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Lets Talk Tecs - Page 2

post #11 of 17
I think you need to stop being so high and mighty.

It is volts (Vmax) that determines the operating point, at that operating point the current draw depends on the Dt (and incidently the hotside temp.). Just look at any chart of any TEC on a manufacturers site.

Your right about lower voltage = lower Dt one of the problems is that TECs are semiconductors and therefore non-linear and the decay of Dt is not linear relative to V. So 60% Vmax does not = 60% Dt, that is also a generally known fact and certainly Flak-spammer ( who has run TEC's.) knows this.

The other problem is that Dt depends not only on V but also on the cooling of the hotside and the load applied to the coldside. It can vary constantly in operation especially if the TEC is mounted directly on the CPU (which also varies in temp with operation.)

Since you are generally getting a lower Dt than you probably hope for Hotside cooling is paramount. Another well known fact.
If you have good cooling of the hotside and a relatively low load you can get subzero on the coldside with only a 25-30 degree Dt.
This subzero on the coldside not subzero on the load or not likely anyway. It will depend on the heat transfer inefficiencies.

Low temps are obtained with a well designed and made chiller using multiple TECs. The problems with multiple TECs are the current draw but by arranging the TECs in series/parallel groups it can help also the TECs are undervolted quite a lot perhaps down to 35% Vmax. Hotside cooling must be A1 and cooling of the coolant is incremantal as it passes the TECs. As the load (the coolant) cools the Dt rises slightly and current draw lowers slightly. And temperatures approaching -20 degrees are feasible.....not easy but feasible.

One fact that people do tend to forget that every attribute of the TEC depends generally on 2 or more other attributes so when one thing changes - it could just be the ambient temp which alter the hotside temp - it will alter other things... if the hotside temp changes by a couple of degrees it will affect the Dt and the current draw. As Elloquin mentioned in his long post just adjusting the voltage 0.1v changed everything.. The only one thing you can be sure of with a TEC is it's physical size and even that is variable enough from one TEC to another to affect your expected performance.

Before you start accusing people of not having run TECs etc i really think you need to get your own house in order first. From the look of the post list it looks like you have installed yourself as the resident TEC champion......shame you don't actually understand how they work yet !!!
Edited by zipdogso - 4/4/11 at 9:20am
post #12 of 17
As I did say I wasn't going to post again in this thread, this is actually an informative post to show the basis of accuracy for Ultrasonics calculator.

In response to the accuracy of ultrasonics calculator, Ultrasonic has provided this information:

On some forms the accuracy of my TEC calculator has been in question.

So it seems the best way to prove the calculator is pretty much right, is to put it against other manufactures numbers.

First my app will go head to head with another TEC simulator then real test numbers performed by a different TEC manufacture.. Seems a fair test to me


Here is the Kryotherm TEC calculator in comparison to mine it's Pretty Pretty close including all the random stuff like COP!



Above is the Kryotherm pic
At delta of 4.4c (TH-TC)
while moving a load of 124 watts (QC(W)
which requires 7.14 amps

Below is my app
it gets
a delta of 4.43c
while moving a load of 124 watts
which requires 7.13 amps







Above is the Kryotherm pic
At delta of 54.2c (TH-TC)
while moving a load of 30 watts (QC(W)
which requires 9.11 amps

Below is my app
it gets
a delta of 54.69c
while moving a load of 30 watts
which requires 9.08 amps




Above is the Kryotherm pic
At delta of 13.5c (TH-TC)
while moving a load of 10 watts (QC(W)
which requires 1.39 amps

Below is my app
it gets
a delta of 13.47c
while moving a load of 10 watts
which requires 1.39 amps




Above is the Kryotherm pic

NOW WHAT HAPPENS IF WE CHANGE THE HOT SIDE TEMP TO 50C
At delta of 33.3c (TH-TC)
while moving a load of 20 watts (QC(W)
which requires 3.44 amps

Below is my app
it gets
a delta of 33.35c
while moving a load of 20 watts
which requires 3.45 amps




http://www.customthermoelectric.com/...Z_spec_sht.pdf

Here we have CTE's 400Qmax TEC with REAL test data so i've put a few points on their graph then i'll bang those numbers into my app and see how close i get. Now remember this is REAL test DATA V my theoretical data





Now at point A they get
At delta of 20c
while moving a load of 150 watts
which requires just over 12 amps

Below is my app
it gets
a delta of 20c
while moving a load of 150 watts
which requires 13.3 amps (within 10%)




Now at point B they get
a delta of 30c
while moving a load of 175 watts
which requires 20 amps

Below is my app
it gets
a delta of 28.8c (within 4%)
while moving a load of 175 watts
which requires 20.13 amps



Now at point C they get
a delta of 60c
while moving a load of 0 watts
which requires 28 amps

Below is my app
it gets
a delta of 62.0c ( i based my numbers on a delta of 62 which it's advertised as )
while moving a load of 0 watts
which requires 28.0 amps



Now at point D they get
a delta of 0c
while moving a load of 400 watts
which requires 28 amps

Below is my app
it gets
a delta of 0.0c
while moving a load of 0 watts
which requires 28.0 amps



Now obviously these is a slight variance in some of the numbers this is partly because im basing the DELTA on 62c while in there test it only achieves 60c and at the end of the day this is theoretical verses real data it's not going to be 100% right but it's DARN CLOSE !

The calculator is only calculating the TEC part of the equation and is not including the thermal resistance of the radiator, water, flow rate, copper water block, TIM. Then TEC then TIM again then copper then TIM again and lastly the Thermal resistance of the IHS and Silicone .

This is how people seem to use calculators.
Ambient is 22 so the hot side of the TEC will be 22c
I’ll apply 12volts and that gives me a TEC cold side of -10
And therefore the CPU temps read from apps like core temp will be -10
Yeah Right!

At the end of the day it's just an estimator

While someone maybe unable to make a block that replicates their understanding of the widely available data, That does not make the mountain of data is wrong. In allot of cases they have miss estimated in the first place though a lack of understanding.
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post #13 of 17
Nice one Flak.....havent seen that before.... it is all good.

A point to remember as Ultrasonic said ALL calculators, charts etc even manufacturers charts are Ballpark figures. They dont take into acount any heat transfer inefficiencies,incorrect mounting, wrong TIM etc.

The real results from a TEC will always be different. In a multiple TEC setup each TEC will be different.

The only way to be sure how a TEC operates is to run it...........
Edited by zipdogso - 4/4/11 at 3:25am
post #14 of 17
Its a shame we can't simulate the complete TEC setup.
post #15 of 17
Quote:
Originally Posted by flak-spammer View Post
Here is the Kryotherm TEC calculator in comparison to mine it's Pretty Pretty close including all the random stuff like COP!
lol, that is one of the other TEC calculators I used to compare with a while back

For anyone interested, it can be downloaded from HERE.

The only problem with it, is just like Ultrasonic's TEC calculators, you can not add more TECs to it - you are stuck with what they include.

I have pretty much moved to THIS one now, because it allows me to enter the TEC specs myself, and a good feature it includes is the ability to estimate your CPU heatload at a specific overclock

And like the Kryotherm calculator, it actually tries to calculate the actual heatsource temp (ie. the CPU temp) by allowing you to enter the coldplate and cooler thermal resistance (only really usefull if you go direct die TEC cooling though).

It is interesting to compare all three actually, as some results from each TEC calculator are almost exactly the same, but at other times this one gives slightly different results - sometimes a higher and sometimes lower.

30W results:




10W results:




I guess the only real way to see how accurate they are would be to buy and test a Kryotherm TEC listed in Ultrasonic's TEC calculator and the Kryotherm calculator.
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post #16 of 17
Quote:
Originally Posted by un-nefer View Post
I guess the only real way to see how accurate they are would be to buy and test a Kryotherm TEC listed in Ultrasonic's TEC calculator and the Kryotherm calculator.
Personally I wouldn't bother, it wont achieve anything worthwhile.

You cannot run a TEC in real tests then compare the results back to any calculator, chart or what have you....Real testing will have loads of inefficiencies built in while the calculators and charts have absolutely 0% inefficiencies built in. It would be like comparing Chalk and Cheese.

ALL CALCULATORS, CHARTS ETC GIVE BALLPARK FIGURES !!!!

Just choose the calculator your happy with, check to see if you can achieve what you want, set your operating point and run it.

Manufacturers charts etc are only to give people a starting point so you have an idea if the TEC you've chosen will be able to do what your hoping....thats it.... nothing more. If they didn't provide at least something to start from no-one would have any idea if a TEC is suitable for their use or not.
Edited by zipdogso - 4/4/11 at 11:19am
post #17 of 17
Thread Starter 
Quote:
Originally Posted by zipdogso View Post
i think you need to stop being so high and mighty.

It is volts (vmax) that determines the operating point, at that operating point the current draw depends on the dt (and incidently the hotside temp.). Just look at any chart of any tec on a manufacturers site.

its amps that determines dt, and volts that determines amps.


your right about lower voltage = lower dt one of the problems is that tecs are semiconductors and therefore non-linear and the decay of dt is not linear relative to v. So 60% vmax does not = 60% dt, that is also a generally known fact and certainly flak-spammer ( who has run tec's.) knows this.

really not sure that flack does know this

Before you start accusing people of not having run tecs etc i really think you need to get your own house in order first. From the look of the post list it looks like you have installed yourself as the resident tec champion......shame you don't actually understand how they work yet !!!
ROFL

^^^
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