Post Rad Chiller Concept

[Uncle Jimbo]

No, you can create a liquid delta
Its done but normally needs much larger systems, I've gotten cold side down a few degrees actually, seems to help temps when the rad can take the heat

If the goal is to achieve and maintain a low temp at the heat source (CPU, GPU, whatever you are cooling) using circulating water to move the heat, then in a steady state model, the water exiting the heat source will be at about the target temp. If that temp is close to ambient, a rad won't do much for you - all it can do is pull out heat inserted after the load (from the pump etc.) . The rad will also keep the temp from going below ambient - it transfers heat both ways. You probably want something like a car thermostat ahead of the rad - route water around it unless the temp is above ambient, to keep the rad from working against you.

That's where a post-rad chiller comes in. In order to maintain ambient or even below ambient at the heat source, you obviously need to have the input cooling water below the desired exit temp. If something close to ambient is desired, then even a degree or so is useful.

Martin's original calculation of 395 watt/seconds for 1.5GPM was actually mathematically correct, and as he later stated, the calculation also needs to take into account heat load. But the calculation went south from there...

If we are looking for max efficiency and are using any of the combinations of TECs I have discussed, we will see about 140W transfer. OC'd CPUs can put out more than that, so maybe a higher design center is needed. We can either sacrifice some efficiency, or go with more TECs. But if your average load is less than the TEC transfer, the water will gradually get colder. You can also maintain temp above a lower limit by running water through the rad - that is more simple than varying the TEC power. Another way to control cooling below the desired level is to use the hot side. If you are using air cooling, slow the fans, if you are using WC, slow the pump or shunt the cooling water. Either way, the TEC hot side gets hotter, the resistance rises, the differential rises, and less heat is transfered out. You can achieve very tight temp control with any of those methods.

It is also fairly easy to control TEC input power directly, for low current loads. Essentially running PCM via a big power MOSFET into a low pass filter so the TEC sees a relatively constant voltage.

If I were designing to cool the big heat loads in a state of the art OC'd system (CPU and GPU), I would expect an average heat load of around 250W and upwards of 400W under heavy load. To match cooling without burning power all the time, we could let the power run up if the system starts to get hot, which means using the PCM control.

Let's say we are using the 4 03178 TECs I described earlier. We run them off the 12V line, but with PCM control around output temp at the load, or at the chiller. At idle, PCM sets the TEC voltage at 5 or 6 volts, you pull 140W out, power use is low (65W or so in addition to the heat load), and you are only burning what you need to maintain temp. If the load dumps in more heat, the TEC ramps up as the PCM duty cycle increases, and with the 600W or so transfer available at 12V, I'm sure you will be able to maintain temp if you can supply the current. But 60A or so is serious power, and the PCM system would need to be big too. You'll be burning some serious power at that point though - around 1000W in - so maybe you clamp the upper end at the 50% point, which I think would be around 300W in and 300W transfer (something like 10V, 30A), and let the rad pick up the slack. Your component temp would go up some, but would still be lower than the rad alone.

[Clue69Less]

No, you can create a liquid delta
Its done but normally needs much larger systems, I've gotten cold side down a few degrees actually, seems to help temps when the rad can take the heat

Here's what I mean:

Run a loop on the cold side and another loop on the hot side. Measure the temps in the cold loop vs. TEC voltage. Now run the loops in series. The temp coming off of the cold side (where one would presumably place the water block) will now be wamer than it was at equal volts across the TEC. Therefoe the temps rose.

[Uncle Jimbo]

Here's what I mean:

Run a loop on the cold side and another loop on the hot side. Measure the temps in the cold loop vs. TEC voltage. Now run the loops in series. The temp coming off of the cold side (where one would presumably place the water block) will now be wamer than it was at equal volts across the TEC. Therefoe the temps rose.

That's pretty straightforward. In a closed loop system you are pumping heat in to power the TEC, and feeding that heat, plus the transfer heat, back to the rad in the same stream as the cooling water? No matter how you do that, it's hard to see how you get benefit. It is possible to run both hot side and cold side to the same rad, but that also kind of defeats the purpose, since you are asking the TEC to cool its own self generated heat, with a little help from the rad.

I think the sensible thing is just run separate loops - way easier to tune and control.

[Uncle Jimbo]

Ferrotec has some nice on-line curves and you can adjust to compensate for hot side temperature. I've been looking at their 9506/031/600 B which is 03160 spec.

The coefficient of performance (COP) is the amount of heat pumping divided by the amount of supplied electrical power. Max CoP for this unit at 30C hot side is 3.3, and occurs at 7.5A and .6V for a 10C differential. For only 4.5W in, it moves about 15W, which is mighty fine efficiency (but not much cooling).

That's a 55mm size, at a nice fat 4.85mm height. Efficiency drops pretty fast as current goes up, with the 50% point (CoP of 1) at 37.5A with 2.3V required, which draws 86.25W to move 86.25W.

Going to the 2.5 CoP point (15A 1V) moves 37.5W across a 10C differential at 30C hot side. So 5 of those on a 5V supply draws 75W and moves 180W. Using 5 of these with 12V PCM control and a 200W cooling design center, we draw 90W on average, and can move 450W at 12V with a total power in of about 480W. That would probably do the job for keeping even a big OC system with dual graphics nice and cool, and with good efficiency (most of the time)... but at max cooling, the hot side cooling needs to unload the power in and the power moved, close to 1000W. Need a big pump and big rad to handle that. But if we are willing to let the cold side rad do some of the cooling, which means we have to let the outlet temp rise a few degrees, we might decide to clamp PCM at the 1.5 CoP, which provides 350W of cooling for 230W in, and a total heat load of under 600W at max load. That setup does not seem totally crazy - it would maintain below ambient for all but the highest loads, and even then would only go a few degrees above ambient.

For the totally freeze crazy, with a big enough cold side setup, you could run 2 sets of 4 of these on a 12V supply. If you can keep the hot side at 40C, you can drive the cold side close to 0C while moving 360W. You will need to unload close to 1500W, but hey, formula 1 is about performance, not cost...

The graphs are fun to play with - for this TEC they are at http://www.ferrotec.com/products/the...ail.php?id=119

[Scarlet Infidel]

Just looked at those graphs, quite interesting. Its a shame none of the models they have match the ones I'm using.

What I'm interested in, is the massive spike in COP at around 1/8 of Imax. Though there's a huge disadvantage of running any lower than this magic point.

Also, at this point you'd only be pumping around 10w per element (on the type of element I'm looking at) so perhaps a slightly higher current is better in that respect (though still at the peak).


For the closest element to mine, for 20w movement at dT of 10c it will require 7w of power. This is a COP of 2.85 with a hot side of around 33c with cheap air cooling.

As I have 10 peltier modules, I'm looking at cooling 200w load with 70w power to ambient (of course this is best case, there are all the thermal interfaces etc). This seems to match nicely to my previous calculations and real world tests.

[Clue69Less]

Just looked at those graphs, quite interesting. Its a shame none of the models they have match the ones I'm using.

What I'm interested in, is the massive spike in COP at around 1/8 of Imax. Though there's a huge disadvantage of running any lower than this magic point.

Also, at this point you'd only be pumping around 10w per element (on the type of element I'm looking at) so perhaps a slightly higher current is better in that respect (though still at the peak).


For the closest element to mine, for 20w movement at dT of 10c it will require 7w of power. This is a COP of 2.85 with a hot side of around 33c with cheap air cooling.

As I have 10 peltier modules, I'm looking at cooling 200w load with 70w power to ambient (of course this is best case, there are all the thermal interfaces etc). This seems to match nicely to my previous calculations and real world tests.

When do you expect to have your coolerheater assembled and tested? I hope you have the time to run a range of conditions to reveal its capabilities.

[Scarlet Infidel]

I expected to have it done by Easter, but that clearly didn't happen.

I'm stuck at University now and have a rush of work before the end of term, then its exam time. luckily I find exams easy, so i might be able to get home for a couple of days during the 'revision time' between exams.

I would like to stress that I have made a lot of compromises on the design so it will not perform amazingly, it is more of a proof of concept which I will try and improve on.

[Clue69Less]

I would like to stress that I have made a lot of compromises on the design so it will not perform amazingly, it is more of a proof of concept which I will try and improve on.

Every castle starts with a single stone.

[Uncle Jimbo]

Just looked at those graphs, quite interesting. Its a shame none of the models they have match the ones I'm using.

What I'm interested in, is the massive spike in COP at around 1/8 of Imax. Though there's a huge disadvantage of running any lower than this magic point.

Also, at this point you'd only be pumping around 10w per element (on the type of element I'm looking at) so perhaps a slightly higher current is better in that respect (though still at the peak).


For the closest element to mine, for 20w movement at dT of 10c it will require 7w of power. This is a COP of 2.85 with a hot side of around 33c with cheap air cooling.

As I have 10 peltier modules, I'm looking at cooling 200w load with 70w power to ambient (of course this is best case, there are all the thermal interfaces etc). This seems to match nicely to my previous calculations and real world tests.

I think you said you have 12709's - you can take the 12712 curves at http://www.ferrotec.com/products/the...ail.php?id=115 and derate by 25% to get an idea of where you should go. You can do a quick double check looking at 12708 and 12710 curves, you should be right in the middle but unfortunately the nice ferrotec calculator doesn't have those values and the thermal enterprises curves are harder to read.

If your hot side is 35C, you have more options for low voltage. You can't achieve better than 2.0 CoP with a differential over 15C.

If the small sinks you describe are kind of 'OEM Standard' solid aluminum, they probably have .7 to .8 C/W rating. So using your numbers, you would be throwing off 27W per element, and would see around a 20C rise. If the sinks are a little better, like a decent sized copper base aluminum fin, you might get .4 C/W, which gets down to the 10C differential level.

Let's look at the 3.0 and 2.0 CoP points. For your units, the 3.0 point puts you at about 1.8A, which with 10C differential and 35C hot side puts you at about 3.7V per unit, pumping about 20W for 6.6W in. That's similar to what you were thinking. You coulkd do 3 groups of 3 in series off of a 12V supply and hit the voltage pretty well.

If you go to the 2.0 CoP, you need a pretty efficient sink - you can't do that CoP with over 15C differential. You'll need about 2.6A and 5.1V, pumping about 26.5W for 13.25W in. So efficiency starts to roll off but you get more transfer, and you are at a nice standard voltage. You have to unload about 40W per unit. That would raise your hot side to 15C over ambient with a .4 W/C sink.

Taking the 3.0 CoP and using the series power scheme off 12V, 9 units would move 180W with a total heat load of 243W. If that meets your cooling needs (that would drop a 1GPM flow about .6C), you might be fine.

Taking the 2.0 CoP and running off 5V parallel, 10 units would move 265W which is respectable, with a total heat load of 400W. That would drop a 1GPM flow about 1C, and if your heat in is lower than 265W, you should also be able to achieve some nice low temps.

[NaeKuh]

dayam uncle jimbo,

You sure know a ton about TEC's.

Well the original plan was having the hotside and cold side seperated. Never in the design did i plan to have them both on 1 loop.

Originally the cold side was to have a radiator. My idea was to take the coolant as closes to ambient as possible, and then use the TEC's to push me slightly into sub ambient.

Well problem came, radiator is no longer that good thing i was hoping for. The capacity for water to hold that much energy was what screwed my thoery up.

So now its going to be a straight TEC setup, no radiator except hotside. The cold side as i said will be connected to a reservoir, where the water inside will be continuously circulated. The water in the chilled reservoir will then be fed to the system.

Or i can just drop that unit inline on the blocks only and run it solo.

If i was to use a lets say 40mm x 2 radiator, you think this would hurt my performance on the cold side? i dont want to dip too far into sub ambient. I really hate preping things for condensation.

Something like this?
http://www.performance-pcs.com/catal...ducts_id=22275

or even this?
http://www.performance-pcs.com/catal...ducts_id=22597

[Uncle Jimbo]

dayam uncle jimbo,

You sure know a ton about TEC's.

Well the original plan was having the hotside and cold side seperated. Never in the design did i plan to have them both on 1 loop.

Originally the cold side was to have a radiator. My idea was to take the coolant as closes to ambient as possible, and then use the TEC's to push me slightly into sub ambient.

Well problem came, radiator is no longer that good thing i was hoping for. The capacity for water to hold that much energy was what screwed my thoery up.

So now its going to be a straight TEC setup, no radiator except hotside. The cold side as i said will be connected to a reservoir, where the water inside will be continuously circulated. The water in the chilled reservoir will then be fed to the system.

Or i can just drop that unit inline on the blocks only and run it solo.

If i was to use a lets say 40mm x 2 radiator, you think this would hurt my performance on the cold side? i dont want to dip too far into sub ambient. I really hate preping things for condensation.

Something like this?
http://www.performance-pcs.com/catal...ducts_id=22275

or even this?
http://www.performance-pcs.com/catal...ducts_id=22597

Since you are sandwiching the TECs between a couple of pretty high performance blocks, you are going to be able to move heat around pretty efficiently. Assuming Martin has given you a clean flat mounting surface, and you use AS ceramique to grease it, you can drive the differential to a very low value with a big enough hot side rad. So the question is how much heat, where do you want to put your operating points?

From Martin's photos it looks like you could put up 3 62mm TECs. If we look at the 12730s we have been fooling with, at 5V they will draw about 6A each, so your total is a 90W load. You will be pulling better than 120W out. Almost any $20 ATX supply will drive the 5V at 90W with no sweat.

You have not talked much about your load, but 120W is not much in today's world. This is a big time chiller and I'm assuming you are planning something fairly big under the hood. With no rad, if the load heat exceeds the TEC transfer, you will run the temps up pretty quickly. Might not be a bad idea to have a small rad in the loop with a bang-bang control at ambient, with maybe a half degree of hysteresis to assure the shunt is on before flow thru the rad is cut off.

Several people have mentioned the '437W TEC' that FrozenCPU has available. That is a 19933 unit. Driving it at 12V with the hot side at 25C puts you at about 15A and a 1.6 CoP, for 180W in, and pumps 280W. And that's just one TEC. Not bad but at these power levels still a lot of juice.

Putting that TEC at 5V puts you way down on the curve - 7A - for a total power in of 35W and a CoP of 3 at 5C differential. That would move 105W. Now you are in a position to control things pretty nicely - with 105W in, you pump 315W. But you are so low on the curve that any differential will basically shut down the TEC, so cold side capacity is important.

But that also gives you a way to control the cold side to the temp you desire - if you only want a few degrees below ambient to minimize condensation, then letting the hot side rise a little will reduce the heat transfer and maintain your desired temp. There are a lot of ways to reduce the cooling - reduce the flow thru the rad with a shunt would be one way. Proportional valves are expensive and a pain to set up, but here a simple solenoid valve would work, if the shunt does not shift all of the coolant. You should be able to set that to maintain whatever cold side temp you want.

By the way, my solution to small amounts of condensation is to direct a fan at the part where condensation would occur - that usually keeps things pretty dry. Since the bottom of the CPU or GPU is going to be few degrees above the cooling face, you shouldn't have to worry about hidden condensation. Just be sure there is enough airflow around the water block to keep drips from forming. That should be decent airflow - I use 70MM CPU fans mounted sideways but anything with good velocity will work.

The Thermochill PA160 has .02 C/W with a 130CFM fan, so with a heat load of 100W or so it will rise 2C. But that's a noisy fan. Going to something a little quieter in the 50-70 CFM range pushes the thermal resistance to .03 or .04, which gives a 4C rise. That's good cooling but about all we can allow running the TECs at that low voltage.

A smaller rad would cost you big time - you would have to go to a higher and less efficient voltage to maintain cooling.

I know I said earlier that running the hot side hot is more efficient - that's important at high voltage and big differential, but works against you at these low voltages. We are all learning on this project...

[NaeKuh]

mmm..

okey all i intend to put on this loop im guessing somewhere between 200-215W max.

Q6600 + Chipset.

I already have a meanwell S320 to power these tec's. Nol has it right now and is probably playing with it on them.

Martin did give it a really nice flat surface, his craftmanship is top notch, if you look at the previous pages, around 3-6 you'll see the WIP.

He made the surface large enough to cover 5x40mm or 4x52mm TEC's my main concern was on the massive power draw, so i wanted to keep the wattage low, and see if i could tweek efficiency.

As for controling the hotside, thats easily done. I guess i can connect both loops to a kaze master and have inline probes for both hotside and cold side.

The controller can also control the fans on the radiator and i could adjust as needed. :\

[Uncle Jimbo]

mmm..

okey all i intend to put on this loop im guessing somewhere between 200-215W max.

Q6600 + Chipset.

I already have a meanwell S320 to power these tec's. Nol has it right now and is probably playing with it on them.

Martin did give it a really nice flat surface, his craftmanship is top notch, if you look at the previous pages, around 3-6 you'll see the WIP.

He made the surface large enough to cover 5x40mm or 4x52mm TEC's my main concern was on the massive power draw, so i wanted to keep the wattage low, and see if i could tweek efficiency.

As for controling the hotside, thats easily done. I guess i can connect both loops to a kaze master and have inline probes for both hotside and cold side.

The controller can also control the fans on the radiator and i could adjust as needed. :\

I have one of the FrozenCPU 427 units - I will test it at 4V to see what it does. If it can move around 80W at that low voltage, you will get your 215W with a little to spare, putting three in series across the MeanWell. Looking at the photo with the ruler in it, it sure looks like you can take a 62mm - that translates to 2.44 inches. I realize that the TEC will be out beyond the finned area, but at these low power levels I don't think that is any handicap as long as it is on the copper. Martin drilled the bolt holes clear through, I think - but again with the low power you are running, I don't see much of an issue even if some small parts of the TEC are over the bolt ends.

If that works it will give you low power for sure - that puts you right at the absolute max efficiency point. But remember these are semiconductors, and so when you get right at the trip points strange things can happen.

I'll let you know what I find out with a simple test. <EDIT> see the note below - I'm a lot happer with 55mm TECs given your geometry.

[Uncle Jimbo]

If you are not happy with the bigger TECs, here's another option - http://ferrotec.com/products/thermal...ail.php?id=114 which is a 33710 unit which is 55mm square. It has a nominal voltage of 46.4, so your 12V MeanWell will put it well down on the curve.

At 12V, it draws 2.6A, so heat in is 31.2W. You are at the 2.3 CoP point with a 10C differential, so it will move 72 watts. You have room for 4, so you could move 288W at a cost of 125W. If you want to start out with 3 units, you would move 216W at a cost of only 94W. If I were you, I would just put in 4 and use some hot side control - that way any power excursions up to 288W are handled, and at lower power transferred, your power in goes down. You are at a much more stable point than with the '437' TEC also, which makes the performance a lot more predictable. You should be able to maintain a few degrees below ambient easily.

If you keep the differential around 5C, you will get even better efficiency - that puts the CoP over 3.

That would be a truly awesome setup, and would revise the thinking of a lot of people about TEC efficiency (me included!)

<EDIT> I discovered that you can plug heatsink performance into the ferrotec calculator so i plugged in the PA160 with 130CFM. At 12V, with .02 C/W cooling, that TEC moves 120W! so 4 of them would pump 480W with 125W in. That is serious cooling.

[NaeKuh]

If you are not happy with the bigger TECs, here's another option - http://ferrotec.com/products/thermal...ail.php?id=114 which is a 33710 unit which is 55mm square. It has a nominal voltage of 46.4, so your 12V MeanWell will put it well down on the curve.

At 12V, it draws 2.6A, so heat in is 31.2W. You are at the 2.3 CoP point with a 10C differential, so it will move 72 watts. You have room for 4, so you could move 288W at a cost of 125W. If you want to start out with 3 units, you would move 216W at a cost of only 94W. If I were you, I would just put in 4 and use some hot side control - that way any power excursions up to 288W are handled, and at lower power transferred, your power in goes down. You are at a much more stable point than with the '437' TEC also, which makes the performance a lot more predictable. You should be able to maintain a few degrees below ambient easily.

If you keep the differential around 5C, you will get even better efficiency - that puts the CoP over 3.

That would be a truly awesome setup, and would revise the thinking of a lot of people about TEC efficiency (me included!)

<EDIT> I discovered that you can plug heatsink performance into the ferrotec calculator so i plugged in the PA160 with 130CFM. At 12V, with .02 C/W cooling, that TEC moves 120W! so 4 of them would pump 480W with 125W in. That is serious cooling.

can you link me to the tec's you recomend.

i'll buy them.

Also i was planning on using a MCR320 for the hotside. :T However i could easily get a 480GTX if needed.

[Uncle Jimbo]

can you link me to the tec's you recomend.

i'll buy them.

Also i was planning on using a MCR320 for the hotside. :T However i could easily get a 480GTX if needed.

The unit is a Ferrotec High Power Thermoelectric Module - Peltier Cooler Model 9500/337/100 B.

Their power TEC page is http://ferrotec.com/products/thermal.../highPower.php

This unit is at
http://ferrotec.com/products/thermal...ail.php?id=114

They have an inquiry form at http://ferrotec.com/products/thermal.../teInquiry.php

You should be able to figure out where there is a distributor or reseller who can supply you with the parts from those links.

The MCR320 has .02 C/W for flow rates 1.5GMP and above. That is the value I used in my model - it should do fine for the hot side. I think it is also less restrictive than the 480GTX.

[n00b 0f l337]

Okay, ran into a problem, my other pump is leaking like a civ. Got another pump I could borrow Naekuh? Else I think I'm at end of line
Gained 4-5C though at the waterblock by running in a single loop, however rad heat output was much higher of course. And actually temps got better with a res then inline, saying that quantity of liquid would help that situation.

[NaeKuh]

Okay, ran into a problem, my other pump is leaking like a civ. Got another pump I could borrow Naekuh? Else I think I'm at end of line
Gained 4-5C though at the waterblock by running in a single loop, however rad heat output was much higher of course. And actually temps got better with a res then inline, saying that quantity of liquid would help that situation.

This is exactly what i was guessing too.

Which is why i wanted to paralell a res where one line goes in a loop just to chiller and back, maybe at a slow flow rate, while the other path is high pressure high head going straight to the cpu.

Do you get my logic nol?

I have a DB-1 i can mail out on monday, i can buy a DDC-3.2 and have John at Jab-tech to mail it to you while i mail you the spare XSPC top i have. Or i can send you another D5 in about 2 weeks as soon as dave mails me my sammy chips.

Take your pick.

[n00b 0f l337]

Another D5 would be good for testing if you can spare the time.
Parallel res though as I tested though really did not work out, not sure why, probably because you lost your temperature differential at the resevoir.

[NaeKuh]

Another D5 would be good for testing if you can spare the time.
Parallel res though as I tested though really did not work out, not sure why, probably because you lost your temperature differential at the resevoir.

mmm... i was hoping to keep the res colder then the return on the cpu. :T

[n00b 0f l337]

Dumps the heat back rather directly. Also this system seems to work best with LOW FLOW, vs HIGH FLOW.

[Uncle Jimbo]

mmm... i was hoping to keep the res colder then the return on the cpu. :T

In your diagram, the res basically acts as a 'capacitor' - it stores energy and stabilizes the system. If it is insulated, and your TEC capacity is greater than the heat load, you can certainly drive the temp below the CPU return.

I did a quick experiment using a setup like this, but with a dummy heat load.
- 1 gallon res, insulated (a Styrofoam portable cooler)
- heat load variable from 0 to 200W
- 100W to 300W TEC cooling in the second loop
- 1.5 GPM in both loops
1. With no heat load, I ran the TEC loop at 200W. Water temp dropped from 25C to 15C in 15 minutes.
2. I set the heat load to 140W. Res temp continued to drop, but much more slowly, reaching 12C in 15 minutes.
3. I set the heat load to 200W. Temp began to rise very slowly, reaching 13C in 15 minutes. That probably reflected pump heat in.

I did the same test, but with the TEC set at 100W. Results were:
1 - water temp dropped from 25C to 20C in 15 minutes with no load.
2 - with 140W heat load, temp started moving up - reaching 23C in 15 minutes.
3 - ran with no heat load until res was at 15C. Ran 200W heat load. temp rose to 20C in 15 minutes.

So the res acts as I would expect - it dampens the rate of change. For a system where you have relatively short spikes of high power, your dual loop design should maintain the average temp for quite a while.

This also opens up an easy way to control the temp - use a bang-bang controller (such as a standard heating control thermostat and relay) to turn the TEC on and off based on res temp. The latent heat will keep the TEC from cycling quickly, and if the TEC transfer power is more than the heat load, you will maintain your load cooling temps nicely.

I tried that using the setup above, but with an old mercury thermostat mounted on a copper plate with most of the plate in the water. The thermostat controlled an air conditioning relay rated at 60A which I happened to have around. That switched the TEC on and off.

With the TEC at 300W and a 200W heat load, and the thermostat set to 18C (the lowest it could go), I powered up the system. The res got to about 17C in a little over 20 minutes, and the TEC switched off. After about a minute, the water in the res got to 18.5C and the TEC switched on. It stayed on for about 2 minutes, the temp went back to 17 C, and the TEC switched off. I ran it for another 20 minutes or so and the duty cycle was very stable, running 2 minutes on, 1 minute off and maintaining temp between 17 and 18.5C with a 200W load.

[scifikg]

NaeKuh, send N0L a camera with the pump.

[THE JEW (RaVeN)]

Jimbo, are you making all these calc's based off of Kryotherm's software, the charts you linked in another thread, or just various math equations? If you somehow find the time, could you run through how you:

1. look up the TEC specs
2. run COP calcs
3. determine the greatest efficiency situation
4. develop an implementation plan

Ie. do an example where you just grab a TEC at random and show how you would calc it. Also, characteristics of TECs that we should look for would be great.

Your knowledge seems quite deep on the matter. If you could explain your methods to the rest of us "lunkheads," perhaps the rest of us could start churning out potential situations where a TEC would make sense peformance and economic-wise. It would be a great service for the TEC community here, abroad, and would be highly appreciated.

[Uncle Jimbo]

Jimbo, are you making all these calc's based off of Kryotherm's software, the charts you linked in another thread, or just various math equations? If you somehow find the time, could you run through how you:

1. look up the TEC specs
2. run COP calcs
3. determine the greatest efficiency situation
4. develop an implementation plan

Ie. do an example where you just grab a TEC at random and show how you would calc it. Also, characteristics of TECs that we should look for would be great.

Your knowledge seems quite deep on the matter. If you could explain your methods to the rest of us "lunkheads," perhaps the rest of us could start churning out potential situations where a TEC would make sense peformance and economic-wise. It would be a great service for the TEC community here, abroad, and would be highly appreciated.

Raven -
I have gotten a lot of valuable information from the people on this forum, and it is especially gratifying because people actually try things, and measure well, so even if they don't get the results they are looking for, there is usually enough data to see where they went wrong. If I can give something back, glad to do it.

To understand how to analyze TEC performance, you need to understand which performance curves are important, and how to apply them to your problem. That is true for most semiconductor work - the relationships are non-linear. I like the curves at: http://ferrotec.com/products/thermal.../highPower.php - they let you set the ambient and play with other stuff, and the basic curves are fine at default for most purposes. Clicking on a curve gives you a blow up version.

The larger the current capacity, the larger the TEC elements, and therefore the resulting TEC will usually be bigger. Bigger TECS stress the elements more, because whatever substrate the elements are mounted on will change in size as the TEC heats up (hot side gets bigger, cold side gets smaller) which physically pulls the elements around. That is why it is a good idea to maintain stable temps when operating a TEC.

Start with a couple of basic pieces of information.
1 - the heat transfer capability of a TEC element is determined by the current through it, and the temperature differential. Nothing else. So the trick is to figure out what current you will have, and what differential, at the operating point you want.

2 - TECs are made of individual cells called elements. These are all basically the same - 2 chunks of bismuth telluride, one with P doping and one with N doping. I won't go into the physics - the important thing to understand is that those elements have similar voltage performance curves no matter what size or shape they have. Their ability to pass current, and therefore heat, is mostly determined by size.

3 - Each element has a maximum voltage drop of about .122V at 25C and .138 at 50C - they have a negative temperature coefficient, so it takes more voltage to drive current when they are hotter. I use .125 as a design center for high power modules used near ambient. That low voltage is not practical to supply, so TEC designs employ a number of elements in series to get to a voltage that is available in the real world. A standard nomenclature to describe what is in a TEC package is the number of elements and the current capacity, almost always at 50C. I like to use the simple NNNAA description, where NNN is the number of elements and AA is amps, so a 12730 has 127 elements and a max current of 30 amps. Some vendors use 3 digits for amps (amps times 10) and might call that same TEC a 127-300 or something like that. So 127 element TECs have about 18V max voltage at 50C, 199 elements have about 28V, and so on. There is nothing magic about the number of elements, they are selected to give the right current at standard operating voltages. 127's are for 12V, 199s for 24V for example.

4 - it is important to know the number of elements and max current, because you can use the curves from almost any TEC to determine operating points (OP) if you know those 2 things.

There are 4 basic curves that I like to use - those are:
1 - CoP versus current - basically shows where you will end up for a given OP
2 - Voltage versus current - shows how much voltage you need to achieve current - this changes with temp and dT but is linear
3 - heat pumped versus current
4 - total heat load versus current (sometimes called heat rejected)

Having everything with current as the x axis makes it easy to look things up as you go from chart to chart.

Something I really took to heart after spending time on this forum is that efficiency over 1 (more power moved than power in) can only be achieved if dT is less than 25C. Efficiency over 2 requires dT less than 15C. So to move any significant power, you either burn a lot of power, or you use WC or some other low C/W cooling on the hot side.

So let's look at a problem we want to solve. Let's say we want to move 200W, and we want to use air cooling. We would like to be moderately efficient - say 200W in to move 200W. That says we want a CoP of 1.

We will have a total heat load of 400W and we need dT of 25C or less for CoP of 1. Let's say we want to get the cold side to 10C. That means our heat budget gives us 10C over ambient, which means our cooler has to achieve .05 C/W. That is what a pair of TRUEs will give, just to put it in perspective.

We also need a TEC - or several TECs - that can move 200W at CoP of 1. We will be at 25&#37; of max current to achieve that CoP, which puts us at 15% of Qc max. So we need a combination of TECs that have Qc max of 200 /.15 or about 1400W.

We could use a 337 element 10A module rated at 250W Qc max. 6 of those gives us 1500W. 25% of current is 2.5A, which from the voltage curve at 35C requires 12.2V. A quick double check shows each TEC pumps 33W at that OP. Our CoP is 1.08.

I like that because 12V is handy. If we have access to a TEC like that, we're done. In the real world, we're more likely to have some other, less ideal TECs on hand, but the principles are the same.

If you don't have curves for the TECs you have, you can interpolate from whatever curves are close, but the basic principles are the same. The heat you want to move and the dT you need determines the OP. The efficiency you want determines the percent of max amps you want. Stack the TECs in series or parallel to get to that amperage percent at the total amps you need, given the supply voltage you have.

It sounds easy, but it takes a little practice to get it right.