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Brake for small windmill?
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| Jordan 2007-09-14, 3:25 am |
|
I've volunteered to help an artist, who wants to place a number of small
vertical rotor windmills in a seaside park, on top of picnic sheds. (He
has permission!)
The rotors will be about 6 ft diameter, 3 ft high, and free-spinning -
won't drive anything.
The challenge is how to control the things so they don't spin too fast,
but still be able to start in a light breeze.
Of course, cost matters.
Ideas so far:
1. Centrifugal-operated "air brake".
2. Permanent-magnet motor, with speed-sensing switch to short out for
back-emf braking.
3. Sails attached with Velcro, to rip out in big wind.
All comments and suggestions welcome.
Jordan
| |
| bealiba@gmail.com 2007-09-17, 9:25 am |
| On Sep 14, 12:49 pm, Jordan <jwprin...@otpusnet.com.au> wrote:
> I've volunteered to help an artist, who wants to place a number of small
> vertical rotor windmills in a seaside park, on top of picnic sheds. (He
> has permission!)
>
> The rotors will be about 6 ft diameter, 3 ft high, and free-spinning -
> won't drive anything.
> The challenge is how to control the things so they don't spin too fast,
> but still be able to start in a light breeze.
>
> Of course, cost matters.
>
> Ideas so far:
> 1. Centrifugal-operated "air brake".
> 2. Permanent-magnet motor, with speed-sensing switch to short out for
> back-emf braking.
> 3. Sails attached with Velcro, to rip out in big wind.
>
> All comments and suggestions welcome.
>
> Jordan
Okay. Take a motorcycle drum brake. Now normally the drum would spin
and the shoes on the backing plate would be stationary.
Proposal; Spin the backing plate with the shoes and have the drum
fixed. You will need to replace the shoe springs with lighter springs.
The faster the backing plate spins the more the braking effect. May
require weight on shoes to increase effect and twin leading shoe brake
would be better.
OR
A chain type governer.
OR
As seems the case you are talking savonius, they are generally self
regulating and by tuning the angle of the blades can be speed limited.
| |
| Jordan 2007-09-17, 8:25 pm |
| bealiba@gmail.com wrote:
> Okay. Take a motorcycle drum brake.
Yes, we considered a centrifugal clutch (eg chainsaw), which is similar
to your suggestion. Motorcycle parts are too bulky, alas.
> A chain type governer.
Not sure what that is, but we're trying to avoid chains, belts, etc if
possible!
> As seems the case you are talking savonius, they are generally self
> regulating and by tuning the angle of the blades can be speed limited.
Sounds like serious engineering - could blow the budget.
I'm investigating an "eddy current brake", which sounds simple to
organise - aluminum disc and magnets only.
Thank you very much for the suggestions.
Jordan
| |
| Neon John 2007-09-18, 3:25 am |
| If you don't want to use any gearing then your choices are very limited. Most
braking devices including simple eddy current brakes require more speed than your
vertical windmill will generate.
Given your constraints, I'd probably go with surplus permanent magnet motors
operating as generators and equipped with 'crowbar' circuit. No speed sensing
necessary.
A crowbar circuit can be as simple as an SCR and something to provide the gate
trigger - a couple of resistors and maybe a zener diode. Google for "crowbar
circuits". The circuit would work thus:
The windmill is essentially free wheeling normally. The PM generator produces a
voltage directly and linearly proportional to the speed. The crowbar circuit is
connected across the generator's terminals. When the speed and therefore voltage
rises to the trip point, the SCR fires, shorting the generator and braking it to an
immediate almost-halt. It will still rotate at a low speed proportional to the
leakage flux in the generator and the voltage drops across the various components.
Once fired, the SCR continues to conduct until the voltage is removed - until the
windmill stops.
By bringing the windmill almost to a halt, the mill stops harvesting wind energy and
therefore you don't have much energy to dissipate. Most everything else you're
considering will require you to dissipate considerable heat.
If you don't want to nearly stop the windmill then you can include a series power
resistor in the circuit. Depending on the size of the windmill, this may involve
dissipating a LOT of power.
An ordinary induction motor functions nicely as an eddy current brake by simply
applying DC current to the input. If a source of DC power is available then that
might be an option. The energy is dissipated in the rotor though, so cooling might
be a consideration. If you brake the windmill almost to a stop, again, the energy
involved won't be great.
If these mills are to be very large then I'd probably include a fail-safe purely
mechanical backup. Say, a centrifugally operated mechanical pawl that extends to
catch a stationary boss. Perhaps backed by a coil spring so the stop won't be so
abrupt.
John
On Tue, 18 Sep 2007 10:58:23 +1000, Jordan <jwprincic@otpusnet.com.au> wrote:
>bealiba@gmail.com wrote:
>
>Yes, we considered a centrifugal clutch (eg chainsaw), which is similar
>to your suggestion. Motorcycle parts are too bulky, alas.
>
>Not sure what that is, but we're trying to avoid chains, belts, etc if
>possible!
>
>Sounds like serious engineering - could blow the budget.
>
>I'm investigating an "eddy current brake", which sounds simple to
>organise - aluminum disc and magnets only.
>
>Thank you very much for the suggestions.
>
>Jordan
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Serenity: That feeling of knowing that your secretary will never tell either of your wives.
| |
| bealiba@gmail.com 2007-09-18, 3:25 am |
| On Sep 18, 10:58 am, Jordan <jwprin...@otpusnet.com.au> wrote:
> beal...@gmail.com wrote:
>
> Yes, we considered a centrifugal clutch (eg chainsaw), which is similar
> to your suggestion. Motorcycle parts are too bulky, alas.
>
>
> Not sure what that is, but we're trying to avoid chains, belts, etc if
> possible!
>
>
> Sounds like serious engineering - could blow the budget.
Nah, preset at assembly, don't have to look at it again.
| |
| Jordan 2007-09-18, 3:25 am |
| bealiba@gmail.com wrote:
>
>
> Nah, preset at assembly, don't have to look at it again.
>
The "blades" will be, for the artistic requirement of these
installations, nothing but four flat panels ("canvasses") with a lip on
the outer edges. Not much room there for interfering with engineering
shapes!
| |
| Jordan 2007-09-18, 3:25 am |
| Neon John wrote:
>
> Given your constraints, I'd probably go with surplus permanent magnet motors
> operating as generators and equipped with 'crowbar' circuit. No speed sensing
> necessary.
>
I've seen how effective shorting a PM generator can be at braking a
friend's AIR400 wind generator. That would be a great result, with cost
again the only constraint. We're talking about seven of these, no time
to go scrounging for individual surplus units, so I've got my fingers
crossed for an "off the shelf" solution. Many thanks!
Jordan
| |
| bealiba@gmail.com 2007-09-18, 3:25 am |
| On Sep 18, 1:28 pm, Jordan <jwprin...@otpusnet.com.au> wrote:
> beal...@gmail.com wrote:
>
>
>
> The "blades" will be, for the artistic requirement of these
> installations, nothing but four flat panels ("canvasses") with a lip on
> the outer edges. Not much room there for interfering with engineering
> shapes!
My point exactly. You are not dealing with a high speed device.
| |
| Neon John 2007-09-18, 3:25 am |
| On Tue, 18 Sep 2007 13:36:41 +1000, Jordan <jwprincic@otpusnet.com.au> wrote:
>Neon John wrote:
>
>I've seen how effective shorting a PM generator can be at braking a
>friend's AIR400 wind generator. That would be a great result, with cost
>again the only constraint. We're talking about seven of these, no time
>to go scrounging for individual surplus units, so I've got my fingers
>crossed for an "off the shelf" solution. Many thanks!
Seven? That might be a problem if you needed 700. These guys alone show several
hundred motors in just one category:
http://www.surpluscenter.com/sort.a...ic&keyword=MADD
Most under $15. Those heater fan motors (most of those on the bottom half of the
page with the large mounting flanges) can handle 30+ amps so they should do the job
for a reasonably sized windmill.
Other places to look include C&H Supply http://www.candhsupply.com and Mendelsons
http://www.mecl.com. Surely it couldn't take more than an hour to look through
there. Hasn't this thread been running a couple of weeks now?
Lambda makes an adjustable crowbar circuit designed to be added onto their power
supplies. I'm sure others do too. Mendelson's usually has some surplus.
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
What do you call 10 blondes standing in a row? Pneumatic air line.
| |
| nicksanspam@ece.villanova.edu 2007-09-18, 3:25 am |
| Neon John <no@never.com> wrote:
>By bringing the windmill almost to a halt, the mill stops harvesting
>wind energy and therefore you don't have much energy to dissipate.
It would seem nicer to keep harvesting at a maximum rate, with
the windmill partially stalled.
Nick
| |
| Jordan 2007-09-18, 3:25 am |
| Neon John wrote:
>
> Seven? That might be a problem if you needed 700. These guys alone show several
> hundred motors in just one category:
>
> http://www.surpluscenter.com/sort.a...ic&keyword=MADD
>
> Most under $15. Those heater fan motors (most of those on the bottom half of the
> page with the large mounting flanges) can handle 30+ amps so they should do the job
> for a reasonably sized windmill.
>
> Other places to look include C&H Supply http://www.candhsupply.com and Mendelsons
> http://www.mecl.com. Surely it couldn't take more than an hour to look through
> there. Hasn't this thread been running a couple of weeks now?
>
I'm in Australia. Some things are easy to find, but I envy folk in "big"
countries - lots of stuff to choose from!
Thread is four days old now.
Jordan
| |
| bealiba@gmail.com 2007-09-18, 9:25 am |
| On Sep 18, 6:06 pm, Jordan <jwprin...@otpusnet.com.au> wrote:
> Neon John wrote:
>
>
>
>
>
> I'm in Australia. Some things are easy to find, but I envy folk in "big"
> countries - lots of stuff to choose from!
> Thread is four days old now.
>
> Jordan
Jordan, your making a problem where there is none. The device you are
talking about is not a high speed device.
Where in Oz are ya. I can introduce you to a guy in Vic who builds
wind mills for fun and profit.
Finding things in Oz is just a matter of looking in the right places.
| |
| Neon John 2007-09-18, 1:25 pm |
| On Tue, 18 Sep 2007 18:06:08 +1000, Jordan <jwprincic@otpusnet.com.au> wrote:
>Neon John wrote:
>
>I'm in Australia. Some things are easy to find, but I envy folk in "big"
>countries - lots of stuff to choose from!
>Thread is four days old now.
Surely there is an equivalent surplus outfit in Australia. I know that GM has a
large manufacturing presence there. There almost has to be some surplus flow from
that.
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
You have a magnetic personality... That must be why all your mental floppies are blank.
| |
| Neon John 2007-09-18, 1:25 pm |
| On 18 Sep 2007 02:47:31 -0400, nicksanspam@ece.villanova.edu wrote:
>Neon John <no@never.com> wrote:
>
>
>It would seem nicer to keep harvesting at a maximum rate, with
>the windmill partially stalled.
Why? He's not doing anything with the energy. The windmills are just for show, an
artsy-fartsy thing. Whatever energy is harvested would all have to be dissipated.
Much simpler to simply slow the mill to an almost stand-still and only have to
dissipate a little energy.
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
You have a magnetic personality... That must be why all your mental floppies are blank.
| |
| nicksanspam@ece.villanova.edu 2007-09-18, 5:25 pm |
| Neon John <no@never.com> wrote:
>
>Why? He's not doing anything with the energy.
I missed that. It would be nice to do something with it, eg grid-tie.
Nick
| |
| Jordan 2007-09-18, 8:25 pm |
| Neon John wrote:
>
> Surely there is an equivalent surplus outfit in Australia. I know that GM has a
> large manufacturing presence there. There almost has to be some surplus flow from
> that.
>
I don't know of any way to access surplus from GM or similar large
companies. We're just not geared up to do sensible stuff like that,
alas. I'd love to find out if there were.
There are some dealers who go to auctions and on-sell stuff, but it's
relatively small beer. Going to real-world auctions is too time
consuming for me. A good source is swap meets, but it's a hit and miss
business.
Still, it's a nice place to live!
| |
| Jordan 2007-09-18, 8:25 pm |
|
>
> I missed that. It would be nice to do something with it, eg grid-tie.
>
> Nick
>
The artist wanted to do something with the wind energy, but budget
constraints won't allow it. However small solar panels and batteries
will be installed as well, to light up some lamps at night.
| |
| Anthony Matonak 2007-09-18, 9:25 pm |
| Jordan wrote:
....
> The artist wanted to do something with the wind energy, but budget
> constraints won't allow it. However small solar panels and batteries
> will be installed as well, to light up some lamps at night.
It looks like a popular thing to do with small decorative wind turbines
is to attach LEDs to the blades.
Anthony
| |
| David Williams 2007-09-18, 9:25 pm |
| -> Why? He's not doing anything with the energy. The windmills are just for sh
-> artsy-fartsy thing. Whatever energy is harvested would all have to be dissip
-> Much simpler to simply slow the mill to an almost stand-still and only have
-> dissipate a little energy.
-> John
Why not just make it strong enough that it can spin as fast as a strong
wind will make it turn without flying apart? It won't be stupendously
fast. The sails will move at no more than a few times the wind-speed,
unless the thing is far more efficient than this thing is likely to be.
Suppose the wind-speed is 50 km/h, which is a pretty stiff breeze.
That's about 14 m/s. Suppose the tips of the sails fly around at 60
m/s, and the radius of the windmill is 1 m. So that's a rotational
speed of only 60 radians per second, or 10 rotations per second. 600
rpm. How hard can it be to make something that will stay together when
turning at that speed?
Brakes just add complexity. Heat has to be dissipated, etc.. There's no
need for them.
dow
| |
| Jordan 2007-09-19, 3:25 am |
| David XXXXXXXX wrote:
>
> Why not just make it strong enough that it can spin as fast as a strong
> wind will make it turn without flying apart?
> Brakes just add complexity. Heat has to be dissipated, etc.. There's no
> need for them.
But, would it turn in a slight breeze?
Re: heat - Wouldn't the wind tend to keep things cool?
Thanks for your thoughts.
Jordan
| |
| David Williams 2007-09-19, 1:25 pm |
| -> > Why not just make it strong enough that it can spin as fast as a strong
-> > wind will make it turn without flying apart?
-> > Brakes just add complexity. Heat has to be dissipated, etc.. There's no
-> > need for them.
-> But, would it turn in a slight breeze?
-> Re: heat - Wouldn't the wind tend to keep things cool?
Having no brakes on it would presumably allow it to turn more easily,
so a lighter wind could move it.
Sure. Wind can carry away heat. But you'll still have to arrange for
the wind to be able to reach the parts that get hot.
dow
| |
|
|
"David XXXXXXXX" <david.XXXXXXXX@bayman.org> wrote in message
news:1190215098.912.1190185772@bayman.org...
>-> > Why not just make it strong enough that it can spin as fast as a
>strong
> -> > wind will make it turn without flying apart?
> -> > Brakes just add complexity. Heat has to be dissipated, etc.. There's
> no
> -> > need for them.
>
> -> But, would it turn in a slight breeze?
> -> Re: heat - Wouldn't the wind tend to keep things cool?
>
> Having no brakes on it would presumably allow it to turn more easily,
> so a lighter wind could move it.
>
> Sure. Wind can carry away heat. But you'll still have to arrange for
> the wind to be able to reach the parts that get hot.
>
> dow
///////////
This is where the Greek wind turbine is at it's best.
The triangular sails are self regulating as it speeds up the sail flattens
out, slowing the tubine down by changing the angle to the wind.
| |
| tallex 2007-09-20, 3:25 am |
| On Sep 13, 10:49 pm, Jordan <jwprin...@otpusnet.com.au> wrote:
> I've volunteered to help an artist, who wants to place a number of small
> vertical rotor windmills in a seaside park, on top of picnic sheds. (He
> has permission!)
>
> The rotors will be about 6 ft diameter, 3 ft high, and free-spinning -
> won't drive anything.
> The challenge is how to control the things so they don't spin too fast,
> but still be able to start in a light breeze.
>
> Of course, cost matters.
>
> Ideas so far:
Several years ago I was testing some prop designs over extended
periods. I set up a mounting rig with a permanent mag motor from a
photocopier. I wired a 50mfd electrolytic across the output with an
ne2 neon light. The cap charged up, flashes the neon and applies the
braking action with increasing wind..the back emf works like a charm
to shunt down the speed of the props totally automatically. Different
caps will give you different braking action at differing wind speeds,
so experiment and find one that works best for you. This was a real
life saver for me and prevented me from getting a few good wacks from
over speeding props. Two parts and the motor, coudn't be simpler and
very reliable.
regards
tallex
> 1. Centrifugal-operated "air brake".
> 2. Permanent-magnet motor, with speed-sensing switch to short out for
> back-emf braking.
> 3. Sails attached with Velcro, to rip out in big wind.
>
> All comments and suggestions welcome.
>
> Jordan
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| |
| Jordan 2007-09-20, 3:25 am |
| tallex wrote:
>
> I wired a 50mfd electrolytic across the output with an
> ne2 neon light. The cap charged up, flashes the neon and applies the
> braking action with increasing wind..the back emf works like a charm
> to shunt down the speed of the props totally automatically.
That's interesting. The generator would have DC output, to charge the cap?
Is neon light in series with cap?
Thanks
Jordan
| |
| Neon John 2007-09-20, 9:25 am |
| On Thu, 20 Sep 2007 18:18:21 +1000, Jordan <jwprincic@otpusnet.com.au> wrote:
>tallex wrote:
>
>That's interesting. The generator would have DC output, to charge the cap?
>Is neon light in series with cap?
What he's describing is a relaxation oscillator. The bulb and lamp are in parallel.
The voltage builds on the cap until it reaches the neon lamp's firing voltage, about
70 volts for the common NE-2 lamp. Once fired, the lamp conducts until the voltage
drops to about 55-60 volts, whereupon it goes out. Then the process repeats.
Unfortunately this guys is blowing smoke up your XXX. He doesn't even understand how
it works. The "braking action" would be the result of energy being transferred from
the generator to the capacitor. The neon lamp firing dissipates that energy as light
and heat.
Problem is, the amount of power a neon lamp can dissipate is vanishingly small. The
most the lamp could dissipate would be when it is on continuously (forget the cap, it
contributes nothing to the equation). According to this spec sheet,
http://www.donsbulbs.com/cgi-bin/r/...%7Cne2~usa.html
about 36 milliwatts. Even if we over-drove the lamp 10X and accepted the resulting
dramatic reduction in life, that would only be 360mw, a third of a watt. Hang a
suitable half watt resistor across the generator and dissipate more.
Unless this guy's "wind mill" was tiny, small enough to wrap your hand around and
generating uselessly trivial power then he didn't do what he claims.
A somewhat more complicated relaxation-triggered load could be built that would limit
the speed and would generate an interesting effect. The effect would be that the
speed of the turbine would gradually increase until a certain point, whereupon it
would be quickly braked to a halt and the process repeated.
In this scheme, the generator would charge a large capacitor. There is an SCR and
optionally a load resistor in parallel with the capacitor so that when the SCR fires
it both shorts the generator and discharges the capacitor. The voltage from the
capacitor is fed through a neon lamp (or a solid state avalanche device such as a
diac if low voltage operation is desired) to the SCR's gate. The operation is thus.
Starting from a stop, the generator gradually accelerates, feeding energy into the
cap. The cap's voltage rises as it accumulates energy. The rising voltage allows
the generator to spin faster. At some point, the voltage rises high enough that the
neon lamp fires. This delivers a pulse to the SCR's gate, firing it. The SCR shorts
the cap and the generator, discharging the cap and stopping the generator. The SCR
commutes and the process repeats.
There would be some details to work out. There would probably need to be a
commutating inductor to help the SCR commute without the generator having to go to
zero output. There would have to be some sort of current limit to limit the
mechanical strain on the turbine. Etc.
The harvested energy will still have to be dissipated as heat somewhere. An SCR
directly shunting the generator will dissipate some energy but the majority will be
dissipated in the generator's windings. The generator will get hot. A suitable
power resistor in the circuit will move some of the dissipation out of the generator.
It would be an interesting effect. Whether it's worth the complication to your
artsy-fartsy friend I don't know.
I can't propose a detailed design because I don't know how big the turbine is to be,
how much mass it has and how much energy it will harvest. The solution can vary
widely, depending on how big the thing is.
A VERY simple speed control that will work with even moderately high power is a
simple water vane absorber. Basically, a vane or two or three on a shaft immersed in
a container of water. Energy is dissipated as friction with and in the water. The
speed vs resistance curve is a cube law I believe (at least square law and without
looking it up, I'm pretty sure a cube law function.) Square or cube law, there is a
speed where the resistance suddenly climbs dramatically or as the saying goes, "it
hits a brick wall".
The effect would be that the turbine accelerates up to a certain speed in even low
wind and then the speed increases only a little even with a dramatic increase in
speed.
The absorber can be very small. A lot of power can be absorbed in just a little
water. A 1000 HP absorber (as used on the SuperFlow dyno) can be held in one hand. A
series of vanes welded or bolted to a shaft and rotating inside a #10 tin can of
water would probably do the job unless this guy is planning on very large windmills.
Almost any conceivably sized windmill could be braked with a 5 gallon bucket
absorber.
Given the dearth of surplus stuff "down there", this water absorber is probably the
cheapest and simplest thing you can build.
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Give Blood. 8 Billion Mosquitoes can't be wrong.
| |
| Jordan 2007-09-20, 9:25 am |
| Neon John wrote:
>
> A VERY simple speed control that will work with even moderately high power is a
> simple water vane absorber.
>
Wow, that's so much info. And you sound as if you know what you're
talking about!
The water brake is worth investigating. If it can work with no
maintenance for 2 months, that'd be great.
Many thanks
Jordan
| |
|
| Why ask a bunch of engineers in an alternative energy newgroup how to
NOT use wind energy? Ask the artists. of course, it seems like they'd
be all about using alternative energy. Here's my suggestion: small 12V
stepper motor coils put out a nice hefty sine wave when its spinning.
Two bridge rectifiers and a cap and a 12v compacy flourescent light,
and the picnic tables will be lit all night.
| |
|
| "Jordan" <jwprincic@otpusnet.com.au> wrote in message
news:46f25713$0$844$afc38c87@news.optusnet.com.au...
> Neon John wrote:
> Wow, that's so much info. And you sound as if you know what you're talking
> about!
> The water brake is worth investigating. If it can work with no maintenance
> for 2 months, that'd be great.
You'd just have to keep the water topped off. I remember back at my 7th
grade science fair, some kid showed how running an eggbeater in a pitcher of
water raised the temp of the water, demonstration of conservation of energy.
Your water could become quite warm.
>
> Many thanks
> Jordan
| |
| Jordan 2007-09-20, 8:25 pm |
| BobG wrote:
> Why ask a bunch of engineers in an alternative energy newgroup how to
> NOT use wind energy? Ask the artists. of course, it seems like they'd
> be all about using alternative energy. Here's my suggestion: small 12V
> stepper motor coils put out a nice hefty sine wave when its spinning.
> Two bridge rectifiers and a cap and a 12v compacy flourescent light,
> and the picnic tables will be lit all night.
>
I've cast a wide net, and got good helpful responses.
Are you kidding about asking artists themselves?
Can you give me circuit details for your suggestion?
Thanks!
Jordan
| |
| Jordan 2007-09-20, 8:25 pm |
| Jim wrote:
>
> You'd just have to keep the water topped off.
>
That won't happen.
| |
| Neon John 2007-09-21, 3:25 am |
| On Fri, 21 Sep 2007 09:20:10 +1000, Jordan <jwprincic@otpusnet.com.au> wrote:
>BobG wrote:
>I've cast a wide net, and got good helpful responses.
>Are you kidding about asking artists themselves?
>Can you give me circuit details for your suggestion?
No need going there. If you don't have surplus dealers where you are then you can't
afford 'em.
Besides, it wouldn't do what you want. A permanent magnet stepper is simply a PM
three (or more) phase alternator when the shaft is driven. The output voltage is
proportional to the speed. A simple 6 diode rectifier identical to that in a car
alternator (google that if you want to see the circuit) will turn it into DC.
Problem is, the voltage is more or less linearly proportional to the speed. A
certain speed would be required to light the lamp. Some sort of gate circuit would
be required to keep undervoltage away from the lamp to avoid damaging the lamp's
electronics. Some OTHER circuitry would be required to limit the voltage as the wind
mill speeds up. The lamp will draw a fixed amount of power, its wattage rating.
Unless the extra power generated at higher speeds is shunted off to some other load,
the windmill will overspeed. Not exactly the response curve you're looking for.
I hate to keep shooting these ideas down but they just won't work, at least not
without a lot of complication. To regulate the speed over a wide range of energy
inputs, one needs a load with a highly non-linear transfer function. It should
consume little power until a certain speed and then the input power vs speed curve
should trend sharply upward. This holds the wind mill at a relatively constant speed
over a wide range of wind speeds.
The ideal "brick wall" is a step response. That is, no drag before the speed
setpoint and infinite drag beyond. That can't be achieved without external logic
(electronic or hydraulic). There are processes that are highly non-linear where the
drag increases as the square, cube or even higher power functions of velocity.
The simple water brake as I described before is about as simple as it gets. The drag
is VERY non-linear vs speed. Did you ever wonder why a boat with only say, a 40 hp
motor can go about half as fast as one with, say, a 300 hp one? Same non-linear drag
principle at work.
In general, a linear power vs speed device will require some sort of external
non-linear control to achieve the "brick wall" effect. A generator is one example.
Another is a positive displacement hydraulic pump. A hydraulic pump can be made
highly non-linear with an orifice. A simple orifice is a square law device. A
limiting or "critical" orifice (where the fluid velocity is at the local speed of
sound in the fluid) is effectively a brick wall.
If you had too much energy to absorb for a reasonably sized water brake, my next
suggestion was going to be just that - a hydraulic pump and valve (thin: adjustable
orifice). There used to be a commercially made engine dynamometer offered for sale
that was designed like that. A hydraulic pump, a valve, a reservoir and a pressure
gauge. Worked great.
I'm still kinda "drifting in the wind" so to speak :-) on specifics because I STILL
don't know how large the mill is to be or how much power it will harvest. Over a
wide range of anticipated sizes, a simple water brake will do the job, though.
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
Alcohol, Tobacco & Firearms should be a convenience store, not a government agency.
| |
| Jordan 2007-09-21, 3:25 am |
| Neon John wrote:
> I STILL
> don't know how large the mill is to be or how much power it will harvest.
>
The artist wants four flat radial squarish vanes, each approx 3ft x 3ft.
There's an electronics guy who's in on the project, and he can make a
speed sensor. This could trigger a circuit that crowbars a PM
motor/generator, to cause it to (almost) stop when it reaches a fixed
maximum speed. This is Plan B, if A doesn't work - the eddy current brake.
| |
|
|
| Jordan 2007-09-21, 3:25 am |
| Anthony Matonak wrote:
>
> I've seen a number of spinning signs
I think they're what inspired the current project, which is gonna be a
fair bit bigger, and possibly dangerous if not controlled.
| |
| Neon John 2007-09-21, 9:25 am |
| On Fri, 21 Sep 2007 15:55:27 +1000, Jordan <jwprincic@otpusnet.com.au> wrote:
>Neon John wrote:
>
>The artist wants four flat radial squarish vanes, each approx 3ft x 3ft.
>There's an electronics guy who's in on the project, and he can make a
>speed sensor. This could trigger a circuit that crowbars a PM
>motor/generator, to cause it to (almost) stop when it reaches a fixed
>maximum speed. This is Plan B, if A doesn't work - the eddy current brake.
As I mentioned before, no speed sensor is necessary. The PM motor's output is
directly proportional to speed. Simply trigger the crowbar on voltage.
An eddy current brake will work if you have a good source of rare earth magnets. An
eddy current brake is fairly linear so it'll take some work to get the slope of the
absorption curve just right to let the thing spin but not over-speed.
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
If stupidity hurt then they'd be putting morphine in the water supply.
| |
|
| On Sep 20, 7:20 pm, Jordan <jwprin...@otpusnet.com.au> wrote:
> Can you give me circuit details for your suggestion?
=======================================================
Stepper motor has two pairs of wires (a pair reads about 50 ohms).
These go to the ~ ~ terminals on the bridge rectifier. The two +
terminals go to the cap. The - terminals and the other end of the cap
go to ground. That's your 12V power supply for your cf lamp.
| |
| David Williams 2007-09-21, 5:25 pm |
| -> Stepper motor has two pairs of wires (a pair reads about 50 ohms).
-> These go to the ~ ~ terminals on the bridge rectifier. The two +
-> terminals go to the cap. The - terminals and the other end of the cap
-> go to ground. That's your 12V power supply for your cf lamp.
I'm sceptical about this circuit. If you just have the cap, it will
charge up to the input voltage, then take no more current, so the motor
will not act as a brake. If you put a neon lamp across it, the lamp
will "strike" at some voltage and discharge the capacitor down to some
lower voltage, then repeat. The braking effect will be periodic, and
the energy will be dissipated in the neon, which won't take much
without burning out.
Much better, make a circuit with a zener diode, a power transistor, and
a couple of resistors, one of which should be capable of dissipating as
much power as needed. Call that one R1. Connect the + side of the zener
and one end of R1 to the + output from the bridge rectifier. Connect
the other end of R1 to the collector of the transistor (assumed NPN).
Connect the - end of the zener to the base of the transistor and to one
end of the other resistor (R2). Connect the emitter of the transistor and
the other end of R2 to the - side of the bridge.
Values? R2 should be biggish. Maybe 10K. R1 should be smaller, maybe
100 ohms. The zener voltage should match the voltage output by the
bridge when the windmill is turning at the desired maximum speed.
When the mill is turning slower than the maximum, no current will flow
through the zener and the transistor will be cut-off. No current will
flow, so there will be no braking effect. When the maximum speed is
reached, the zener will conduct, the transistor will turn on, and
current will flow through R1, dissipating energy. The mill's speed will
stay very constant.
That's how I'd do it, but then I'm much more familiar and comfortable
with electronics than hydraulics. Other people will have different
preferences.
dow
| |
| bealiba@gmail.com 2007-09-21, 8:25 pm |
| On Sep 21, 6:24 pm, Jordan <jwprin...@otpusnet.com.au> wrote:
> Anthony Matonak wrote:
>
>
> I think they're what inspired the current project, which is gonna be a
> fair bit bigger, and possibly dangerous if not controlled.
Build one and test it. It won't turn that fast.
| |
| bealiba@gmail.com 2007-09-21, 8:25 pm |
| On Sep 21, 7:17 pm, Anthony Matonak
<anthony...@nothing.like.socal.rr.com> wrote:
> Jordan wrote:
>
>
> I've seen a number of spinning signs that sound much like what you're
> talking about here. A quick websearch found me these products and they
> don't seem to have brakes of any sort.
>
That's because this type of windmill is not a high speed device.
| |
| Jordan 2007-09-22, 3:25 am |
| Neon John wrote:
>
> An eddy current brake will work if you have a good source of rare earth magnets. An
> eddy current brake is fairly linear so it'll take some work to get the slope of the
> absorption curve just right to let the thing spin but not over-speed.
>
Others have said that the eddy brake is not linear?
The attaction to me was that, if the braking effect follows a square
law, that'd be ideal.
| |
| Jordan 2007-09-22, 3:25 am |
| BobG wrote:
> On Sep 20, 7:20 pm, Jordan <jwprin...@otpusnet.com.au> wrote:
> =======================================================
> Stepper motor has two pairs of wires (a pair reads about 50 ohms).
> These go to the ~ ~ terminals on the bridge rectifier. The two +
> terminals go to the cap. The - terminals and the other end of the cap
> go to ground. That's your 12V power supply for your cf lamp.
>
Got that - thank you Bob.
Jordan
| |
| Jordan 2007-09-22, 3:25 am |
| David XXXXXXXX wrote:
>
> Much better, make a circuit with a zener diode, a power transistor, and
> a couple of resistors, one of which should be capable of dissipating as
> much power as needed.
Thanks Dave
I've copied that and will forward to the electronics guy.
Jordan
| |
|
| On Sep 21, 4:15?pm, david.willi...@bayman.org (David XXXXXXXX) wrote:
> I'm sceptical about this circuit.
==========================================
I'm not. Its sitting in front of me here at the computer., attached to
my stepper motor from Skycraft with a crank on the shaft. It runs a
12V incandescent lamp No Problemo. 80ma as I recall. That should run a
7W compact fluorescent. Do they have 12V cfls at home depot?
| |
| David Williams 2007-09-22, 1:25 pm |
| -> David XXXXXXXX wrote:
-> >
-> > Much better, make a circuit with a zener diode, a power transistor, and
-> > a couple of resistors, one of which should be capable of dissipating as
-> > much power as needed.
-> Thanks Dave
-> I've copied that and will forward to the electronics guy.
-> Jordan
I think I guessed that R1 should be something like 100 ohms. On second
guess, I think it should be closer to 10 ohms, or maybe even less. It
will be receiving only a few volts from the bridge, and we want it to
be able to dissipate a few watts, which is what the decorative windmill
will probably produce.
Actually, you might be able just to put a zener across the bridge
output. If it's chunky enough to be able to dissipate a few watts
(probably mounted on a heat sink), it may be all you need.
dow
| |
| Arnold Walker 2007-09-22, 1:25 pm |
|
"David XXXXXXXX" <david.XXXXXXXX@bayman.org> wrote in message
news:1190477964.912.1190452120@bayman.org...
>-> David XXXXXXXX wrote:
> -> >
> -> > Much better, make a circuit with a zener diode, a power transistor,
> and
> -> > a couple of resistors, one of which should be capable of dissipating
> as
> -> > much power as needed.
>
> -> Thanks Dave
>
> -> I've copied that and will forward to the electronics guy.
>
> -> Jordan
>
> I think I guessed that R1 should be something like 100 ohms. On second
> guess, I think it should be closer to 10 ohms, or maybe even less. It
> will be receiving only a few volts from the bridge, and we want it to
> be able to dissipate a few watts, which is what the decorative windmill
> will probably produce.
>
> Actually, you might be able just to put a zener across the bridge
> output. If it's chunky enough to be able to dissipate a few watts
> (probably mounted on a heat sink), it may be all you need.
>
> dow
Sounds like dynamic(regenerative to green guys) braking on a railway
locomotive on a smaller scale.
>
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| |
| David Williams 2007-09-22, 5:25 pm |
| -> > I'm sceptical about this circuit.
-> ==========================================
-> I'm not. Its sitting in front of me here at the computer., attached to
-> my stepper motor from Skycraft with a crank on the shaft. It runs a
-> 12V incandescent lamp No Problemo. 80ma as I recall. That should run a
-> 7W compact fluorescent. Do they have 12V cfls at home depot?
12V x 0.08A = 0.96W. Less than *one* watt.
A lot of buses have fluorescent lights in their interiors, presumably
running off 12 or maybe 24 volts. I think they use some sort of
inverter and transformer to step the voltage up.
dow
| |
| David Williams 2007-09-22, 5:25 pm |
| -> Sounds like dynamic(regenerative to green guys) braking on a railway
-> locomotive on a smaller scale.
Yup. Same idea.
dow
| |
|
| On Sep 22, 4:23?pm, david.willi...@bayman.org (David XXXXXXXX) wrote:
> -> > I'm sceptical about this circuit.
> -> ==========================================
> -> I'm not. Its sitting in front of me here at the computer.,
================================
> 12V x 0.08A = 0.96W. Less than *one* watt.
================================
Ouch... I guess I was thinking .8 amps.... In my defense, I think the
small motor I have is capable of generating several watts... it runs
the 12V lamp easily, with not much added cranking affort... 4 or 5
revs per sec (240-300 rpm)... I guess that would take a Real Stiff
Breeze or maybe some toothed belts and pulleys.... maybe some sort of
switch with hyteresis that would let a BFC charge up, switch on the
light, run till discharged, repeat.
| |
| David Williams 2007-09-23, 1:25 pm |
| -> Ouch... I guess I was thinking .8 amps.... In my defense, I think the
-> small motor I have is capable of generating several watts... it runs
-> the 12V lamp easily, with not much added cranking affort... 4 or 5
-> revs per sec (240-300 rpm)... I guess that would take a Real Stiff
-> Breeze or maybe some toothed belts and pulleys.... maybe some sort of
-> switch with hyteresis that would let a BFC charge up, switch on the
-> light, run till discharged, repeat.
The voltage on a capacitor declines as it discharges. Your lamp would
come on bright, then dim down until it goes out altogether.
If you're looking for 12-volt stuff, an auto-parts store is likely to
be a better hunting ground than Home Hardware.
dow
| |
|
| "Jordan" <jwprincic@otpusnet.com.au> wrote in message
news:46f30030$0$13999$afc38c87@news.optusnet.com.au...
> Jim wrote:
> That won't happen.
Lack of water? Sealed container??
Use something that won't evaporate, like used motor oil?
| |
| David Williams 2007-09-24, 5:25 pm |
| -> > 12V x 0.08A = 0.96W. Less than *one* watt.
-> ================================
-> Ouch... I guess I was thinking .8 amps.... In my defense, I think the
-> small motor I have is capable of generating several watts... it runs
-> the 12V lamp easily, with not much added cranking affort... 4 or 5
-> revs per sec (240-300 rpm)... I guess that would take a Real Stiff
-> Breeze or maybe some toothed belts and pulleys.... maybe some sort of
-> switch with hyteresis that would let a BFC charge up, switch on the
-> light, run till discharged, repeat.
0.8 amps at 12 volts is nearly 10 watts. You'd definitely notice the
extra cranking effort to put out that much power. One horsepower is
something like 700 watts. A "manpower" - the amount of mechanical power
a man can put out for a fairly long time - is only about 200 watts. The
amount he can put out with one arm is probably only 20 or 30 watts, so
you're talking about a substantial fraction of that.
Maybe your earlier estimate of one watt was closer to the mark. There
are plenty of 12V, 1W bulbs around, such as the ones that are used for
dashboard lights in cars. I can imagine you might power one of those
from your circuit without much cranking effort.
dow
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