Magnified Sunlight
njm1
Can magnified sunlight be used for practical power generation?
I recollect reading that two particular metals (one is copper
and I can't remember the other) when connected together and
heated on one end, will generate a current on the other end.
If this is true is the concept being used anywhere?
Tnx -- Norm
Chris Pollard
: Can magnified sunlight be used for practical power generation?
: I recollect reading that two particular metals (one is copper
: and I can't remember the other) when connected together and
: heated on one end, will generate a current on the other end.
: If this is true is the concept being used anywhere?
photocells work better with concentrated light. There are some cells that
work in the infrared region and then bimetal type units. The latter are
used for remote power generation but are very inefficient.
Bob Peterson
writes:
>
>Please remove -nospam- to reply.
>
>Can magnified sunlight be used for practical power generation?
>I recollect reading that two particular metals (one is copper
>and I can't remember the other) when connected together and
>heated on one end, will generate a current on the other end.
>If this is true is the concept being used anywhere?
>
>Tnx -- Norm
>
many dissimilar metals will generate a voltage at the junction between them.
the voltage increases with temperature. its not a real practical way to
generate much electricity. I have seen some camping/survival catalogs that
have a kerosene lantern with such a generator built in it to power a radio.
$5 free! https://secure.paypal.com/refer/pal=peter...@aol.com
Learn all about how the NSA spys on you. Search on "Project Echelon" at your
favorite search engine. Another service brought to you by the Clintons.
Lewis Cosper
appliances as gas water heaters, and gas furnaces to control gas flow. The
pilot flame heats the thermocouple and sends electric current to the main
gas valve. Pilot out, thermocouple stops producing electric current, and
main gas valve is off.
I have a few plans for larger usage of the critters, but they seem to be
better suited for low power generation.
Lewis
Steve Spence
http://www.webconx.com/thermoelectric.htm
--
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Steve Spence
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"njm1" <n-nosp...@ghplus.infi.net> wrote in message
news:38D253...@ghplus.infi.net...
cliff eden
voltage it is called a thermopile, and will generate enough current to power
a thermostat system. there is also a furnace equipped w/ a thermopile big
enough to run its own blower.
"Lewis Cosper" <cos...@ria.net> wrote in message
news:38d37...@news.info2000.net...
> These things are called thermocouples, and have been used for years in
such
> appliances as gas water heaters, and gas furnaces to control gas flow.
The
> pilot flame heats the thermocouple and sends electric current to the main
> gas valve. Pilot out, thermocouple stops producing electric current, and
> main gas valve is off.
>
> I have a few plans for larger usage of the critters, but they seem to be
> better suited for low power generation.
>
> Lewis
>
>
>
>
> n article <38D253...@ghplus.infi.net>, njm1
> <n-nosp...@ghplus.infi.net>
> writes:
>
> >
George Brown
Virtually any dissimilar metal junction will generate a potential
(although often negligible) that increases with temperature. The
potential (voltage) verses temperature curve for each type of
dissimilar metal junction is essentially unique and is the basis for
temperature measurement via thermocouples. The available generated
current in a single thermocouple junction is a function of the
cross-sectional area of the dissimilar metal junction interface.
For a given temperature, one can theoretically calculate the required
amount of cross-sectional area for a required current flow and the
required number of junctions in series for the needed voltage. The
resistive losses in the wires must be accounted for (also calculable).
Unfortunately, the resistive losses are often high for the "better
performing" thermocouple junctions (one must recognize that
thermocouples are generally used for sensing temperature, not
generating useful current).
All this aside, one can theoretically design any size system (of
course, the heat transfer from your hot source into the thermocouples
must also be carefully considered). Unfortunately, it becomes quickly
obvious that the cost and efficiency (particularly capital or economic
efficiency) are not very good for large systems. This does not imply
that there are no uses for this type of system (i.e. source for
controlling safety gas valve on heaters and hot water heaters).
George
Remove "no-spam" from e-mail address to reply by e-mail.
Mystic
> Please remove -nospam- to reply.
>
> Can magnified sunlight be used for practical power generation?
> I recollect reading that two particular metals (one is copper
> and I can't remember the other) when connected together and
> heated on one end, will generate a current on the other end.
> If this is true is the concept being used anywhere?
>
> Tnx -- Norm
The concept is being used just about anywhere where natural gas, or
propane are being used.
The valve that controls the flow of gas is kept open by a thermocouple.
A device that is activated by the heat of the pilot flame. If the flame
goes out for any reason the thermocouple is no longer heated and the
valve closes. As far as I know this only produces very small quantities
of electricity. Perfect for this application but not practical for power
generation.
As for using magnified sunlight as a power source...I suggest you read
A Golden Thread by Ken Butti and John Perlin
This book gives very good information on the history and use of solar
power.
*MYSTIC*
Chris Pollard
: The valve that controls the flow of gas is kept open by a thermocouple.
: A device that is activated by the heat of the pilot flame. If the flame
: goes out for any reason the thermocouple is no longer heated and the
: valve closes. As far as I know this only produces very small quantities
: of electricity. Perfect for this application but not practical for power
: generation.
thermocouples. Thermocouples are not passive - they require signal
conditioning and power to operate a valve. The thermostats are, I
believe, wax filled and operate on a thermal expansion basis - therefore
being passive and have enough force to operate a valve.
Bob Peterson
<cpol...@teal.sni.net> writes:
>
>I think you are confused - they are controlled by thermostats not
>thermocouples. Thermocouples are not passive - they require signal
>conditioning and power to operate a valve. The thermostats are, I
>believe, wax filled and operate on a thermal expansion basis - therefore
>being passive and have enough force to operate a valve.
>
the thermostat controls the main gas valve and the blower on a forced air
system. the thermocouple is mounted in the pilot light fire area and keeps the
pilot valve open via the energy generated by the pilot flame. if the flame
goes out then the pilot valve closes.
Larry Brasfield
peter...@aol.comnospam says...
> In article <ol7B4.27$nG2....@wdc-read-01.qwest.net>, Chris Pollard
> <cpol...@teal.sni.net> writes:
>
> >
> >I think you are confused - they are controlled by thermostats not
> >thermocouples. Thermocouples are not passive - they require signal
> >conditioning and power to operate a valve. The thermostats are, I
> >believe, wax filled and operate on a thermal expansion basis - therefore
> >being passive and have enough force to operate a valve.
> >
>
> the thermostat controls the main gas valve and the blower on a forced air
> system. the thermocouple is mounted in the pilot light fire area and keeps the
> pilot valve open via the energy generated by the pilot flame. if the flame
> goes out then the pilot valve closes.
I'm just expanding a bit on Mr. Peterson's statement,
not disagreeing with it.
The pilot flame on many (all?) gas furnaces is fed
thru a valve which is held open by a relatively
high current and low voltage electro-magnet. The
magnetic gap is closed by hand power when somebody
lights the pilot and the thermocouple need only
supply enough amp-turns to hold that gap closed,
(holding the valve open). If you look at such a
valve, you will see a few turns of very heavy
guage wire. (I fixed one once which was failing
because the connection had got cruddy and was
dropping to much voltage for its high current.)
While it is true that thermocouples tend to have
a low output voltage, they can be made with very
low output resistance and hence can provide more
power to a properly matched load than one might
guess when thinking about ordinary circuits.
--
Larry Brasfield
Above opinions may be mine alone.
(Humans may reply at unundered l.bras_field@computer.o_r_g )
team...@webtv.net
Lindsay Publications reprint. Has enuf info to help you make your first
thermopile.
A fresnel lens from Edmund Scientific is a cheap way to heat your
thermopile, on sunny days. Lens holder plans are available from Edmund.
Teledyne Energy Systems, Inc., manufactured a l2VDC, 60 Watt unit,
powered by a backyard barbecue propane tank. This unit was designed to
run 24 hours a day, in any weather. If you get your thermopile
up-and-running, you might want to consider the propane option.
Stove-top thermopiles were widely used in Alaska and Siberia, during the
1920s, to recharge radio batteries.
Some l9th cent. telegraph stations were equipped with stove-top
thermopiles to back-up their battery power.
Experiment with dissimilar metals! See which combinations give the best
results! While you're having fun with this project, you might make a
discovery that will advance the science of thermoelectrics! You might
be surprised.
Good luck!
njm1
Thank You all for taking the time to reply to my questions about
Magnified Sunlight! It's been very enlightening.
Norm
--
Best Regards,
Norm
[mailto:nj...@ghplus.infi.net]
http://freepages.genealogy.rootsweb.com/~njm1
http://www.geocities.com/nmeinert
Larry Brasfield
cpol...@teal.sni.net says...
> Sylvan Butler <xsylvan...@cyberhighway.net> wrote:
>
> : Many gas furnaces use a thermocouple just as described by Mystic.
> : Thermocouples are very passive. They produce electricity when heated,
> : and when not heated do not.
>
> They produce a voltage that is rather small and incapable of doing
> anything like open a valve.
The voltage may be only a few hundred mV, but
a thermocouple can deliver lots of current.
Your preconceived notion that unsmall voltage
is required to drive electromagnetic devices
is wrong. In fact, solenoid coils can be
configured for a wide range of voltages by
changing the wire guage and turns count. The
relevant measure of energization is Amp-turns.
> THEY DON'T USE THERMOCOUPLES - your valve isn't electrically operated.
They do use thermocouples. I have observed
one of these devices with my own eyes. There
is no external power source. The thermocouple
directly drives the coil that holds the valve
in the open position. If you read my post on
this thread of 3/19, you can get more details.
> Geeze.
>
> The voltage is analogue - when does it switch - what is the comparison
> circuit - there isn't one.
The threshold is at the level of current which
produces just enough closing force in the gap
to equal the spring force tending to open it.
At higher current, the gap is held closed and
the valve is held open. At lower current, the
spring open the gap a little bit which reduces
the magnetic field strength causing the valve
to be closed, quickly, by the spring.
Sylvan Butler
>Mystic <mys...@bigvalley.net> wrote:
>: The valve that controls the flow of gas is kept open by a thermocouple.
>: A device that is activated by the heat of the pilot flame. If the flame
>: goes out for any reason the thermocouple is no longer heated and the
>: valve closes. As far as I know this only produces very small quantities
>: of electricity. Perfect for this application but not practical for power
>: generation.
>thermocouples. Thermocouples are not passive - they require signal
No Chris, you are confused.
Many gas furnaces use a thermocouple just as described by Mystic.
Thermocouples are very passive. They produce electricity when heated,
and when not heated do not.
sdb
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User should be sylvan and host is cyberhighway.net.
Do NOT send me unsolicited commercial e-mail (UCE)!
Chris Pollard
: Many gas furnaces use a thermocouple just as described by Mystic.
: Thermocouples are very passive. They produce electricity when heated,
: and when not heated do not.
They produce a voltage that is rather small and incapable of doing
anything like open a valve.
THEY DON'T USE THERMOCOUPLES - your valve isn't electrically operated.
Geeze.
Bob Peterson
<cpol...@teal.sni.net> writes:
>
>They produce a voltage that is rather small and incapable of doing
>anything like open a valve.
>
>THEY DON'T USE THERMOCOUPLES - your valve isn't electrically operated.
>
>Geeze.
>
>The voltage is analogue - when does it switch - what is the comparison
>circuit - there isn't one.
>
you are wrong. the pilot valve i sopened by hand but the little bit of juice
generetaed by the t/c being in the flame is enough to keep it open. if the
pilot goes out the little bit of juice goes away and the pilot valve closes.
Duane C. Johnson
Chris Pollard <cpol...@teal.sni.net> wrote:
> Sylvan Butler <xsylvan...@cyberhighway.net> wrote:
> : Many gas furnaces use a thermocouple just as described
> : by Mystic. Thermocouples are very passive. They produce
> : electricity when heated, and when not heated do not.
> They produce a voltage that is rather small and incapable
> of doing anything like open a valve.
> THEY DON'T USE THERMOCOUPLES -
> your valve isn't electrically operated.
What are you talking about. Mine is.
I'm Looking at a thermocouple powered one right now.
I even have a thermostat, an old Honeywell with a mercury
switch, connected in series to control the temperature.
There is no external power connected. Only the thermocouple!
I now have a modern thermostat that drives a power
MOSFET transistor output.
LUX model 1500 with fully programmable day/night setback.
This thermostat is self powered with a 1.5V AA battery.
Runs for a couple of years. The point is that the switch
is the MOSFET in series with the thermocouple and gas valve.
The AA battery is NOT powering the gas valve.
The thermocouple powers the valve!
> Geeze.
> The voltage is analogue - when does it switch -
> what is the comparison circuit - there isn't one.
My system is the example.
Have fun! Duane
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Fred McGalliard
"Duane C. Johnson" wrote:
...
> I'm Looking at a thermocouple powered one right now.
> I even have a thermostat, an old Honeywell with a mercury
> switch, connected in series to control the temperature.
> There is no external power connected. Only the thermocouple!
>
> I now have a modern thermostat that drives a power
> MOSFET transistor output.
> LUX model 1500 with fully programmable day/night setback.
> This thermostat is self powered with a 1.5V AA battery.
> Runs for a couple of years. The point is that the switch
> is the MOSFET in series with the thermocouple and gas valve.
> The AA battery is NOT powering the gas valve.
> The thermocouple powers the valve!
The old honeywell unit uses a metal pair whose differential expansion
rotates the mercury switch. No thermocouple. The electronic thermostates
were, I thought just the same plan. The power is provided by a step down
transformer at the load out in the garage. I have also seen some systems
that use a tube of some sort as sensor. Near as I could tell last time I
took one apart this was not a thermocouple but some sort of mechanical
system. Could you double check your facts??
Fred McGalliard
Larry Brasfield wrote:
...
> The voltage may be only a few hundred mV, but
> a thermocouple can deliver lots of current.
Hey. I dink around with some of our home stuff, and I would rather know
for fact. A standard thermocouple sensor is too small a junction to
deliver more than a few milliamps. I could design one to deliver enough
current to drive a solenoid, but it would look very strange and you
would quickly recognize it as unique. I would be very surprised to see a
solenoid directly driven by a thermocouple. I would like to know how
they did it.
Chris Pollard
: The voltage may be only a few hundred mV, but
: a thermocouple can deliver lots of current.
: Your preconceived notion that unsmall voltage
: is required to drive electromagnetic devices
: is wrong. In fact, solenoid coils can be
: configured for a wide range of voltages by
: changing the wire guage and turns count. The
: relevant measure of energization is Amp-turns.
That has nothing to do with thermocouples and Amp-turns has everything to
do with energy.
: The threshold is at the level of current which
: produces just enough closing force in the gap
: to equal the spring force tending to open it.
: At higher current, the gap is held closed and
: the valve is held open. At lower current, the
: spring open the gap a little bit which reduces
: the magnetic field strength causing the valve
: to be closed, quickly, by the spring.
and doesn't "switch" so it would never work.
: --
Chris Pollard
: you are wrong. the pilot valve i sopened by hand but the little bit of juice
: generetaed by the t/c being in the flame is enough to keep it open. if the
: pilot goes out the little bit of juice goes away and the pilot valve closes.
Larry Brasfield
frederick.b...@boeing.com says...
>
>
> Larry Brasfield wrote:
> ...
> > The voltage may be only a few hundred mV, but
> > a thermocouple can deliver lots of current.
>
> for fact.
I observed it with my own eyes with the advantage
of having used thermocouples and designed a chopper
stabilized amplifier for using one as part of a kiln
controller. I have also designed electromagnetic
devices, so I'm well qualified to say that amp-turns
is the relevant measure of solenoid energization.
> A standard thermocouple sensor is too small a junction to
> deliver more than a few milliamps.
Fine. For sensing, a small junction and fine wire
are sufficient since little current is delivered.
The pilot light thermocouple is built with large
gauge wire (about 12 or 14 AWG, as I recall its
appearance) and the sensing end is joined over
an inch or so of the wire's length. The device
is connected to the valve solenoid by heavy wire
and the solenoid is just 4 to 12 turns of heavy
wire. Obviously, it's a low impedance system.
> I could design one to deliver enough
> current to drive a solenoid, but it would look very strange and you
> would quickly recognize it as unique.
They are replicated in gas furnaces across the
world. "Unique" does not describe it. They do
look different from thermocouples used to sense
temperature, being thicker and longer. In use,
they extend clear thru the pilot flame. A metal
sheath spreads the heat over more of the junction
length than is hit by the flame.
> I would be very surprised to see a
> solenoid directly driven by a thermocouple. I would like to know how
> they did it.
See above. As I explain in other articles, the
solenoid is hand driven to the position where
the magnetic gap is closed. The thermocouple
is only called upon to keep it closed.
Larry Brasfield
cpol...@teal.sni.net says...
> Larry Brasfield <l.bras_field@computer.o_r_g> wrote:
> : The voltage may be only a few hundred mV, but
> : a thermocouple can deliver lots of current.
So, please reveal what limits the output current
of a thermocouple. Do you know what a Thevenin
equivalent source is? What do you suppose the
output impedance is? Can you imagine that it's
related to the resistance of the junction and
the wires? What is to prevent a thermocouple
junction being made large enough to deliver
whatever current is required by the application?
Please be specific or withdraw your ignorant
comments.
> : Your preconceived notion that unsmall voltage
> : is required to drive electromagnetic devices
> : is wrong. In fact, solenoid coils can be
> : configured for a wide range of voltages by
> : changing the wire guage and turns count. The
> : relevant measure of energization is Amp-turns.
> :
> That has nothing to do with thermocouples and Amp-turns has everything to
> do with energy.
Do a dimensional analysis of those measures and
you will find that you are mistaken. The relation
between amp-turns and power is totally dependent
on the coil resistivity and winding configuration.
I hope you do not often confuse energy and power.
> : The threshold is at the level of current which
> : produces just enough closing force in the gap
> : to equal the spring force tending to open it.
> : At higher current, the gap is held closed and
> : the valve is held open. At lower current, the
> : spring open the gap a little bit which reduces
> : the magnetic field strength causing the valve
> : to be closed, quickly, by the spring.
> A thermocouple doesn't create enough energy to do that.
> and doesn't "switch" so it would never work.
It works exactly as I said. In fact, it switches
with some hysteresis due to the positive feedback
created by the increased reluctance as the gap
opens. Your notion that some particular amount of
"energy" is required to hold a solenoid in position
is misguided. In fact, your willingness to shoot
from the hip on subjects you know virtually nothing
about is misguided.
Mike
http://hvacwebtech.com/thermocouple.htm
-Mike
Fred McGalliard
Larry Brasfield wrote:
...
> See above. As I explain in other articles, the
> solenoid is hand driven to the position where
> the magnetic gap is closed. The thermocouple
> is only called upon to keep it closed.
Meets my criteria of being "unusual". I have an old High School lab
experiment in mind. A metal pair with a square inch or so of contact
surface and around a half inch thick tubing wrapped a few turns around a
soft iron core, rather like a speaker magnet in structure. Heat one end
of the pair up with a flame, while the other end is cooled, and a metal
plate across the face is kept there with a very substantial force. When
the flame goes out, after a bit, the plate drops off. I haven't had a
gas furnace or stove in over 20 years, so I am really not familiar with
this application. Thanks for the data.
Lewis Cosper
Chris Pollard wrote in message ...
>THEY DON'T USE THERMOCOUPLES - your valve isn't electrically operated.
>
>Geeze.
Mine is. I'll bet yours is.
Lewis
Chris Pollard
Distribution:
Larry Brasfield <l.bras_field@computer.o_r_g> wrote:
: > : The voltage may be only a few hundred mV, but
: > : a thermocouple can deliver lots of current.
: > BS.
: So, please reveal what limits the output current
: of a thermocouple. Do you know what a Thevenin
: equivalent source is? What do you suppose the
: output impedance is? Can you imagine that it's
: related to the resistance of the junction and
: the wires? What is to prevent a thermocouple
: junction being made large enough to deliver
: whatever current is required by the application?
The BS was to the "few hundred mv" - according to my charts most
thermocouples only generate 5 to 10mV at reasonable temepreatures
: Please be
specific or withdraw your ignorant : comments.
: > That has nothing to do with thermocouples and Amp-turns has everything to
: > do with energy.
: Do a dimensional analysis of those measures and
: you will find that you are mistaken. The relation
: between amp-turns and power is totally dependent
: on the coil resistivity and winding configuration.
True - but one tiny thermocouple isn't going to drive a car either.
: I hope you do not often confuse energy and power.
Mostly never - we were discussing energy/power in a magnetic field - this
has nothing to do with the coil resisitivity.
: It works exactly as I said. In fact, it switches
: with some hysteresis due to the positive feedback
: created by the increased reluctance as the gap
: opens. Your notion that some particular amount of
: "energy" is required to hold a solenoid in position
: is misguided. In fact, your willingness to shoot
: from the hip on subjects you know virtually nothing
: about is misguided.
Unless the solenoid is a bistable it WILL require energy to hold it.
What are the materials used in the wire/bus bars of this thermocouple?
Bob Peterson
<cpol...@teal.sni.net> writes:
>Unless the solenoid is a bistable it WILL require energy to hold it.
>
>What are the materials used in the wire/bus bars of this thermocouple?
>
the hold in energy required is lots less then the energy required to open the
valve in the first place. thats why you have to opne the valve with your
finger. the energy the t/c makes is only enough to keep it open.
Lewis Cosper
Fred McGalliard wrote in message <38D8E502...@boeing.com>...
Hi Fred,
>The old honeywell unit uses a metal pair whose differential expansion
>rotates the mercury switch. No thermocouple. The electronic thermostates
>were, I thought just the same plan. The power is provided by a step down
>transformer at the load out in the garage.
Most of the use of thermocouple are for a safety feature. There is a main
gas valve that shuts off gas flow even if the thermostat calls for heat.
This is to prevent some big bangs.
The mechanism that holds this main valve open is a thermocouple heated by
the pilot light. When you light the pilot light you have to hold the valve
in to get gas to even flow to the pilot flame. One the flame is established
there is enough current generated by the thermocouple to hold the valve open
by a solenoid. If the pilot goes out for any reason the thermocouple cools
and current flow to the solenoid lowers and the valve is closed by a spring.
If you don't believe me just go to your local furnace repair place and ask
them to show you a thermocouple for a gas water heater or gas furnace.
Technique has been in use for a LONG time.
Lewis
Plaidp
>Mine is. I'll bet yours is.
>
>Lewis
OK - there appear to be several types:-
750 mV mercury generator that is used in "self-generating" heating controls.
30mV standard thermocouple systems for active controls.
Capillary thermostats used in most gas controls.
bimetallic coils used in "honeywell" type room control thermostats
from a description in a post that didn't appear on my ISP there are apparently
some old rare furnaces that use a large thermocouple to drive a coil directly
for a manual reset (but it doesn't generate hundreds of millivolts).
Hopefully this addresses all the types.
Chris Pollard
Chris Pollard
If the thread looks like a debate then this may not be my opinion.
Jack Previdi
> Chris Pollard wrote in message ...
>
> >THEY DON'T USE THERMOCOUPLES - your valve isn't electrically operated.
> >
> >Geeze.
I hesitate to tread in this thread but...
The device which holds a gas valve open on a gas appliance is NOT
a thermocouple. It is a mechanical device with a high coefficient of
expansion, that when heated forces the valve open.
NOT a bi-metallic strip (thermostat) or thermocouple, but a capillary
tube (copper?)
or bulb, filled with the above mentioned material with a high C of E.
(bismuth?)
This is the same principle that was (and may still be used in some
vehicles)
was used to actuate water and or oil temperature gauges in autos and
trucks.
Please forgive the (...?) , if someone remembers the correct materials I
will
be happy to wear orthopedic shoes.
Jack
Larry Brasfield
cpol...@teal.sni.net says...
> K2.1...@wdc-read-01.qwest.net> <MPG.1342a75c9...@news.uswest.net>
> Distribution:
>
> Larry Brasfield <l.bras_field@computer.o_r_g> wrote:
> : > : The voltage may be only a few hundred mV, but
> : > : a thermocouple can deliver lots of current.
> : > BS.
[Comments regarding low output impedance cut.]
> The BS was to the "few hundred mv" - according to my charts most
> thermocouples only generate 5 to 10mV at reasonable temepreatures
The thermocouple chart I have, from "Electronic
Engineers' Handbook" 3rd edition by Fink and
Christiansen, shows, at 1500 oF, type E at 62 mV,
type J at 46 mV, and type K at 34 mV. The Cu/Ni
pair is closest to type J. My "few hundred mV"
seems a little high. It was a guess based on
an unknown (to me) temperature that causes the
device to glow bright red. With what I know,
that temperature is somewhere between 1500 oF
and 2500 oF.
Whether it's 50-70 mV or "a few hundred mV"
does not alter my point which is that a low
impedance, low voltage source can be used
to keep a solenoid operated.
...
> : The relation
> : between amp-turns and power is totally dependent
> : on the coil resistivity and winding configuration.
> True - but one tiny thermocouple isn't going to drive a car either.
No argument on that.
> : I hope you do not often confuse energy and power.
> Mostly never - we were discussing energy/power in a magnetic field - this
> has nothing to do with the coil resisitivity.
> : It works exactly as I said. In fact, it switches
> : with some hysteresis due to the positive feedback
> : created by the increased reluctance as the gap
> : opens. Your notion that some particular amount of
> : "energy" is required to hold a solenoid in position
> : is misguided. In fact, your willingness to shoot
> : from the hip on subjects you know virtually nothing
> : about is misguided.
> Unless the solenoid is a bistable it WILL require energy to hold it.
The solenoid force that resists the spring is
developed at a gap with a magnitude that is
nearly proportional to the energy density of
the magnetic field in the gap. The energy in
that field and the iron part of the magnetic
circuit is incidental. To a first order
approximation, where the non-air part of the
path has 0 reluctance and the gap closes so
as to enclose no volume, no energy is needed
to develop the force. It is only because the
iron has finite permeability and the gap has
imperfect mating surfaces that some energy
must be stored to develop the holding force.
The power required to maintain the field is
another issue, related to winding losses.
> What are the materials used in the wire/bus bars of this thermocouple?
The solenoid windings were copper. The
connecting terminals were something else,
harder. I understand from other sources
that the thermocouple is copper/nickel.
team...@webtv.net
a consenus, so he can start work on his project?
Duane C. Johnson
Fred McGalliard wrote:
> "Duane C. Johnson" wrote:
> > I'm Looking at a thermocouple powered one right now.
> > I even have a thermostat, an old Honeywell with a mercury
> > switch, connected in series to control the temperature.
> > There is no external power connected. Only the thermocouple!
> > I now have a modern thermostat that drives a power
> > MOSFET transistor output.
> > LUX model 1500 with fully programmable day/night setback.
> > This thermostat is self powered with a 1.5V AA battery.
> > Runs for a couple of years. The point is that the switch
> > is the MOSFET in series with the thermocouple and gas valve.
> > The AA battery is NOT powering the gas valve.
> > The thermocouple powers the valve!
>
> The old honeywell unit uses a metal pair whose differential
> expansion rotates the mercury switch. No thermocouple. The
> electronic thermostates were, I thought just the same plan.
> The power is provided by a step down transformer at the
> load out in the garage. I have also seen some systems that
> use a tube of some sort as sensor. Near as I could tell
> last time I took one apart this was not a thermocouple but
> some sort of mechanical system.
> Could you double check your facts??
My facts are correct!
Ok, of course there is a bimetalic strip in the thermostat.
But who cares. It only operates the mercury switch.
It's the switch in series with the coil and thermocouple
that opens and closes the valve.
Yes, I said both OPENS and CLOSES the valve. I don't
even need to manually hold it shut.
There ain't no transformer. Get it? Only the thermocouple.
What's so mysterious about a low voltage high current solenoid
being operated by a low voltage high current thermocouple.
Seams a perfect match to me. Mine works.
There is no bulb or tube. It's a thermocouple in the pilot light
flame. It's got wires and no other power source. Get it?
Do you need a picture.
Chris Pollard
: Looks like Norm's request has triggered a pissing contest. Are we near
: a consenus, so he can start work on his project?
than I knew.
But we didn't uncover any new physical properties - an old invention yes.
njm1
>
> Looks like Norm's request has triggered a pissing contest. Are we near
> a consenus, so he can start work on his project?
Thanks for jumping in. I had no intention of creating such a
debate. I'm trying to absorb all the pro/con arguments and I
appreciate everyone's comments.
I posted the original inquiry with the thought in mind that
if a "bank" of say 20 or even more of these devices (dissimilar
pieces of metal being heated by magnified sunlight (using lenses)
were connected, either in series or parallel, the resultant
output could be used to power something! Initial costs would
be almost nil and you end up with an inexpensive power source.
Thanks.
--
Best Regards,
Norm
bikerbabe in black leather
> I posted the original inquiry with the thought in mind that
>if a "bank" of say 20 or even more of these devices (dissimilar
>pieces of metal being heated by magnified sunlight (using lenses)
>were connected, either in series or parallel, the resultant
>output could be used to power something! Initial costs would
>be almost nil and you end up with an inexpensive power source.
Not really almost nil. Sure the metal costs for the junctions could
be low, but you also have the magnifier costs (not so low) and the
frame costs (to hold the whole assembly together and keep it protected
from the weather).
I think you will find your dollars per watt ratio to be pretty bad,
and your "time per watt" (how long it takes you to make the thing)
really horrible (much worse than it would be if you were earning
minimum wage and bought a commercial solar panel using the proceeds).
About the only advantage it has is that it's something that you can
build out of "found" materials, it requires no elaborate fabrication
systems.
--
Anmar Mirza # Tranquility is an intentional community project, we're looking
EMT-D TBTW10# for people to join. http://php.indiana.edu/~amirza/tranquil.htm
N9ISY (tech)# Have sawmill, will travel.
EOL DoD#1147# http://php.indiana.edu/~amirza/home.html
George Brown
><snip>
> I posted the original inquiry with the thought in mind that
>if a "bank" of say 20 or even more of these devices (dissimilar
>pieces of metal being heated by magnified sunlight (using lenses)
>were connected, either in series or parallel, the resultant
>output could be used to power something! Initial costs would
>be almost nil and you end up with an inexpensive power source.
> Thanks.
>--
>Best Regards,
> Norm
There is a lot more involved than you think. The junctions
will need to be brazed together if you do not want significant
corrosion. It is my undersatnding that corrosion will happen rather
quickly under heavy current loads if the junctions have a simple
mechanical contact.
For any serious voltage/power, you will need a lot more than
20 thermocouples in series. Power conditioning is not particularly
cheap either.
A friend of mine was involved in a feasability study for this
quite a number of years ago for a private firm. He told me that the
conclusion at that time was that it wasn't economically viable
(theoretically there was no problems with designing any size unit that
one desired). This was from a commercial venture standpoint of
course, not a hobbyist view.
George
Remove "no-spam" from e-mail address to reply by e-mail.
Anthony Matonak
...
> There is a lot more involved than you think. The junctions
> will need to be brazed together if you do not want significant
> corrosion. It is my undersatnding that corrosion will happen rather
> quickly under heavy current loads if the junctions have a simple
> mechanical contact.
> For any serious voltage/power, you will need a lot more than
> 20 thermocouples in series. Power conditioning is not particularly
> cheap either.
> A friend of mine was involved in a feasability study for this
> quite a number of years ago for a private firm. He told me that the
> conclusion at that time was that it wasn't economically viable
> (theoretically there was no problems with designing any size unit that
> one desired). This was from a commercial venture standpoint of
> course, not a hobbyist view.
I know the general consensus is that thermocouples are pretty
inefficient and, when purchased, fairly expensive but if a hobbyist
wanted to experiment what would be the most effective and least
cost materials to use and how would you recommend constructing a
thermopile? Do you just take say, sheet metals, stamp or cut out
squares or circles, stack them up like the old fashioned voltaic
piles and weld them together?
As far as the concentrating solar energy thing goes someone with
a welder, some sheet metal and a pattern for a parabolic curve could
bang out something a couple of meters on a side fairly quickly that
would work ok. The more tightly focused you want it, the more finicky
you need to be with precision in your construction. I imagine those
solar parabolic cookers made from cardboard and tin foil could be as
easily made (much larger) from sheet steel.
Anthony
George Brown
<ant...@matonak.org> wrote:
><snip>
> if a hobbyist
>wanted to experiment what would be the most effective and least
>cost materials to use and how would you recommend constructing a
>thermopile? Do you just take say, sheet metals, stamp or cut out
>squares or circles, stack them up like the old fashioned voltaic
>piles and weld them together?
One can easily look up the best performing materials but not
necessarily the most cost effective. I'm not sure where that
information is readily found, but I'm sure it's available. If I can
find any info on that, I'll let you know. Unfortunately, the best
source I know on this subject passed away a couple of years ago.
Before you go to design a thermopile unit, you need to
understand how a thermocouple works. My previous notes here with
respect to how a thermocouple works weren't very specific and, after
rereading them, possibly misleading. The "magic" is not actually in
the dissimilar metal junction. Let's start from scratch.
Let's begin with "half" of a thermocouple. Let's look at a
single length of wire (type of metal is unimportant at this point).
If we heat one end of this wire in relation to the other, then a
higher portion of the electrons in the heated end will have their
energy state increased (this involves the temperature sensitivity of
the fermi function for the metal of choice).
This increased energy state will create a driving force to
move the electrons from the hot end to the cold end resulting in a
more electrons at the cold end and a negative voltage potential with
reference to the hot end. This results from the fact that gradients
in nature cause a driving force. Here we have the energy gradient in
the electrons causing a driving force to balance the energy
distribution, which will be counterbalanced by an electron
"concentration" (electron density) gradient which will resist a
complete balance of the energy gradient.
This is the basis for a thermocouple. The next problem that
arises is how to measure the potential or get the energy out of the
system. Any wire that we connect to the hot end and cold ends to
conduct the power to our load will also experience the same effect,
which will create an opposite potential (i.e. subtracting from) the
potential we created in the first wire. The trick is to select a wire
that doesn't develop as great a potential as the first half. Then the
available potential will be the difference between the two. In other
words, you want one metal that creates a large potential difference
between the hot & cold ends while the second metal creates a very low
potential between the hot & cold ends.
To maximize the performance in a thermopile, EACH thermocouple
"cell" needs to have a "hot" junction AND a "cold" junction. If you
simple place the hot junctions in series in the heat source, you will
find very little available potential (voltage). This is due to the
fact that relatively large potentials will be created by the
temperature difference from hot to cold ends of the "good" performing
metal compared to the difference from the hot end of one metal to the
hot end of the other metal.
I incorrectly stated in an earlier note that the available
current was a function of the cross-sectional area of the dissimilar
metal junction. The cross-sectional area of the dissimilar metal
junction CAN BE a current limiting factor if it is to small, but the
determination of the current is primarily a function of the mass of
metal and the temperature difference. Heat transfer is also important
(for both the hot and cold ends).
In order to answer what the best method of construction is,
additional information needs to be considered. The basic guide is to
create a thermopile that meets the above information and has good heat
transfer for the hot and cold junctions. I had indicated that
corrosion between the junctions was an issue (and it is) and that the
best method was to braze the to dissimilar metals together. Although
this is ideally correct, one may, depending on the metals and the
solder used, be able to solder them together with very little loss in
performance.
I probably have missed some points, but it was the best I
could due in the short time I have right now. If there are any
further questions or clarifications, I'd be happy to answer them as
best I can.
George Brown
with respect to the wires connecting the "hot" side of a junction with
the "cold" side of the junction.
First, off the top of my head, I think you want to use the
same type of metal. Otherwise, you have to evaluate possible losses
due to the different performances of the two types of metal.
Secondly, the size of the wires for current carrying purposes
is VERY misleading. You can't size the interconnecting wires based on
the typical tables you see for sizing house & industrial wiring.
These tables are designed with "economically acceptable"
losses (along with temperature rise considerations) for the balance
of cost of power verses the cost of the larger wire. You have to
remember that you will be generating on the order of tens of millvolts
per junction.
You will need to size the wire so that the voltage drop for
the desired (or possible) current flow in EACH thermocouple leg is
much less than the net volatge generated per thermocouple junction. I
think you will be very surprised at the seriousness of this issue.
Good Luck!
George Brown
wrote:
><snip>
> Secondly, the size of the wires for current carrying purposes
>is VERY misleading. You can't size the interconnecting wires based on
>the typical tables you see for sizing house & industrial wiring.
>
Not just because typical tables will be for copper or aluminum.
> These tables are designed with "economically acceptable"
>losses (along with temperature rise considerations) for the balance
>of cost of power verses the cost of the larger wire. You have to
>remember that you will be generating on the order of tens of millvolts
>per junction.
>
Possibly a couple of hundred or so millivolts, but now your getting
into very large temperature differentials or exotic materials.
Scott Babb
peter...@aol.comnospam (Bob Peterson) wrote:
> In article <38D253...@ghplus.infi.net>, njm1
<n-nosp...@ghplus.infi.net>
> writes:
>
> >
> >Please remove -nospam- to reply.
> >
> >Can magnified sunlight be used for practical power generation?
> >I recollect reading that two particular metals (one is copper
> >and I can't remember the other) when connected together and
> >heated on one end, will generate a current on the other end.
> >If this is true is the concept being used anywhere?
> >
> >Tnx -- Norm
> >
>
> many dissimilar metals will generate a voltage at the
> junction between them. the voltage increases with
> temperature. its not a real practical way to generate
> much electricity. I have seen some camping/survival
> catalogs that have a kerosene lantern with such a
> generator built in it to power a radio.
Hmmm. Would it be more efficient to use concentrated
sunlight to create steam and drive a turbine? I recall
an old Mother Earth News cover with a drawing of a 10x10
array of 1-foot-square mirrored tiles tracking the sun
and concentrating it onto a focal point (think of a
satellite dish-type setup.)
>
> $5 free! https://secure.paypal.com/refer/pal=peter...@aol.com
> Learn all about how the NSA spys on you. Search on
> "Project Echelon" at your favorite search engine. Another
> service brought to you by the Clintons.
>
From what I've read in the FAQ at http://www.echelonwatch.org
it appears that Echelon has been around since Nixon was in
office, and Clinton signed a funding bill requiring the NSA to
report their legal basis for Echelon. Echelon sounds ugly, but
you can't blame it on Clinton.
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Steve Spence
--
--
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