>If you already have something rotating, why worry about any funny
>transmissions. Just create a magnetic field with a permanent or
>electromagnet, mount some sort of coil on the rotating device, and
>presto, you have an alternator. The real power source is whatever
>is doing the spinning.
>
>I am coming in late, so I may well have missed something mentioned
>earlier.
In this particular case, IIRC it spins too slow and needs too much
power for that the be practical.
A rotating transformer is the best answer in this case. It's just
like any other transformer, except the primary and secondary can
rotate relative to each other. Standard, off-the-shelf technology.
Reply by CBFalconer●August 1, 20042004-08-01
Joerg wrote:
>
>>> How about transmitting a little power on a license free band
>>> such as ISM (maybe 13.65MHz?), picking it up via small coils
>>> on the shaft andrectifying it there.
>>>
>>> Of course you'd have to check the legal situation in the
>>> countries wherethis is going to be marketed.
>>>
>> We tried it - the shaft is prone to get most of the power and
>> convert it to heat due to iron losses. The coupling link
>> geometry has to be designed so that the magnetic field hits
>> the secondarycoil but not the shaft and surrounding metal parts.
>
> The coils would have to be perpendicular to the shaft, not wound
> around it. For example, you could have several oblong coils
> wound on flex or baked into a molding and the winding would
> never loop around the shaft. You could even have only one coil
> but that is difficult to mount and clean unless you use a flex
> circuit that can be wrapped around and held at a distance from
> the shaft's surface. The thing is to create an antenna that has
> a reasonable effectiveness.
>
>> The solution in our case was a ferrite transformer at 20 kHz.
>> The power transferred was small, some hundreds of mW. It showed
>> that the transformer air-gap variation due to mechanical
>> tolerances of shaft mounting had a pronounced effect on the
>> transfer efficiency.
>
> Yes, the air gap can be a problem. But it may be ok if you only
> need little power and there is no hardcore limit on primary
> power (not battery powered etc.).
If you already have something rotating, why worry about any funny
transmissions. Just create a magnetic field with a permanent or
electromagnet, mount some sort of coil on the rotating device, and
presto, you have an alternator. The real power source is whatever
is doing the spinning.
I am coming in late, so I may well have missed something mentioned
earlier.
--
"The most amazing achievement of the computer software industry
is its continuing cancellation of the steady and staggering
gains made by the computer hardware industry..." - Petroski
Reply by Joerg●July 26, 20042004-07-26
Hi Tauno,
>>How about transmitting a little power on a license free band such as ISM
>>(maybe 13.65MHz?), picking it up via small coils on the shaft and
>>rectifying it there.
>>
>>Of course you'd have to check the legal situation in the countries where
>>this is going to be marketed.
>>
>>
>>
>We tried it - the shaft is prone to get most of the power and
>convert it to heat due to iron losses. The coupling link geometry
>has to be designed so that the magnetic field hits the secondary
>coil but not the shaft and surrounding metal parts.
>
>
The coils would have to be perpendicular to the shaft, not wound around
it. For example, you could have several oblong coils wound on flex or
baked into a molding and the winding would never loop around the shaft.
You could even have only one coil but that is difficult to mount and
clean unless you use a flex circuit that can be wrapped around and held
at a distance from the shaft's surface. The thing is to create an
antenna that has a reasonable effectiveness.
>The solution in our case was a ferrite transformer at 20 kHz. The
>power transferred was small, some hundreds of mW. It showed
>that the transformer air-gap variation due to mechanical tolerances of
>shaft mounting had a pronounced effect on the transfer efficiency.
>
>
Yes, the air gap can be a problem. But it may be ok if you only need
little power and there is no hardcore limit on primary power (not
battery powered etc.).
Regards, Joerg
http://www.analogconsultants.com
>
> Jim Stewart <jstewart@jkmicro.com> says...
>>
>>I enjoy helping people, but not when the
>>questions are posed in a "smash-and-grab"
>>style. If I'm going to give away my time
>>and knowledge, I'd at least like my intellectual
>>curiosity pleased out of the deal.
>>
>>I think most of the regulars here would
>>agree.
We agree, but some posters do need a little help in framing their questions
properly.
Ahhh!! you beat me to it Guy. Great page for advice but a bit long winded
(could all have been said in much fewer paragraphs).
--
********************************************************************
Paul E. Bennett ....................<email://peb@a...>
Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972 .........NOW AVAILABLE:- HIDECS COURSE......
Tel: +44 (0)1235-811095 .... see http://www.feabhas.com for details.
Going Forth Safely ..... EBA. www.electric-boat-association.org.uk..
********************************************************************
Reply by Tauno Voipio●July 23, 20042004-07-23
"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:LwVLc.194$0Y7.113@newssvr27.news.prodigy.com...
> Hi Rodo,
>
> How about transmitting a little power on a license free band such as ISM
> (maybe 13.65MHz?), picking it up via small coils on the shaft and
> rectifying it there.
>
> Of course you'd have to check the legal situation in the countries where
> this is going to be marketed.
>
We tried it - the shaft is prone to get most of the power and
convert it to heat due to iron losses. The coupling link geometry
has to be designed so that the magnetic field hits the secondary
coil but not the shaft and surrounding metal parts.
The solution in our case was a ferrite transformer at 20 kHz. The
power transferred was small, some hundreds of mW. It showed
that the transformer air-gap variation due to mechanical tolerances of
shaft mounting had a pronounced effect on the transfer efficiency.
Tauno Voipio
tauno voipio (at) iki fi
Reply by Guy Macon●July 23, 20042004-07-23
Jim Stewart <jstewart@jkmicro.com> says...
>
>I enjoy helping people, but not when the
>questions are posed in a "smash-and-grab"
>style. If I'm going to give away my time
>and knowledge, I'd at least like my intellectual
>curiosity pleased out of the deal.
>
>I think most of the regulars here would
>agree.
There is a great web page on this very subject:
How To Ask Questions The Smart Way
http://www.catb.org/~esr/faqs/smart-questions.html
--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/
Reply by Neil Kurzman●July 23, 20042004-07-23
Rodo wrote:
> Hi all...
>
> I need to make a circuit that needs to spin on the shaft of a small dc
> brushless motor. I thought I could use a permanent magnet mounted on the
> base of the shaft of the motor (not moving) and some coils that will be
> spinning on the pcb. I don't know if this will work or provide enough power
> (need 5mA) to the spinning pcb . Any better ways ?
>
> BTW I can't seem to find a dc brushless motor manufacturer. Can you suggest
> any ?
>
> Thanks
Try a search for "Propeller clocks" they much power a spinning led bar
Reply by Joerg●July 22, 20042004-07-22
Hi Rodo,
How about transmitting a little power on a license free band such as ISM
(maybe 13.65MHz?), picking it up via small coils on the shaft and
rectifying it there.
Of course you'd have to check the legal situation in the countries where
this is going to be marketed.
Regards, Joerg
http://www.analogconsultants.com
Reply by Jim Stewart●July 22, 20042004-07-22
Paul E. Bennett wrote:
> Jim Stewart wrote:
>
>
>>Rodo wrote:
>>
>>>Hi all...
>>>
>>>I need to make a circuit that needs to spin on the shaft of a small dc
>>>brushless motor. I thought I could use a permanent magnet mounted on the
>>>base of the shaft of the motor (not moving) and some coils that will be
>>>spinning on the pcb. I don't know if this will work or provide enough
>>>power (need 5mA) to the spinning pcb . Any better ways ?
>>
>>You left out too many details.
>>
>>1. How fast?
>>2. How many are you going to build?
>>3. How much money do you have?
>>4. How long does it have to last?
>
>
> He left out more than a few details (I have seen his responses to the above
> some of which were just a bit vague).
I enjoy helping people, but not when the
questions are posed in a "smash-and-grab"
style. If I'm going to give away my time
and knowledge, I'd at least like my intellectual
curiosity pleased out of the deal.
I think most of the regulars here would
agree.
Reply by Mike Turco●July 22, 20042004-07-22
"Rodo" <dsp1024@yahoo.com> wrote in message
news:WtALc.13795$Iz3.9732@nwrddc01.gnilink.net...
> Hi all...
>
> I need to make a circuit that needs to spin on the shaft of a small dc
> brushless motor. I thought I could use a permanent magnet mounted on the
> base of the shaft of the motor (not moving) and some coils that will be
> spinning on the pcb. I don't know if this will work or provide enough
power
> (need 5mA) to the spinning pcb . Any better ways ?