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Old 12-07-2006, 05:33 PM   #71
Raymond Koh
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hi ,
like to find out if there Is any stuff we can recycle from old used aircon for the construction of the DIY micro chiller??
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Old 12-07-2006, 10:57 PM   #72
Ingwe
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hi are there pictures for the individual components of the micro chiller? afraid i may not be able to identify them in SLT.
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Old 14-07-2006, 08:23 PM   #73
squallaq
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I got myself a 8A 40x40 at the basement shop, I ask the uncle what type of psu is suitable. He recommend the type in his showcase which cost ard $125. Expensive lah...
Can I use the normal cpu psu that provide 12v more than 8A type, if yes any recommendation?
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Old 15-07-2006, 01:43 AM   #74
xtrekker
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Quote:
Originally Posted by squallaq
I got myself a 8A 40x40 at the basement shop, I ask the uncle what type of psu is suitable. He recommend the type in his showcase which cost ard $125. Expensive lah...
Can I use the normal cpu psu that provide 12v more than 8A type, if yes any recommendation?
Of course. Just make sure that its able to supply at least 12A on the 12V of your PSU.

cheers
xtrekker
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Old 15-07-2006, 10:25 AM   #75
squallaq
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Quote:
Originally Posted by xtrekker
Of course. Just make sure that its able to supply at least 12A on the 12V of your PSU.

cheers
xtrekker
great!! Mean I can save some $.
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Old 16-07-2006, 10:45 PM   #76
squallaq
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Just build a tem chiller 8A looking to see how it goes... When without water, I can see ice forming on the cooling fin.
Anyone know if this can cool down a 380mm x 246mm x 306mm tank?
Is the tank too large to cool down to 24deg c?
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Old 20-07-2006, 09:55 PM   #77
squallaq
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I was wondering what wrong with my tem setup?
When I test it in a small cup of water, it can only drop from 28 to 22 deg C. It not even a 1 litre water

Regarding the heatsink, I find that it is quite hot, could it be the restriction to the cooling fin? Any experts can help?
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Old 21-07-2006, 02:49 PM   #78
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Quote:
Originally Posted by squallaq
I was wondering what wrong with my tem setup?
When I test it in a small cup of water, it can only drop from 28 to 22 deg C. It not even a 1 litre water

Regarding the heatsink, I find that it is quite hot, could it be the restriction to the cooling fin? Any experts can help?
when your heatsink is hot , its mean that your heatsink is not dissipating the heat away from your TEM. Get a bigger heatsink or more powerful fan to improve the performance.

btw , I was at the shop you mentioned a couple of days ago. I saw the heatsink they selling as a kit set with the TEM. Its too small...


cheers
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Old 30-07-2006, 05:16 PM   #79
taygu
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Hi Xtrekker, do you have the info on temp controller? and How to build one?

I got excited after reading this thread and have found most of the items needed, I need some advice before I start buying all the required item to DIY.

1) Is a CPU heatsink good enough?
2) What do you get the heatsink for the cool side?
3) Est how much it cost to build the temp controller?

Thanks in advance.
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Old 01-09-2009, 12:15 AM   #80
ksc133
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Hi xtrekker,

a nice article.

need your advice if TEM chillers can cool down to 22*C from room temp of 28*C?

thanks


Quote:
Originally Posted by xtrekker View Post
Hi All , I have decided to start this thread due the renew interests in TEM cooler. The writeup below is a simplifed version of how to design and built your own chiller. The calculations are theoretical and actual value might differ. All the data used is taken from supplier's datasheet.

cheers
xtrekker
ps:Upzzz me as a form of encouragement if you find this useful.

Introduction to Thermo-Electric Module (TEM)

Xtrekker
Silane

In 1821, J. T. Seebeck (1770-1831) discovered that different metals junctions will develop a small voltage potential when both of them are at different temperature. This effect is known as the "Seebeck effect". Thermocouples are based on "Seebeck effect".
In 1834, a scientist called Peltier discovered the inverse of the Seebeck effect, known as the "Peltier effect". He found that applying a voltage to a thermocouple would induce a active heat pump. This is now known as Thermoelectric Cooler (TEC).

There are quite a few thing you need to know before everyone rush into buying TEM.

Ask yourself the following questions :

1. What is your target temperature of your tank ?
2. How much heat (Qc) you intend to remove from your tank ?
3. What type of heatsink to use ?
4. Are you willing to fork out extra $$ to power your chiller ?

Using a 1ft x 1ft x 1ft tank of 27L as a case study ,

Lets say the temperature of my 30L tank is to be cooled to 24C. The ambient temperature of my room is 28C. The temperature difference ( dT = 28 -24 ) is 4C . We can determine the heatload (Qc) this can be easily done by using any heatload calculating software. Values of Qc for typical tank volumes is plotted on the graph below for your convenience.


Step 1 : Determine the value of Qc from the graph below.
From the graph, Qc of 1ft x 1ft x 1ft tank is about 40W


Step 2 : Choosing a suitable TEM

With Qc known we can proceed to the next step of choosing a suitable TEM for the Job. Don¡¦t be confused by the power ratings of TEM. The power rating is the maximum electrical power the TEM will ¡§consumed¡¨ from you power supply. Qc is the ¡§Cooling Power¡¨ of the TEM its usually about 50% of the electrical power you supplied. Some retailers sell "80W peltier element", without stating what this value actually means. This is misleading - what you want is a high transport capability, but a low power consumption.

For Example

TEM rated at
62W will give Qc = 35.1 W (model CP1-12704)
77W will give Qc = 44.5 W (model CP1-12705)
93W will give Qc = 53.1W (model CP1-12706)

Choosing CP1-12705 77W TEM seems suitable for the rated Qc. But in this design consideration , choosing a higher rated TEM at 77W to give a some excess cooling power to play with. TEM can easily turn off when the set point temperature of 24C is reached.

dT = (1 - (heat load/max cooling power)) * max temp difference

where
heat load Qc = cooling requirement
max cooling power = TEM rating
max temp difference = TEM max dT under no load.

For example, the 77 watt TEM can cool a tank with ambient at 28 C as follows:

dT load = (1 - (40/44.5w)) * 68 C = 15.9 C

Theoretical tank temperature = 28 C - 15.9 C = 12.1 C

With an ambient of 28C, the TEM theoretically will cool the tank to 12.1 C. The actual temp will depend on how well it's insulated, power supply amperage, etc. I also took some shortcuts by using the TEM's rating from the supplier's datasheet, so actual temperature will be much higher.

Step 3 : Choosing a suitable Heatsink.

Heatsink performance is measured in C/W (or K/W ) We refer to this as thermal resistance. For this design , the lower thermal resistance the better .An example for what these values mean: if a thermal load of 20W is applied to a heatsink, and this causes the temperature of the heat source to raise by 10¢XC, the heatsink has a rating of 10C/20W = 0.5C/W. What does this number mean? A resistance of 0.5 C/W means that if one Watt of heat goes through the object, the temperature drops by 0.5 degrees.

In this case a ¡§forced Convention¡¨ type is heatsink is most suitable.

Below shows the theoretical temperature of heatsink in the micro chiller using this equation ,

THS = TA + RT Qh

where
THS = Heatsink Temperature
TA = Ambient Temperature 28C
RT = Thermal resistance of heatsink = 0.15 C/watt

Thermal load on heatsink Qh = Qc + Pin
= 40 watts + (5 amps) * (15.4 volts)
= 40 watts + 77 watts
= 117 watts

Therefore THS = 28C + (0.15 C / watt) (117 watts)
= 28C + 17.55C
= 45.55C
That is to say , 45.55C is the temperature of the heatsink when the micro chiller unit when running. This heatsink temperature will play a part in the actually temperature in the tank.

As a general guide for choosing a heatsink for the TEM , look for heatsink with
- big heatsink with lots of fins and surface area.
- the fan should be higher power rating. i.e. at least above 0.4amps


Step 4 : Getting a Power Supply Unit (PSU)

There are 2 common types of PSU on the market. Switch mode power supply and Linear Power supply. The latter is common know to us as the ¡§set down transformer¡¨ . Switch mode is more efficient .At least 80% of the input power is converted while the linear PSU stands at only 60% meaning 40% is lost as heat.

When choosing a PSU, look for one that at least 1.25 times the power of the chiller. The 77W TEM, would need a PSU rated at least 77W x 1.25 = 96W


End of part 1 Choosing a Suitable TEM, Heatsink and PSU
Coming soon ,Part 2 : Assembly tips
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