Uspring wrote ...

Dr. Slack wrote:

c) Assume the rotation rates are identical.

If I can get my head round this properly, I think it makes a rectifier with a controllable output voltage*. If the armature is driven synchronously to the field excitation, then it will output any DC voltage from fully negative to fully positive, controlled by adjusting the phase of the armature with respect to the field excitation.

For a DC voltage output of an inductor a constant dphi/dt is required. That's only possible for a limited duration.

Only for a limited duration. Duh! Of course. I was right to put that asterisk in there!

Salvador

Tue Sept 08 2015, 02:36PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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that video by the way isn;t mine , but I found it out a while ago when I was talking about the faraday discs here. well hsi idea seems to work , I wonder how would the output look like if I excited my type of generator with a high frequency AC field.

I guess what i propose is not that different from already existing typed of reluctance motors/generators like this one for example

radiotech

Tue Sept 08 2015, 04:38PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Consider a non magnetic serrated disk spinning close to a solenoid connected to
a load resistor.

Eventually the residual magnetism in the solenoid core would induce a current in
the rotor, which by Lenz law would induce a voltage back into the solenoid. This
would build with the current through the load resistor.

About 50 years ago, a gadget I built was published in a radio magazine. It
was a Telechron clock motor with gear box attached to a 6 inch lever. When
the lever was pushed, the aluminum rotor spun much faster than the 60 Hz
rate it usually operated at. It made a fine, quick audio glide tone generator,
putting out a few volts, used for speaker tests.

So, the question is this: Do you think the frequency of the item first stated
would produce twice the frequency of the number of serrations ?

Salvador

Tue Sept 08 2015, 05:42PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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pardon me radiotech , but I'm not sure I fully understood your question.
well if the disc is excited with dc , then I assume it would work as a typical reluctance generator and the frequency induced would be the result of the poles (cuts) in the rotor and the rpm of it.

Judging by your explanation of the device for speaker testing you made I assume this principle was at work there hence when the disc was spun to its highest rate the frequency also was the highest and as it got slower the frequency decreased and the speaker was kinda tested in the audible range probably.

but i didnt understand the very question could you please elaborate ?

radiotech

Tue Sept 08 2015, 10:36PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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A solenoid with a iron core, develops a voltage in that device when an aluminum
rotor with slots, is spun close to one end.

Any iron will have a feeble degree of magnetization because of the earth's field.
The aluminum rotating in that field, will develop a voltage. This voltage will cause a current
in the aluminum, which will have its own magnetic field. This field will induce a voltage in the solenoid.

To an extent this alternator uses no DC whatsoever.

If you remove the magnetism from a loudspeaker, the speaker will produce a
note twice that of the voltage fed to it.

So if this loudspeaker acted as a microphone, would the voltage produced be
one half the frequency of the sound wave exciting it ?

Salvador

Wed Sept 09 2015, 08:08AM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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well a loudspeaker , atleast the most common form of it is nothing more but a linera motor to my mind driven with variable frequency AC.
so the field of the coil when energized pushes against the field of the permanent magnet.much like the rotor field pushes against the stator field in universal motors.
I know in the old times some electricians told me that they were putting extra magnets at the end of the magnet to make the field stronger to sort of improve the speakers ability.

as for your question well I'm not sure to be honest.if the speaker coil has virtually no magnetic field against which to push itself would it work at all if excited with any voltage? Or maybe it would because the endplates of the permanent magnet are iron and the field produced by the coil would induce an oppposite field in the iron ?

I assume the answer to your question is yes , but mainly due to the fact you talked about the voltage and the note being twice as strong.

radiotech

Wed Sept 09 2015, 07:31PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

Think of it this way:

If you wound a coil, and passed a current through it, the coil would exert a force of attraction
on a ferrous material.

If you repeated the experiment, and used a magnetized ferrous material, it would attract
the magnet . But if you reversed the battery, it would repel the magnet.

AC current has two polarities, separated by time.

An AC current would attract and then repel the magnet. This would form a sound
pressure wave, of a specific frequency, that of the AC current

Now if the speaker just had just the non magnetized structures (i.e. you took off the magnet) , the AC current would draw the voice coil in during the positive peak, and
also draw the coil in during the negative peak.

This would mechanically translate into a sound wave of twice the frequency of the
AC current. (it would raise an octave )

Why I brought these matters up for your post, is these actions enter in to an area known
as 'square law' devices in electricity.

I have worked in audio, and the ability of a transducer to NOT produce overtones
is very important. So magnet strength, gap design, cone compliance all go into the brew.

Salvador

Wed Sept 09 2015, 08:25PM

Registered Member #54402 Joined: Mon Feb 02 2015, 11:09PM
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Posts: 86

Ok, well I am very grateful for any feedback and I enjoy any technical chat, but could you please elaborate on the reasons why you brought this up? I mean I feel like I missed something here.

Oh by the way what are your thoughts on the very things i started talking in this thread? also about the video of the faraday ac generator that i linked as an example of what I was thinking of.
as I said sadly it has to use brushes , otherwise i think it would make an interesting device.

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