Peltier Cooling Module Data sheet understanding

Am 21.10.2015 um 22:24 schrieb Banshee For:

I am working on a project which envolves the implementation of Peltier

modules. I am a mechanical engineering student. Currently, I am dealing

with a Peltier cooling Module whose data sheet is shown below in the

link from Farnell UK. We have Peltier cooling modules in the project

which are supposed to cool down some flowing air. This is the first time

I encounter Peltier modules.

http://www.farnell.com/datasheets/1693164.pdf

(https://mail.yandex.com/re.jsx?h=a,ggFabqW2FW_fTrpozMU2CQ&l=aHR0cDovL3d3dy5mYXJuZWxsLmNvbS9kYXRhc2hlZXRzLzE2OTMxNjQucGRm)

 

1-

I would like to ask about any good books available on the

Thermo-electric effect, and more particularly Peltier modules, the

physics behind them, mathematical models of them and their

implementation.

 

2-

Also I would like to ask about the performance graph of the Peltier

module (see the link below). According to what I understood from the

explanation available on the Internet, the Pc notation on the graph

refers to the cooling power. Is it the rate at which heat energy is

absorbed on the cold side ??

 

3-

There is a heat little heat exchanger which consists of a heat sink,

which holes filled in it and pipes are connected to flow water through

the heat sink to increase the convective heat loss and prevent any

overheat. While Tc the temperature on the cold side, can Th be

considered as the ambient temperature ?

 

http://oi57.tinypic.com/34hj2m8.jpg

(https://mail.yandex.com/re.jsx?h=a,Ve6XfGxq9DeW05E65tYxrQ&l=aHR0cDovL29pNTcudGlueXBpYy5jb20vMzRoajJtOC5qcGc)

 

4-

On the performance graph, the "Th" at which the data in the graphs were

collected is noted to be 25 C. Does this mean that I can refer to the

graphs only in case that that the temperature on the hot side at that

temperature ??

 

This because I found some sources on the Internet claiming at an offset

of ±10 C, with a slight margin of error.

 

 

5-

The other thing I need to understand is that if my understanding of the

cooling power "Pc", and if the temperature on the hot side "Th" remains

constant as shown on the graph, for a given value of current as shown

with the ascending lines on the right side in the lower section of the

graph, why would the cooling power (the power absrobed on the cold side)

fall if the temperature on the cold side falls as well. If my

understanding of the cooling power is correct, then wouldn't the

temperature of the cold side drop as more power "Pc" is absrobed ??

 

 

6-

In the lower section of the graph, if I choose two different

intersection points on the straight line of the current value 4.8 Amp,

when at "Tc = -20 C & Pc = 40 W" and when at "Tc = -5 C & Pc = 60 W",

the corresponding temperature differential "dT" between "Tc" and "Th" is

"45 C" and "30 C" in relation to the "Th" shown on the graph

respectively. Thus, on the upper section of the graph, on the current

line of 4.8 Amp, the intersection of the line with "dT= 45 C" & "dT= 30

C", yields voltage values of "V= 24.5 volts" & "V=23.5 volts"

respectively. How can the same amount of current, and slight difference

in voltage create a substantial difference in the temperature on the

cold side ??

 

 

7-

How can I start with the implementation of the Peltier module, as I need

a starting point. According to what I understood, I need to specify the

temperatures I need on both sides of the module, with the cooling power

(the power to be absorbed on the cold side, if my understanding of the

cooling power shown on the graph is correct), so that I can specify the

electric current value I need. Based on the temperature differetial

between the hot and the cold side, and the value of the current, I can

then determine the value of voltage I need to supply to the Peltier

module, so that it generates the difference in temperature I need. Am I

on the right track, and is there any piece of advise that I can make use

of ??

 

 

Sorry for the very long thread.

 

Thanks in Advance

 

Regards

 

--

To view any images and attachments in this post, visit:

http://www.element14.com/community/message/163918

 

This is certainly the wrong  forum place for your questions.

This is the  eagle forum and here we discuss problems and possibilities

about the  eagle CAD software.

--

Mit freundlichen Grüßen / With best regards

Joern Paschedag

This page may answer some of your questions:

TEC / Peltier Element Design Guide | Compendium

Your link doesn't lead to a picture but to some website requiring clicking and who knows what else. If you insert your picture directly into your E14 post I'll be able to look at it.

Did you get the information you need from the link Paul gave you or are you still stuck ?

MK

Dear Mr. Joern

I am so sorry for this, mistake, I just did not notice that I was posting in the wrong place. I just clicked on the "Start a Discussion" button on the home page, as I found some difficulities surfing my way in the website.

Who can I contact (an admin or moderator) who may be capable of helping me to move this thread/discussion to the right section ?

Thnaks for your reply and notice, and sorry for the very late reply, as I have been very busy lately.

Regards

Dear Mr. @Michael Kelltett

I am sorry for the link not workig. The link works fine with me. Anyway, it contains the performance graph of Peltier Module I have, and the same graph is shown in the first link, which is the datasheet from the manufacturer. I uploaded both as attachments.

The link of @Paul Ellison presented some similar explanation I found online regarding the graph itself. However, it does not explain the reason behind the Peltier behavior. I have not had the greenlight from my supervisor to operate the last Peltier module we have, because I still do not know why for a given value of current, the temperature differential (dT) falls when the power of cooling (Qc) increases. I suppose when the Peltier module pumps more heat, the different in temperature between the Peltier junctions has to increase, as the cold side's temperature will drop with more heat drawn from the cooled object.

These links are from the website Mr. Paul poasted.

http://www.meerstetter.ch/images/compendium/heat_vs_current.png

http://www.meerstetter.ch/images/compendium/peltier_chart.jpg

An initial experiment that I have to conduct before implementing the Peltier module in the project is to cool an amount of water and determine the efficiency of the Peltier module, using an insulated container. Thus, I assume that for a given value of current, the higher the cooling power (heat drawn), the larger the difference will grow between the junctions, as the cold side of the Peltier will fall in temperature compared to the hot side.

Plus, the datasheet of the Peltier module we have, you can notice that for a given amount of current (the straight lines in the lower section), the cooling power falls with the increase of the temperature gradient (the temperature of the cold side falls while the temperature of the hot side remains 25 C as indicated on the graph), and that's according to the voltage supplied with that amount of current, as shown in the upper section of the graph. nevertheless, I see that with a slight difference in voltage, a large difference in temperature gradient in generated, which is not very logical to me. Add to that, that I have no control over the current supplied, as the electronics guys in our project set up the power supply to be through PWM for all the parts of the project, and I have no much idea about that.

Sorry again for the long post.

Thanks for your reply

Regards

Dear Mr. Paul

Thanks very much for your help and reply, and allow me to apologise for my very late reply. Please check my reply to Mr. Michael Kellett, where I explained my case in more detail.

Regards

Hi Banshee,

I will ask element14jamie to move your question to a better group.

John

Hello Paul,

Thank you I have moved this to Passive area

Jamie

The upper set of curves in your graph are telling you how the voltage cross the device will vary for each of 5 constant currents as the temperature difference across the device is varied. ie  - the variation in temperature is being forced (ie is the cause) and the variation of voltage is the effect.

If you wish to control temperature with a Peltier device then you MUST have linear control over the applied voltage - if you try to drive it with a thermostat (turning a constant voltage on and off) it will have a very short life due to the repeated thermal shocks.

You can buy drive electronics ready made (quite expensive) or make your own (quite difficult).

For you water cooling (or heating) experiment you need to make sure that the other side of the Peltier device is maintained at a constant temperature (as far as you can)  - the easiest way to do this is to use a PC processor cooler - pick a good one with heat-pipes from the cooling base to the fins. You will have to make metal (aluminum or copper) adapter plates to couple the Peltier device to the water container and the heatsink and you will have to embed temperature sensors in the plates. Use good performance thermal grease between all the mating surfaces.

You can learn a lot by Googling - I have hundreds of links recorded  - better you do you own searches so you can find the things that interest you.

MK