movement sensor

Silent Shrill

Hi all,

I want a movement sensor that will work with a metal object. No infared or heat or light. Just want the sensor to activate on movement of a pulley wheel. It will be enclosed in darkness and outside, but protected from elements.
Any suggestions?
Thanks

Keplar240B

some type of hall sensor maybe?

A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications


https://en.wikipedia.org/wiki/Hall_effect_sensor

Hall effect gear tooth sensors

http://www.spectecsensors.com/mobile/hall-effect-gear-tooth-sensors.html

Silent Shrill

Keplar240B wrote: »

some type of hall sensor maybe?

A Hall effect sensor is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications

[IMG]https://upload.wikimedia.org/ wikipedia/commons/thumb/7/7e/Hall_sensor_tach.gif/220px-Hall_sensor_tach.gif[/IMG]
https://en.wikipedia.org/wiki/Hall_effect_sensor

Hall effect gear tooth sensors

http://www.spectecsensors.com/mobile/hall-effect-gear-tooth-sensors.html

Would I need to fit a magnet or two to the pulley?

Keplar240B

Silent Shrill wrote: »

Would I need to fit a magnet or two to the pulley?

Depends ... there are hall effect gear tooth sensors and hall effect WSS wheel speed sensors out there. have a look at second link in post #2

Can you give more details on project?
why rule out IR or light?

Hall effect gear tooth sensor applications such as fine gears, detection of very low to zero speed and the change in target direction. Hall effect sensors are used as vehicle speed sensors, wheel speed sensors, in ABS brake systems and as camshaft sensors. Additional applications are flow metering and in vehicle transmissions.

https://www.youtube.com/watch?v=ujc6pjftZ_w

Silent Shrill

Can you give more details on project?
why rule out IR or light?

I've built a wind generator with a 12v dc car alternator.
Everything works A+
As you probably know, there's a wire to connect to the "charging light", which needs to be in the system. When there's no wind this light comes on, when the blades turn, it goes out, but only when certain revs are reached. I wanted to break that circuit as soon as blades turn to allow the charging process, and connect back when they are still.

You can most likely just short it with a diode forward biased from the alternator and reverse biased from the battery.

The D+ is diode protected anyways but usually in the car.
At least mine is, dunno if it would work for sure you could bench test it with a battery a drill and an ammeter.


[QUOTE=Hugh Piggott Wind turbine recipe book 2013 METRIC edition page 7
]
Why some popular ideas are not good ideas
Car alternators

A car alternator appears attractive for
home-brew power
generation, because it
is made for the job of
charging batteries and
is widely available at
low cost. But it is a
bad choice for a wind
generator. The
efficiency in normal
use is never more than
about 60%. In practice it usually wastes over half of
the power that drives it. The bearings are too small to
reliably support large blades (over about 1500 mm
diameter). There are three main problems:
1. It is designed to be lightweight and robust and to
withstand running at very high rpm. At low speed
(below 1000 rpm) it produces no usable output. If you
mount wind turbine blades on the shaft then they will
turn it relatively slowly. This speed mismatch can be
addressed in one of several unsatisfactory ways:
§ Use shorter blades. The tips have less far to go per
revolution, so they can spin at higher rpm. This
solution can produce power in high winds when
the speed and power are sufficient to energise the
field coil. But you will find that most of the time
the wind is insufficient and the turbine produces
nothing. Small blades cannot catch much energy
nor run vary fast in low windspeeds.
§ Use gearing to increase the rpm. This involves
extra cost, extra power losses, extra unreliability
and overall ugly and clumsy engineering. Wasted
effort for a disappointing output.
§ Rewind the coils to work at lower speed. Use more
turns of thinner wire in each coil. This reduces the
cut-in rpm but also increases the losses in the coils
themselves, limiting the power output and further
reducing the already low efficiency.
2. The alternator field coil needs to be supplied with
power to excite the magnetic flux. To get output at low
speed, you need the flux to be maximised. This
current in the field coil represents a constant power
loss of 30-40 watts during operation. The loss
clobbers the output in low winds. 40 watts continuous
nearly adds up to one full kWh of energy per day.
Solutions? You can fit it with permanent magnets.
This is very laborious and what you are left with is still
rather small and light, so the efficiency is still very
poor unless the machine is very small (50 -100 watts
say).
3. The internal regulator in the alternator is not
suitable for charging a remote battery. If the battery is
not close by then the voltage at the alternator will be
higher than battery voltage and so the regulator will
start to limit the output before the battery is charging
properly. Also the way it reduces output is to reduce
the magnetic field. This unloads the blades, which will
run faster and cause noise, vibration and wear to all
components (bearings, blade tips, etc).
You will have to remove and bypass the internal
regulator.
While it is cheap and attractive at first look, the car
alternator is more trouble than it is worth. It is
simpler and better to build a purpose-built alternator
for a wind turbine.
Steel cores in the stator coils
Most conventional
alternators have
cores made of
laminated steel that
enhance the magnetic
circuit through the
coils of copper wire
and thus increase the
output voltage you can get from a given amount of
magnet material.
The axial flux alternators described here do not use
cores in the coils and so they need much more magnet
volume to achieve the same performance. You could
fit cores into the coils, but it would not be advisable.
The magnets would seek to align themselves with the
coil cores and this would make the alternator very hard
to start and very rough in operation. The uneven
torque is known as ‘cogging’.
Alternators with steel cores are harder to start
generally and they do experience quite a noticeable
magnetic drag, which impacts on the efficiency in low
winds. The axial flux alternators in this book are very
free turning and much easier to build. The only
disadvantage is the higher cost of magnets.

[/QUOTE]

Silent Shrill

Jazus!!
If I wanted to read a book I'd go to the library.
who gives a rat's arse about 60% efficiency,.... it's free power! And charged a big battery for free.
The blades were made with Wavin pipe, 2' long, and I run my workshop lights with it. Plenty of power left over to run outside 12v floodlights all night long!
If everyone in the country did the same, and installed 12v lighting in their house, it would save not only money, but reduce carbon emissions. My cost for it all, €20.
This country is rich in wind, blowing approximately 80% of the time.
There's only 1 person here being clever....me!

ShRT

Silent Shrill wrote: »

There's only 1 person here being clever....me!

Says the one looking for help

whizbang

Nice to hear its working for you Op.

Salvage a hall sensor from a floppy drive or similar.
Stick some small magnets around the edge of the pulley.
Wire an RC network on the output of the sensor to filter the pulses before connecting to the switch.
Adjust the number of magnets on the pulley to vary the cut-in speed of the sensor.