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Muliple Peltier elements: parallel or series?
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Richard Rasker
Jul 19, 2012, 7:57:11 AM7/19/12
to
Hello,
I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm aluminium
surface (6" x 6" x 1/6"), which has to be kept at a precise temperature
throughout (+/- 0.1 degree centigrade). Since both heating and cooling are
required, the whole design is based on one or more Peltier elements.
Ideally, one would use a Peltier element of comparable size as the aluminium
surface, to minimize temperature differences due to small local heat
losses. However, for reasons of cost and available electrical power (100W
max), I'm limited to commonly available Peltier elements with a 40 x 40 or
50 x 50 mm surface area.
So I thought I'd use four identical 25W Peltier elements (40 x 40 mm)
instead of one 100W Peltier element (50 x 50 mm). My question: is it better
to connect these Peltier elements in parallel or in series? In other words:
is a Peltier element's heat transport mainly determined by voltage
difference or by current? Any ideas are appreciated.
And oh, I thought about using much thicker aluminium to minimize local
temperature differences, but with the above dimensions, I already have a
heat capacity of > 200 J/C, so with 100W power it already takes at least 2
seconds to heat it up by one degree.
Doubling the thickness also doubles this time, and that quickly becomes a
problem: users will want to change the temperature often, and don't want to
wait several minutes every time until the temperature settles to its final
value.
Thanks in advance for any ideas.
Richard Rasker
--
http://www.linetec.nl
I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm aluminium
surface (6" x 6" x 1/6"), which has to be kept at a precise temperature
throughout (+/- 0.1 degree centigrade). Since both heating and cooling are
required, the whole design is based on one or more Peltier elements.
Ideally, one would use a Peltier element of comparable size as the aluminium
surface, to minimize temperature differences due to small local heat
losses. However, for reasons of cost and available electrical power (100W
max), I'm limited to commonly available Peltier elements with a 40 x 40 or
50 x 50 mm surface area.
So I thought I'd use four identical 25W Peltier elements (40 x 40 mm)
instead of one 100W Peltier element (50 x 50 mm). My question: is it better
to connect these Peltier elements in parallel or in series? In other words:
is a Peltier element's heat transport mainly determined by voltage
difference or by current? Any ideas are appreciated.
And oh, I thought about using much thicker aluminium to minimize local
temperature differences, but with the above dimensions, I already have a
heat capacity of > 200 J/C, so with 100W power it already takes at least 2
seconds to heat it up by one degree.
Doubling the thickness also doubles this time, and that quickly becomes a
problem: users will want to change the temperature often, and don't want to
wait several minutes every time until the temperature settles to its final
value.
Thanks in advance for any ideas.
Richard Rasker
--
http://www.linetec.nl
Martin Brown
Jul 19, 2012, 8:32:34 AM7/19/12
to
On 19/07/2012 12:57, Richard Rasker wrote:
> Hello,
>
> I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm aluminium
> surface (6" x 6" x 1/6"), which has to be kept at a precise temperature
> throughout (+/- 0.1 degree centigrade). Since both heating and cooling are
> required, the whole design is based on one or more Peltier elements.
>
> Ideally, one would use a Peltier element of comparable size as the aluminium
> surface, to minimize temperature differences due to small local heat
> losses. However, for reasons of cost and available electrical power (100W
> max), I'm limited to commonly available Peltier elements with a 40 x 40 or
> 50 x 50 mm surface area.
>
> So I thought I'd use four identical 25W Peltier elements (40 x 40 mm)
> instead of one 100W Peltier element (50 x 50 mm). My question: is it better
> to connect these Peltier elements in parallel or in series? In other words:
> is a Peltier element's heat transport mainly determined by voltage
> difference or by current? Any ideas are appreciated.
Current. They are in essence a bunch of high power diode PN junctions.
> Hello,
>
> I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm aluminium
> surface (6" x 6" x 1/6"), which has to be kept at a precise temperature
> throughout (+/- 0.1 degree centigrade). Since both heating and cooling are
> required, the whole design is based on one or more Peltier elements.
>
> Ideally, one would use a Peltier element of comparable size as the aluminium
> surface, to minimize temperature differences due to small local heat
> losses. However, for reasons of cost and available electrical power (100W
> max), I'm limited to commonly available Peltier elements with a 40 x 40 or
> 50 x 50 mm surface area.
>
> So I thought I'd use four identical 25W Peltier elements (40 x 40 mm)
> instead of one 100W Peltier element (50 x 50 mm). My question: is it better
> to connect these Peltier elements in parallel or in series? In other words:
> is a Peltier element's heat transport mainly determined by voltage
> difference or by current? Any ideas are appreciated.
Their efficiency as a cooler isn't all that great so insulation is
important if you are to obtain good thermal stability as is a suitable
heatsink on the dump side. Good for having no moving parts thought.
--
Regards,
Martin Brown
Phil Hobbs
Jul 19, 2012, 9:29:14 AM7/19/12
to
Peltiers have a nasty thermal instability, where they start getting
hotter as you go to higher current instead of colder.
If you put them in series, they all see the same current, which along
with a spreader plate top and bottom) helps prevent runaway. If you put
them in parallel, the ones with higher delta-T will draw less current
than the lower delta-T ones, which gives you a nice stabilizing action
at low drive current.
If you push them, or you lose cooling water to your heat exchanger, the
sign of the gain can invert and the whole thing turns to lava very
fast. (That can happen with individual control or series-connection as
well, but the melty ones can't hog current from the cooler ones, so it
isn't so unstable.)
The other thing is that you have to allow the Peltiers to slide around a
bit as the cold plate cools down, because otherwise they'll crack. So
use Arctic Silver or a very small amount of very good thermal grease on
one side, and solder on the other. IIRC you can solder the 30 mm ones,
but not the 50 mm ones--it'll be in the datasheet. (Solder is about 100x
better than ordinary thermal grease.)
I talk a lot about Peltiers in my free thermal chapter,
http://electrooptical.net/www/book/thermal.pdf . There's also an
incomplete draft that was intended to accompany the second edition,
which has some more stuff in it, at
http://electrooptical.net/www/book/draftthermal.pdf .
Cheers
Phil Hobbs
--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics
160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
Phil Hobbs
Jul 19, 2012, 9:37:42 AM7/19/12
to
heaters, they can make the system far less vulnerable to thermal
forcing. With just a heater, you have to have a big heat leak in order
for the loop to work at any reasonable speed, so the bandwidth and the
thermal forcing go up together. With a Peltier you don't have that
constraint, because it can pull as well as push.
Martin Brown
Jul 19, 2012, 9:50:00 AM7/19/12
to
On 19/07/2012 14:29, Phil Hobbs wrote:
> Martin Brown wrote:
> Martin Brown wrote:
>> Current. They are in essence a bunch of high power diode PN junctions.
>
>
> I'd control them individually, or wire them in series. Compound
> Peltiers have a nasty thermal instability, where they start getting
> hotter as you go to higher current instead of colder.
>
> If you put them in series, they all see the same current, which along
> with a spreader plate top and bottom) helps prevent runaway. If you put
> them in parallel, the ones with higher delta-T will draw less current
> than the lower delta-T ones, which gives you a nice stabilizing action
> at low drive current.
>
> If you push them, or you lose cooling water to your heat exchanger, the
> sign of the gain can invert and the whole thing turns to lava very
> fast. (That can happen with individual control or series-connection as
> well, but the melty ones can't hog current from the cooler ones, so it
> isn't so unstable.)
>
> The other thing is that you have to allow the Peltiers to slide around a
> bit as the cold plate cools down, because otherwise they'll crack. So
> use Arctic Silver or a very small amount of very good thermal grease on
> one side, and solder on the other. IIRC you can solder the 30 mm ones,
> but not the 50 mm ones--it'll be in the datasheet. (Solder is about 100x
> better than ordinary thermal grease.)
>
> I talk a lot about Peltiers in my free thermal chapter,
> http://electrooptical.net/www/book/thermal.pdf . There's also an
> incomplete draft that was intended to accompany the second edition,
> which has some more stuff in it, at
> http://electrooptical.net/www/book/draftthermal.pdf .
Handy info thanks. Although the TECs are available their datasheets are
> Peltiers have a nasty thermal instability, where they start getting
> hotter as you go to higher current instead of colder.
>
> If you put them in series, they all see the same current, which along
> with a spreader plate top and bottom) helps prevent runaway. If you put
> them in parallel, the ones with higher delta-T will draw less current
> than the lower delta-T ones, which gives you a nice stabilizing action
> at low drive current.
>
> If you push them, or you lose cooling water to your heat exchanger, the
> sign of the gain can invert and the whole thing turns to lava very
> fast. (That can happen with individual control or series-connection as
> well, but the melty ones can't hog current from the cooler ones, so it
> isn't so unstable.)
>
> The other thing is that you have to allow the Peltiers to slide around a
> bit as the cold plate cools down, because otherwise they'll crack. So
> use Arctic Silver or a very small amount of very good thermal grease on
> one side, and solder on the other. IIRC you can solder the 30 mm ones,
> but not the 50 mm ones--it'll be in the datasheet. (Solder is about 100x
> better than ordinary thermal grease.)
>
> I talk a lot about Peltiers in my free thermal chapter,
> http://electrooptical.net/www/book/thermal.pdf . There's also an
> incomplete draft that was intended to accompany the second edition,
> which has some more stuff in it, at
> http://electrooptical.net/www/book/draftthermal.pdf .
often inadequate and miss out details needed for real world designs.
Can I pick your brains for a slightly odd requirement? Ideally one that
can be done with at most a pair of TECs one high temp and one normal. On
paper they were rated for 3A and 14v or so each but in practice I was
struggling in reverse to get 2v and a few mA out with a candle flame
heated plate at 250C on one side and a slab of aluminium at -18C on the
other. I gave up in the end as it was taking too long and safety
concerns of very hot metal plates and children scuppered it in the end.
The aim would be for an Xmas science demo to harvest some of the ~100W
waste heat of a candle flame and drive a ~1W LED. This seemed a modest
aim when I started out but in practice it proved impossible. To be any
good the LED must be a *lot* brighter than the candle flame!
I am guessing that to stand any chance I also need a fan assisted heat
sink and to be authentic it must all be powered by the TECs. It is for a
physics demo so hiding a button cell somewhere is just not on...
--
Regards,
Martin Brown
George Herold
Jul 19, 2012, 10:12:48 AM7/19/12
to
range? And most important what's on the other side of the TEC's? In
my limited experience you need to spend at least as much time thinking
about how you keep the temperature of the 'other side' of the TEC
roughly constant.
George H.
Robert Macy
Jul 19, 2012, 10:13:20 AM7/19/12
to
getting a heat pipe made up for it, or at least talk to those people.
Can't find their contact info. But, at trade shows they hand out
little 'hockey stick' coppercolored heat pipes as promos. The surface
temperature of those sticks is uniform, fast.
Probably sell to multicore processor cooling too. transfer heat out to
fan area.
Phil Hobbs
Jul 19, 2012, 10:21:29 AM7/19/12
to
Peltiers are really stinky at power generation--their maximum efficiency
is only about 3% iirc.
George Herold
Jul 19, 2012, 10:28:53 AM7/19/12
to
On Jul 19, 9:50 am, Martin Brown <|||newspam...@nezumi.demon.co.uk>
wrote:
>
> - Show quoted text -
Interesting, I take your question to be, "Where along the I/V curve
is a TEC most efficient when run as a generator?" (heat to electric
power.)
That should be fairly easy to determine experimentally.
Perhaps you need more elements in series?
And how did you get the -18C?
If this is in the winter time perhaps you'd allow for the cold end to
be dunked into an ice bath... cooled with snow from the great
outdoors.
George H.
wrote:
> On 19/07/2012 14:29, Phil Hobbs wrote:
>
>
>
>
>
> > Martin Brown wrote:
> >> Current. They are in essence a bunch of high power diode PN junctions.
>
> > I'd control them individually, or wire them in series. Compound
> > Peltiers have a nasty thermal instability, where they start getting
> > hotter as you go to higher current instead of colder.
>
> > If you put them in series, they all see the same current, which along
> > with a spreader plate top and bottom) helps prevent runaway. If you put
> > them in parallel, the ones with higher delta-T will draw less current
> > than the lower delta-T ones, which gives you a nice stabilizing action
> > at low drive current.
>
> > If you push them, or you lose cooling water to your heat exchanger, the
> > sign of the gain can invert and the whole thing turns to lava very
> > fast. (That can happen with individual control or series-connection as
> > well, but the melty ones can't hog current from the cooler ones, so it
> > isn't so unstable.)
>
> > The other thing is that you have to allow the Peltiers to slide around a
> > bit as the cold plate cools down, because otherwise they'll crack. So
> > use Arctic Silver or a very small amount of very good thermal grease on
> > one side, and solder on the other. IIRC you can solder the 30 mm ones,
> > but not the 50 mm ones--it'll be in the datasheet. (Solder is about 100x
> > better than ordinary thermal grease.)
>
> > I talk a lot about Peltiers in my free thermal chapter,
> >http://electrooptical.net/www/book/thermal.pdf. There's also an
>
>
>
>
>
> > Martin Brown wrote:
> >> Current. They are in essence a bunch of high power diode PN junctions.
>
> > I'd control them individually, or wire them in series. Compound
> > Peltiers have a nasty thermal instability, where they start getting
> > hotter as you go to higher current instead of colder.
>
> > If you put them in series, they all see the same current, which along
> > with a spreader plate top and bottom) helps prevent runaway. If you put
> > them in parallel, the ones with higher delta-T will draw less current
> > than the lower delta-T ones, which gives you a nice stabilizing action
> > at low drive current.
>
> > If you push them, or you lose cooling water to your heat exchanger, the
> > sign of the gain can invert and the whole thing turns to lava very
> > fast. (That can happen with individual control or series-connection as
> > well, but the melty ones can't hog current from the cooler ones, so it
> > isn't so unstable.)
>
> > The other thing is that you have to allow the Peltiers to slide around a
> > bit as the cold plate cools down, because otherwise they'll crack. So
> > use Arctic Silver or a very small amount of very good thermal grease on
> > one side, and solder on the other. IIRC you can solder the 30 mm ones,
> > but not the 50 mm ones--it'll be in the datasheet. (Solder is about 100x
> > better than ordinary thermal grease.)
>
> > I talk a lot about Peltiers in my free thermal chapter,
> > incomplete draft that was intended to accompany the second edition,
> > which has some more stuff in it, at
> >http://electrooptical.net/www/book/draftthermal.pdf.
>
> Handy info thanks. Although the TECs are available their datasheets are
> often inadequate and miss out details needed for real world designs.
>
> Can I pick your brains for a slightly odd requirement? Ideally one that
> can be done with at most a pair of TECs one high temp and one normal. On
> paper they were rated for 3A and 14v or so each but in practice I was
> struggling in reverse to get 2v and a few mA out with a candle flame
> heated plate at 250C on one side and a slab of aluminium at -18C on the
> other. I gave up in the end as it was taking too long and safety
> concerns of very hot metal plates and children scuppered it in the end.
>
> The aim would be for an Xmas science demo to harvest some of the ~100W
> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
> aim when I started out but in practice it proved impossible. To be any
> good the LED must be a *lot* brighter than the candle flame!
>
> I am guessing that to stand any chance I also need a fan assisted heat
> sink and to be authentic it must all be powered by the TECs. It is for a
> physics demo so hiding a button cell somewhere is just not on...
>
> --
> Regards,
> Martin Brown- Hide quoted text -
> > which has some more stuff in it, at
> >http://electrooptical.net/www/book/draftthermal.pdf.
>
> Handy info thanks. Although the TECs are available their datasheets are
> often inadequate and miss out details needed for real world designs.
>
> Can I pick your brains for a slightly odd requirement? Ideally one that
> can be done with at most a pair of TECs one high temp and one normal. On
> paper they were rated for 3A and 14v or so each but in practice I was
> struggling in reverse to get 2v and a few mA out with a candle flame
> heated plate at 250C on one side and a slab of aluminium at -18C on the
> other. I gave up in the end as it was taking too long and safety
> concerns of very hot metal plates and children scuppered it in the end.
>
> The aim would be for an Xmas science demo to harvest some of the ~100W
> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
> aim when I started out but in practice it proved impossible. To be any
> good the LED must be a *lot* brighter than the candle flame!
>
> I am guessing that to stand any chance I also need a fan assisted heat
> sink and to be authentic it must all be powered by the TECs. It is for a
> physics demo so hiding a button cell somewhere is just not on...
>
> --
> Regards,
>
> - Show quoted text -
Interesting, I take your question to be, "Where along the I/V curve
is a TEC most efficient when run as a generator?" (heat to electric
power.)
That should be fairly easy to determine experimentally.
Perhaps you need more elements in series?
And how did you get the -18C?
If this is in the winter time perhaps you'd allow for the cold end to
be dunked into an ice bath... cooled with snow from the great
outdoors.
George H.
Richard Rasker
Jul 19, 2012, 10:31:35 AM7/19/12
to
George Herold wrote:
> On Jul 19, 7:57 am, Richard Rasker <spamt...@linetec.nl> wrote:
>> Hello,
>>
>> I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm
>> aluminium surface (6" x 6" x 1/6"), which has to be kept at a precise
>> temperature throughout (+/- 0.1 degree centigrade). Since both heating
>> and cooling are required, the whole design is based on one or more
>> Peltier elements.
...
> On Jul 19, 7:57 am, Richard Rasker <spamt...@linetec.nl> wrote:
>> Hello,
>>
>> I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm
>> aluminium surface (6" x 6" x 1/6"), which has to be kept at a precise
>> temperature throughout (+/- 0.1 degree centigrade). Since both heating
>> and cooling are required, the whole design is based on one or more
>> Peltier elements.
>> is it better to connect these Peltier elements in parallel or in series?
> TEC's in series as other have suggested. What's the temperature
> range?
Ideally from 10 to 60 degrees centigrade, with a 20-25 degrees ambient
> range?
temperature. This should not be a problem.
> And most important what's on the other side of the TEC's? In
> my limited experience you need to spend at least as much time thinking
> about how you keep the temperature of the 'other side' of the TEC
> roughly constant.
with a fan. I'm not certain about the fan though, because I have a feeling
that this might cause faster temperature changes in the heat sink than the
control loop is capable of compensating. If necessary, I'll use a bigger
heat sink.
Bill Sloman
Jul 19, 2012, 10:32:45 AM7/19/12
to
transfers heat from one side to the other at so many watts per amp, but
it also resistively heats the junction, at so many watts per amp squared.
There's a maximum current above which more heat is generated in the
junction than gets pumped across it; if you do the detailed
calculations, this maximum useful current depends on the thermal
resistance to ambient of the exhaust side.
Sloman A.W., Buggs P., Molloy J., and Stewart D. “A
microcontroller-based driver to stabilise the temperature of an optical
stage to 1mK in the range 4C to 38C, using a Peltier heat pump and a
thermistor sensor” Measurement Science and Technology, 7 1653-64 (1996),
includes the formula in Appendix A.
I also managed to get it into a comment in Rev. Sci. Instrum, a few
years later.
Sloman A.W. “Comment on ‘Implementing of a precision fast thermoelectric
cooler controller using a personal computer parallel port connection and
ADV8830 controller’[Rev.Sci. Instrum. 74, 3862 (2003)]” Review of
Scientific Instruments, 75 788-9 (2004).”
It's a very good idea to monitor the temperature of the exhaust side of
the junction as well as the temperature you are trying to control - you
don't have to do it all that accurately to avoid getting into trouble,
and with a microcontroller based solution, you can figure in the net
heat-transfer per watt and keep the control loop critically damped over
a range of thermal loads.
>> The other thing is that you have to allow the Peltiers to slide around a
>> bit as the cold plate cools down, because otherwise they'll crack. So
>> use Arctic Silver or a very small amount of very good thermal grease on
>> one side, and solder on the other. IIRC you can solder the 30 mm ones,
>> but not the 50 mm ones--it'll be in the datasheet. (Solder is about 100x
>> better than ordinary thermal grease.)
>>
>> I talk a lot about Peltiers in my free thermal chapter,
>> http://electrooptical.net/www/book/thermal.pdf . There's also an
>> incomplete draft that was intended to accompany the second edition,
>> which has some more stuff in it, at
>> http://electrooptical.net/www/book/draftthermal.pdf .
>>
>
> One other thing about Peltiers that's often overlooked: compared with
> heaters, they can make the system far less vulnerable to thermal
> forcing. With just a heater, you have to have a big heat leak in order
> for the loop to work at any reasonable speed, so the bandwidth and the
> thermal forcing go up together. With a Peltier you don't have that
> constraint, because it can pull as well as push.
Bill Sloman, Nijmegen
Richard Rasker
Jul 19, 2012, 10:22:07 AM7/19/12
to
Phil Hobbs wrote:
> Martin Brown wrote:
>>
>> On 19/07/2012 12:57, Richard Rasker wrote:
...
> Martin Brown wrote:
>>
>> On 19/07/2012 12:57, Richard Rasker wrote:
>> > So I thought I'd use four identical 25W Peltier elements (40 x 40 mm)
>> > instead of one 100W Peltier element (50 x 50 mm). My question: is it
>> > better to connect these Peltier elements in parallel or in series? In
>> > other words: is a Peltier element's heat transport mainly determined by
>> > voltage difference or by current? Any ideas are appreciated.
>>
>> Current. They are in essence a bunch of high power diode PN junctions.
>>
>> Their efficiency as a cooler isn't all that great so insulation is
>> important if you are to obtain good thermal stability as is a suitable
>> heatsink on the dump side. Good for having no moving parts thought.
> I talk a lot about Peltiers in my free thermal chapter,
> http://electrooptical.net/www/book/thermal.pdf . There's also an
> incomplete draft that was intended to accompany the second edition,
> which has some more stuff in it, at
> http://electrooptical.net/www/book/draftthermal.pdf .
x 30 mm 10W) single-Peltier setup working properly, but this information
will be very useful when scaling things up.
tm
Jul 19, 2012, 10:47:03 AM7/19/12
to
"George Herold" <ghe...@teachspin.com> wrote in message
news:68a5592b-2d41-467f...@s1g2000vbj.googlegroups.com...
It's been a while but I have worked with thermal electric generators (TEG)
that used propane and a catalytic heater as a power source. The unit was
made by Teledyne Energy Systems. I don't know if they are still around.
When I met with their engineers, I ask about the TEC make-up. They did say
that it was optimized to be a generator. It used different junctions than
what was used for heating/cooling applications. I don't remember much more
other than it was made up of five modules, each running about 6 volts and 2
amps. Overall, it did run at 28 volts and provided 50 watts of power. It
consumed a 100 gal tank in about two weeks.
Please don't hold me to exact numbers, it was more than 20 years ago.
Regards,
Tom
Jan Panteltje
Jul 19, 2012, 10:45:12 AM7/19/12
to
On a sunny day (Thu, 19 Jul 2012 14:50:00 +0100) it happened Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote in
<1gUNr.50376$iI7....@newsfe03.iad>:
>The aim would be for an Xmas science demo to harvest some of the ~100W
>waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>aim when I started out but in practice it proved impossible. To be any
>good the LED must be a *lot* brighter than the candle flame!
I would use a thermocouple (or some i nseries) and a JFET oscillator with step up transformer.
JFET oscillators oscillate from about next to zero volts up.
Have not tried it on a thermocouple, but did try the low voltage JFET oscillator.
Only a few parts needed...
<|||newspam|||@nezumi.demon.co.uk> wrote in
<1gUNr.50376$iI7....@newsfe03.iad>:
>The aim would be for an Xmas science demo to harvest some of the ~100W
>waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>aim when I started out but in practice it proved impossible. To be any
>good the LED must be a *lot* brighter than the candle flame!
JFET oscillators oscillate from about next to zero volts up.
Have not tried it on a thermocouple, but did try the low voltage JFET oscillator.
Only a few parts needed...
John Devereux
Jul 19, 2012, 11:00:50 AM7/19/12
to
It was 20 years ago but IIRC...
In my old flat I was surprised to discover than the boiler gas valve was
powered directly from a thermocouple assembly in the gas flame. (I only
realised this after finding what I assumed was a "thermal switch" had a
permanent short circuit and the valve had no external power source...)
I wonder if one of these could be used? Sort of thing you could get off
ebay to try.
--
John Devereux
George Herold
Jul 19, 2012, 11:00:02 AM7/19/12
to
other heat sink makers will give you some numbers.) If it's just air
cooled and has to dissipate 100 Watts, it will need a lot of surface
area or have a fan... Unless you are doing single shot cooling.
(Cooling for a short time and tehn allowing the heat sink to cool down
again.)
George H.
George Herold
Jul 19, 2012, 11:41:49 AM7/19/12
to
On Jul 19, 10:47 am, "tm" <No_one_h...@white-house.gov> wrote:
> "George Herold" <gher...@teachspin.com> wrote in message
> Tom- Hide quoted text -
1 gal gas ~ 33kW*hr
100gals = 3,300 kW*hr.
50 watts for two weeks ~17 kW*hr
eff. ~ 0.5%
George H.
> "George Herold" <gher...@teachspin.com> wrote in message
>
> - Show quoted text -
Interesting thanks.... punching numbers...
> - Show quoted text -
1 gal gas ~ 33kW*hr
100gals = 3,300 kW*hr.
50 watts for two weeks ~17 kW*hr
eff. ~ 0.5%
George H.
Syd Rumpo
Jul 19, 2012, 11:44:52 AM7/19/12
to
Peltier is that you can have the cold junctions some way from the heat.
Say use Iron/Constantan at about 55uV/K so for 1.8V at 200C you'd need
about 160 thermocouples which is doable I reckon, probably many fewer
depending on flame temperature. You can just twist the ends together to
make the junctions, should last a while.
Cheers
--
Syd
Jan Panteltje
Jul 19, 2012, 12:56:26 PM7/19/12
to
On a sunny day (Thu, 19 Jul 2012 16:44:52 +0100) it happened Syd Rumpo
<use...@neonica.co.uk> wrote in <ju9a13$jor$1...@dont-email.me>:
I think that is how those RTGs work.
But 160 is a lot, JFET oscillator works from about 20 mV (in my test).
16 theromocouples is doable.
I was also wondering if one could make a low voltage oscillator with a depletion mode
power MOSFET, just to touch that subject again (I still have to order some).
<use...@neonica.co.uk> wrote in <ju9a13$jor$1...@dont-email.me>:
But 160 is a lot, JFET oscillator works from about 20 mV (in my test).
16 theromocouples is doable.
I was also wondering if one could make a low voltage oscillator with a depletion mode
power MOSFET, just to touch that subject again (I still have to order some).
Spehro Pefhany
Jul 19, 2012, 1:08:55 PM7/19/12
to
On Thu, 19 Jul 2012 14:50:00 +0100, Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote:
>
>Handy info thanks. Although the TECs are available their datasheets are
>often inadequate and miss out details needed for real world designs.
>
>Can I pick your brains for a slightly odd requirement? Ideally one that
>can be done with at most a pair of TECs one high temp and one normal. On
>paper they were rated for 3A and 14v or so each but in practice I was
>struggling in reverse to get 2v and a few mA out with a candle flame
>heated plate at 250C on one side and a slab of aluminium at -18C on the
>other. I gave up in the end as it was taking too long and safety
>concerns of very hot metal plates and children scuppered it in the end.
>
>The aim would be for an Xmas science demo to harvest some of the ~100W
>waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>aim when I started out but in practice it proved impossible. To be any
>good the LED must be a *lot* brighter than the candle flame!
>
>I am guessing that to stand any chance I also need a fan assisted heat
>sink and to be authentic it must all be powered by the TECs. It is for a
>physics demo so hiding a button cell somewhere is just not on...
>
>--
>Regards,
>Martin Brown
You can buy fans that sit on top of a stove. I picked one up at a
<|||newspam|||@nezumi.demon.co.uk> wrote:
>
>Handy info thanks. Although the TECs are available their datasheets are
>often inadequate and miss out details needed for real world designs.
>
>Can I pick your brains for a slightly odd requirement? Ideally one that
>can be done with at most a pair of TECs one high temp and one normal. On
>paper they were rated for 3A and 14v or so each but in practice I was
>struggling in reverse to get 2v and a few mA out with a candle flame
>heated plate at 250C on one side and a slab of aluminium at -18C on the
>other. I gave up in the end as it was taking too long and safety
>concerns of very hot metal plates and children scuppered it in the end.
>
>The aim would be for an Xmas science demo to harvest some of the ~100W
>waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>aim when I started out but in practice it proved impossible. To be any
>good the LED must be a *lot* brighter than the candle flame!
>
>I am guessing that to stand any chance I also need a fan assisted heat
>sink and to be authentic it must all be powered by the TECs. It is for a
>physics demo so hiding a button cell somewhere is just not on...
>
>--
>Regards,
>Martin Brown
fellow's cottage and it looked like it was a little toy motor run by a
bog-standard 30x30 or 40x40mm Peltier.
I would not expect much efficiency.. maybe a couple percent.
http://infinitebeautysupply.store.buy.com/p/heat-powered-wood-stove-fan/223536999.html
The Peltier is horizontal and sandwitched between the two aluminum
plates (below the heat sink).
Martin Brown
Jul 19, 2012, 1:21:54 PM7/19/12
to
On 19/07/2012 18:08, Spehro Pefhany wrote:
> On Thu, 19 Jul 2012 14:50:00 +0100, Martin Brown
> <|||newspam|||@nezumi.demon.co.uk> wrote:
>
>>
>> The aim would be for an Xmas science demo to harvest some of the ~100W
>> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>> aim when I started out but in practice it proved impossible. To be any
>> good the LED must be a *lot* brighter than the candle flame!
>>
>> I am guessing that to stand any chance I also need a fan assisted heat
>> sink and to be authentic it must all be powered by the TECs. It is for a
>> physics demo so hiding a button cell somewhere is just not on...
>
> On Thu, 19 Jul 2012 14:50:00 +0100, Martin Brown
> <|||newspam|||@nezumi.demon.co.uk> wrote:
>
>>
>> The aim would be for an Xmas science demo to harvest some of the ~100W
>> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>> aim when I started out but in practice it proved impossible. To be any
>> good the LED must be a *lot* brighter than the candle flame!
>>
>> I am guessing that to stand any chance I also need a fan assisted heat
>> sink and to be authentic it must all be powered by the TECs. It is for a
>> physics demo so hiding a button cell somewhere is just not on...
>
> You can buy fans that sit on top of a stove. I picked one up at a
> fellow's cottage and it looked like it was a little toy motor run by a
> bog-standard 30x30 or 40x40mm Peltier.
Yes. I know. I made one from the bits I had left over from this failed
> fellow's cottage and it looked like it was a little toy motor run by a
> bog-standard 30x30 or 40x40mm Peltier.
Xmas demo after seeing one at a neighbours house. Expensive for what
they are - though his is prettier than mine. A cheap "solar" motor will
run happily off the output voltage and a light weight aluminium fan.
To be fair it does a good job of moving warm air out into the room that
would otherwise be trapped in the fireplace alcove above the stove.
> I would not expect much efficiency.. maybe a couple percent.
>
> http://infinitebeautysupply.store.buy.com/p/heat-powered-wood-stove-fan/223536999.html
>
> The Peltier is horizontal and sandwitched between the two aluminum
> plates (below the heat sink).
than 0.01%. Problem I ran into was I could not get both voltage and
current sufficient to drive a white LED (or a red one for that matter).
--
Regards,
Martin Brown
Tim Wescott
Jul 19, 2012, 2:55:20 PM7/19/12
to
Consider your 150x150mm table, being oh-so-carefully held at temperature
by one gawdaful big Peltier device (or a bunch of them in parallel,
whatever).
Now consider some smartass (me, if I'm in your lab), putting a 2cm cube
of something good and warm (or good and cold) on your table.
What happens to your average temperature?
What happens to the temperature right underneath the hot thing?
What happens to the temperature elsewhere?
Me, I think I'd go with a bunch of small Peltiers glued to a moderately
thin (I'm visualizing 1/8") plate, each with a thermistor or other easy
to use temperature probe placed in a pocket of the plate, smack in the
center of the Peltier device.
Then a controller for each device, with whatever tuning is necessary so
that the controllers don't get into fights and make temperature
oscillations that are unstable spatially as well as in time.
How many devices and coolers you use depends on how uneven the
anticipated thermal load will be on the plate, how tightly you feel you
need to control its temperature, and on the thermal conductivity of your
plate.
--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?
Tim Wescott, Communications, Control, Circuits & Software
http://www.wescottdesign.com
Tim Wescott
Jul 19, 2012, 3:11:44 PM7/19/12
to
Or, for a complete demo, have one TE element complete with lots of hype,
and one "150 year old technology" Sterling engine for comparison...
Tim Wescott
Jul 19, 2012, 3:12:30 PM7/19/12
to
Phil Hobbs
Jul 19, 2012, 3:14:04 PM7/19/12
to
Jon Elson
Jul 19, 2012, 3:31:35 PM7/19/12
to
Martin Brown wrote:
> The aim would be for an Xmas science demo to harvest some of the ~100W
> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
> aim when I started out but in practice it proved impossible. To be any
> good the LED must be a *lot* brighter than the candle flame!
>
You are using the wrong junction for this purpose. There are far
> The aim would be for an Xmas science demo to harvest some of the ~100W
> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
> aim when I started out but in practice it proved impossible. To be any
> good the LED must be a *lot* brighter than the candle flame!
>
better junctions made specifically for this, although the thermocouple
in a gas furnace will almost do it. About 3 or 4 in series will
light an LED plenty brightly, in fact you'll need a current limiting
resistor. I think they use copper and iron, nothing exotic at all,
and in a gas flame, I think you get 600 mV out of these. A candle
flame should be a bit less, so 4 junctions at 400 mV each should
light a red LED.
Jon
George Herold
Jul 19, 2012, 3:25:31 PM7/19/12
to
On Jul 19, 11:44 am, Syd Rumpo <use...@neonica.co.uk> wrote:
> On 19/07/2012 15:45, Jan Panteltje wrote:
>
> > On a sunny day (Thu, 19 Jul 2012 14:50:00 +0100) it happened Martin Brown
> > <|||newspam...@nezumi.demon.co.uk> wrote in
> On 19/07/2012 15:45, Jan Panteltje wrote:
>
> > On a sunny day (Thu, 19 Jul 2012 14:50:00 +0100) it happened Martin Brown
> > <1gUNr.50376$iI7.22...@newsfe03.iad>:
>
> >> The aim would be for an Xmas science demo to harvest some of the ~100W
> >> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
> >> aim when I started out but in practice it proved impossible. To be any
> >> good the LED must be a *lot* brighter than the candle flame!
>
> > I would use a thermocouple (or some i nseries) and a JFET oscillator with step up transformer.
> > JFET oscillators oscillate from about next to zero volts up.
> > Have not tried it on a thermocouple, but did try the low voltage JFET oscillator.
> > Only a few parts needed...
>
> I'd go with several thermocouples in series. The advantage over a
> Peltier is that you can have the cold junctions some way from the heat.
>
> Say use Iron/Constantan at about 55uV/K so for 1.8V at 200C you'd need
> about 160 thermocouples which is doable I reckon, probably many fewer
> depending on flame temperature. You can just twist the ends together to
> make the junctions, should last a while.
>
> Cheers
> --
> Syd
Hey, speaking of thermopiles I heard Hamamatsu has a new line of them.
> >> The aim would be for an Xmas science demo to harvest some of the ~100W
> >> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
> >> aim when I started out but in practice it proved impossible. To be any
> >> good the LED must be a *lot* brighter than the candle flame!
>
> > I would use a thermocouple (or some i nseries) and a JFET oscillator with step up transformer.
> > JFET oscillators oscillate from about next to zero volts up.
> > Have not tried it on a thermocouple, but did try the low voltage JFET oscillator.
> > Only a few parts needed...
>
> I'd go with several thermocouples in series. The advantage over a
> Peltier is that you can have the cold junctions some way from the heat.
>
> Say use Iron/Constantan at about 55uV/K so for 1.8V at 200C you'd need
> about 160 thermocouples which is doable I reckon, probably many fewer
> depending on flame temperature. You can just twist the ends together to
> make the junctions, should last a while.
>
> Cheers
> --
> Syd
http://www.hamamatsu.com/news/2011/2011_09_21.html
I can't find a spec sheet or price though.
George H.
Jon Elson
Jul 19, 2012, 3:36:47 PM7/19/12
to
John Devereux wrote:
> It was 20 years ago but IIRC...
>
> In my old flat I was surprised to discover than the boiler gas valve was
> powered directly from a thermocouple assembly in the gas flame. (I only
> realised this after finding what I assumed was a "thermal switch" had a
> permanent short circuit and the valve had no external power source...)
This is called a millivolt system, still fairly common. Uses no mains
> It was 20 years ago but IIRC...
>
> In my old flat I was surprised to discover than the boiler gas valve was
> powered directly from a thermocouple assembly in the gas flame. (I only
> realised this after finding what I assumed was a "thermal switch" had a
> permanent short circuit and the valve had no external power source...)
electricity. It basically uses the same thermocouple used in the
common gas safety controls on water heaters and furnaces. The solenoid
coil is a small number of turns of heavy-gauge copper wire, and the
current to operate the solenoid is up to several Amps.
Jon
Spehro Pefhany
Jul 19, 2012, 4:09:09 PM7/19/12
to
On Thu, 19 Jul 2012 14:31:35 -0500, Jon Elson <jme...@wustl.edu>
wrote:
Those must be thermopiles, a single Cu-Fe thermocouple would produce
MUCH less voltage.
wrote:
MUCH less voltage.
tm
Jul 19, 2012, 4:33:46 PM7/19/12
to
news:8439768c-44bb-4288...@n33g2000vbi.googlegroups.com...
_____________________________________________________
Again, I may be mis-remembering the exact quantity of propane. It might have
been 100 pounds.
What do the numbers look like for 1000 gallons and one year? We used it to
run a mountain top microwave relay site with no commercial power within
miles. We refueled it in the summer. It lasted for more than 5 years until
development brought power closer to the site (an old fire tower). The most
important thing is to get the combustion products out of the shelter as a
lot of water vapor is produced. It sure beat solar because of the problems
with snow.
I believe the efficiency was much better than 0.5 % , more like 5% or
better.
Back of the envelope shows 13%
Regards,
tm
Again, I may be mis-remembering the exact quantity of propane. It might have
been 100 pounds.
What do the numbers look like for 1000 gallons and one year? We used it to
run a mountain top microwave relay site with no commercial power within
miles. We refueled it in the summer. It lasted for more than 5 years until
development brought power closer to the site (an old fire tower). The most
important thing is to get the combustion products out of the shelter as a
lot of water vapor is produced. It sure beat solar because of the problems
with snow.
I believe the efficiency was much better than 0.5 % , more like 5% or
better.
Back of the envelope shows 13%
Regards,
tm
k...@att.bizzzzzzzzzzzz
Jul 19, 2012, 6:59:35 PM7/19/12
to
'60s, complete with a solid-state power supply (string of Germanium DO-3
PNPs). I had a couple of them in the basement to play with when I was a kid.
It was designed to go in a car but never made it past prototype. It got beat
out by Styrofoam disposables. ;-)
Don Lancaster
Jul 19, 2012, 7:22:30 PM7/19/12
to
Their delta T across the heatsink usually EXCEEDS their intended delta T
drop
See < http://www.tinaja.com/glib/hack68.pdf >
--
Many thanks,
Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: d...@tinaja.com
Please visit my GURU's LAIR web site at http://www.tinaja.com
Phil Hobbs
Jul 19, 2012, 7:32:02 PM7/19/12
to
If you try cooling a CPU or a voltage regulator with one, you deserve
what you get. But many kinds of instruments would be far harder to
build without them. Oh, and of course the telecom infrastructure
wouldn't work without them either, because Peltiers are what keep all
the DWDM lasers from scribbling across neighbouring channels.
lang...@fonz.dk
Jul 19, 2012, 7:38:19 PM7/19/12
to
On 20 Jul., 00:59, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
wrote:
> >> >>>http://electrooptical.net/www/book/thermal.pdf. There's also an
you can get plenty of 12V TEC refrigerators/coolers but I don't think
they have
much if any smarts in them, they just say something like "up to 20'C
below ambient"
-Lasse
wrote:
they have
much if any smarts in them, they just say something like "up to 20'C
below ambient"
-Lasse
k...@att.bizzzzzzzzzzzz
Jul 19, 2012, 7:49:29 PM7/19/12
to
tm
Jul 19, 2012, 8:35:00 PM7/19/12
to
"Phil Hobbs" <pcdhSpamM...@electrooptical.net> wrote in message
news:500898F2...@electrooptical.net...
for TECs.
tm
George Herold
Jul 19, 2012, 8:53:39 PM7/19/12
to
>
> - Show quoted text -
Oh propane. I was getting my numbers from here.
> - Show quoted text -
http://en.wikipedia.org/wiki/Gasoline_gallon_equivalent
But don't worry about exact numbers
George H.
George Herold
Jul 19, 2012, 9:02:25 PM7/19/12
to
>
> - Show quoted text -
Hi Don,
> - Show quoted text -
I've used TEC's successfully in two applications.
Diode laser temp control. (done before)
And controlling the temp of a permanent magnetic.
The trick for the magnet was to just stabilize the magnet at whatever
the room temperature is... and not try and drag it to any specific
temp. (This is to do NMR and we can adjust the frequency to whatever
the B field is.)
As Phil H. said the great thing about TEC's is they 'go both ways'.
George H.
Phil Hobbs
Jul 19, 2012, 9:35:38 PM7/19/12
to
amusement, but IMO it's beneath engineers of Don's calibre. Of course
he's been in the biz for probably 50 years or more, and so feels
entitled to take the occasional potshot from his porch, and who's to say
that isn't OK.
I bought a copy of his TTL Cookbook in about 1974, when I was 14 years
old, and it helped me a lot back then, and for several years
thereafter. I was also intrigued by his TV Typewriters, but since I
couldn't type they weren't that compelling. They were really just a
tease anyway, aimed at those of us who didn't have our own private
PDP-10.
However, saying that "Peltier coolers are almost always totally
worthless", when in fact they enable most of modern communications and
the Internet, is just plain nonsense, and needs to be called out. Maybe
it'll improve Don's aim. ;)
tm
Jul 19, 2012, 9:57:23 PM7/19/12
to
news:5008B5EA...@electrooptical.net...
Well, saying "they enable most of modern communications and the internet" is
a bit Algoreish in its own right. :)
I have yet to see a 10 gig SFP long haul module that is cooled. I would
guess a good bit of the Internet uses them.
tm
a bit Algoreish in its own right. :)
I have yet to see a 10 gig SFP long haul module that is cooled. I would
guess a good bit of the Internet uses them.
tm
Phil Hobbs
Jul 19, 2012, 10:14:32 PM7/19/12
to
or so, you don't have the modern Internet.
Jan Panteltje
Jul 20, 2012, 2:11:53 AM7/20/12
to
On a sunny day (Thu, 19 Jul 2012 14:31:35 -0500) it happened Jon Elson
<jme...@wustl.edu> wrote in <HqednTtKXpNZw5XN...@giganews.com>:
Calculating for 200 C, with my 'th' program,
I get the following voltages for the different themocouples:
Panteltje (c) th-0.5 thermocouple voltage (in mV) to temperature and reverse calculator.
Usage:
th -a [E|J|K|R|S|T] [-d] [-h] [-m C|K|F] -v voltage || -t temperature
-a type thermocouple type, either E, J, K, R, S, or T.
-c temperature cold junction temperature in units as described with -m.
-d debug mode, prints functions and arguments, and some variables.
-h help, this help.
-m mode temperature mode for temperature to voltage, either C, K, or F for Celsius, Kelvin, or Fahrenheit.
-v voltage voltage in mV, for voltage to temperature conversion.
-t temperature temperature.
Type K:
panteltje: ~/compile/pantel/gpspc # th -a K -c 25 -m C -t 200
voltage is 7.138231 mV
Type E:
panteltje: ~/compile/pantel/gpspc # th -a E -c 25 -m C -t 200
voltage is 11.926184 mV
Type J:
panteltje: ~/compile/pantel/gpspc # th -a J -c 25 -m C -t 200
voltage is 9.501458 mV
Type R:
panteltje: ~/compile/pantel/gpspc # th -a R -c 25 -m C -t 200
voltage is 1.328004 mV
Type S:
panteltje: ~/compile/pantel/gpspc # th -a S -c 25 -m C -t 200
voltage is 1.298185 mV
Type T:
panteltje: ~/compile/pantel/gpspc # th -a T -c 25 -m C -t 200
voltage is 8.296125 mV
So looks like a type E gives the most
You can buy a pack of 5 of type E at omega for abut 14 UKP:
http://www.omega.co.uk/ppt/pptsc.asp?ref=IRCO-BW
That makes 5 x 12 = 60 mV
Should run a JFET oscillator.
I have use 200 C as example, candle flame is much hotter,
these small themocouples do not interfere with the visibility of the flame I think.
I uses 200 as I solder some togetehr myself (not type E), and the solder melts at 200...
The 'th' (Linux) program is available from me.
http://panteltje.com/panteltje/newsflex/th-0.4.tgz
Hey. Microsoft made a loss for the firt time this year,
wonder when Ba;lmer get lynched...
and it will be bought by 'investors', broken up, renamed,
burried...
Fun fun fun :-)
<jme...@wustl.edu> wrote in <HqednTtKXpNZw5XN...@giganews.com>:
I get the following voltages for the different themocouples:
Panteltje (c) th-0.5 thermocouple voltage (in mV) to temperature and reverse calculator.
Usage:
th -a [E|J|K|R|S|T] [-d] [-h] [-m C|K|F] -v voltage || -t temperature
-a type thermocouple type, either E, J, K, R, S, or T.
-c temperature cold junction temperature in units as described with -m.
-d debug mode, prints functions and arguments, and some variables.
-h help, this help.
-m mode temperature mode for temperature to voltage, either C, K, or F for Celsius, Kelvin, or Fahrenheit.
-v voltage voltage in mV, for voltage to temperature conversion.
-t temperature temperature.
Type K:
panteltje: ~/compile/pantel/gpspc # th -a K -c 25 -m C -t 200
voltage is 7.138231 mV
Type E:
panteltje: ~/compile/pantel/gpspc # th -a E -c 25 -m C -t 200
voltage is 11.926184 mV
Type J:
panteltje: ~/compile/pantel/gpspc # th -a J -c 25 -m C -t 200
voltage is 9.501458 mV
Type R:
panteltje: ~/compile/pantel/gpspc # th -a R -c 25 -m C -t 200
voltage is 1.328004 mV
Type S:
panteltje: ~/compile/pantel/gpspc # th -a S -c 25 -m C -t 200
voltage is 1.298185 mV
Type T:
panteltje: ~/compile/pantel/gpspc # th -a T -c 25 -m C -t 200
voltage is 8.296125 mV
So looks like a type E gives the most
You can buy a pack of 5 of type E at omega for abut 14 UKP:
http://www.omega.co.uk/ppt/pptsc.asp?ref=IRCO-BW
That makes 5 x 12 = 60 mV
Should run a JFET oscillator.
I have use 200 C as example, candle flame is much hotter,
these small themocouples do not interfere with the visibility of the flame I think.
I uses 200 as I solder some togetehr myself (not type E), and the solder melts at 200...
The 'th' (Linux) program is available from me.
http://panteltje.com/panteltje/newsflex/th-0.4.tgz
Hey. Microsoft made a loss for the firt time this year,
wonder when Ba;lmer get lynched...
and it will be bought by 'investors', broken up, renamed,
burried...
Fun fun fun :-)
John Devereux
Jul 20, 2012, 3:29:37 AM7/20/12
to
designed a temperature controller with a thermocouple input by then. But
I was not used to thinking of them generating amps!
--
John Devereux
Martin Brown
Jul 20, 2012, 3:45:18 AM7/20/12
to
On 19/07/2012 20:12, Tim Wescott wrote:
> On Thu, 19 Jul 2012 14:11:44 -0500, Tim Wescott wrote:
>
>> On Thu, 19 Jul 2012 14:50:00 +0100, Martin Brown wrote:
>>
>>> The aim would be for an Xmas science demo to harvest some of the ~100W
>>> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>>> aim when I started out but in practice it proved impossible. To be any
>>> good the LED must be a *lot* brighter than the candle flame!
>>>
>>> I am guessing that to stand any chance I also need a fan assisted heat
>>> sink and to be authentic it must all be powered by the TECs. It is for
>>> a physics demo so hiding a button cell somewhere is just not on...
>>
>> You may do much better with a fan-powered Sterling engine.
>
> CANDLE-powered Sterling. Oops.
Trouble is I had already done a candle powered heat engine and then a
> On Thu, 19 Jul 2012 14:11:44 -0500, Tim Wescott wrote:
>
>> On Thu, 19 Jul 2012 14:50:00 +0100, Martin Brown wrote:
>>
>>> The aim would be for an Xmas science demo to harvest some of the ~100W
>>> waste heat of a candle flame and drive a ~1W LED. This seemed a modest
>>> aim when I started out but in practice it proved impossible. To be any
>>> good the LED must be a *lot* brighter than the candle flame!
>>>
>>> I am guessing that to stand any chance I also need a fan assisted heat
>>> sink and to be authentic it must all be powered by the TECs. It is for
>>> a physics demo so hiding a button cell somewhere is just not on...
>>
>> You may do much better with a fan-powered Sterling engine.
>
> CANDLE-powered Sterling. Oops.
more sophisticated coffee cup powered rotary motion one in previous
years. I was trying to find yet another candle based demo for Xmas.
--
Regards,
Martin Brown
Martin Brown
Jul 20, 2012, 4:05:16 AM7/20/12
to
1000K there would be around 12mV per junction pair to play with.
I presume the boiler thermostat is a big bunch in series. A pair of
those would provide enough power capture with a bit of luck.
How big are they?
I did try messing about with iron and copper wire too, but it didn't
look good and produced a miniscule voltage for the amount of effort.
Whoever said 160 reliable thermocouple wire junctions in a candle flame
is "doable" is something of an optimist. I got fed up at about a dozen.
I didn't know about these gas boiler thermopile contraptions.
--
Regards,
Martin Brown
Syd Rumpo
Jul 20, 2012, 5:16:31 AM7/20/12
to
On 20/07/2012 09:05, Martin Brown wrote:
<snipped>
> I presume the boiler thermostat is a big bunch in series.
No, just one junction. It provides enough current to *hold* a
low-voltage solenoid valve open against a spring, but you need to
manually hold the valve open - usually a button - until the pilot flame
has heated the thermocouple. This may take a minute.
I had a boiler once where the pilot kept going out and needed
relighting. It was an 'instant heat' boiler which only turned on the
main burners when a hot water tap was turned on. Eventually I got
around to taking a look and discovered a 2" layer of dead wasps inside.
Seems they'd been attracted in from a nearby nest by the warmth of the
pilot flame, then incinerated as someone turned on a tap. Over and over
again for many weeks, occasionally snuffing out the pilot flame on their
way.
Cheers
--
Syd
<snipped>
> I presume the boiler thermostat is a big bunch in series.
low-voltage solenoid valve open against a spring, but you need to
manually hold the valve open - usually a button - until the pilot flame
has heated the thermocouple. This may take a minute.
I had a boiler once where the pilot kept going out and needed
relighting. It was an 'instant heat' boiler which only turned on the
main burners when a hot water tap was turned on. Eventually I got
around to taking a look and discovered a 2" layer of dead wasps inside.
Seems they'd been attracted in from a nearby nest by the warmth of the
pilot flame, then incinerated as someone turned on a tap. Over and over
again for many weeks, occasionally snuffing out the pilot flame on their
way.
Cheers
--
Syd
Martin Brown
Jul 20, 2012, 5:47:56 AM7/20/12
to
On 19/07/2012 20:31, Jon Elson wrote:
these gas thermocouples seem to provide about 30mV in a flame. Though
apparently at sufficient current to pull in some kind of solenoid.
http://ecc.emea.honeywell.com/downloads/MU1R9124.PDF
A pair or more would generate enough voltage to run a step up. This
might be more satisfactory for demo than flat plates over the flame.
--
Regards,
Martin Brown
Tim Wescott
Jul 20, 2012, 11:17:20 AM7/20/12
to
someone sticking their finger into a hole. Connect it to a string that's
connected to a generator that charges up a capacitor, with the capacitor
powering some LEDs. Set the bear trap up so that after the string is
pulled out a foot or so, it releases.
Set up the thing so that once the finger in question triggers the bear
trap, a candle flame is brought to bear directly on the finger.
Voila! An LED lighter that's powered by candle flame and gullibility.
Not only does it have the advantage of being unique, but you won't have
to worry about thinking of something next year, because you won't be
invited back.
--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
Jon Elson
Jul 20, 2012, 3:48:55 PM7/20/12
to
Spehro Pefhany wrote:
>
> Those must be thermopiles, a single Cu-Fe thermocouple would produce
> MUCH less voltage.
Well, I've only picked at a BAD one, and it was quite burned up after
>
> Those must be thermopiles, a single Cu-Fe thermocouple would produce
> MUCH less voltage.
years of exposure to the pilot flame. But, it couldn't have had more
than a couple of junctions in a coaxial arrangement. I tend to think it
really was just a single junction. I'll try to find details. But, maybe
the voltage produced is way lower than what I suggested.
Jon
lang...@fonz.dk
Jul 20, 2012, 3:47:02 PM7/20/12
to
On 20 Jul., 01:49, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
wrote:
> On Thu, 19 Jul 2012 16:38:19 -0700 (PDT), "langw...@fonz.dk"
my dad was still in school then so I wouldn't know :p
-Lasse
wrote:
> On Thu, 19 Jul 2012 16:38:19 -0700 (PDT), "langw...@fonz.dk"
-Lasse
cristhian...@gmail.com
May 21, 2020, 2:53:28 AM5/21/20
to
El jueves, 19 de julio de 2012, 6:57:11 (UTC-5), Richard Rasker escribió:
> Hello,
>
> I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm aluminium
> surface (6" x 6" x 1/6"), which has to be kept at a precise temperature
> throughout (+/- 0.1 degree centigrade). Since both heating and cooling are
> required, the whole design is based on one or more Peltier elements.
>
> Ideally, one would use a Peltier element of comparable size as the aluminium
> surface, to minimize temperature differences due to small local heat
> losses. However, for reasons of cost and available electrical power (100W
> max), I'm limited to commonly available Peltier elements with a 40 x 40 or
> 50 x 50 mm surface area.
>
> So I thought I'd use four identical 25W Peltier elements (40 x 40 mm)
> instead of one 100W Peltier element (50 x 50 mm). My question: is it better
> to connect these Peltier elements in parallel or in series? In other words:
> is a Peltier element's heat transport mainly determined by voltage
> difference or by current? Any ideas are appreciated.
>
> And oh, I thought about using much thicker aluminium to minimize local
> temperature differences, but with the above dimensions, I already have a
> heat capacity of > 200 J/C, so with 100W power it already takes at least 2
> seconds to heat it up by one degree.
> Doubling the thickness also doubles this time, and that quickly becomes a
> problem: users will want to change the temperature often, and don't want to
> wait several minutes every time until the temperature settles to its final
> value.
>
> Thanks in advance for any ideas.
>
> Richard Rasker
> --
> http://www.linetec.nl
and to think im a total newbie who stubled upon this trhead while looking for a correct way of conecting 2 peltier modules using an xbox 360 power supply a 1209 temp control and pc parts for an upgrade to an old black and decker BNA17B peliter cooler....
god i love internet!!!!
> Hello,
>
> I'm designing a 'thermo table', consisting of a 150 x 150 x 4 mm aluminium
> surface (6" x 6" x 1/6"), which has to be kept at a precise temperature
> throughout (+/- 0.1 degree centigrade). Since both heating and cooling are
> required, the whole design is based on one or more Peltier elements.
>
> Ideally, one would use a Peltier element of comparable size as the aluminium
> surface, to minimize temperature differences due to small local heat
> losses. However, for reasons of cost and available electrical power (100W
> max), I'm limited to commonly available Peltier elements with a 40 x 40 or
> 50 x 50 mm surface area.
>
> So I thought I'd use four identical 25W Peltier elements (40 x 40 mm)
> instead of one 100W Peltier element (50 x 50 mm). My question: is it better
> to connect these Peltier elements in parallel or in series? In other words:
> is a Peltier element's heat transport mainly determined by voltage
> difference or by current? Any ideas are appreciated.
>
> And oh, I thought about using much thicker aluminium to minimize local
> temperature differences, but with the above dimensions, I already have a
> heat capacity of > 200 J/C, so with 100W power it already takes at least 2
> seconds to heat it up by one degree.
> Doubling the thickness also doubles this time, and that quickly becomes a
> problem: users will want to change the temperature often, and don't want to
> wait several minutes every time until the temperature settles to its final
> value.
>
> Thanks in advance for any ideas.
>
> Richard Rasker
> --
> http://www.linetec.nl
and to think im a total newbie who stubled upon this trhead while looking for a correct way of conecting 2 peltier modules using an xbox 360 power supply a 1209 temp control and pc parts for an upgrade to an old black and decker BNA17B peliter cooler....
god i love internet!!!!
Bill Sloman
May 21, 2020, 3:34:26 AM5/21/20
to
Sloman A.W., Buggs P., Molloy J., and Stewart D. “A microcontroller-based driver to stabilise the temperature of an optical stage to 1mK in the range 4C to 38C, using a Peltier heat pump and a thermistor sensor” Measurement Science and Technology, 7 1653-64 (1996)
It hasn't been cited all that recently - nothing since 2018 - so there may be something better around.
It covers the theory, if not in any great detail - there's only so much that you can squeeze into ten pages.
--
Bill Sloman, Sydney
Phil Hobbs
May 21, 2020, 6:39:09 PM5/21/20
to
interface, but in fact this is a Usenet newsgroup, sci.electronics.design.
Usenet started in 1979, and covered the whole world within a couple of
years, at least for folks that had Internet access at that time. It was
and is based on the NNTP protocol, rather than HTTP/HTTPS.
That makes it a decade older than the World Wide Web, and 19 years older
than Google. It's the original social media platform, and has virtually
none of the censorship problems associated with the Big Tech-dominated
platforms. If you dislike somebody's posts super badly, you don't try
to get them banned, you just set a filter so you don't see them.
Democracy and freedom, right?
Some groups, such as this one, include folks with world-class expertise.
C'mon and join the fun!
You can view Usenet with Google Groups, which does have a pretty deep
archive of posts (*) (you would probably have had trouble replying to an
eight-year-old post on Twitter, for instance). However, the best way is
to get a real newsreader such as Thunderbird or Forte Agent, and an
account on a free news server such as aioe.org or eternal-september.org.
There are also nearly-free ones such as Giganews and Supernews, which
also have deep archives, but have recently been experiencing some
performance problems.
Cheers
Phil Hobbs
(*) Google bought out the original Usenet archiver, DejaNews, in 2001,
and acquired both its extensive archive and its Usenet search technology.
--
Dr Philip C D Hobbs
Principal Consultant
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.net
http://hobbs-eo.com
DecadentLinux...@decadence.org
May 21, 2020, 9:27:55 PM5/21/20
to
Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote in
news:ra6vu5$b82$1...@gioia.aioe.org:
the surface you wish to have a homogenous temperature across its
surface on. First off, you cannot go to big or even local room
currents will throw you off.
I used to make black body calibration source 'ovens' for IR
Thermometry some decades ago, and we used a huge, 6" diameter
Aluminum ingot with a single rod heater shoved about 40% of the way
up its ass. The face had a concentric set of sawtooth wave grooves
across it at about 1mm height, and the best damned carbon black black
body high emissivity surface coating around. The outer half inch was
obscured by the front aperture plate/cabinet opening, and it sits
back about 30mm behind that. The surface temp homogeneity was pretty
damned good for simple IR thermometry. But for a larger surface a
thick slab front surface was needed and a liquid oil behind that with
the homogeneous temperature to spread. So for the peltiers run them
at full tilt in whatever direction you desire (hot or cold) and use
that to heat or cool a vessel and pump assembly to heat the oil that
lies behind the panel surface. But a huge 50 kilo block of Al thick
enough to allow several backside heat/cold sources to soak through
enough thickness of media to homogenize the temperature on the front
side surface works good too.
That array would all have to be individually managed and calibrated
in, likely for each big set point jump. OR put a nice sloshy oil
chamber between them and let it soak into the front mass evenly.
The surface has to be recessed back into the cabinet it is in as
room air currents mess it up, and IR imaging devices don't like
calibrating from 'bad' surfaces.
We used to calibrate Optical tube, resistor bolometer thermometry
devices with it from a 1" focus to my 4" gold mirrored, 1.5 foot long
tubed, rifle scope aimed, rifle stock fitted IR thermometer with
about a 50' focus that electrical linesmen used to look at insulators
and transformers for overheating and leakage from the ground. Now we
just use IR imagery.
Did not have that back in '86, without HUGE bucks and LN handy. So
we sold a lot to the power company guys. Cool thermometer too.
I probably built this one...
<https://picclick.com/MIKRON-PORTABLE-INFRARED-THERMOMETER-GUN-10-to-
272283002167.html>
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