Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote in
news:ra6vu5$b82$1@gioia.aioe.org:
> On 2020-05-21 02:53, cristhian.hellsing@gmail.com wrote:
>> 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!!!!
>>
>
> Welcome. You're accessing this group using the Google Groups WWW
> 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.
>
You need a hot (or cold) slurry between the heat or cold source and
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>
Reply by Phil Hobbs●May 21, 20202020-05-21
On 2020-05-21 02:53, cristhian.hellsing@gmail.com wrote:
> 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!!!!
>
Welcome. You're accessing this group using the Google Groups WWW
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
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510
http://electrooptical.nethttp://hobbs-eo.com
Reply by Bill Sloman●May 21, 20202020-05-21
On Thursday, May 21, 2020 at 4:53:28 PM UTC+10, cristhia...@gmail.com wrote:
> 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!!!!
If you e-mail me at bill.sloman@ieee.org I'll send you a reprint of my paper on the subject.
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
Reply by ●May 21, 20202020-05-21
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!!!!
Reply by lang...@fonz.dk●July 20, 20122012-07-20
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"
>
>
>
>
>
>
>
>
>
> <langw...@fonz.dk> wrote:
> >On 20 Jul., 00:59, "k...@att.bizzzzzzzzzzzz" <k...@att.bizzzzzzzzzzzz>
> >wrote:
> >> On Thu, 19 Jul 2012 15:14:04 -0400, Phil Hobbs
>
> >> <pcdhSpamMeSensel...@electrooptical.net> wrote:
> >> >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:
>
> >> >> >> 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. =A0Compo=
und
> >> >> >>> Peltiers have a nasty thermal instability, where they start get=
ting
> >> >> >>> 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. =
=A0If you
> >> >> >>> put them in parallel, the ones with higher delta-T will draw le=
ss
> >> >> >>> 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 exchan=
ger,
> >> >> >>> the sign of the gain can invert and the whole thing turns to la=
va very
> >> >> >>> fast. =A0(That can happen with individual control or series-con=
nection
> >> >> >>> as well, but the melty ones can't hog current from the cooler o=
nes, 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 c=
rack.
> >> >> >>> So use Arctic Silver or a very small amount of very good therma=
l
> >> >> >>> grease on one side, and solder on the other. =A0IIRC you can so=
lder 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. =A0There's also =
an
> >> >> >>> incomplete draft that was intended to accompany the second edit=
> >> >> >> often inadequate and miss out details needed for real world desi=
gns.
>
> >> >> >> Can I pick your brains for a slightly odd requirement? Ideally o=
ne that
> >> >> >> can be done with at most a pair of TECs one high temp and one no=
rmal.
> >> >> >> On paper they were rated for 3A and 14v or so each but in practi=
ce I
> >> >> >> was struggling in reverse to get 2v and a few mA out with a cand=
le
> >> >> >> flame heated plate at 250C on one side and a slab of aluminium a=
t -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 t=
he 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 assiste=
d 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. =A0Oops.
>
> >> >> > Or, for a complete demo, have one TE element complete with lots o=
f hype,
> >> >> > and one "150 year old technology" Sterling engine for comparison.=
..
>
> >> >> --
>
> >> >Of course, TECs are 60-year-old technology....
>
> >> Yup. =A0My father designed a TEC refrigerator in the late '50s or very=
early
> >> '60s, complete with a solid-state power supply (string of Germanium DO=
-3
> >> PNPs). =A0I had a couple of them in the basement to play with when I w=
as a kid.
> >> It was designed to go in a car but never made it past prototype. =A0It=
got beat
> >> out by Styrofoam disposables. =A0;-)
>
> >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"
>
> Fifty years ago you couldn't. =A0;-)
my dad was still in school then so I wouldn't know :p
-Lasse
Reply by Jon Elson●July 20, 20122012-07-20
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
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
Reply by Tim Wescott●July 20, 20122012-07-20
On Fri, 20 Jul 2012 08:45:18 +0100, Martin Brown wrote:
> 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
> more sophisticated coffee cup powered rotary motion one in previous
> years. I was trying to find yet another candle based demo for Xmas.
Well, in that case, make a padded bear-trap gizmo that's triggered by
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
Reply by Martin Brown●July 20, 20122012-07-20
On 19/07/2012 20:31, Jon Elson wrote:
> 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
> 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.
Seems to be entirely wrong order of magnitude here - at least in the UK
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
Reply by Syd Rumpo●July 20, 20122012-07-20
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
Reply by Martin Brown●July 20, 20122012-07-20
On 19/07/2012 20:31, Jon Elson wrote:
> 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
> 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.
My back of the envelope suggests that for a candle flame delta-T of
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