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Eric's Ultimate Guide to TECs

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Old 07-02-04, 03:11 PM Thread Starter   #1
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Post Eric's Ultimate Guide to TECs


Everything You Wanted to Know About TECs: but were too afraid to ask.
--------------------------------------------
This guide was written for those who are already familiar with the basics of air and possibly water cooling and are looking to integrate TECs into their cooling system. I take full responsibly for everything in this guide and if you can find me you can sue me.


-Prerequisites: Whatt is a Watt? -

Watt (in terms of electricity) = Current * Energy (Amps * Volts = Watt)
Watt (in terms of heat) = Energy/Time (Joule per second); 4.18Joules = 1 Calorie; 1 Calorie is the energy required to raise 1gram (or 1cc) of water by 1C.

- Appreciating the Watt in terms of heat -

A heat source radiating 60-watts radiates 60-Joules per second. It would take the typical processor (generating 60-watts) 1 hour and 54 minutes to bring 1 liter of water at 1C to the boiling point (100C). Whereas a heat source generating 70watts would only take 36minutes. Thatís a 2 liter coke bottle of water near freezing to boiling in 73minutes!


- TEC? -

When a low voltage DC current is applied to a thermoelectric module, heat can be moved through the TEC from one side to the other. One side is therefore cooled [cold-side] while the opposite side is simultaneously heated [hot-side]. The temperature differences can be upwards 50C in real world application. TECs help enhance your cooling ability by creating a temperature differential that can be more easily moved out of the system. Water-cooling systems can only cool an object to ambient temperatures (room temp), but they still have excess cooling capacity (provided they have sufficient flow-rate and a capable radiator). TECs allow more of the cooling capacity to be utilized and therefore achieve lesser-than-ambient temperatures.


- Playing with Ratings -

TECs have two basic ratings that determine overall cooling ability. Itís maximum temperature difference (in degrees C) and itís maximum cooling capacity (in watts).

Maximum Temperature Difference (degrees C)
TECs work by creating a temperature difference between the cold-side and hot-side. The maximum temperature difference lets you know how many degrees C that difference can be under Ďperfect theoreticalí conditions.

Maximum Cooling Capacity (watts)
The maximum cooling capacity lets you know how close to the TECís maximum temperature difference, at a given heat load, the TEC can achieve.

-) Many 40-watt TECs can achieve a maximum temperature difference of 69C.
-) Many 226-watt TECs can also achieve only a maximum temperature difference of 69C.
-) This leads some to speculate that a 40-watt TEC is more efficient than a 226watt TEC with both having the same maximum temperature difference. This is not the case.
-) The maximum temperature difference can ONLY be achieved under a theoretical setting in which the heat load (what the TEC is trying to cool) is zero. This never happens.
-) The higher the number of watts the TEC is rated for Ė the higher percentage(%) of the theoretical maximum temperature difference (69C) it can achieve per increase in heat load. That percentage of the theoretical temperature difference is called Delta T. Time to illustrate the point by using a little friendly mathÖ

- The Formula to Determine the Delta T (bet you wished you had paid attention in algebra) -

Delta T = (1 - (Heat Load/Max Cooling Power)) * Max Temp Difference

*) Delta T = The actual difference in temperature between the hot-side and the cold-side that you should experience in the real world.
*) Heat Load = The heat generated (in this case) by the processor measured in watts.
*) Max Cooling Power = Maximum TEC rating in watts. (e.g. a 221-watt TEC or a 80-watt TEC)
*) Max temp = TECís maximum temperature rating in degrees C (theoretical Delta T, a.k.a. Delta T max).


- So Show Me -

Here are a few examples with difference watt TECs cooling a modern processor which usually generate around 60+ watts of heat. Practice the formula on at least one of these examples before calculating Delta T for your own project!

*) A 40watt TEC cooling a modern processor generating 60-watts of heat.
Delta T = -34C (negative 34C). Thatís an INCREASE in temperature on the cold side, so the processor would have been warmer than before! Using an under powered TEC can destroy the processor. Cooking your CPU with your TEC is NOT a good thing, avoid this common mistake.

*) A 60-watt TEC cooling a modern processor generating 60-watts of heat.
Delta T = 0 (no change in temp). Congratulations, youíve accomplished nothing!

*) A 176-watt TEC cooling a modern processor generating 60-watts of heat.
Delta T = 46C. Thatís a decrease in temperature on the cold side, making the cold-side 46C cooler than the hot-side. Not bad.

*) A 226-watt TEC cooling a modern processor generating 60-watts of heat.
Delta T = 51C. Thatís a decrease in temperature on the cold-side, making the cold-side 50C colder than the warm-side. Even better, but it took a lot more energy from the TEC (28% increase from 176-watt TEC) to get an additional 5C (only 11% increase in Delta T).

Conclusions from the Examples
The larger the wattage of the TEC in proportion to the watts of heat generated by the heat load (CPU) the closer delta T approaches the theoretical limit of 69C. But, the closer you get to the theoretical limit (in this case 69C) the more and more watts it takes for the TEC to achieve it. Thus the less efficient it becomes. Fortunately itís not like TECs were the kings of efficiency to begin with.


-Use the Formula Ė

There are various resources where you can find the thermal properties of various processors (e.g. the amount of heat they generate in watts). Click here to find out how many watts of heat your CPU will generate at both stock and overclocked speeds!. You can also check the documentation online at AMD or Intel for your specific CPUís heat output and itís maximum safe operating temperatures.



-Dangers to be Avoided (stuff you donít wanna do) Ė

The biggest danger is attaching a TEC that is underpowered; many have cooked their brand new processors doing this. :cry Of course, this is easily avoided; just donít attach a TEC will less cooling power than your CPU generates. Duh.

The second best method to frying your CPU is to have an insufficient method of cooling the hot side of the TEC. The hot-side can become so hot that it begins to warm the cold side which adds to the heat load of the cold-side which adds to the hot-sideís heat and the cycle begins. Not a pretty thing. Iíll go into more detail about TEC cooling further down.



- Finding the Actual Temperature of the Cold-Side (after finding Delta T) -

As you probably can tell from the title, youíll need to have figured out the value of Delta T for your system before you can determine what the final temperature will actually be on the cold-side of the plate. Also, if you thought that Delta T IS the temperature of the cold-side then you must be very confused right now so Iíll quickly explain.

Delta T is the difference in temperature between the hot-side and the cold-side. If Delta T was 50C and the hot-side was 25C, then the cold side would be -25C (thatís negative 25C). If the hot-side were raised to 50C then the actual temperature on the cold-side would be 0C. Moving right alongÖ


- The Critical Element: Controlling the Temperature of the Hot-Side -

As we have seen from the example above, you must control the hot-sideís temperature to achieve a given temperature on the cold-side. This, however, can be more difficult than it seems.

Letís say Bob wants to cool his XP 2000+ which generates 60-watts of heat. Bob just so happens to have a ĎMagic Heatsinkí that magically cools a heat load of 60-watts to room temperature (in this case room temp is 25C, remember that). Not a bad heatsink (must be a Thermalright). So Bob figures, ďIf I attach this bad boy to the hot-side of my 226-watt TEC then I can maintain room temperature on the hot-side of 25C, then the cold-side will be -26C assuming a Delta T = 51C.Ē Bob is about to get a rude awaking.

Whatís Bobís problem? The heat load generated on the hot-side of the 226-watt TEC is not just 60-watts anymore (the original heat output of his CPU). It is the original heat output of the CPU (60-watts) plus the Cooling Power of the TEC (226-watts). 60watts+226watts = 286-watts of heat generated on the hot-side of the TEC. Thatís enough watts to heat 1 liter of water by 4.1C in one minute. See Bobís problem? Well, itís about to become yours.


THL = Heat Load + Max Cooling Power

-THL (Total Heat Load) = The heat load generated on the hot-side of the TEC in watts.
-Heat Load = The heat generated (in this case) by the processor measured in watts.
-Max Cooling Power = Maximum TEC rating in watts. (e.g. a 226-watt TEC)

So even with the TEC, your back to playing the same cooling game as you had been before. Except this time you have a few more watts of heat to deal with. Remember, you can get much better results using a TEC with good water cooling than you could with good water cooling alone.


- How to Cool the Hot-Side (the real game) -

This is where my little TEC guide becomes less specific. Beyond this point is the realm of more traditional cooling in order to cool the TEC. Itís a whole different ball game. Remember, cooling the hot-side of the TEC is as important as choosing the appropriate TEC for your heat load in order to obtain your temperature expectations.

Where did the math go?! Well, this is where things start getting theoretical too. Yes, you can determine the thermal resistance of a given water-block at a given flow rate and then determine the amount of watts you can dissipate in a given radiator at a given flow rate at a given CFM (air flow) with a given static pressure. It can be done, and I wish you much luck. Donít forget to carry the 1.

Your best bet is to find others on the forums with similar setups youíre considering and find out how theyíre performing versus your needs/expectations. If you donít have a lot to go on or are unsure, think big; big radiator, high flow rate, etc.

Air Cooled TEC? Can we say terribly inefficient? You might be able to slap a SLK-800 and 120CFM fan on the TEC and see what happens, but generally you should stick with water cooling when it comes to TECs.

- Condensation -
When using a TEC to bring temperatures down significantly below ambient temperatures, condensation becomes an issue. Condensation is the process whereby water condenses and forms on your expensive computer equipment and thus ends up costing you a small fortune when it all shorts out. Proper insulation methods are a must.

Whether or not condensation will occur depends entirely on what temperatures you achieve and what the dew point is for where you live, which by the way changes with every day, and even every hour. The dew point is the temperature at which condensation will occur for a given ambient temperature (outside temperature), pressure, and humidity. The dew point is a measurement you can find alongside your normal weather report for your area. You will want to find the normal and record dew point lows for your area (make sure to consider all four seasons). After you have taken this into account, compare the lowest temperature you will achieve on the cold-side of your TEC to the lowest dew point expected [plus any necessary room for error], and make the determination if you need insulation.

In other words: if expected low dew point exceeds the cool side of the TEC, then condensation will occur and will require proper insulation.

To give you an idea,
here's a link to show you the current dew points across the US.


- Other Important Points to Consider -

A 226-watt TECs can use up to 25-amps to run. Even if your PSU has enough current to run it, you might want to check the rail youíll be running it off of (usually 12V) to ensure it has enough current minus various other components drawing current from it. More than likely youíll need to get another power supply specifically for the TEC. Remember nothing is 100% efficient in this world so a TEC with the cooling capacity of 226-watts can pull upwards 300-watts in energy (the volts*current kind), hope youíre not on a strict electricity budget.

Yes, if you cross the charges (the red(+) and black(-) wires) on you're TEC, you will cause the TEC to operate inversely. In other words, you'll cook your CPU. So pay attention to what you're doing.

Yes, you can stack multiple TECs to for additional cooling. No, Iím not going to into that now.

Common TEC ratings: 40-watts, 80-watts, 176-watts, 226.1-watts all at maximum temperature difference of 69C.

Although Iím currently unsure of the exact heat output of GPUs are (video card processors) popular opinion states that a 80watt TEC should be sufficient.

Finally note, that just because the cold-side of your TEC is at 0C, don't think your processor's die will be as well. Essentially your touching the CPU to a freezing piece of metal so donít expect your math to give you the final temp of your processorís die.

Many TECs can not be used in ambient conditions below -40C. Generally adding a TEC to a phase-change system or using very extreme water cooling will not yield any additional benefit.


Helpful link for your calculations. - Let's you know what your heat load will be (in watts) given your specific processor, clock, and Vcore. The site also has other helpfull calculator programs. - Check it out!


Product Links:
http://www.swiftnets.com Ė Pre-built TEC and Waterblock
http://www.dangerden.com Ė Some Assembly Required



Just remember to spend plenty of time doing your homework and youíll be able to deploy a cooling system that knows no limit to Vcore increases [note: the Mobo still will soÖ]. Good Luck! :thumbup:

[Originally written 2/9/03]
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Old 07-02-04, 05:27 PM   #2
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NICE POST!

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Old 07-03-04, 01:23 AM   #3
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Old 07-03-04, 01:52 AM   #4
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nice guide, i vote sticky

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Old 07-03-04, 02:01 AM   #5
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Old 07-03-04, 02:20 AM Thread Starter   #6
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Thanks guys, I'm glad you like it.

I wrote it a little while back on EOC. If you have any questions concerning TECs just drop me a line.
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Old 07-06-04, 08:37 PM   #7
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I'm making a ambient water cooler using TEC's, I was going to order a 226 watt but then realized how many amps it would need and that it may freeze the water if the loop was going too slow.

So I'm getting a 80W ICE-71 Potted tec, one that can be seen at dangerden. It says its Vmax = 16.1 Volts, so running it at 12 is like 74.5%, Iíve read that TECs are usually run from 20%-80% maximum current and using the formula from this post I get 5.96 Amps. So I can basically run 2 of these on a basic AT/ATX PSU.

What would be great is if someone could make a post about the relations between Imax, Qmax, Vmax and Telta Tmax and any important formulas, such as calculating %efficiency at 12v, what the most efficient voltage would be, how much current it would require for a given voltage. What the optimum TEC watt rating for a given processor/heat sourse would be if it will be run at 12v, what is the Vmax, Imax, etc they should be looking for.

It has been a while for some of us since physics class and I donít really want to start reading a physics book to get the info I need. Iím sure there are more people out there that feel the same. We want the knowledge without the full effort

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Old 07-06-04, 09:58 PM Thread Starter   #8
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Quote:
Originally Posted by Bad_CEKTOP
I'm making a ambient water cooler using TEC's, I was going to order a 226 watt but then realized how many amps it would need and that it may freeze the water if the loop was going too slow.

So I'm getting a 80W ICE-71 Potted tec, one that can be seen at dangerden. It says its Vmax = 16.1 Volts, so running it at 12 is like 74.5%, Iíve read that TECs are usually run from 20%-80% maximum current and using the formula from this post I get 5.96 Amps. So I can basically run 2 of these on a basic AT/ATX PSU.

Thanks
What are you cooling with this? I hope not a CPU.

To be honest I always suggest a power supply capable of 125% of Vmax * Imax (watts) and run at as nearest to Vmax as possible. Generally people run 16v Vmax TECs off 12v rails, this is fine and you can use I = 12V/Vmax * Imax to determine actual I and simply 12v * I *1.25 = need power supply watts.

Since generally 226w pelts are what is used for CPUs, even with 12v you're still pulling 230watts and with +25%, that's 285watts PSU. Such a power requirement is generally going to need a dedicated PSU. Pulling of a ~15.2v rail (Vmax) + 125% then 365watts with a ~450 watt PSU.

They is no two ways about it, TECs are going to take some power, but generally no more than a second computer would.
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Old 07-06-04, 10:18 PM   #9
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Trying an 80 watt to see how it will effect the temps, then I'll buy a range of them if it's not enough, which I'm pretty sure it won't be. Since it's a water loop I'm cooling I can put a few in series. I don't have a spare 400-500watt PSU round for a 226w pelt yet so I'll have to come up with something when the time comes.

I would love to get a tubed cold plate if anyone knows a good place to get them other than lytron.com.
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Old 07-07-04, 06:15 AM Thread Starter   #10
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Quote:
Originally Posted by Bad_CEKTOP
Trying an 80 watt to see how it will effect the temps, then I'll buy a range of them if it's not enough, which I'm pretty sure it won't be. Since it's a water loop I'm cooling I can put a few in series. I don't have a spare 400-500watt PSU round for a 226w pelt yet so I'll have to come up with something when the time comes.

I would love to get a tubed cold plate if anyone knows a good place to get them other than lytron.com.

I wouldn't even bother with the 80w TEC, you'd be more likely to warm up your CPU than cool it down. A 176w TEC is still going to use ~270watts and need ~ 330watt PSU. You won't get away using anything less than a 176w, unless you have a XP-M generating stock 35w heat load.

Yeah, lytron stuff is hard to come by at a good price, but it's the best. I have a lytron 6320 radiator, very luck find, and keeps my water temps at ambient with a ~340watt heat load.
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Old 07-22-04, 12:42 PM   #11
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Quote:
Originally Posted by eweast
I wouldn't even bother with the 80w TEC, you'd be more likely to warm up your CPU than cool it down. A 176w TEC is still going to use ~270watts and need ~ 330watt PSU. You won't get away using anything less than a 176w, unless you have a XP-M generating stock 35w heat load.

Yeah, lytron stuff is hard to come by at a good price, but it's the best. I have a lytron 6320 radiator, very luck find, and keeps my water temps at ambient with a ~340watt heat load.
It generates more than 35w of heat stock on a desktop board...

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Old 10-07-04, 09:09 PM   #12
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Quote:
Originally Posted by eweast
- Appreciating the Watt in terms of heat -

A heat source radiating 60-watts radiates 60-Joules per second. It would take the typical processor (generating 60-watts) 1 hour and 54 minutes to bring 1 liter of water at 1C to the boiling point (100C). Whereas a heat source generating 70watts would only take 36minutes. Thatís a 2 liter coke bottle of water near freezing to boiling in 73minutes!
I know this is certainly not the most important part of the post, but my math gives me 1h55 and 1h39 times, not 1h55 and 36min.


Quote:
Conclusions from the Examples
The larger the wattage of the TEC in proportion to the watts of heat generated by the heat load (CPU) the closer delta T approaches the theoretical limit of 69C. But, the closer you get to the theoretical limit (in this case 69C) the more and more watts it takes for the TEC to achieve it. Thus the less efficient it becomes. Fortunately itís not like TECs were the kings of efficiency to begin with.
Actually TEC aren't that bad, all depends at what voltage you run them. For example, if you were to use a 170W on your gpu and run it at 12V, you'd end up with much better result than using a 80W at 12V. Both would have about the same Max HeatLoad, but the 170W will be running at a COP of 1.86, while the 80W will be running at a COP of 0.86. COP mean Coefficient Of Performance, it is basically a measure of the TEC capacity of moving heat in respect to the power it needs to do it - the higher the better.

Now, just to illustrate my point, lets do some math
running both the 80 and 170 Watter at 12V we get:

80W - 90W of heat generated by the pelt (dT = 36C)
170W - 60W of heat generated by the pelt (dT = 37C)

I calculate the dT using a theorical gpu with a heat output of 40W. So with the heat generated by the gpu and a waterblock with a c/w of 0.2 (arbitrary number, just for the example) and water temp of 25C:

80W - Qtot=130W - C/W=0.2 Tcold = (25 + 130*0.2 - 36) = 15C

170W - Qtot=100W - C/W=0.2 Tcold = (25 + 100*0.2 - 37) = 8C

The better the waterblock, the smaller the difference between the 2 solutions and vice/versa.



Quote:

THL = Heat Load + Max Cooling Power

-THL (Total Heat Load) = The heat load generated on the hot-side of the TEC in watts.
-Heat Load = The heat generated (in this case) by the processor measured in watts.
-Max Cooling Power = Maximum TEC rating in watts. (e.g. a 226-watt TEC)
A better measure of the THL will rather be:

THL = cpu heat load (or gpu) + Volts*Amp

Running a 226Watter at its max voltage rating (usually around 15V) will generate much more than 225W of heat. At 15V, the pelt would draw around 24A, that would give you a whooping 350W of heat generated by the TEC alone!!!

One last thing, I dont think I ahve read anything about cold plate, shouldn't a little something about them be included in there?
All in all, a very good post, keep up the good work!

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Old 01-08-05, 02:09 PM   #13
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1st timer please help


Hello everyone, this my first time posting and i just would like to say first that I am glad to be here and hope to learn alot from this forum.
If you look at my profile rig specs I would like to see what you would suggest on what type of tec to use and of course cooling system if it were yours. I'm cuurrently running my rig w/pressy3.4 ghz oc @ 3.7 and want to go higher [cpu@current time is 43c and case 47c with side panel off]. I dont know how to raise vcore and ram speeds with my peticular mobo. I have read a guide for ocing but was very confusing especially if you never done this before. I had a friend who built rig for me but I really want to learn on my own.

"PLEASE HELP"
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Old 02-06-05, 03:12 PM   #14
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Great thread! Just what I was looking for.

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Old 02-22-05, 04:03 AM   #15
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I must say this is an awesome thread well worthy of it's sticky!!

i have been wondering about TEC and it's probabilities...and you just knocked out 80% of my questions! Thanks for everything! :cool
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Old 02-22-05, 07:13 AM   #16
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Good sticky, but you have some math errors. Going from 60 to 70 watts is about a 16.6% change in power, this will not result in a change time from 1 hr 54 min to 36 min. It would be more like 99 min, therefore I think your 2 liter calculation is in error also. Still a good sticky.
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Old 06-06-05, 02:25 AM   #17
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Hai guys,
I'm stuck with a problem. how do u exactly fix how much the cold side temperature should be. Is it some thing which depend on the voltage(to TEC) u can support in your board or the maximum heat that u will be able to dissipate from the Hot side. For example i have a processor which has a power dissipation of 28W(Tj = 105C, Rjc= 0.1 C/W) , i have decided to use a 33W TEC, how do i fix the cold side temperature?
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Old 06-30-05, 03:50 AM   #18
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Good Post. Now an assumption i would like to see confirmed.

My chip (pentium-M 1.6) overclocked to 2.8Ghz on 1.6v will generate about 65W of heat. An 80W peltier with decent watercooling will be doing that easily.

Is that right?

*edit* a few more questions.

65 + 80 = 145. So that will be 145W of heat into my water loop?
80W + some overhead = 100. The pelt will draw about 100W, 8/9A on the 12v line. Am i right to assume that a decent PSU (450+ W and 16+ A 12v) will handle that?

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Old 07-06-05, 05:00 PM   #19
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Quote:
Originally Posted by Sjaak
Good Post. Now an assumption i would like to see confirmed.

My chip (pentium-M 1.6) overclocked to 2.8Ghz on 1.6v will generate about 65W of heat. An 80W peltier with decent watercooling will be doing that easily.

Is that right?

*edit* a few more questions.

65 + 80 = 145. So that will be 145W of heat into my water loop?
80W + some overhead = 100. The pelt will draw about 100W, 8/9A on the 12v line. Am i right to assume that a decent PSU (450+ W and 16+ A 12v) will handle that?
Yup, 80w should provide OK cooling on the dothan and 145w should be easy for a midrange water cooling setup. However I would worry about running the pelt off of your main power supply. Some people over at xs were having problems with the dothan and power hungry gfx cards. You may encounter the sam problem with the dotan and a power hungry pelt.
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Old 07-06-05, 05:05 PM   #20
Sjaak
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Quote:
Originally Posted by datura3
Yup, 80w should provide OK cooling on the dothan and 145w should be easy for a midrange water cooling setup. However I would worry about running the pelt off of your main power supply. Some people over at xs were having problems with the dothan and power hungry gfx cards. You may encounter the sam problem with the dotan and a power hungry pelt.
Then i have to choose whether to get a second medium PSU or buy a single kickass one...

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