power supply - More Data on the app.

Archiver

Thanks for the response. Here's more information
on what I'm doing.

I'm currently using a LM7812 to get the 12 volts, and
an op-amp to limit the current. Of course capacitors
to eliminate the AC ripple and resistors to adjust the
Op-amp output for current limiting. This power supply is larger
than the rest of my circuit.

The wind speed sensor board 1 inch by 1.3 inches and
almost 100 feet from the Stamp. The power supply section
adds 2" x 1.2" to the board size. I am using AC just because of
the distance from the stamp as a way to eliminate any
voltage drop and resultant power loss.

I'm planning on replacing the remote unit and am making it
with many components surface mount so I can put it in a
smaller enclosure, actually up on the roof and inside of a pole.
The unit will be subjected to temperature changes here in
New Jersey of 0°F in the winter to about 100°F in the summer.

The temperature of the power supply will see that 100 degree
swing and since most of the components have temperature
parameters that will change the output along with the change
of temperature, I am concerned that the power supply will not
be stabile.

My option is to put the power inside of the building, about 10 feet
from the sensor, where the temperature is more stabile at between
60° and 80°.

As you can see, a I'm not sure a simple power supply
will satisfy the environmantal conditions, and the physical size.
Any suggestions on making it more stabile or smaller are welcome.


Dave





--- In basicstamps@egroups.com, Jon Enoch <jone@n...> wrote:
> You could Rectify the AC with a diode bridge and filter the DC with
a couple
> of electrolytic capacitors. use any one of the TO-220 type voltage
> regulators (either fixed or adjustable eg. LM317) to set your
desired
> voltage. As for the current limiting, these devices can be set up
as
> constant current sources also. Check out National Semiconductor's
voltage
> regulator line.
>
>
>
> Jon Enoch,
> PCB Design Engineer,
> Northern Airborne Technology.
>
>
>
>
> I am looking to reduce a power supply to get a small unit.
>
> There is up to 24 VAC available for this circuit.
> What is needed ia 12VDC and only 12 ma.
> The 12 ma is the max for the circuit so it needs to be limited for
> power at 12ma.
>
> Any tips or tricks ?

Archiver

Hi Dave,

Huh? It is not at all clear to me why you need such a complicated power
supply for a wind speed sensor. Most that I know of produce either a
frequency from a reed switch or hall effect device, or a frequency from an
AC generator. Those do not require much of a fancy power supply. Tight
current limiting and high stability with temperature are not an issue.
What does your circuit do?

BTW, an important consideration with anemometers is lightning and ESD. By
their nature, anemometers are antennas for everything out there and funnel
it happily back to your sensitive electronics. Need protection.

-- Tracy Allen
Electronically Monitored Ecosysstems
http://www.emesystems.com

---

original message tread:

---

>
Here's more information
on what I'm doing.

I'm currently using a LM7812 to get the 12 volts, and
an op-amp to limit the current. Of course capacitors
to eliminate the AC ripple and resistors to adjust the
Op-amp output for current limiting. This power supply is larger
than the rest of my circuit.

The wind speed sensor board 1 inch by 1.3 inches and
almost 100 feet from the Stamp. The power supply section
adds 2" x 1.2" to the board size. I am using AC just because of
the distance from the stamp as a way to eliminate any
voltage drop and resultant power loss.

I'm planning on replacing the remote unit and am making it
with many components surface mount so I can put it in a
smaller enclosure, actually up on the roof and inside of a pole.
The unit will be subjected to temperature changes here in
New Jersey of 0 F in the winter to about 100 F in the summer.

The temperature of the power supply will see that 100 degree
swing and since most of the components have temperature
parameters that will change the output along with the change
of temperature, I am concerned that the power supply will not
be stabile.

My option is to put the power inside of the building, about 10 feet
from the sensor, where the temperature is more stabile at between
60 and 80 .

As you can see, a I'm not sure a simple power supply
will satisfy the environmantal conditions, and the physical size.
Any suggestions on making it more stabile or smaller are welcome.


Dave

--- In basicstamps@egroups.com, Jon Enoch <jone@n...> wrote:
> You could Rectify the AC with a diode bridge and filter the DC with
a couple
> of electrolytic capacitors. use any one of the TO-220 type voltage
> regulators (either fixed or adjustable eg. LM317) to set your
desired
> voltage. As for the current limiting, these devices can be set up
as
> constant current sources also. Check out National Semiconductor's
voltage
> regulator line.
>
>
>
> Jon Enoch,
> PCB Design Engineer,
> Northern Airborne Technology.
>
>
>
>
> I am looking to reduce a power supply to get a small unit.
>
> There is up to 24 VAC available for this circuit.
> What is needed ia 12VDC and only 12 ma.
> The 12 ma is the max for the circuit so it needs to be limited for
> power at 12ma.
>
> Any tips or tricks ?

Archiver

The wind speed sensor is a thermal anemometer using King's law
to compare two thermal sensors. One is heated and one is measuring
ambient temperature. The voltage difference at wind speeds is very
low. Since one sensor is heated, any large change in the power
supply changes the settling time of the sensor. long drifts of power
are overcome by the settling of the heated vs unheated sensors.

So, the more stabile the input power, the more stabile the readings.

I know that the rotating anemometer will yield pulses per revolution
and for counting pulses, the power is not as important.

About lightning, Yikes, Anything connected (even the house) is at
risk. But you are correct that I will lose the the sensor MINIMUM!

(maybe I should put a 2 iron on the post, as a golfer told one time
that even the Almighty has a hard time hitting a 2 iron [noparse]:)[/noparse]

Do you any ideas what weather stations do for lightning protection?
Seems if the building got hit, the resultant electrical fields around
the building would zap any electronics, even with a complete ground
rod system. ??

Dave




--- In basicstamps@egroups.com, Tracy Allen <emesys@c...> wrote:
> Hi Dave,
>
> Huh? It is not at all clear to me why you need such a complicated
power
> supply for a wind speed sensor. Most that I know of produce either
a
> frequency from a reed switch or hall effect device, or a frequency
from an
> AC generator. Those do not require much of a fancy power supply.
Tight
> current limiting and high stability with temperature are not an
issue.
> What does your circuit do?
>
> BTW, an important consideration with anemometers is lightning and
ESD. By
> their nature, anemometers are antennas for everything out there and
funnel
> it happily back to your sensitive electronics. Need protection.
>
> -- Tracy Allen
> Electronically Monitored Ecosysstems
> http://www.emesystems.com
>
>
>

---

original message tread:

---

>
> Here's more information
> on what I'm doing.
>
> I'm currently using a LM7812 to get the 12 volts, and
> an op-amp to limit the current. Of course capacitors
> to eliminate the AC ripple and resistors to adjust the
> Op-amp output for current limiting. This power supply is larger
> than the rest of my circuit.
>
> The wind speed sensor board 1 inch by 1.3 inches and
> almost 100 feet from the Stamp. The power supply section
> adds 2" x 1.2" to the board size. I am using AC just because of
> the distance from the stamp as a way to eliminate any
> voltage drop and resultant power loss.
>
> I'm planning on replacing the remote unit and am making it
> with many components surface mount so I can put it in a
> smaller enclosure, actually up on the roof and inside of a pole.
> The unit will be subjected to temperature changes here in
> New Jersey of 0 F in the winter to about 100 F in the summer.
>
> The temperature of the power supply will see that 100 degree
> swing and since most of the components have temperature
> parameters that will change the output along with the change
> of temperature, I am concerned that the power supply will not
> be stabile.
>
> My option is to put the power inside of the building, about 10 feet
> from the sensor, where the temperature is more stabile at between
> 60 and 80 .
>
> As you can see, a I'm not sure a simple power supply
> will satisfy the environmantal conditions, and the physical size.
> Any suggestions on making it more stabile or smaller are welcome.
>
>
> Dave
>
> --- In basicstamps@egroups.com, Jon Enoch <jone@n...> wrote:
> > You could Rectify the AC with a diode bridge and filter the DC
with
> a couple
> > of electrolytic capacitors. use any one of the TO-220 type voltage
> > regulators (either fixed or adjustable eg. LM317) to set your
> desired
> > voltage. As for the current limiting, these devices can be set
up
> as
> > constant current sources also. Check out National
Semiconductor's
> voltage
> > regulator line.
> >
> >
> >
> > Jon Enoch,
> > PCB Design Engineer,
> > Northern Airborne Technology.
> >
> >
> >
> >
> > I am looking to reduce a power supply to get a small unit.
> >
> > There is up to 24 VAC available for this circuit.
> > What is needed ia 12VDC and only 12 ma.
> > The 12 ma is the max for the circuit so it needs to be limited
for
> > power at 12ma.
> >
> > Any tips or tricks ?

Archiver

> I'm currently using a LM7812 to get the 12 volts, and
> an op-amp to limit the current. Of course capacitors
> to eliminate the AC ripple and resistors to adjust the
> Op-amp output for current limiting. This power supply is larger
> than the rest of my circuit.

>The wind speed sensor is a thermal anemometer using King's law
>to compare two thermal sensors. One is heated and one is measuring
>ambient temperature. The voltage difference at wind speeds is very
>low. Since one sensor is heated, any large change in the power
>supply changes the settling time of the sensor. long drifts of power
>are overcome by the settling of the heated vs unheated sensors.
>
>So, the more stabile the input power, the more stabile the readings.
>
>I know that the rotating anemometer will yield pulses per revolution
>and for counting pulses, the power is not as important.
>
>About lightning, Yikes, Anything connected (even the house) is at
>risk. But you are correct that I will lose the the sensor MINIMUM!
>
>(maybe I should put a 2 iron on the post, as a golfer told one time
>that even the Almighty has a hard time hitting a 2 iron [noparse]:)[/noparse]
>
>Do you any ideas what weather stations do for lightning protection?
>Seems if the building got hit, the resultant electrical fields around
>the building would zap any electronics, even with a complete ground
>rod system. ??
>Dave

Hi Dave,

More questions... Are you driving the heated sensor with a constant
voltage, or with a constant current? Is it the heater that takes the 12 ma
(that is not much at all for a heater!). And then does the circuit contain
an amplifier and/or differential amplifier? A voltage regulator other than
the 7812 might serve you better. The '7812 is designed for higher current
levels.

There is not much you can do about direct lightning strikes, but the more
common occurance is lesser surges of electromagnetic energy from relatively
distant lightning that are picked up by your "antenna". Running the cable
from the annemometer through a shield, such as the mounting pole is the
best thing you can do, and then a heavy wire from the shield directly to
ground (real ground). The 2-iron is a great idea (hehe!). Each lead that
comes from the thermal anemometer to your circuit should be protected with
a transorb to ground, that is, to the shield. Most of the ESD energy will
dissipate down the shield, but the transorb catches the rest that gets
directly into your wiring. A gas discharge tube (NE2 neon bulb!) can be
used there. Keep resistors and ferrite beads and 1kv 0.001uf capacitors in
there too. It depends on the circuit. Then inside the house, add some
zeners to the signal lines to catch any residual energy to protect your
inside wiring. The inside wiring should be grounded at one point. And use
well-grounded surge protectors on any connections you have to the house
wiring or telephone lines. A lot of damage can come when voltages that
come in over one "antenna" (your anemometer tower) are substantially
different from voltages that come in from a different "antenna" (the
telephone or power grid).

I hope that helps,


-- Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com