Cold Electricity?

Technical Electrical
1

I know it’s been a long time since I have posted, mostly because I’ve chosen not to go into Engineering. But I came across an interesting news article that sparked some interest.

Google searching left me to no avail…

The article was about 3 Frat boys that are inventing a “Keg Wrap”, an electric cooling blanket for kegs. While the use isn’t the interesting thing to me, the technology is.
We all know to create heat with electricity, you must cause resistance in the current. But how, without fans, would it be possible to remove heat?

Long time no see, I’ll be back for more…
Gadget

2

Heat removal is done by expanding a gas. This is how refrigerators and air conditioners work. You put gas into a cylinder and then pull back on a piston (like the opposite of what a compressor does). The expansion of the gas causes the temperature of the gas to drop. If you remember the ideal gas law from chemistry class, you can see the relationship.

3

The CPU overclocking community has been doing this for a while now:

http://www.overclockers.com/topiclist/index21.asp#PELTIERS

They are called “Peltier” coolers and they use electricity to provide very low temperature “cold plates”. I always thought it was a pretty cool idea myself too.

4

Without fans, Peltier devices can’t do much. The very best ones have a ratio of heat moved to energy applied of around 1. That means that for every watt that the device moves out of the keg, it will have to dissipate at least two watts of heat on the hot side, using a heat sink (with a fan, most likely) or some other means. It’s better to just use an ice bath.

While we’re on creative ways to cool beverages, check this one out, from sunny New Zealand:

http://www.asciimation.co.nz/beer/

5

I’ll dabble some research into the ideal gas law tonight. The article didn’t say, I guess I assumed it was “wire-cooled”. If I’m reading that right, it would basically have something like a fridge cooling system, just toned down for a keg?

Would this be silent (or relatively quiet)? I just can’t picture how one would repetitivly expand a gas without releasing, unless the gas is standard air and is released back into the general air supply after each stroke.

6

As several people stated, this is using a Peltier cooler, not a conventional compressor based cooler.

If you are familiar with the function of a thermo couple, a peltier cooler isn’t too hard to understand. A temperature gradient across two different metals (they have to have some a large difference in some electrical property, i’m not sure exactly) creates an electrical potential and that’s how you can measure temperature. Reverse the situation, and an electrical potential induces a temperature difference.

7

The Pell cells in earlier posts have been used for a number of years in portable coolers. You plug into the cigarette lighter in your car and the inside gets cold. Turn the power around and the inside gets hot. The cell is attached to a large heatsink that is molded into the outside of the cooler, no fan is needed. It is not an efficient way to get cool but it does fill a niche.

8

I didn’t know that the new one used a Peltier cooler. I’ve seen ones in the past that used a small compressor.

-Chris

9

I read the linked articles - looks pretty cool.

But now the most important question - is there a practical application for one of these devices on a FIRST robot?

10

A really hardcore motor tempurature regulator. You buy a few peliters fairly cheap (my friend has a bunch laying around for overclocking purposes) and make some sort of motor enclosure that allows for maximum peltier to motor contact and then it’s just a matter of a few big fans and, hey, next thing you know you’ve got the coolest (no pun intended) drive train out there. You’d want a temp sensor to insure you aren’t over-cooling the motors though…

11

I’d imagine that it -could- be used on a FIRST robot for cooling motors some something in that vein…might be a bit simpler than handling dry ice for cooling (cough)firebirds :smiley: (cough).

Whether we’d want to, or even need to, is really up to next year. It might be just about as simple to use a good heat sink and a muffin fan.

12

With no restriction on the use of muffin fans, I’d just setup a mean duct around a motor. From what I know about CPU cooling, there’s a good chance most of the heatsinks you see around on FIRST robots are having a negative effect. If a heatsink doesn’t have absolutely great contact, it really does a good job at insulating. Every metal-to-air interface is like a narrow road for heat. Even a good weld doesn’t conduct as well as a single piece of metal.

13

That’s an area I know about. WOO HOO!

Look up Thermoelectric Device - you’ll have better luck.

Peliter effect is the heating and cooling.
It can be reversed, and controlled. It’s solid state (just a bunch of P-Type and N-type doped materials linked together) so it’s TOTALLY silent. It’s a solid state heat pump, which means that heat energy is pumped from one side to the other. The side that has energy removed gets cold, and the energy comes out on the hot side. Of course, because you power the unit, you end up with ALOT more energy on the hot side than you removed on the cold side. Not very efficient. But there is NO refridgerent. NO moving parts. NO fluids.

Also…
Seebeck effect covers the ability of a thermoelectric to produce electricity. If you heat one side, and cool the other, presto-change-o, you are producing a current.

I could write a few pages on how they work, but it’ll be quicker for you to look here: Lots of Thermoeletric links

Want to buy a few, cheap? Go to: BG Micro it’s a surplus place, but they normally have some cheap.

They have been around for years, and there have been VERY few advances for like 60-70 years. UNTIL the last few years - there have been some really good, big breakthroughs in the last few years.

And I leave you with a list of a FEW uses…
Little mini-desktop pop coolers
Travel coolers
Personal coolers at the Sharper Image (with the HUGE battery pack)
Heated/Cooled seats in vehicles (Amerigon is the company name.)
Lantern powered radios
Data collection on the Alaskan Pipeline (Relativly warm oil on one side, cold Alaska air on the other side = power)
Cooling on ICBM navigation systems (The Soviet scientists were way ahead on alot of this technology)
I have seen a prototype Semi truck with the alternator removed and a 1kW power generator hooked up to the hot air exhaust
And I think some NASA deep space probes used TEDs to produce power. Cold of space and warmth of nuclear material = power.

By the way, I have easy access to these things. So I ran the numbers last year. I can’t remember all the numbers, but you’ll use more battery power than it’s worth. Design your drive correctly in the first place (MANY white papers to help you out) and use fans if necessary. If you HAVE to, the can of cool will also work. But don’t do that unless you are REALLY having trouble. It’s expensive, it can damage motors, and it only fits the LEGAL definition of non-flamable. (It’s R-152, and I can make HUGE fireballs with it.)

Now, I am still playing with the dry ice* thermocapacitor idea…

*Dry ice can be VERY dangerous if you don’t know how to handle it. Don’t mess with it without help.

OK, my skills are all used up here, going back to lurking…

14

This is all complicated stuff, and I heard something to that extent of electron cooling. I though for a split second that it would work well, but then I remembered P=IV, and that a metal will dissipate heat. For the frat boys, a better solution is to have a camoflaged refrigerator to house the keg (ie, a desk with a “computer bench”, a false floor, a bed/refrigerator, or just (because they will most probably be up north) in the ground at the frat building. My 2cents

15

Thermo Electric Modules ( Pell Cells ) are pretty neat but are really only very useful in certain applications, and have to be designed specifically for it.

A Thermo Electric Module in ideal conditions ( with correct voltage amperage blah blah blah ) will be roughly 40 degrees centigrade cooler than the hot side. Now of course this is what it should be but there are many x factors that can bring this down. ( Ie fluxuation in voltage and not properly connected ) Which makes it useful, but usually only in certain applications, because you typically need to try to keep the hot side cool . The cooler the hotside, the cooler the cold obviously.

Another thing is that a thermo electric module can only peak about about 140 btu’s of cooling,which is somewhat a small amount, if you consider 1lb of ice has 143.3 btus of stored cooling energy in it, And then it takes a .48 btu’s to raise it each degree F which I believe is close to about 1btu per degree c.

But for this application acting as a chiller with not too much other involvement if your boys want to use thermo electric modules just to chill it should work well atleast well enough. As long as they design the packaging correctly and make sure that none of the dispensed heat re-enters the cooling package and dispensed into the atmospher then your ambient temperature could actually do the cooling. I mean your not asking for the thermo electric modules to cool the liquid … just to keep it cold. Again it could perform fine if designed correctly. Plus, for as long as it would keep it cold, it prob. would be killed off before the effects of the chiller began to digress :-P.

Main problem with most heat sink designs is lack of common sense and double checking things. People fly by with the calculations then design things that completely screw up everything they already figured out. Of course it happens in all kinds of engineering… but you see it soo much commercial style heatsink product.

As for FIRST applications of thermo electric modules, i doubt you’ll see them incorporated. One they drain more battery life, 2 they are hard to adapt to the units you’ll need them on. The work put into them and the benefit produced is likely to be in great disfavor. I tends to work better if you are worried about cooling a motor by more effecient power management and maybe bonded fins with a muffin fan. We had custom designed heatsinks by the heatsink company I work for now ( as a psuedo intern/lab rat ) and the amount of work put into them/ over benefit recieved was very disfavorable. So its all where you find your nitch as far as FIRST goes.

Dan

16

Can of cool? are you referring to the compressed air cor cleaning keyboards or simmilar? my team used that in 2002 I believe when somehow our motors decided to overheat after 3 competitions only then did it get hot.

This past year my mom got dry ice from a supplier in a small cooler for use in a larger cooler to keep sandwiches cool. I had fun with a few pieces while it was sitting in my kitchen. I had a small fog covering my kitchen… errr house.

17

I got a few things to say…
As an overclocking advocate and avid cooling freak, I need to put in my two cents about peltiers.
One: They are not very controllable. Adjusting the voltage or current does NOT adjust the heat difference. You must remeber, the peltier is always working to keep those two sides at an exact temp away from each other. (I heard 20 degrees C, but I guess 40 isn’t unthinkable) By adjusting the voltage or current to a peltier, you start preventing the unit from keeping those sides at different temps. Simply put, you cannot adjust the amount between the hot side and the cold side, but you can adjust its ability to keep the hot side and cold side different. A slight difference, but important nonetheless.
Two: Battery life. These things drain current like no other. I have had one pull 15 amps out of a battery, and that was a small, low powered one. If you were to keep that up constantly, you may blow one of your fuses on the robot or maybe even run the battery down. Keep in mind that even though some motors drain at 40 amps, that’s typically not a continuous measure. It spikes at 40 amps. A peltier stays at a high number all the time.
Three: This may sound like a mundane problem, but one thing a peltier causes a lot of is CONDENSATION, the bane of electronics. CPU coolers typically use copious amounts of thermal paste or neoprene to block off airflow, but nothing is for sure. When you turn it on, stuff freezes on it. When it’s off, it melts back into water and frys what you are trying to cool. Bad.
Four: Stud Man Dan is absoultely correct in his post. A peltier is not so much a cooler as a, as many overclocking sites refer to it as, a heat pump, so it may be farther away from the component being cooled, but you still have the heat to deal with. People often do water or phase-change cooling on peltiers to get the drop in temp, but it often is hard and complex. Not the kind of thing you want on a robust machine that is going to get pummeled by two robots that are about 130 lbs each. (three, if your teammate is really mean!)

That’s my 2 cents. Peltiers are cool, but rather complex. Try putting a heat sink on your component. Even better, connect a block of aluminum to your component and the other end to the chassis. Don’t use peltiers.

Sparks