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[GUIDE] What Size Peltier Do I Need?

8K views 23 replies 9 participants last post by  Skyl3r 
#1 · (Edited)
How To Size Your Peltier


This will be a walk through on a couple of key points involved with picking out a peltier. In this guide, I hope to provide easy to follow formulas, useful links and helpful suggestions. The guide will be broken up into the following topics:


Index:
  1. Vocabulary Reference
  2. Peltier Naming Convention
  3. Identifying eBay Peltiers
  4. How much cooling do I need?
  5. What Are Possible Configurations For Peltiers?
  6. How much power will it take to provide that cooling?
  7. How much heat will that create?
  8. TL;DR



Vocabulary Reference
Warning: Spoiler!I realize I used a lot of words sort of assuming the reader would already know what they meant, so here we will define these words so there's a quick reference when you stumble across something that's not making sense.


  • dT - delta Temperature. This is a general term to mean difference in temperature; but when referring to peltiers, it means the difference between the hot side and the cold side of the peltier
  • Multistage - Used to refer to a cooling setup which uses one means of cooling to handle the heat load generated from another means of cooling. IE. One peltier cooling another to achieve a lower temperature
  • Qc - Stands for Watts of Cooling. This is how much watts a peltier can cool while maintaining at least a delta temperature of 0c
  • Qw - Stands for Watts of Work. This is how much heat in watts a peltier will use in order to achieve a specific Qc
  • Stage - Refers to a single layer of cooling in a multistage setup.



Peltier Naming Convention
If you've gone on eBay and searched "peltiers" you've probably stumbled across something like "TEC1-12715" or "TEC1-12730". This name is an indicator of how the peltier is constructed and how it's rated. Let's break it down nice and simple like.

TEC1-12715


TEC:
TEC stands for "Thermo Electric Cooler". It is synonymous with "peltier".

1:
The 1 following TEC is the amount of stages this individual peltier contains. In cooling computers, you will almost never see someone using a 2+ stage TEC. They typically can not provide the cooling power necessary for CPU's and GPU's.

127:
Bare with me here - 127 is the number of thermocouples in the peltier. The two numbers you'll see most often in the computer cooling rings are 127 and 199, but there are certainly individuals using more and less. Generally speaking, the more thermocouples, the more potential cooling capacity or the more efficient cooling capacity a peltier could have. This is application specific, but for max cooling power, higher thermocouple counts tend to be desirable.

15
15 is the amount of amps the peltier will draw in order to achieve it's max cooling capacity (Qmax) (please see the next section for more on ebay peltiers).



Identifying eBay Peltiers
If you've gone on ebay and searched for powerful peltiers you probably have stumbled across something like the following:

On face value, that would seem to be a good choice... right? 400w is plenty?

No!

Let's take a closer look at why. The peltier is 26a peltier (TEC1-12726 tells us this), and it is being advertised as 12v. So at 12v, it should draw 26a to achieve its maximum cooling capacity. Multiply 26a by 12v to find that this peltier will be drawing 312w at QMax. If the ebay ad were to be telling the truth, then this peltier would be cooling 400w while drawing 312w. This would be the best peltier in existence


Unfortunately, it's not the best peltier in existence. A good way to find closer to accurate ratings is to go to http://customthermoelectric.com/tecs_Qcmax.html .
Search the list available on that page for a peltier with the same amp rating and thermocouples. I've found it under the name 12711-5P31-26CW

On this page you can see that at 14v this peltier's true rating 245w. In otherwords, this peltier is drawing 52w more and cooling 155w less than the peltier from ebay advertised. Do not trust the numbers eBay sellers provide. They typically use various "tricks" to make the peltier appear to be stronger than it is. They'll do things like show power consumption at it's most inefficient point and make it appear to be the cooling capacity.



How Much Cooling Do I Need?
A common misconception when looking for a peltier is assuming that if your CPU puts of 200w of heat, you need a peltier rated to cool 200w.
From the example provided in the Identifying Ebay Peltiers section, you can click the PDF link on the TEC 12711-5P31-26CW and view the TECs information spreadsheet. http://customthermoelectric.com/tecs/pdf/12711-5P31-26CW_spec_sht.pdf

You will find two graphs there. Qc Vs Amps and Volts Vs Amps. Using the Volts Vs Amps chart, you can find the voltage you will be running at (12v is common) and trace over to find the range of power consumption for your peltier. I've illustrated this below:



Once you've determined your high and low amp draw (more on this later), you can examine the other graph to determine how much the peltier can cool. Based on your expected load, you can find the shaded region that your load falls within to determine the expected delta T. This Delta T is the difference between the hot side and the cold side of your peltier. So 0c means the hot side and the cold side are exactly the same. 10c Means the cold side is 10c colder, etc.




What Are Possible Configurations For Peltiers?
There are two common configurations for peltier cooling setups. They are referred to as direct die and a chiller. Below you can find details on these setups and pros and cons in order to help you figure out what you would like to do.

Direct Die

A direct die setup involves having a peltier in direct contact with your processor or heat source. This setup has the benefits of being simple, (potentially) cost effective and efficient. It is efficient because it reduces the amount of times heat is transferred on the cold side of the peltier. This limits how much extra heat could be added from the surroundings and loss in performance due to thermal resistance during heat transfer.

Chillers

A chiller is a system in which chilled liquid is run through a waterblock ontop of your processor or heat source. This liquid carries the heat to a separate system where peltiers will pump the heat out of it. Typically, this will involve a "cold side loop" and a "hot side loop".

The hot side loop will be a watercooling setup that cools the hot side of the peltiers. This can be done with air coolers, which can be more cost effective, but watercooling is more efficient.

The cold side loop is the liquid loop that is in contact with the cold side of the peltiers. Waterblocks will be placed on the cold side of the peltiers. These waterblocks will transfer heat out of the liquid passing through them and allow it to be pumped out of the hot side of the peltiers.

The benefits of chillers are that you can typically achieve a much great Qmax - that is, you can likely cool a much larger amount of heat. This is because you are not constrained to the limits of a single peltier.


Parallel vs Series Configurations

There are two possible configurations of peltiers. Parallel and Series. In a parallel configuration, peltiers are run so that all of the cold sides of the peltiers are on the same loop. A series configuration has the cold side of one peltier cooling the hot side of another peltier.

In a parallel system, the Qmax, or potential heat pumping capability, of all the peltiers are added together. This setup is good for cooling a large amount of heat.

In a series (or multi-stage) system, the delta temperature of the peltiers are added together (keep reading). This is good for cooling a small and targeted heat source much colder than a parallel system can. Please remember though that a peltiers are not efficient and heat is created while the peltier effect takes place. What this means is that in reality, you can not achieve a temperature difference of both peltier's dT added together.



How Much Power Will It Take To Provide That Cooling?
An often overlooked but crucial consideration when using peltiers is efficiency. For instance, a peltier that will cool 245w and draw 364w to do it will have a total heat load of 609w (245w + 364w). That means the hotside of this peltier will be emitting 609w of heat. That's a lot!

To determine how efficient a peltier is, we have a term called the "coefficient of performance" or COP for short. The coefficient of performance is Qc/Qw or the ratio of watts of cooling to the watts of work. The watts of work is how much power the peltier draws in order to achieve its cooling effect. So the higher the COP value, the more efficient the peltier is performing. Below you can see a standard COP chart for a peltier.



What you should take away from this chart are the two following points:
  1. As you increase voltage towards Vmax (voltage required to achieve Qmax) the efficiency tends to go down.
  2. Peltiers tend to be less efficient as the delta temperature between the hot side and the cold side increases
So in order to decrease that 609w number, you should try to use peltiers within their more efficient range of operation. To do this, you can either use one large peltier at a voltage much lower than its Vmax or you can use multiple smaller peltiers in parallel.



How Much Heat Will That Create?
A problem that a lot of first time peltier users run into is they simply can't cool the hot side of their peltier. Consider for a moment that a 360mm radiator might be able to cool your CPU and GPU so that your GPU peaks at 35c and your CPU peaks at 60c. Your radiator isn't cooling very much! When you add peltiers to that loop, you are more than doubling the heat output. And remember! The peltier only will maintain a delta temperature. So lets say your peltier has the cooling capacity to maintain a dT of 20c on load. You're cooling the hotside of your peltier to 60c. Your peltiers cold side will only be 40c and you will have thermal performance loss due to conductivity resulting in your CPU running higher than 40c. In other words, if you can't cool your peltier to near ambient temps, you're probably better off not even using it.

The formula for determining the hot side heat load of the peltier is:
Th = CPUw + V * A

Th = Total Heat load
CPUw = The wattage the cpu is using in heat
V = The voltage you are running the peltier at
A = The amp draw of this peltier at that voltage. You can use the COP chart to find this value or meter it.



TL;DR
Of course this is a lot of words and not everyone will read all of it. This section will give you the 10,000ft view. Below are the important considerations when choosing and speccing out peltiers:
  1. How much heat will your processor put off? Can your peltier cool it to a reasonable temperature?
    (A rule of thumb that seems to work well for me is take your CPU's heat output and multiply it by 4.
    Use that number to search for the Qmax of peltiers. If your CPU puts off 100w of heat, look for a setup that gives you a combined 400w Qmax of cooling)
  2. How much heat will the hot side of your peltier put off? Can your cooling setup keep it at ambient?
    Remember that it will take multiple radiators to keep 400w+ of heat at ambient.
  3. How will you power the peltier? Peltiers draw a lot of power. It may not be safe to power it via a molex.
    How will you power your peltier? Switching power supplies are good place to begin searching
  4. How will you control power delivery to your peltier? If you plan to keep your coolant temperature above dew point to avoid condensation, you will need a way to quickly control the peltier to avoid any failures.




Contributing:

That's all I have time for right now. If anyone would like to write sections to be added here; please just write it, post it and I will update this post with your added information and your name.
 
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6
#3 ·
Quote:
Originally Posted by Puck View Post

Great post! Answers a lot of questions we typically get in the TEC forum
smile.gif
.
Thanks Puck!
If you have any suggestions or would like to add anything, feel free. I'd like to gather a good amount of information here to help new or would be peltier users get started.
 
#5 ·
Quote:
Originally Posted by Master Chicken View Post

Nice. Great place for people to start looking.
Thanks! If you've got anything you'd like to add or change, just let me know
biggrin.gif
 
#7 ·
Quote:
Originally Posted by Master Chicken View Post

I'll have to read through it several times and then see if I can find something. You've got a lot covered in there. Maybe a section on direct die vs. chiller setups or something ... the common configs. or something.
Ah yeah good point. I'll look into writing something up for that.
I'll go through it a few more times. I'm not completely happy with the How Much Cooling Do I Need? section.

EDIT:
Okay, I added a new section called "What Are Possible Configurations For Peltiers?" to go over that.
 
#8 ·
One thing that always thought important but might be too detailed is the difference in ratings with the hot side at 27 vs 50 on some manufacturers charts. TN gives both which is nice and I usually interpolate to the middle since our hot side water temps are likely to hang in the mid to upper 30's. Obviously the TEC looks better (more throughput) at the higher hot side and I think some sellers show that chart while people assume they are looking at the 27 degree chart.
 
#9 ·
that is pretty straight forward, I like it, I think that it will be of help to a lot of people, that are looking into TEC cooling.
 
#10 ·
Quote:
Originally Posted by Master Chicken View Post

One thing that always thought important but might be too detailed is the difference in ratings with the hot side at 27 vs 50 on some manufacturers charts. TN gives both which is nice and I usually interpolate to the middle since our hot side water temps are likely to hang in the mid to upper 30's. Obviously the TEC looks better (more throughput) at the higher hot side and I think some sellers show that chart while people assume they are looking at the 27 degree chart.
Yeah this is a good point. Maybe I'll add this to the eBay TEC section. I've mostly only seen eBay TECs being sold without this information.

Quote:
Originally Posted by toolmaker03 View Post

that is pretty straight forward, I like it, I think that it will be of help to a lot of people, that are looking into TEC cooling.
I hope so
smile.gif
After answering the same questions a few times I figured it would be helpful to put together a community driven information page.
 
#13 ·
Quote:
Originally Posted by LiamG6 View Post

nice work!
Thanks LiamG6!

If you've got anything you'd like to add/change, please feel free to contribute. I'm really hoping to get a good starting point for new peltier users going here.
 
#15 ·
Quote:
Originally Posted by kgtiger View Post

Excellent work Sky13r
thumb.gif

It can't of been to may words as I read it to the end
rolleyes.gif

Thanks for spending the time in putting this all togeter, I do appreciate it and it was helpful.
Glad to hear, and thanks for the kind words
biggrin.gif

As always, let me know if there's anything that can be improved so I can continue making this a better resource.
 
#16 ·
Thank you for the great post! I am new to Peltier cooling and plan to build one myself in the near future. I do still have some questions though:

1.How do you determine your high and low amp draw?

2. How do you determine what your Delta T will be? Everything seems to be measured in Watts, excerpted for the delta T, so how do you calculate it?

3. Is there a way to cool a GPU using a TEC via direct die like a cpu?

Thanks!
 
#17 ·
Quote:
Originally Posted by DragonArmy124 View Post

Thank you for the great post! I am new to Peltier cooling and plan to build one myself in the near future. I do still have some questions though:

1.How do you determine your high and low amp draw?

2. How do you determine what your Delta T will be? Everything seems to be measured in Watts, excerpted for the delta T, so how do you calculate it?

3. Is there a way to cool a GPU using a TEC via direct die like a cpu?

Thanks!
Hi! Welcome to the forums and hopefully before too long we'll be welcoming you to the TEC club
thumb.gif


1. Amp draw on the TECs is based on a couple factors:
  • Voltage
  • delta temperature
  • TEC temperature
The voltage is a factor you control. That's how much voltage you're sending to the TEC. A lot of people run their TECs somewhere from 10v to 12v. You can find a list of datasheets for TECs here where you can get information on amp draw: http://customthermoelectric.com/tecs_imax.html
For instance, if you look at the 400w Qmax TEC here http://customthermoelectric.com/tecs/pdf/19911-5M31-28CZ_spec_sht.pdf
Look at the Volts vs Amps chart. Let's say you're gonna give it 12v. Find 12v on the chart and trace over until you hit the first line:

It's the green line. So if you look at the legend, you see that represents a delta temperature of 60c. That means your amp draw is something like 11a at 60c dT. If you continue tracing over, you can find the amp draw at 50c, 40c, etc. until you reach 0c.

Now, I mentioned TEC temperature too. At the top right of the graph it says: 27c = Th. That means this is the graph of performance when the hot side of the TEC is 27c.

2. Once you find your amp draw, you can use that on the other chart Qc Vs Amps. Qc is watts of cooling. This tells you what delta temperature the TEC can maintain with a heat lead on the cold side.

3. It's difficult to direct die cool a GPU because of physical space constraints. The problem is that if you want a TEC that can cool 100w+ to a reasonably cold temperature, you're looking at TECs that are mostly 62x62mm Which is bigger than the GPU die and likely to not be able to fit against the GPU die due to other components on the GPU.
 
#18 ·
So if the voltage is the only thing I can control,

1. How do I know what the hot side of the TEC will be in practical use?

2. If I can only control voltage, and cannot control amp levels, how do I know what my DT will be?

3. If you look at this graph: http://www.thermonamic.com/TEC1-19940-English.PDF, how do I determine the amp and DT?

4. I have seen people in other forums post pictures of peltier cpu blocks that use 2-4 TEC blocks, but when searching online I could only find blocks that use 1 TEC block. Where do you find those multi TEC blocks?

5. Would something like this be able to cool a GPU if 62 x 62 TEC is too large? http://www.thermonamic.com/TEC1-28722-English.pdf or http://www.thermonamic.com/TEC1-19916-English.PDF

Sorry for all the noob questions, I just want to be careful and make sure that I do not destroy any of my parts in the process. Thx!
 
#19 ·
Quote:
Originally Posted by DragonArmy124 View Post

So if the voltage is the only thing I can control,

1. How do I know what the hot side of the TEC will be in practical use?

2. If I can only control voltage, and cannot control amp levels, how do I know what my DT will be?

3. If you look at this graph: http://www.thermonamic.com/TEC1-19940-English.PDF, how do I determine the amp and DT?

4. I have seen people in other forums post pictures of peltier cpu blocks that use 2-4 TEC blocks, but when searching online I could only find blocks that use 1 TEC block. Where do you find those multi TEC blocks?

5. Would something like this be able to cool a GPU if 62 x 62 TEC is too large? http://www.thermonamic.com/TEC1-28722-English.pdf or http://www.thermonamic.com/TEC1-19916-English.PDF

Sorry for all the noob questions, I just want to be careful and make sure that I do not destroy any of my parts in the process. Thx!
with proper cooling the hot side of the TEC will be in the 50C range. the 28722 is a 36 volt TEC a good air cooler could handle that TEC in a water chiller setup up to about half voltage. anything above that would require water cooling, in my opinion. same thing could be said for most TEC's.

at half voltage you will get about 40C DT, the DT goes up from there as you add voltage to the TEC.

ultrasonic2 makes a multi TEC block. or you could make your own.



I am not going to commit on the direct die to the GPU, as I really would suggest against doing that.
 
#20 ·
No time to read now but I'm subbing, thanks for sharing.
 
#21 ·
Hi Skyl3r!

Great job on the documentation!

Question about direct connection of a Peltier to a CPU: Can you place a 60 x 60 mm peltier directly onto a 40x40mm CPU and get the full cooling capacity of the peltier, or would a 60x60mm heat spreader be needed between the CPU and the peltier to take full advantage of the peltier cooling capacity? I understand the potential risk of condensation/icing on the 10mm overhang; just wanted to know if the surface of the larger peltier is good enough to cool the smaller surface of the CPU without having to add a heat spreader.

Hope my question is clear! Please let me know otherwise.

Thanks!
 
#22 ·
Thank you!

This sounds like another item that should be included in the write up :)

Yes, you will lose cooling capacity. The thermocouples that produce the peltier effect are relatively evenly distributed throughout the entirety of the peltier. You can see the picture below for an example:

How much cooling capacity depends on the thermal conductivity of the materials the peltier is made of, and honestly I can't tell you how much that is.
Doing the quick math, 40x40mm is 1600sq mm, and 60x60 is 3600sq mm, so about only 44% of the peltier will be in contact with the CPU. I would guess you will lose a lot of cooling capacity due to inefficiencies in thermal conductivity.

What most people recommend is to use a heat spreader in between the CPU and peltier. You can find some neat and crazy examples here: http://www.overclock.net/forum/62-peltiers-tec/1218698-list-awesome-projects-tec-cooling.html

Also another point to mention even though you didn't specifically ask, you want to make sure the entire hot side of the peltier is cooled as well! There's been numerous reports of people using slightly too small heatsinks/waterblocks and killing their peltiers.


Hope you stick around for a while and add some more life to the peltier section :)
 
#23 ·
Hi Skyl3r!

Thanks for the details and confirmation of needing a heat spreader. I am going to assume a sheet of aluminum or copper will suffice, with sufficient thermal paste in between.

In an attempt to contribute, I did look up what ceramic material is being used on the popular TEC1-12706. It is Alumina (Al2O3), which as first I saw it has aluminum, so I thought I might not need a heat spreader. But then after doing some digging, found it has a thermal conductivity much less then aluminum or copper.

After studying the stack up of the peltier, I wonder if the ceramic layer could be replace with a equal sized piece of aluminum, with a very thin layer of an insulator (spray paint??)on the side that will touch the P and N material. This would be an attempt at increasing the thermal conductivity of the hot and cold side of the peltier. However, in the end, it may not be worth the hassle. Or someone may have already tried it and I have run across it yet.

Thanks for the link on previous projects. I have already poked around on some of the designs, including yours! If I ever decide to do something like this for real, I will need to study past projects to try and avoid repeating old mistakes. I am good enough making new mistakes on my own! :)

Thanks for your time!
 
#24 ·
Thanks! I'll definitely include that in the first post. That's very useful to know. When I was responding to you earlier I googled a little bit and couldn't find what material it was.
For Gee Wiz sake, I threw em on a bar chart to kinda visualize how bad it actually is compared to copper and aluminum.

I'm not sure what it would take to remove the alumina and replace it with something like aluminum. I'm also not sure why it hasn't been done, but I can only assume that there's probably a reason. In the past I've emailed Custom Thermo Electric to try to get answers like this, they've been pretty responsive, so I might try them again.


My experience has been there's a lot of misinformation out there. Someone will find something doesn't work and guess what the cause was wrong and that tidbit of misinformation just gets passed along until it becomes practically canonical.
My goal with these sorts of posts is to find good solid scientific reasons for why things do or don't work so that when anyone wants to try peltier cooling in the future, we have a collection of everyone's inputs on the matter.
 
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