All about TECing

By Ultrasonic2 & Friends

CONTENTS

• How is a TEC Rated ?
• I just bought a 540watt TEC from E-bay so it can cool a load of 400watts?
• Why do i need a cold plate and a hot plate. Why can i just place the TEC directly on the CPU ?
• What can i use for a Cold / Hot plate and can i use Aluminum?
• How much pressure should i apply to the TEC?
• Why can't I air cool my TEC and get good performance
• Can I run my TEC off my PSU?
• Which waterblocks are TEC-compatible?
• Which power supplies are preferred when it comes to TEC-ing?
• Where can I get TEC related supplies? (condensation-proofing, TEC's, etc.)
• What is a TEC
• How can i control the power going to a TEC
• I want to TEC cool my PC BUT i DONT want to go below ambient to avoid condensation.
• Do i have to insulate my Board and Block
• Can a TEC cool my load as well as Phase Change can ?
• I’ve heard that TEC’s are very inefficient is this true. And what about phase change ?
• I have a cooler with a TEC that draws 75watts of power so it’s Qmax or Pmax is 75watts right ?
• TEC's in Parallel or Series ( stacking, Cascade)
• Where can i get a TEC calculator app to do all the math for me ?

Q. How is a TEC Rated ?
Qmax Umax Vmax Imax Amax dTmax Pmax

All of the above are NORMALLY rated at a HOT side Temp of 300 kelvin or 27c. As you increase the Hot side temp all of the above will also increase. This is one way people use to miss lead others.

A.
Qmax
This is the amount of heat that can be transferred form the cold side of the TEC to the Hot.
Note:When Qmax is transferred the Delta between the 2 sides is 0. Qmax is NOT the amount of electricity a TEC uses


dTmax
This is the max delta between the two sides. A delta of 69 indicates that the cold side is 69c below the temp of hot side.
Note: When dTmax is achieved NO load is applied to the cold side of the TEC (This is normally achieved in a vacuum)

Umax, Vmax
The input Voltage that that dTmax and Qmax are achieved

Imax, amax
The input Amp that that dTmax and Qmax are achieved


Pmax
This is a measure of how much electricity a TEC uses to move a load of Qmax.
Note: E-Bay sellers normally advertise their TEC based on Pmax not Qmax, which makes them look more powerful than a TEC based on Qmax

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Q. I just bought a 540watt TEC from E-bay so it can cool a load of 400watts?


A
NO
E-bay sellers advertise their TEC's on Pmax or the amount of ELECTRICITY a TEC will use not MOVE (Qmax). The Qmax of a TEC will always be significantly lower than the quoted Pmax ..
The 540 Pmax TEC sold on E-bay has a Qmax of about 360watts SO it is unable to cool a load of 400 as the load is greater than what the TEC can remove .

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Q. Why do i need a cold plate and a hot plate. Why can i just place the TEC directly on the CPU ?


A.
You HAVE to cover all the TEC with a hot and cold plate for 3 main reasons

A TEC has no inherent heat spreading ability. This means that if the TEC isn't covered by a heat spreader the percent sticking out wont be able to cool anything. This will obviously lead to reduce performance or failure of the TEC if the hot side isn't covered.

A TEC needs a far amount of pressure pushing it together other wise magnetic forces will result in poor life expectancy.

Most Water blocks and Air coolers don't have perfectly flat bases, in most cases this is intentional. However this is a very bad thing when applied to a perfectly flat TEC. A water block maybe able to cover a 50x50mm TEC but all of it's surface may not actually be touching the TEC let allown applying pressure to it !

If using a TEC greater than about 50x50mm (you should be using a 62mm one) Then it's unlikely that you be able to use a perfectly flat cold plate becasue there are normally some capacitors or something in the way so it's best to machine a step into the base so the cold plate can clear these.



Here are some cold plates for a 62mm TEC. The face not showing (the bottom in the pic) is the large surface where the TEC is clamped down via the bolt holes. The left plate is the Cold plates and you can see the Step down that has been machined in it to clear caps and so on. The right plate is the hot plate it has a step down to be compatible with most AM2 and 775 mounting hardware

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Q. What can i use for a Cold / Hot plate and can i use Aluminum ?

A
There was a detailed study undertaken quite a few years ago now that showed that a copper block of about 10mm (3/8) performed the best. But obviously the absolute best block thickness would very depending on your application. When copper is used manufactures generally recommend a minimum Cold and hot plate thickness of 3mm to keep bowing to a minimum.

As for Aluminum you can certainly use it if you want too. People don't use it in PC cooling for 2 reasons

* Aluminum and copper dont mix well leading to galvanic corrosion

* Copper conducts heat almost Twice as well as Aluminum so your results are ALWAYS better when copper is used.

If you do use Aluminum you'll need to use thicker hot and cold plates because aluminum is softer than copper, so it bends more easily.

Contributors (Ira-K, flak-spammer)

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Q. How much pressure should i apply to the TEC

A.
You should apply about 300 PSI to your TEC to work out how to apply this pressure see the equation below
T = (C x D x F x in2) / (# of screws)

Using the following equation you can solve for torque per screw:
T = torque per screw (in-lbs)
C = torque coefficient (0.20 as received, 0.15 lubricated)
D = nominal screw size (4/40 = 0.112, 6/32 = 0.138, 8/32 = 0.164)
F = Force (lbs / in2)
in2 = Module surface area (length x width)

This per module

C= 0.20 (who oils their bolts)
D= 0.157 (4mm)
F= 300 (150 is the minimum recommended)
in2= 3.875 (50x50mm TEC)
# of screws = 2

18.25125 = (0.20 x 0.157 x 300 x 3.875) / (2)

So to achieve 300psi on the TEC i'd have to tighten each bolt up to 18.25 inch pounds. i'll probably round that up to 20inch pounds


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Q. Why can't I air cool my TEC and get good performance

A
It's not a simple answer really
The reason that people dont air cool TEC's is largely due to the inability to keep the TEC cooled well. A TEC may require a large amount of electricity to move the heat from one side of the TEC to the other. If the cooler is unable to remove the heat efficiently enough the result is the hot side of the TEC just ends up getting hotter so any possible gain from having a delta between the two sides of the TEC are lost. the cold side might still be 20c lower than that of the hot but the hot side may now be 80c instead of 60. Resulting in the same performance. But with a significant increase in cost

Another reason why people dont Air cool TEC's other than the above is the possible benefits of having a TEC is relatively low if not worse when compared to a normal water cooled system. A normal water cooled system also has a lower running cost and you dont have to worry about condensation.

However you certainly can air cool a modern overclocked quad while reducing its temps if you use a big enough TEC and heat sink.

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Q. Can I run my TEC off my PSU?

A.
The reason why people don't recommend you use a normal PC's PSU is that a TEC will draw ALOT of current. This current will exceed the rated value of the molex connector (about 8 amps) leading to excess heating and possible fire. ALSO alot of PSU's have multiple rails and it's not advisable to connect all the rails together.

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Q. Which waterblocks are TEC-compatible?

A.
W/C Blocks designed for TEC's
50x50mm TEC's
Swiftech 6500 for

62x62mm TEC
freddys
Ultrasonic2's Block

Help me out guys the have to be CURRENTLY available though

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Q. Which power supplies are preferred when it comes to TEC-ing?

A.
Meanwell's are pretty much the only way to go. They also have a voltage adjustment of about 10% which is good for getting the right voltage. The correct voltage for your TEC will depend on many factors.

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Q. Where can I get TEC related supplies? (condensation-proofing, TEC's, etc.)

A.
Frozen CPU
Swiftech

Help me out guys

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Q. What is a TEC

A.
T hermal Electric Cooling
I wont go into how it works as the Wicki page is pretty good on that
http://en.wikipedia.org/wiki/Thermo-electric_cooler
http://en.wikipedia.org/wiki/Peltier...Peltier_effect

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Q. How can i control the power going to a TEC

A.
The only realistic way of doing this is to PWM it (Turning the current on and off every fast like a switch). This is what the manufacturers recommend.

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Q. I want to TEC cool my PC BUT i DONT want to go below ambient to avoid condensation.

A.
If this is you then TEC's ARE NOT for you . The whole point of using TEC's is so you CAN go below ambient. If you want to stay above ambient then your possible gains over a normal W/C cooled system is very minimal and not worth the money and time involved in TECing

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Q. Do i have to insulate my Board and Block

A.
Yes
A TEC will cool your CPU far below dew point especially when the CPU is at idle. So it will generate condensation. Water and electricity isn't a good mix. Also if the block and CPU isn't covered the TEC is then trying to cool your CPU and air in your case, which reduces it's efficiency.

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Q. Can a TEC cool my load as well as Phase Change can ?

A.
Comparing a single stage TEC v A single stage Phase. The answer is NO. Phase change has a greater Delta that's not dependent on it's input voltage. So excluding size or electricity used for the moment a Phase change system should always result in lower temps.

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Q. I’ve heard that TEC’s are very inefficient is this true. And what about phase change ?

A.
To begin with the Term “Efficient” is NOT the correct term to use when comparing the amount of electricity used to what It’s able to move. As this can exceed 100% by a long way. When talking about moving heat we use the term C.O.P (Coefficient of Performance)

The C.O.P number is ascertained by taking the Qc (Which may NOT be QMax) and dividing it by the input power. Higher the number equals higher the “Efficiency”

Now there is NO blanket rule to whether or not a TEC is “Efficient” (high COP). This is the case because the COP of a TEC changes depending on the input power relative to it’s max. As you increase the input power the COP is reduced (Less efficient).

If we compare the COP of common phase change systems to a TEC system including pumps and fans. The COP can be very similar PROVIDING you have a relatively low input power relative to the max of the TEC. However to achieve a TEC system with such high COP you’ll need to use many under voted TEC’s. Making the unit far to large to direct die cool your PC. You’ll have to make a water chillier for that kind of COP. A Single TEC direct die cooling a PC will require a high input power relative to it’s max giving it a comparably MUCH lower COP than phase change.

For a 360Qmax TEC running at 100% of Umax it would have a COP of about 0.6 (360Q/600)
For a 360Qmax TEC running at 50% of Umax it would have a COP of about 2.3 (269Q/114)



This graph shows you the relation ship between input power and watts moved in Q (orange) and Electricity used (purple) and total watts your cooling system will be cooling.
As long as the orange line is above the purple one the TEC has a COP greater than 1


NOTE: As you decrease the input power relative to the Max of the TEC, the maximum achievable delta is also decreased. So if you have a phase change and TEC system running at the SAME COP the phase change system will always result in lower temps because the phase change unit will have a far greater delta.



This graph shows you the relationship between input voltage V delta

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Q. I have a cooler with a TEC that draws 75watts of power so it’s Qmax or Pmax is 75watts right ?

A.
You can NOT make this deduction since you have no idea what the input power is relative to its un- known max. Theoretically the TEC could have a Qmax or Pmax greater or smaller than 75watts.

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TEC's in Parallel or Series ( stacking, Cascade )
(The physical placement of the TEC's NOT their electrical wiring configuration)

Parallel TEC's is when you have two or more TECs that are placed NEXT to each other

TEC's in Parallel are used to increases the Q but keep the deltas the same

If one TEC has a Qmax of 360watts and a Delta of 69c then two in parallel will result in a combined total of their Qmax so 360 + 360 = 720watts of Q . Their delta will stay the same of 69c. The delta is not added together.


Series TEC's is when you mount one TEC on top of the other. So you have your load then the cold side of TEC1(lower TEC). Then you mount the cold side of TEC 2 (upper TEC) to the hot side of TEC 1. You then cool all of the below TEC's by cooling the hot side of TEC 2 with your water block.

TEC's in series is used to increase the Delta But the Q is significantly reduced.

The delta is increased in a series config because you have one TEC cooling the other.

If your hot side is 20c and you have only ONE TEC then in a best case scenario your cold side will be 69c below it or -49. Now it doesn't matter if you have one or a thousand TEC's in PARALLEL the cold sides will still be -49c

In an overly simplelestic example if you had 2 TECs, one cooling the other then the upper TEC would cool the lower TEC's HOT side to -49c . Then the lower TEC would cool your load from its hot side temp of -49 to a cold side temp of -118c

Now the reality is you don't get a delta of 138 (69+69), if you were to try the above for 2 reasons

1 As you decrease the hot side of the lower TEC it's maximum Delta and Q is reduced.

2 The max delta (dTmax) is achieved when NO load is applied to the cold side of a TEC . In a Series config the upper TEC is ALWAYS under load because it's having to move the heat from the lower TEC which is ATLEATS the electrical wattage applied to the lower TEC. (explained more below ) This load then reduces the maximum achievable delta and a Q


The BIG disadvantage of stacking TEC's is that the Q is reduced in the process

With ONE TEC or TEC's in PARALLEL all of their rated Q is available to move heat. If a TEC has a Qmax of 360 then this TEC is able to move 360 watts of heat from one side to the other to a Delta of 0. (like it should)

However this is not the case in a Series config. This is because the upper TEC has to not only move the load applied to the bottom TEC but ALSO any electricity that the LOWER TEC uses.

An example of how important this factor is follows. If we used 2 360Qmax TECs and ran them at the Umax (full power) the lower TEC would be able to move 360watts while converting 746watts of electricity to heat. Now the combined total is 1106watts. This load then gets passed to our upper TEC to be moved. Now since the upper TEC can ONLY move 360 watts we have a VERY large problem.. actually the above is impossible.

SO to get it to work you have to reduce the voltage applied to the lower TEC so it's not converting 746 watts of electricity to heat. If we reduced the lower TEC's input voltage to say 32% of Umax to increase its COP it would now be only converting 47watts to heat for the upper TEC to cooler . However by reducing the input voltage to the lower TEC you have also decreased it's delta and Q .. so the lower TEC can now only move a maximum of 199 watts of Q. Unfortunately 200watts of Q isn't enough to cooler a modern over clocked CPU.


Stacking can work with larger loads, but only with a combined parallel series stack. You use the Series stack to increase the Delta you then have multiple stacks in parallel to increase the Q. Such a cooler would require a lot of TEC's and space so Direct die cooling a CPU is out of the question leaving a water to water chiller the only option. Such a chiller has never been built to my knowledge

Now for some practical examples of Single, Parallel and Series Configs . I will presume we are able to keep the hottest side of the TEC's at 27c (though this is possibly unrealistic)


load of 240 watts ( OC'd i7)

One 360watts of Q TEC running at 100% of Umax would = a cold side of about 4c. It would be using about 700 watts of electricity

One 360watts of Q TEC running at 52% of Umax would = a cold side of about 19c. It would be using about 200 watts of electricity


Two PARALLEL 360watts of Q TECs running at 100% of Umax would = a cold side of about -19c. It would be using about 1300 watts of electricity

Two PARALLEL 360watts of Q TECs running at 52% of Umax would = a cold side of about -4c. It would be using about 340 watts of electricity


Two SERIES 360watts of Q TECs running at 100% of Umax. This config would be unable to cool a load of 240 because the Upper TEC would be unable to cool the 1040watts (240 CPU load + Electricity used by the lower TEC 700) being applied to it

Two SERIES 360watts of Q TECs running at 52% of Umax. This config would be unable to cool a load of 240 because the Upper TEC would be unable to cool the 440watts being applied to it


Now i know there will be some saying but i dont have a OC'd i7 using 240watts i only have a 60watt CPU. Well it might be 60 watts stock but really unless your planning to over clocking it there's no point in TEC cooling it let alone a series stack. So it will far exceeding the 60 watts. However i will proceed with our unrealistic 60 watts


load of 60 watts ( OC'd 286)

One 360watts of Q TEC running at 100% of Umax would = a cold side of about -31c. It would be using about 623 watts of electricity

One 360watts of Q TEC running at 52% of Umax would = a cold side of about -15c. It would be using about 152 watts of electricity


Two PARALLEL 360watts of Q TECs running at 100% of Umax would = a cold side of about -36c. It would be using about 1231 watts of electricity

Two PARALLEL 360watts of Q TECs running at 52% of Umax would = a cold side of about -21c. It would be using about 294 watts of electricity


Two SERIES 360watts of Q TECs running at 100% of Umax. This config would be unable to cool a load of 240 because the Upper TEC would be unable to cool the 683watts (60 CPU load + Electricity used by the lower TEC 623) being applied to it


Two SERIES 360watts of Q TECs running at 52% of Umax Now this works just

The lower Level would be able to move the 60watt load to a delta of 43c while using 153 watts of electricity. (Q of 282)

The upper level would just be able to move the lower levels load of 212 (60 +153) to a delta of 14c while using 192 watts of electricity
So the delta is now -57c (43+14) and the load is now -30, while consuming 345watts of electricity. (these numbers are NOT hot side adjusted ( the lower TEC's hot side is less than 27c so it's delta and Q are reduced ,so it would use slightly less power and the total delta would be reduced a bit)


Two SERIES 360watts of Q TECs. The lower TEC running at 52% of Umax and the upper TEC running at 100% of Umax
The lower Level would be able to move the 60watt load to a delta of 43c. While using 152watts of electricity (Q of 282)
The upper level would be able to move the lower levels load of 212 (60 +153) to a delta of 25.6c while using 690watts of electricity (Q is 360)
The total delta is now 26 + 43 = 69 so our load is now -42c while using a total of 843watt of electricity (This is unadjusted as stated above)

With adjusted numbers the lower level TEC will have a delta of 38c not 43 so the combined total is 64 or a load temp of -37c


Now some of you more experienced guys will of course know you generally stack TEC's with different Qmax's which im not going to cover for now


If you are intending on making Series Parallel water chiller please ensure you have a heat spreader between the 2 levels IF you use different TEC's for the lower and upper levels. That includes TEC's with the same physical dimensions but have a different number of couples.

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Where can i get a TEC calculator app to do all the math for me ?

A.
You can get the one i wrote from here
http://www.overclock.net/peltiers-tec/249758-ultrasonic2s-tec-calculator.html
Now this app doesn't account for a change in Umax when the hot side temp is increase so it's most accurate left at 27c
This app doesn't let you add your own TEC's to it because then people would add all these dodge E-bay TEC's in there that are rated at Pmax or have 50c hot side temps. making the app useless