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:
Vocabulary Reference
Peltier Naming Convention
Identifying eBay Peltiers
How Much Cooling Do I Need?
What Are Possible Configurations For Peltiers?
How Much Power Will It Take To Provide That Cooling?
How Much Heat Will That Create?
TL;DR
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.
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:
- Vocabulary Reference
- Peltier Naming Convention
- Identifying eBay Peltiers
- How much cooling do I need?
- What Are Possible Configurations For Peltiers?
- How much power will it take to provide that cooling?
- How much heat will that create?
- 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).
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.
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.
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.
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:
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:
- As you increase voltage towards Vmax (voltage required to achieve Qmax) the efficiency tends to go down.
- Peltiers tend to be less efficient as the delta temperature between the hot side and the cold side increases
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.
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:
- 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) - 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. - 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 - 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.