Need Advice on TEC setup

[Vinas]

I installed the TEC and so far I'm happy with the performance. It's running about 10C better under load which is allowing me to stay at 4.4GHz where as before I was just getting too hot. Here is my work log:
http://s279.photobucket.com/albums/kk127/vinas_photo/
Be warned I'm not very skilled with a camera =)

[Vinas]

Ok men (and ladies... there are some here aren't there?)

The power supply is working, sort of. Here's the deal. The TEC runs great up to about 4GHz. Using 1.45vcore it's causing my PSU 12v rail to drop to 11.9vdc. That's all fine and well but the problem is that over 1.45 vcore the PSU drops further to 11.87vdc, this is where my problems start.

Running 11.87vdc is limiting my max OC because I can not run stable at 4.4GHz anymore. The highest I can achieve is 4.2GHz with much higher vocre than before (before the TEC @ 4.2GHz 1.53vcore) now it takes 1.6vcore.

So anyway I'm looking for a meanwell or preferably something cheaper so I can do 15vdc into this TEC without dropping my 12v rail. The PSU does work but not as good as a dedicated supply. Also I should note that you CAN INDEED hook the ATX PSU up safely using 6 wires, but it's not preferred due to the possible unstable OC and some instability of your 12v rail. Completely safe though if you have enough capacity and a mild OC.

I'm off to ebay to find a nice little 15v meanwell. Wish me luck =)

[littleowl]

Ok men (and ladies... there are some here aren't there?)

The power supply is working, sort of. Here's the deal. The TEC runs great up to about 4GHz. Using 1.45vcore it's causing my PSU 12v rail to drop to 11.9vdc. That's all fine and well but the problem is that over 1.45 vcore the PSU drops further to 11.87vdc, this is where my problems start.

Running 11.87vdc is limiting my max OC because I can not run stable at 4.4GHz anymore. The highest I can achieve is 4.2GHz with much higher vocre than before (before the TEC @ 4.2GHz 1.53vcore) now it takes 1.6vcore.

So anyway I'm looking for a meanwell or preferably something cheaper so I can do 15vdc into this TEC without dropping my 12v rail. The PSU does work but not as good as a dedicated supply. Also I should note that you CAN INDEED hook the ATX PSU up safely using 6 wires, but it's not preferred due to the possible unstable OC and some instability of your 12v rail. Completely safe though if you have enough capacity and a mild OC.

I'm off to ebay to find a nice little 15v meanwell. Wish me luck =)

so tell us what is your temps at idle and full load for 1hr?? Also what is room temp when you post temps?

Oh and one more thing no one ever said you can't run an ATX psu, We just said it is not a good idea. for 2 reasons you have said in this post as well as fire hazard!

[Uncle Jimbo]

so tell us what is your temps at idle and full load for 1hr?? Also what is room temp when you post temps?

Oh and one more thing no one ever said you can't run an ATX psu, We just said it is not a good idea. for 2 reasons you have said in this post as well as fire hazard!

I agree that running a TEC off your primary supply is a bad idea, but a dedicated ATX is not a bad choice if you know what you are doing. The standard MOLEX connectors on ATX are only good for 7A max, so you need to use a different connector. The 18GA wire is good for maybe 8A, fine for a disk drive but not a TEC. The solution there is to take a bunch of the yellow 12V and black ground wires, cut them loose from the MOLEX, and crimp them into a 30A automotive space lug, then put the matching part on the TEC. Using male on positive and female on negative will avoid an unfortunate accident. If you are dedicating the PSU to the TEC, do a whole bunch of the 18GA supply lines, as many as will fit into a 10GA spade lug. Just be cautious about mixing leads from split supplies - sometimes that creates issues.

The next question is what derating to apply to the supply. that depends a lot on the quailty, many supplies can maintain their rated value for only 30 seconds or so but some are rated continuous. One way to get a feel for that is to open up the supply. Big beefy sinks and monster MOSFETs are a good sign, cheesy ones are probably bad news. But also consider air flow - adding a big variable speed fan can help the PSU live longer. I generally look to keep loading under 70% of listed power just to assure some margin.

I like to test the supply heat rise against a static load drawing about the current I intend to draw. For a big TEC like a 12730, that draw is around 24A at 12V, so a .5 Ohm resistor is about right. Since it needs to handle a bunch of power, I sometimes just use a big roll of wire, nothing like 10 lbs of copper wire to take a little heat. But you can also get there with a bunch of 25W wirewounds in parallel.

If the internal sinks get over 60C then it's not big enough. Even though the MOSFETs are probably 150C or 200C rated, the other things in there are not, and the likely failures are electrolytics.

I have seen some posts about needing to load the 5V or 3.3V lines with significant power. The control chips used for the last several years do not require that kind of load, and it just wastes power. drawing a few hundred MA from the 5V line should be sifficient to keep any modern supply stable, and a 5W 33 Ohm resistor works fine for me and burns less than a watt.

Taking those things into account, I have been able to get a nice stable PSU capable of delivering 32A continuous at 12V, for about $40. You can sometimes get a meanwell on eBay for that price, and that's certainly a more rugged supply, but the ATX works well on a budget. I have several of these which have run for years without problems.

[Uncle Jimbo]

Ok men (and ladies... there are some here aren't there?)

The power supply is working, sort of. Here's the deal. The TEC runs great up to about 4GHz. Using 1.45vcore it's causing my PSU 12v rail to drop to 11.9vdc. That's all fine and well but the problem is that over 1.45 vcore the PSU drops further to 11.87vdc, this is where my problems start.

Running 11.87vdc is limiting my max OC because I can not run stable at 4.4GHz anymore. The highest I can achieve is 4.2GHz with much higher vocre than before (before the TEC @ 4.2GHz 1.53vcore) now it takes 1.6vcore.

So anyway I'm looking for a meanwell or preferably something cheaper so I can do 15vdc into this TEC without dropping my 12v rail. The PSU does work but not as good as a dedicated supply. Also I should note that you CAN INDEED hook the ATX PSU up safely using 6 wires, but it's not preferred due to the possible unstable OC and some instability of your 12v rail. Completely safe though if you have enough capacity and a mild OC.

I'm off to ebay to find a nice little 15v meanwell. Wish me luck =)

You need to understand TEC performance a little better to get where you want to go. There is nothing fixed about the heat transfered or heat in - it depends on the hot side temp, differential, and current. Voltage determines current for a given operating point but not performance. At the top of their curves, TECs lose a LOT of efficiency, and moving from 12V to 15V on a 15V rated TEC increases the waste power by 50% but you only gain 10% in cooling. For example, with a 50C hot side and 12V, across a 30C differential, a 12730 TEC will draw 24A (input of 288W) and move 160W. Moving to 15V increases current draw to 29A, so now you are burning 435W in, but the heat moved only goes to 180W.

You would be a lot better off to use a pair of TECs in parallel if that is possible in your setup. Even better would be running at a lower voltage - the lower you go, the better the efficiency but you move less heat.

By the way, you can't use the -12V line for anything - total current is limited to what a small single IC can pass, usually a lot less than 1A. But there is a more important reason - most PSUs have the ground tied to equipment ground, so any funny wiring is likely to result in bad smells and dead components.

[Vinas]

So I ended up checking my mounting and they were quite loose. A silly mistake but after getting a little pressure on the TEC it's performing much better. I know you want to have 150psi but I just tightened them down best I could.

I'm pleased to report that my temps dropped immediately. Stock speed & vcore is below zero at idle. Overclocked with high vcore (1.64v yeah i know it's high) is idle at 18C and Orthos stable for 2 hours so far at 61C max. It might not be the best TEC setup but this is beating my old water by about 14C on load temps. Ambient temps are exactly 27C.

I also knew it's not preferred to run the TEC past 80% capacity or so. After reading what Jimbo wrote I think I'll just wait a bit and run some more tests before I pick up that dedicated PSU. If there's one thing I know it's that you can't rush these projects. That's how I ended up with a loose mount after all (working many hours these last few months).

Thanks for clearing up the -12v and that's pretty much what I thought too.

Thanks all... Will get some screens posted up here soon.

[Uncle Jimbo]

There are some great references on the Melcor site which give detailed assembly instructions.
http://melcor.com/assmtips.html
http://melcor.com/procedl.html

On tightening, smooth and even torque is important. If you don't have a torque limiting screwdriver (I don't), you can do a simple torque screwdriver by drilling a hole in a regular screwdriver and putting a rod through it. I then use a simple postal spring scale to measure the force, attached 6 inches from the screwdriver center line. That's the easiest way to assure even torque at the right level. 150-300 PSI is actually not as much as you might think - I have seen people crack their TEC putting on too much pressure.

Also note their grease recommendation. You want a very thin film of AS Ceramique or similar - Silver or other metal bearing grease can contaminate the setup. Twist and slide the TEC "gently!" until resistance is felt, then slide it into place. I use their bolt and washer recommendations exactly - gives great results. Melcor's own sinks are very nice, and come pre-tapped for 3mm stainless bolts.

Here's their advice on torque:
Step 9. Before bolting, best results are obtained by preloading in compression the cold plate/heat exchanger/module assembly, applying a light load in line with center of module, using clamp or weights. For two module assemblies, use 3 screws located on module center line, with middle screw located between modules. To preload, torque middle screw first. Bolt carefully, by applying torque in small increments, alternating between screws. Use a torque limiting screw driver. The recommended compression for a TEC assembly is 150 to 300 pounds per square inch of module surface area. Using the following equation you can solve for torque per screw:

*
T = (C x D x F x in2) / (# of screws)

T = torque per screw (in-lbs)
C = torque coefficient (0.20 as received, 0.15 lubricated)
D = nominal screw size (4/40 = 0.112, 6/32 = 0.138, 8/32 = 0.164)
F = Force (lbs / in2)
in2 = Module surface area (length x width)

Check torque after one hour and retighten if necessary. Use Stainless Steel Screws, fiber insulating shoulder washers, and steel spring (Belleville or split lock type) washers