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'[EE]: Inducing power'
2001\05\29@085953 by Jinx

face picon face
Hi all, perhaps someone can help with a wee power problem. I've
got a circuit board mounted on a motor shaft. The circuit is there to
measure the movement of an escapement mechanism (kind of
like a governor) as the shaft turns from 100 to 3500rpm. The
circuit itself is not a problem, I've managed to attached a small
slider pot to the escapement and it's measuring OK with an ADC.
What I'd like to do is induce power to the circuit using some kind
of magnet/coil system. I need around 15mA at 6VDC. A possibility
is to use a 7-segment LED (synched with the rotation) to indicate
the escapement movement, hence the power requirement. Using
batteries is not really an option because of the duration of the
measurements and particularly if the LED idea goes ahead. I've
got plenty of envultured materials - strong HDD magnets and
more scrap transformers (enamelled wire of all gauges and
laminate cores) you can shake a stick at. I thought I may be able
to attach a small DC motor to the main motor's shaft as a
generator but that's proved too tricky because of space limitations.
So, any ideas on the most efficient way to induce power into coils
on the PCB from stator magnets ?

TIA

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2001\05\29@092144 by Russell McMahon

picon face
> Hi all, perhaps someone can help with a wee power problem. I've
> got a circuit board mounted on a motor shaft. The circuit is there to
> measure the movement of an escapement mechanism (kind of
> like a governor) as the shaft turns from 100 to 3500rpm. The
> circuit itself is not a problem, I've managed to attached a small
> slider pot to the escapement and it's measuring OK with an ADC.
> What I'd like to do is induce power to the circuit using some kind
> of magnet/coil system. I need around 15mA at 6VDC. A possibility
> is to use a 7-segment LED (synched with the rotation) to indicate
> the escapement movement, hence the power requirement. Using
> batteries is not really an option because of the duration of the
> measurements and particularly if the LED idea goes ahead. I've
> got plenty of envultured materials - strong HDD magnets and
> more scrap transformers (enamelled wire of all gauges and
> laminate cores) you can shake a stick at. I thought I may be able
> to attach a small DC motor to the main motor's shaft as a
> generator but that's proved too tricky because of space limitations.
> So, any ideas on the most efficient way to induce power into coils
> on the PCB from stator magnets ?

More high Jinx ???

If you have room for a magnet field all the way around the stator this is a
trivially simple task. It becomes a basic alternator. The task is not much
worse with a coil passing a fixed magnet once per revolution although
mechanical balance may be more of a problem. Typical olde days motorcycle
alternators and magnetos tended to use a coil in one place which was passed
by a rotating magnet once per rev. Come to think of it, most every lawn
mower I have ever seen does just that.

Main requirements are half a closed magnetic path around the coil (eg a
metal u of laminations) with the moving magnet almost closing the gap across
the U as it passes - air gaps of mm's are going to be OK.
             N
  IIIIIIIIII   N
L II L     S
  IIIIIIIIII   S
              \/

You COULD use a coil to coil transfer with a highish frequency field in the
stator coil but this is probably less simple than a magnet and coil and adds
extra complexity. If using coil to coil then resonating the receiver can
give good results with largish air gaps (many millimetres).

The power level of 100 mW should be easy enough to achieve.


           Russell McMahon

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2001\05\29@093824 by Alan B. Pearce

face picon face
> Hi all, perhaps someone can help with a wee power problem. I've
> got a circuit board mounted on a motor shaft. The circuit is there to
> measure the movement of an escapement mechanism (kind of
> like a governor) as the shaft turns from 100 to 3500rpm. The
> circuit itself is not a problem, I've managed to attached a small
> slider pot to the escapement and it's measuring OK with an ADC.
> What I'd like to do is induce power to the circuit using some kind
> of magnet/coil system. I need around 15mA at 6VDC. A possibility
> is to use a 7-segment LED (synched with the rotation) to indicate
> the escapement movement, hence the power requirement. Using
> batteries is not really an option because of the duration of the
> measurements and particularly if the LED idea goes ahead. I've
> got plenty of envultured materials - strong HDD magnets and
> more scrap transformers (enamelled wire of all gauges and
> laminate cores) you can shake a stick at. I thought I may be able
> to attach a small DC motor to the main motor's shaft as a
> generator but that's proved too tricky because of space limitations.
> So, any ideas on the most efficient way to induce power into coils
> on the PCB from stator magnets ?

How about starting off with a brushless DC fan, but fixing the fan unit, and
mounting the (what used to be) drive coils on your PCB, rectifying the
output for your circuit. Use an old fan from a PC power supply or similar
(although from your description it may be a bit big, but would be a starting
point).

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2001\05\29@120614 by Olin Lathrop

face picon face
> Hi all, perhaps someone can help with a wee power problem. I've
> got a circuit board mounted on a motor shaft. The circuit is there to
> measure the movement of an escapement mechanism (kind of
> like a governor) as the shaft turns from 100 to 3500rpm. The
> circuit itself is not a problem, I've managed to attached a small
> slider pot to the escapement and it's measuring OK with an ADC.
> What I'd like to do is induce power to the circuit using some kind
> of magnet/coil system. I need around 15mA at 6VDC.

One of my current projects has this problem also.  We are using a
transformer with the secondary rotating on the shaft.  It works fine to
power up a PIC and a bunch of LEDs.

Instead of putting the display on the rotating board, how about using an IR
LED to send information to a stationary board and display the result there?


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, spam_OUTolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2001\05\29@123952 by Roman Black

flavicon
face
Jinx wrote:
I thought I may be able
> to attach a small DC motor to the main motor's shaft as a
> generator but that's proved too tricky because of space limitations.
> So, any ideas on the most efficient way to induce power into coils
> on the PCB from stator magnets ?

To get it efficient and small you need to reduce
air gaps and consider magnetic flux paths. I think
a sensible option would be to pull some bits from
a commercially made dc motor or generator, and
use a magnet and coil device that are already
curved and designed to be efficient in a rotating
system.

Like a small dc brush motor, has a rotating coil.
You could fit this to your shaft somehow and use
its curved perm magnets around that. Then just
full wave rectify and use a zener for regulation.
:o)
-Roman

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2001\05\29@132923 by Jose Angel Navarro

flavicon
face
Have a look in Google at "propeller clocks" They have good ideas about
transmiting power in a motor shaft.


At 00:57 30/05/01 +1200, you wrote:
{Quote hidden}

________________________________
_______Jose Angel Navarro_______
_____welcome.to(ba/rra)janc_____
___janc(arroba)altavista.net____
________________________________

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2001\05\29@164746 by Jinx

face picon face
> Like a small dc brush motor, has a rotating coil.
> You could fit this to your shaft somehow and use
> its curved perm magnets around that. Then just
> full wave rectify and use a zener for regulation.

That's a good suggestion, and one reason why I considered a
small DC motor driven as a generator. Problem with modifying
such a motor (ie "cheap") is that the main shaft has a 12mm
diameter, and  it'll be awful tricky to take parts from a smaller
motor and make them fit "somehow". But, as they say, it ain't
over till the fat lady sings

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2001\05\29@165551 by Jinx

face picon face
> Have a look in Google at "propeller clocks" They have good ideas
> about transmiting power in a motor shaft.

Thanks. I'd seen Bob Blick's pages some time ago and one was
powered using a rotary transformer (the others use modification
of the motor, which isn't an option here). Unfortunately there are
no details on that rotary transformer and I've got no reply from the
author

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2001\05\29@170201 by Jinx

face picon face
> One of my current projects has this problem also.  We are using a
> transformer with the secondary rotating on the shaft.  It works fine to
> power up a PIC and a bunch of LEDs.

Was this a specially-made transformer ? My usual winder says he
knows what I want but hasn't the formers to do the job. He's just my
first stop of course, but for this level of power I'm sure I could have
a go at something in the shed that gives results. And as I said, I've
got the materials to make a transformer if I can get a ball-park idea
of what's required

> Instead of putting the display on the rotating board, how about using
> an IR LED to send information to a stationary board and display the
> result there?

Yes, that's a possibility. Minimising the transmissions would certainly
save a lot of power and perhaps make batteries an option, although
I have to say I'm in a tinkering mood

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2001\05\29@171412 by hard Prosser

flavicon
face
As another idea - what about the magnetic transformer used at the base of
the heads on a VCR.? More or less a double pot core with the primary
rotating and the secondary fixed.  Tuning the windings to resonance will
omprove the efficiency.
Or a solar cell with a focussed lamp providing the illumination?
Richard P




                   Jinx
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                   microcontroller
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                   MIT.EDU>


                   30/05/01 09:01
                   Please respond
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> One of my current projects has this problem also.  We are using a
> transformer with the secondary rotating on the shaft.  It works fine to
> power up a PIC and a bunch of LEDs.

Was this a specially-made transformer ? My usual winder says he
knows what I want but hasn't the formers to do the job. He's just my
first stop of course, but for this level of power I'm sure I could have
a go at something in the shed that gives results. And as I said, I've
got the materials to make a transformer if I can get a ball-park idea
of what's required

> Instead of putting the display on the rotating board, how about using
> an IR LED to send information to a stationary board and display the
> result there?

Yes, that's a possibility. Minimising the transmissions would certainly
save a lot of power and perhaps make batteries an option, although
I have to say I'm in a tinkering mood

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2001\05\29@171833 by David VanHorn

flavicon
face
Light??
90mW dosen't seem like an outrageous amount.
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2001\05\29@175232 by Jinx

face picon face
I had a thought this morning - I replaced the filament bulb in
the front light on a bicycle with a white LED. It's very bright
at only 9mA, and so perhaps a spin-off to my motor project
could be a trickle charger for the LED battery (6V gel cell).
Anyone seen this already applied ?

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2001\05\29@175629 by Jinx

face picon face
> Light??

How do you mean ? Just shine a bright light at on detector(s) ?

> 90mW dosen't seem like an outrageous amount.

No it isn't, and as long as the whole lot is balanced there's no
option than can be dismissed. Ease of assembly and repeatability
are desirable, which is one possible drawback to winding my own
transformers

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2001\05\29@180305 by David VanHorn

flavicon
face
At 09:55 AM 5/30/01 +1200, Jinx wrote:
> > Light??
>
>How do you mean ? Just shine a bright light at on detector(s) ?

On solar cells.

You only can illuminate 1/3 of them at any moment, with only one light, but
it may be that you can have multiple light sources around the casing.

No mechanical tolerance problems in this approach, either.

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the text of an email, I am forbidden to have it.

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2001\05\29@181601 by Jinx

face picon face
> As another idea - what about the magnetic transformer used at the
> base of the heads on a VCR.? More or less a double pot core with
> the primary rotating and the secondary fixed.  Tuning the windings
> to resonance will improve the efficiency

That's an idea. Roman, you're Mr WhatgoesoninsideVCRs, any
comment ?

> Or a solar cell with a focussed lamp providing the illumination?

I used to have a source for the miniature 0.5V calculator cells but
they disappeared. Maybe I'll start looking around again

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2001\05\29@182237 by Jinx

face picon face
> >How do you mean ? Just shine a bright light at on detector(s) ?
>
> On solar cells.
>
> You only can illuminate 1/3 of them at any moment, with only one light,
> but it may be that you can have multiple light sources around the casing.

No reason why a hexagonal ring of small cells couldn't be used.
My experience with solar cells is that they're pretty fussy regarding
the incident angle of the light if you want a good output

And I believe flexible cells are on the market now, wonder if they could
be rolled into a cylinder to keep a constant 90 degree perpendicular
between the light source(s) and the cell. Or was that batteries

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2001\05\29@183338 by Gennette, Bruce

flavicon
face
Does it have to be induced across a gap?  It should be easy to fit 2 or 3
insulated rings to the rotating shaft (for power in and data out) and fit 2
or 3 spring loaded contacts on a bracket somewhere.
If noise is too great a problem when crossing the joints in the rings use
the noise as a synchronisation signal for data transmissions.  At 3500rpm
you have 17ms per rev, more than enough time to send 5 bytes @ 2400 baud
8,N,0 each rev.

Bye.

{Original Message removed}

2001\05\29@212155 by Alexandre Domingos F. Souza

flavicon
face
>I had a thought this morning - I replaced the filament bulb in
>the front light on a bicycle with a white LED. It's very bright
>at only 9mA, and so perhaps a spin-off to my motor project
>could be a trickle charger for the LED battery (6V gel cell).
>Anyone seen this already applied ?

       BTW, today I saw the FIRST semaphore with LEDs in Brazil!!! Nice one! :oD

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2001\05\30@013757 by Vasile Surducan

flavicon
face
On Wed, 30 May 2001, Jinx wrote:

> So, any ideas on the most efficient way to induce power into coils
> on the PCB from stator magnets ?
>

 The answer is in your basement. The smallest way is the to use  the 6
pole brushless motor from your defective laser printer.
Usual this motor have a 6 face mirror clasped with permanent motor.
The coils are mounted on the pcb. If you rotate the rotor with 3500 rpm
you can rectify the voltage using a diode hexabridge. I don't know if
you'll get 6V but if not, a voltage doubler may solve your problem ( only
for small curents up to 15mA )

TIA ?
Vasile

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2001\05\30@031238 by Russell McMahon

picon face
I can point you to the man with the NZ (and possibly US & European too)
patent :-)
(No, it's not me)


     Russell McMahon



> I had a thought this morning - I replaced the filament bulb in
> the front light on a bicycle with a white LED. It's very bright
> at only 9mA, and so perhaps a spin-off to my motor project
> could be a trickle charger for the LED battery (6V gel cell).
> Anyone seen this already applied ?

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2001\05\30@031251 by Russell McMahon

picon face
> > >How do you mean ? Just shine a bright light at on detector(s) ?
> >
> > On solar cells.
> >
> > You only can illuminate 1/3 of them at any moment, with only one light,
> > but it may be that you can have multiple light sources around the
casing.
>
> No reason why a hexagonal ring of small cells couldn't be used.
> My experience with solar cells is that they're pretty fussy regarding
> the incident angle of the light if you want a good output
>
> And I believe flexible cells are on the market now, wonder if they could
> be rolled into a cylinder to keep a constant 90 degree perpendicular
> between the light source(s) and the cell. Or was that batteries


Twas solar cells. Available locally too.

The effective area is the projection of the cells in the plane at 90 degrees
to the light.
eg if you have a ring of cells with a 100mm od and the calls are 10mm wide
then you always effectively get 1000 mm^2 of cell at 90 degrees to the
light.

Lessee modern cells are 15% odd (more for :"real" ones) and at 1 sun you get
1000w x 15% = 150w/m^2
For 100 mW you need effective area of 0.1/150 = 666 mm^2 or about the 100mm
x 10mm ring above.
Actual cell length for a circle = Pi.d = about say 400 mm (allow a polygon).
400mm x 10mm = 80 x 50 mm = about $20 in Dick Smiths. Start cutting.

Getting the 1 sun is another matter. That's about a 100 watt bulb at 100mm
or something a bit more optimised for IR emission and reflectorised -
probably about 20 watts in???

RM

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2001\05\30@042057 by Roman Black

flavicon
face
Jinx wrote:
>
> > Like a small dc brush motor, has a rotating coil.
> > You could fit this to your shaft somehow and use
> > its curved perm magnets around that. Then just
> > full wave rectify and use a zener for regulation.
>
> That's a good suggestion, and one reason why I considered a
> small DC motor driven as a generator. Problem with modifying
> such a motor (ie "cheap") is that the main shaft has a 12mm
> diameter, and  it'll be awful tricky to take parts from a smaller
> motor and make them fit "somehow". But, as they say, it ain't
> over till the fat lady sings


Do you have access to the end of the big shaft?
Maybe you could just glue the small armature to
the end of the big shaft.

What about a simple brush, since you are only
talking low currents you can use the big motor shaft
as an earth and use one brush or wiper, it doesn't
have to be a complete slipring or anything special.
You were planning to use filtering and regulation
anyway?:o)
-Roman

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2001\05\30@042731 by Roman Black

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face
Jinx wrote:
>
> > As another idea - what about the magnetic transformer used at the
> > base of the heads on a VCR.? More or less a double pot core with
> > the primary rotating and the secondary fixed.  Tuning the windings
> > to resonance will improve the efficiency
>
> That's an idea. Roman, you're Mr WhatgoesoninsideVCRs, any
> comment ?


I would't bother. Yes it is a clever suggestion, but
the rotary transformer in VCR heads are about 3.5cm
across and permanently bonded to the large alloy head
halves. Much harder to integrate into your design
compared to a dc motor armature or simple brush.
:o)
-ROman

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2001\05\30@062451 by Jinx

face picon face
> What about a simple brush, since you are only
> talking low currents you can use the big motor shaft

If this is an almost continuously running motor how will the brushes
(carbon I presume) hold up ? For example, what sort of replacement
period would you consider average and/or reasonable ?

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2001\05\30@062716 by Jinx

face picon face
> I would't bother. Yes it is a clever suggestion, but
> the rotary transformer in VCR heads are about 3.5cm
> across and permanently bonded to the large alloy head
> halves. Much harder to integrate into your design
> compared to a dc motor armature or simple brush.
> :o)
> -ROman

Bugger

They sound very similar to some of the old 5 1/4" floppies and
HDD that have a circular magnet and coils integral to the PCB

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2001\05\30@063110 by Jinx

face picon face
> The answer is in your basement. The smallest way is the to use
> the 6 pole brushless motor from your defective laser printer

Well, it has been sitting there for a while, and I've more than one.
What I shall be doing is getting busy with some ideas and report
back. One obvious use for the hobbyist is propellor clockery. And
as Olin mentioned, he too needed to do something similar. Perhaps
not a common application, but worth documenting

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2001\05\30@064812 by Patrik Husfloen

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Very interesting, is it as bright as the old bulb?

/Patrik
----- Original Message ----- From: "Jinx" <TakeThisOuTjoecolquittEraseMEspamspam_OUTCLEAR.NET.NZ>
To: <RemoveMEPICLISTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Tuesday, May 29, 2001 11:50 PM
Subject: Re: [EE]: Inducing power


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2001\05\30@072323 by Jinx

face picon face
> I had a thought this morning - I replaced the filament bulb in
> the front light on a bicycle with a white LED. It's very bright

> Very interesting, is it as bright as the old bulb?

Yes, well, bright but blue rather than the yellow of a filament. I
think two LEDs would be better. You place them facing backwards
at the focus of the reflector. At night it does illuminate ahead
somewhat, for example it will make a reflective road sign sparkle,
and you can see with it. Using two in series on 6V (at present I use
one through a 330R resistor) would still be only 18mA, which is a
fraction of filament current. But it's more about being seen. At the
back I have a big rear light (also LEDs) and reflectors.

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2001\05\30@073331 by Patrik Husfloen

picon face
less current means less resitance from the dyamo/generator..
I like it :)

----- Original Message ----- From: "Jinx" <RemoveMEjoecolquittEraseMEspamEraseMECLEAR.NET.NZ>
To: <RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU>
Sent: Wednesday, May 30, 2001 1:24 PM
Subject: Re: [EE]: Inducing power


{Quote hidden}

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2001\05\30@080045 by Alexandre Domingos F. Souza

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face
>The coils are mounted on the pcb. If you rotate the rotor with 3500 rpm
>you can rectify the voltage using a diode hexabridge. I don't know if

       Hexabridge? Never heard it! More info? :o)

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2001\05\30@081908 by Bob Ammerman

picon face
Hexabridge: Three-phase equivalent of a bridge rectifier.

Contains 6 diodes.

For each of three phases:

   Anode of one diode connected to phase,
   cathode connected to +out.

   Cathode of a second diode connected to phase,
   anode connected to -out.

Commonly found on automobile alternators.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)




{Original Message removed}

2001\05\30@090509 by Olin Lathrop

face picon face
> > One of my current projects has this problem also.  We are using a
> > transformer with the secondary rotating on the shaft.  It works fine to
> > power up a PIC and a bunch of LEDs.
>
> Was this a specially-made transformer ?

Yes.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olinSTOPspamspamspam_OUTembedinc.com, http://www.embedinc.com

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2001\05\30@090712 by Jinx

face picon face
less current means less resitance from the dyamo/generator..
I like it :)

I hate rim dynamos. Auckland's hilly enough without the extra work.
A 6V gel cell, even a smallish 3Ah one, will last a long time with LEDs

You may have seen Russell McMahon's I'm-gonna-spoil-your-day
reply to my idea of using an induction system to recharge the battery.
I never did thank you for that did I Russell  :<  Sigh, pipped at the
post again

I've put a couple of pictures up

http://home.clear.net.nz/pages/joecolquitt/bikelamp.html

On the left is the lamp from about 10ft. On the right (not the easiest
pic to get right), the illumination on a grey wall from 20ft. Underneath
shows how the LED is mounted using stiff wire

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2001\05\30@090908 by Jinx

face picon face
> > Was this a specially-made transformer ?
>
> Yes.

Ah

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2001\05\30@093705 by Russell McMahon

picon face
less current means less resitance from the dyamo/generator..
I like it :)


True, but you will not notice the actal power taken by a properly engineered
dynamo.
The old friction dynamos were attrocities with very very very low mechanical
to electrical effciiencies.
The Lucas "hub dynos" of the same period were always drivcen (as they were
in the hub) and only loaded the bike when you turned on the light. The
difference when pedalling was imperceptible. A proper moderm bike dynamo
need not be felt at all by the rider.

RM



{Original Message removed}

2001\05\30@104948 by Chris Carr

flavicon
face
> Hi all, perhaps someone can help with a wee power problem. I've
> got a circuit board mounted on a motor shaft. The circuit is there to
> measure the movement of an escapement mechanism (kind of
> like a governor) as the shaft turns from 100 to 3500rpm. The
> circuit itself is not a problem, I've managed to attached a small
> slider pot to the escapement and it's measuring OK with an ADC.
> What I'd like to do is induce power to the circuit using some kind
> of magnet/coil system. I need around 15mA at 6VDC. A possibility
> is to use a 7-segment LED (synched with the rotation) to indicate
> the escapement movement, hence the power requirement. Using
> batteries is not really an option because of the duration of the
> measurements and particularly if the LED idea goes ahead. I've
> got plenty of envultured materials - strong HDD magnets and
> more scrap transformers (enamelled wire of all gauges and
> laminate cores) you can shake a stick at. I thought I may be able
> to attach a small DC motor to the main motor's shaft as a
> generator but that's proved too tricky because of space limitations.
> So, any ideas on the most efficient way to induce power into coils
> on the PCB from stator magnets ?
>
Modified Video Head mechanism from a Video Recorder ?

Chris Carr

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2001\05\30@112827 by Roman Black

flavicon
face
Jinx wrote:
>
> > What about a simple brush, since you are only
> > talking low currents you can use the big motor shaft
>
> If this is an almost continuously running motor how will the brushes
> (carbon I presume) hold up ? For example, what sort of replacement
> period would you consider average and/or reasonable ?


Years. The same VCR head drum we have been discussing
has a tiny carbon brush (earth wiper) on the bottom
or top of it's shaft.

There is very little brush wear as there is little
current with (ideally) no arcing. You can put a spot
of oil in it too. If you use a hard steel ring and
a vcr brush it will go for many years.
:o)
-Roman

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2001\05\30@113141 by Ed Koffeman

flavicon
face
> > Hi all, perhaps someone can help with a wee power problem. I've
> > got a circuit board mounted on a motor shaft.

Could you mount a coil close to the motor rotor such that it picks up the magnetic field of a few Hertz from the slip? (Assuming an
induction motor).  Lots of turns and a bridge rectifier?


>A possibility
> > is to use a 7-segment LED (synched with the rotation) to indicate
> > the escapement movement

If you are only turning on the LEDs for an instant, at one particular angle of shaft rotation, then the average power will be very
low.

Use a PhotoLithium battery.

You could also presumably just count some revolutions between indications, if you don't need a reading very often (e.g. once per
second give the reading).

Or, use one LED, and change the length of time it's on for - you'll get a variable-length streak.

Or, flash a single LED from 1 to 10 times, starting at the known index of rotation, and then you can count the number dots it makes
visually.

Use 5 or 7 leds in an axial line and make the digits by forming them sequentially with rotation.  Using very high efficiency LEDs
may allow less current to be used than a 7-segment display, if the 7-segment display just has "ordinary" efficiency LEDs.

Use a Sony night-vision camera to allow you to have very dim LEDs and therefore low current requirements.

How about an LCD bar graph?

Ed Koffeman

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2001\05\30@115020 by David VanHorn

flavicon
face
>
>Years. The same VCR head drum we have been discussing
>has a tiny carbon brush (earth wiper) on the bottom
>or top of it's shaft.

That's just there to drain off static charge that builds up.
It's not carrying any current to speak of.

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2001\05\30@120441 by Alan B. Pearce

face picon face
>That's just there to drain off static charge that builds up.
>It's not carrying any current to speak of.

Micropolis used to have them on their full height 5.25 inch hard discs. the
trouble was the brush would get to a point where it would squeak or squeal.
We had a recommendation from Micropolis to remove them, as they did not seem
to serve a useful purpose in that case.

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2001\05\30@120935 by Roman Black

flavicon
face
Alan B. Pearce wrote:
>
> >That's just there to drain off static charge that builds up.
> >It's not carrying any current to speak of.
>
> Micropolis used to have them on their full height 5.25 inch hard discs. the
> trouble was the brush would get to a point where it would squeak or squeal.
> We had a recommendation from Micropolis to remove them, as they did not seem
> to serve a useful purpose in that case.


A drop of oil fixes the squeal and the brushes
last practically forever. I know they are designed
for use other than carrying current, but a few mA
would be well within their range. :o)
-Roman

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2001\05\30@121313 by David VanHorn

flavicon
face
At 05:00 PM 5/30/01 +0100, Alan B. Pearce wrote:
> >That's just there to drain off static charge that builds up.
> >It's not carrying any current to speak of.
>
>Micropolis used to have them on their full height 5.25 inch hard discs. the
>trouble was the brush would get to a point where it would squeak or squeal.
>We had a recommendation from Micropolis to remove them, as they did not seem
>to serve a useful purpose in that case.

Seagate, and many others had the same problem.
All you had to do was tweak it a bit, so it didn't sit in exactly the same
place as before.

Still, brushes are a PITA, and I'm not sure they really accomplished anything.

It's amazing how static can sneak up on you though.  Had that problem on a
MICR reader. Static built up on the checks, accumulated on the head, and
zapped into the head amp, making false peaks. Had to ground the head to
stop it.


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2001\05\30@201559 by Alexandre Domingos F. Souza

flavicon
face
>> > Was this a specially-made transformer ?
>> Yes.
>Ah

       wow

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2001\05\30@211641 by Dale Botkin

flavicon
face
On Wed, 30 May 2001, Alan B. Pearce wrote:

> >That's just there to drain off static charge that builds up.
> >It's not carrying any current to speak of.
>
> Micropolis used to have them on their full height 5.25 inch hard discs. the
> trouble was the brush would get to a point where it would squeak or squeal.
> We had a recommendation from Micropolis to remove them, as they did not seem
> to serve a useful purpose in that case.

Micropolis had WAY too much spring tension on those spindle grounding
brushes.  So did Seagate on drives of that era.  I fixed a lot of 'em.

Dale
--
A train stops at a train station.  A bus stops at a bus station.
On my desk I have a workstation...

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2001\05\31@131216 by Peter L. Peres

picon face
> most efficient

You don't want that, you want something you can build. A simple one is a
spoked wheel cut from some magnetizable material with low hysterezis (like
soft iron nee mild steel passed through an oven at 800C and cooled
slowly). On this you wind a single wire such that each spoke bears an
identical winding and all are in series. This goes like left-hand winding
on spoke #1, right hand on #2, left on #3 ... The number of spokes will be
even and small, but large enough that you can put a good sized magnet
between two adjacent spokes (i.e. the space between two spoke tips equals
the distance between the poles on your magnet. You can put as many magnets
around the wheel as you have, and reduce the gaps using more bits of
softened iron pole pieces). For 6V, 50mA at 100 rpm, you will need an
awful lot of wire however, even with a 12-pole generator.

Beware that these generators tend to make very high voltage at high rpm (a
few 1000's). 400V is easy with 6 spokes (each winding makes only 66V).
Maybe you can run Nixie tubes off of it ;-).

If you can manage it, arrange for a rotary transformer at 50Hz. I do not
know if one scrapped from a VCR head will work at LF, but you can make a
good rotary transformer from almost any electric brake (inline disc or
bell type). You need two of the same kind and some skill. When done, one
is spinning and the other not. This would make it work even at low rpm (or
zero rpm).

bye,

Peter

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