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Peltier Controller Schematic

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iCod
Guest

Tue Sep 14, 2010 2:07 pm   



Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

Tim Wescott
Guest

Tue Sep 14, 2010 3:22 pm   



On 09/14/2010 06:07 AM, iCod wrote:
Quote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

AFAIK the important point to bear in mind is that the Peltier device
acts like constant-heat pump, driven by junction current, in parallel
with a resistor that shows I^2-R losses. So the overall heat pump
action will be nonlinear (because of the I^2 factor), and it's really a
good idea to not try to PWM the thing (because of the I^2 factor).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Joerg
Guest

Tue Sep 14, 2010 3:28 pm   



iCod wrote:
Quote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads


http://www.analog.com/static/imported-files/tech_articles/37488110918229TEC_Application_Brief2.pdf

Looks like they are finally ditching this chip but if you need a one-off
prototype it'll work:

http://www.analog.com/static/imported-files/data_sheets/ADN8830.pdf

Maybe I am, to a small extent, guilty regarding its demise because I
bought the demo kit and then decided I didn't like it that much, and
rolled my own.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Joerg
Guest

Tue Sep 14, 2010 3:32 pm   



Tim Wescott wrote:
Quote:
On 09/14/2010 06:07 AM, iCod wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

AFAIK the important point to bear in mind is that the Peltier device
acts like constant-heat pump, driven by junction current, in parallel
with a resistor that shows I^2-R losses. So the overall heat pump
action will be nonlinear (because of the I^2 factor), and it's really a
good idea to not try to PWM the thing (because of the I^2 factor).


However, with a sizeable Peltier, one should PWM the driver and then
lowpass accordingly so that the Peltier sees DC. Or almost DC.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Joerg
Guest

Tue Sep 14, 2010 4:49 pm   



Bill Sloman wrote:
Quote:
On Sep 15, 12:32 am, Joerg <inva...@invalid.invalid> wrote:
Tim Wescott wrote:
On 09/14/2010 06:07 AM, iCod wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?
Thanks for any leads
AFAIK the important point to bear in mind is that the Peltier device
acts like constant-heat pump, driven by junction current, in parallel
with a resistor that shows I^2-R losses. So the overall heat pump
action will be nonlinear (because of the I^2 factor), and it's really a
good idea to not try to PWM the thing (because of the I^2 factor).
However, with a sizeable Peltier, one should PWM the driver and then
lowpass accordingly so that the Peltier sees DC. Or almost DC.

That exactly what I did. Unfiltered pulse width modulation has been
known to melt the solder inside the Peltier cooler, but if you can
keep the ripple down to less than - say - 10% of the peak current, the
extra resistive losses aren't dramatic. Radio-frequency interference
from the leads to the Peltier cooler can be a problem a ripple current
levels that won't generate significant extra heating and it can pay to
filter this current to reduce the ripple content to much lower levels.


Yup, RF-wise I filtered the dickens out of it. Ferrite bead, cap,
another ferrite bead ...

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Joerg
Guest

Tue Sep 14, 2010 4:52 pm   



Bill Sloman wrote:
Quote:
On Sep 15, 12:28 am, Joerg <inva...@invalid.invalid> wrote:
iCod wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?
Thanks for any leads
http://www.analog.com/static/imported-files/tech_articles/37488110918...

Looks like they are finally ditching this chip but if you need a one-off
prototype it'll work:

http://www.analog.com/static/imported-files/data_sheets/ADN8830.pdf

Maybe I am, to a small extent, guilty regarding its demise because I
bought the demo kit and then decided I didn't like it that much, and
rolled my own.

They are now pushing the ADN8831. I've not been interested enough to
work out how it differs from the ADN8830.


I think that's the datasheet where I found some inconsistency in a
formula or two and I let them know. Basically those chips are ok but I
found it can also be done for much less money. I mean, over $7 is a
hefty price. Even if you need a few dozen jelly-bean parts you can beat
that. Or use a low-cost uC. I can't imagine the ADN8831 selling like
hotcakes.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Bill Sloman
Guest

Tue Sep 14, 2010 5:14 pm   



On Sep 14, 11:07 pm, iCod <sir...@lineone.net> wrote:
Quote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

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's fairly detailed. E-mail me for a reprint - bill.sloman_at_ieee.org
is a real address.

Analog Devices sell the ADN8831 integrated circuit controller for this
job

http://www.analog.com/static/imported-files/data_sheets/ADN8831.pdf

http://www.analog.com/static/imported-files/tech_articles/37488110918229TEC_Application_Brief2.pdf

and the data sheet includes a circuit diagram. It won't do as well as
my circuit, but it is a lot simpler.

The Linear Technology LTC1923 is comparable, and the data sheet is
more informative

http://cds.linear.com/docs/Datasheet/1923f.pdf

When I last looked, neither of them included my formula for
calculating the heat transferred by the Peltier junction (in watts per
amp)as a function of the temperature difference across the junction
and the thermal resistances in the path.

I've recently sneaked that into the Review of Scientific Instruments

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)

so that Americans - who tend not to have access the the British
journal "Measurement Science and Technology" - can take advantage of
it.

--
Bill Sloman, Nijmegen

http://cds.linear.com/docs/Application%20Note/an89.pdf

Tim Wescott
Guest

Tue Sep 14, 2010 5:42 pm   



On 09/14/2010 07:32 AM, Joerg wrote:
Quote:
Tim Wescott wrote:
On 09/14/2010 06:07 AM, iCod wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

AFAIK the important point to bear in mind is that the Peltier device
acts like constant-heat pump, driven by junction current, in parallel
with a resistor that shows I^2-R losses. So the overall heat pump
action will be nonlinear (because of the I^2 factor), and it's really a
good idea to not try to PWM the thing (because of the I^2 factor).


However, with a sizeable Peltier, one should PWM the driver and then
lowpass accordingly so that the Peltier sees DC. Or almost DC.

I should have been more clear on that -- yes. But it's _not_ like a

motor driver where even if you PWM slowly enough that the motor doesn't
filter it out you're still (usually) not losing massive amounts to I^2-R
losses.

So -- generate the current however you want, but make it reasonably
smooth going into the Peltier.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott
Guest

Tue Sep 14, 2010 5:45 pm   



On 09/14/2010 08:52 AM, Joerg wrote:
Quote:
Bill Sloman wrote:
On Sep 15, 12:28 am, Joerg<inva...@invalid.invalid> wrote:
iCod wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?
Thanks for any leads
http://www.analog.com/static/imported-files/tech_articles/37488110918...

Looks like they are finally ditching this chip but if you need a one-off
prototype it'll work:

http://www.analog.com/static/imported-files/data_sheets/ADN8830.pdf

Maybe I am, to a small extent, guilty regarding its demise because I
bought the demo kit and then decided I didn't like it that much, and
rolled my own.

They are now pushing the ADN8831. I've not been interested enough to
work out how it differs from the ADN8830.


I think that's the datasheet where I found some inconsistency in a
formula or two and I let them know. Basically those chips are ok but I
found it can also be done for much less money. I mean, over $7 is a
hefty price. Even if you need a few dozen jelly-bean parts you can beat
that. Or use a low-cost uC. I can't imagine the ADN8831 selling like
hotcakes.

I never understood the need for a specialized Peltier cooler IC, unless
it's because they do something fancy to compensate for the nonlinearity.

Unless your problem demands hugely tight regulation you can just design
a loop with enough margin to handle the nonlinearity, and if it _does_
need the tight regulation then you either handle it with a few discretes
or with a micro.

So why a special chip?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Tim Wescott
Guest

Tue Sep 14, 2010 5:47 pm   



On 09/14/2010 08:36 AM, George Herold wrote:
Quote:
On Sep 14, 9:07 am, iCod<sir...@lineone.net> wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

My only advice is; If you are going to air cool the TEC then make sure
the heat sink is big enough. We use a ~10Watt TEC with perhaps a
square inch foot print and the heat sink is 6 inches by 4 inches. My
boss was amazed that such a big heat sink was needed... but thermal
runaway is not good.

The electronics is pretty simple. Thermistor->bridge->PI(D)->power
gain.

The _only_ advantage those things have is that they are small and have
no moving parts. It's interesting to educate someone who doesn't
realize how inefficient they are, or how much heat they generate, or how
you have to get that heat away.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

Bill Sloman
Guest

Tue Sep 14, 2010 5:53 pm   



On Sep 15, 12:28 am, Joerg <inva...@invalid.invalid> wrote:
Quote:
iCod wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

http://www.analog.com/static/imported-files/tech_articles/37488110918...

Looks like they are finally ditching this chip but if you need a one-off
prototype it'll work:

http://www.analog.com/static/imported-files/data_sheets/ADN8830.pdf

Maybe I am, to a small extent, guilty regarding its demise because I
bought the demo kit and then decided I didn't like it that much, and
rolled my own.

They are now pushing the ADN8831. I've not been interested enough to
work out how it differs from the ADN8830.

--
Bill Sloman, Nijmegen

Bill Sloman
Guest

Tue Sep 14, 2010 6:13 pm   



On Sep 15, 12:32 am, Joerg <inva...@invalid.invalid> wrote:
Quote:
Tim Wescott wrote:
On 09/14/2010 06:07 AM, iCod wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

AFAIK the important point to bear in mind is that the Peltier device
acts like constant-heat pump, driven by junction current, in parallel
with a resistor that shows I^2-R losses.  So the overall heat pump
action will be nonlinear (because of the I^2 factor), and it's really a
good idea to not try to PWM the thing (because of the I^2 factor).

However, with a sizeable Peltier, one should PWM the driver and then
lowpass accordingly so that the Peltier sees DC. Or almost DC.

That exactly what I did. Unfiltered pulse width modulation has been
known to melt the solder inside the Peltier cooler, but if you can
keep the ripple down to less than - say - 10% of the peak current, the
extra resistive losses aren't dramatic. Radio-frequency interference
from the leads to the Peltier cooler can be a problem a ripple current
levels that won't generate significant extra heating and it can pay to
filter this current to reduce the ripple content to much lower levels.

--
Bill Sloman, Nijmegen

George Herold
Guest

Tue Sep 14, 2010 6:36 pm   



On Sep 14, 9:07 am, iCod <sir...@lineone.net> wrote:
Quote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

My only advice is; If you are going to air cool the TEC then make sure
the heat sink is big enough. We use a ~10Watt TEC with perhaps a
square inch foot print and the heat sink is 6 inches by 4 inches. My
boss was amazed that such a big heat sink was needed... but thermal
runaway is not good.

The electronics is pretty simple. Thermistor->bridge->PI(D)->power
gain.

You can look at C.C. Bradley etal, Rev. Sci. Inst. 61, 2097 (1990)

George H.

Tim Wescott
Guest

Tue Sep 14, 2010 10:11 pm   



On 09/14/2010 12:38 PM, George Herold wrote:
Quote:
On Sep 14, 12:47 pm, Tim Wescott<t...@seemywebsite.com> wrote:
On 09/14/2010 08:36 AM, George Herold wrote:

On Sep 14, 9:07 am, iCod<sir...@lineone.net> wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

My only advice is; If you are going to air cool the TEC then make sure
the heat sink is big enough. We use a ~10Watt TEC with perhaps a
square inch foot print and the heat sink is 6 inches by 4 inches. My
boss was amazed that such a big heat sink was needed... but thermal
runaway is not good.

The electronics is pretty simple. Thermistor->bridge->PI(D)->power
gain.

The _only_ advantage those things have is that they are small and have
no moving parts. It's interesting to educate someone who doesn't
realize how inefficient they are, or how much heat they generate, or how
you have to get that heat away.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details athttp://www.wescottdesign.com/actfes/actfes.html

Oh it's very nice that they can cool as well as heat. Otherwise I'm
stuck running something above ambient... And then dealing with the
fact that most likely I can get heat into the thing faster than it
comes out.... so the control loop has to follow the slow side.

Say with a micro controlling things could you have different time
constants for cooling and heating? Do you do that sort of thing?

Yes and yes.

I'm not sure that is the best way.

If you could measure the temperature at both sides of the Peltier (or if
you had a way to estimate the temperature on the heatsink side) you
could take a heat flow command and turn it into a current command. This
would keep the loop dynamics mostly independent of the temperatures --
except for the fact that you'd always have way more power to heat than
to cool.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

George Herold
Guest

Tue Sep 14, 2010 10:38 pm   



On Sep 14, 12:47 pm, Tim Wescott <t...@seemywebsite.com> wrote:
Quote:
On 09/14/2010 08:36 AM, George Herold wrote:

On Sep 14, 9:07 am, iCod<sir...@lineone.net>  wrote:
Can anyone point me to a schematic for a Peltier constant temperature
controller?

Thanks for any leads

My only advice is; If you are going to air cool the TEC then make sure
the heat sink is big enough.  We use a ~10Watt TEC with perhaps a
square inch foot print and the heat sink is 6 inches by 4 inches.  My
boss was amazed that such a big heat sink was needed... but thermal
runaway is not good.

The electronics is pretty simple.  Thermistor->bridge->PI(D)->power
gain.

The _only_ advantage those things have is that they are small and have
no moving parts.  It's interesting to educate someone who doesn't
realize how inefficient they are, or how much heat they generate, or how
you have to get that heat away.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details athttp://www.wescottdesign.com/actfes/actfes.html

Oh it's very nice that they can cool as well as heat. Otherwise I'm
stuck running something above ambient... And then dealing with the
fact that most likely I can get heat into the thing faster than it
comes out.... so the control loop has to follow the slow side.

Say with a micro controlling things could you have different time
constants for cooling and heating? Do you do that sort of thing?

George H.

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