Hey folks.

I need to find a good EE/CE that knows how to actually build a functional circuit. I've met lots that know in theory how things work but they do not seem to know how to obtain, build, and deliver a working product. This is a one time design project. It needs to happen quickly but we are willing to wait until after exams.



While I don't have all the requirements compiled yet, this is the basic scenario: My brother builds high-end custom furniture and has built a small refrigerator in a bar cabinet. He has purchased a thermoelectric cooler, power supply, and temperature controller. See:
http://www.tetech.com/assys/ac046.shtml
http://www.tetech.com/temp/power2.shtml
http://www.tetech.com/temp/tc48-20.shtml

The refrigerator door is about 18x18, then there is a separate 5x18 false drawer front just above that which folds down and will reveal the user controls. The power supply and controls will fit in the 5x18x20" space above the insulated box. The TE unit is mounted on a removable Plexi panel so that the owner can occasionally pull it out to clean dust out of the heat sink.

The control module will have one power line in, and from it will be a switched 120V line for the lights, a line to the door switch (I imagine this to be a low voltage line to a microswitch for safety), and a neat and tidy line to the cooler unit which will include hot side fan power, TE power, cool side fan power, and overtemperature sensing. The hot side fan is a 120mm 24V box fan and it is too noisy for an expensive consumer product. It should run at half voltage most
of the time and ramp up to full speed only when necessary. The TE tech temperature controller has an alarm that could be used for this function.

This is a consumer product that will be used for a couple decades at minimum. It needs to look consumer-pretty, not like a garage project. Safety is a significant concern. It is housed in an all-wood enclosure. When it fails, it cannot cause a fire.

Your job is read the technical specs from above. (Most of the specs are under the tc48-20.) Take into consideration our requirements. Propose a solution. And possibly build a small project box that we can assemble into our project.

Some of the requirements are:
-Door switch: Door open: turn on interior light. Door closed: light off. Optional: after 2 minutes (open) shutdown entire system including TE devices. Reset on door close.
-Solid state relays desired. Unless recommended otherwise.

Overload protection and heat control:
-If hot side of TE device reaches (certain temperature) disable circuit. Require service when this happens. This is fail safe for fire protection. If we ever reach this temperature the user may not reset.
-Circuit breaker/fuse: if current is exceeded then allow user to replace fuse or reset breaker.
-Temperature sensor on TE cold heat sink. Assume air temperature will match.

Packaging:
-Professional looking project box.
-Quick connect cables to control TE, light, switches, power, and temperature controller. There are quite a few connectors that go between the power supply, controller and TE. Remember the unit can be removed for cleaning from the front side of the refrigerator since the whole bar is too large to move. I've thought of a bus type cable
similar to a PC's motherboard connector.
-External cables are to be bundled with shrink tubing
-All control and non-control connections are to be made through central box. This is to have a clean and neat appearance.

Deliverables:
A full schematic with full parts list and supply house that carries each item. Simple load calculations to prove that this will not overheat or cause fire.


Payment: hourly after negotiated rate. Estimated design time: <15 hours

Send email to jblow5599@hotmail.com. Please include phone number.
I'll talk to a couple people before committing to an engineer.
Thanks, Leo

Pictures

photos:
http://www.thewolfweb.com/photo_photo.aspx?user=11406&photo=488873
http://www.thewolfweb.com/photo_photo.aspx?user=11406&photo=488874

11/20/2007 1:09:54 PM

A CE could build you a house.
A CE could build you an office.
A CE could build you a road.
A CE could build you a foundation.
A CE could build you a dam.
A CE could build you a water distribution network.

A CE could not build you a functional circuit.

An ECE could build you a functional circuit though.

11/22/2007 12:15:34 AM

Some schools call what we know as CPE, CE.

11/22/2007 12:20:22 AM

Is it bad that this is interesting and makes me want to tackle this project, even though I'm in ME? Definitely an awesome project, if I were you I'd post some flyers over in the engineering buildings on centennial for seniors or grad students looking for a little easy money.

[Edited on November 22, 2007 at 1:26 AM. Reason : .]

11/22/2007 1:26:10 AM

I think I could do it, but I wouldn't want to waste someone else's money if I was wrong

I haven't graduated yet though.

11/22/2007 2:46:30 AM

Theres no way to possibly deliver all that your asking for for only 15hours.

I could ghetto rig something to WORK in 15hours... but for safety you need to test it, and testing it takes a lot of time. Making it pretty takes a LOT of time ... and money to intentionally destroy things b/c safety stuff HAS to be tested live...

That seems to be a pretty good TEC setup... but your probabaly going to want somebody with a mechanical background to do the thermal mass stuff... The TEC's I worked with were a PITA

Overall this actually seems to be more of a mechanical type application than an EE... ME's with robotics experience would be ideal...

11/23/2007 2:23:57 PM

hell there's nothing to the circuit--the PITA part is programming the damned controller

11/24/2007 9:48:39 PM

The problem you've got isn't that nobody knows how to deliver (well maybe it is, most people around here are just tech support monkeys)

Even still, I think your biggest problem is, "Estimated design time: <15 hours "


HAHAHAHAHAHAHAHAHA @ you moron

11/25/2007 10:29:44 AM

Find someone with an HVAC cert and build a phase change system like everyone else has been doing to cool confined spaces for 1232 years

11/25/2007 11:31:39 AM

Quote :

"jblow5599@hotmail.com"

lol

11/25/2007 1:23:24 PM

^^ yea i agree with that - I don't think it would be a good idea to use a solid state cooling device PERIOD - not unless you're gonna send that shit to UL (which you won't)

its too damn risky and, shit, they don't even cool worth a damn

11/26/2007 7:55:21 AM

they are reliable, field proven, and with accessable valves and good brazing should last for longer than the caps in your power supply/tec wacko idea.

11/26/2007 8:29:00 AM

Thanks for [some of] your responses. I think I need to address the time issue of this project. I believe that I've given too much information and confused the situation. This whole thing could be built with a simple timer and 3 relays.

[simple(r) overview]
There is a timer switch that is also the door switch. When open timer starts: turns off a master relay after about 2 minutes. When closed leave the power flowing through the relay.

This door switch also controls a relay that turns on an interior light. This light will switch off because the master relay turns off after said time.

The 3rd relay is controlled by another signal from the temperature controller. It controls the fan speed.

Beyond that there is a temperature sensor that blows the master relay. A fuse or two. An on off switch. And some cables.



As I see it if the design (not build) takes more than 15 hours then I've completely mistaken what it this takes. Although I appreciate goFigure's comments about quality and testing. Unfortunately, no I'm not sending this to UL for testing.

I only conceptually know how this works. But recommending changes, drawing accurate schematics, and specifying parts is (hopefully) your job. You do not necessarily even have to build anything. The "simple timer" in my mind is the most difficult part. I've searched online and it looks like a 555 timer is the ticket. But I did not understand how to do it.

Also I just don't care if you would build a phase change cooler. This is what it is and what it will be. Why argue?

11/30/2007 11:36:18 AM

Go buy your relays

VGS > VTN

Put diodes across the relay V=L di/dt

if you can type that much jibberish you can learn how to bias a transistor. once you figure that out, you wont be using relays anymore.



warmest regards

11/30/2007 12:28:55 PM

warmest regards, haha, like how the fire they're gonna have in a few years is warm

11/30/2007 2:15:46 PM

there isnt anything preventing it from working.

11/30/2007 3:18:26 PM

anybody who uses a solid state heat-exchanger in a non-UL approved device is just asking for trouble

11/30/2007 3:30:35 PM

I glanced at the tc data sheet and I got the impression that 15 hours is probably reasonable for an ECE worth his salt. Seems like the controller is doing a lot of the work for you. Just need a sensor or two and some relays/safetys that either reset with some sort of hysteresis or break open permanently.

Quote :

"anybody who uses a solid state heat-exchanger in a non-UL approved device is just asking for trouble"

Why don't you do something you don't normally do, which is stop being snarky and impart some knowledge in this section. I don't know much about cooling devices, so I am interested to learn what you have to say about them.

11/30/2007 10:14:05 PM

i'm not being snarky. go spend $10 on one of those bad-boys and come back to the thread once you've applied 12V to it

tell us how comfortable you'd feel putting it inside a wooden enclosure that wasn't UL approved

its an engineer's job to be pessimistic. only a fool would hire an optimistic engineer.

[Edited on November 30, 2007 at 11:59 PM. Reason : s]

11/30/2007 11:55:55 PM

You are being snarkytrolly, just like you have done in this section for years. Tell me why I need to go buy the cooler and try it myself when you have so much experience? You haven't read any of the documentation and you have no idea what you are talking about, just like always.

I read enough of the .pdfs + used some rough guess numbers for ambient air temps, etc, to realize that everything being proposed seems reasonable from a safety point of view.

Feel free to do anything other than what you always do, which is troll this section. God you're lame.

12/1/2007 11:07:51 AM

*shrug*

i'm not trolling, and i stand by my assertion that anyone who actually physically handles a solid-state heat exchanger will (or at least should) have second thoughts about installing it in a non-UL (not to mention wooden!) enclosure.

i don't care how many damn papers you just read, its no substitute for feeling that thing scorch ya.

[Edited on December 1, 2007 at 11:48 AM. Reason : s]

12/1/2007 11:47:55 AM

So basically you have no idea what you are talking about? Got it.

12/1/2007 1:15:34 PM

sure.... (?)

12/2/2007 8:23:54 AM

Solid state heat exchangers are rediculously inefficient, but that is why he is using an active cooling system with thermal shutdown. As such, I don't see that much of a problem with the design as far as safety.

12/2/2007 10:09:10 AM

its one thing to feel like you don't need UL approval for random electrical projects (even though they do pose a certain amount of risk)

but when you're starting at ground level with a device that gets scorching hot as a part of its normal function.... wow. i hope none of you guys ever get a design job.

on second thought i guess this partially explains why 90% of you work glorified tech support

12/2/2007 11:14:31 AM

Quote :

"its one thing to feel like you don't need UL approval for random electrical projects (even though they do pose a certain amount of risk) but when you're starting at ground level with a device that gets scorching hot as a part of its normal function.... wow. i hope none of you guys ever get a design job. on second thought i guess this partially explains why 90% of you work glorified tech supportI have no idea what I am talking about"

Fixed it for you!

12/2/2007 11:26:53 AM

aw, did they let you out of your little tech-support cubicle? don't you need to go help somebody set up their DSL?

12/2/2007 12:06:46 PM

you cant use the solid state relay cause your pnp transistor will have a buffer overflow
once the inductor has reached critical mass
i would go with an rf transducer to generate the sinusoid resistance which your amplifier circuit
can then propagate

12/2/2007 12:18:16 PM

^^ I know about as much as setting up DSL and tech support as you do ECE

12/2/2007 2:02:41 PM

Quote :

"its one thing to feel like you don't need UL approval for random electrical projects (even though they do pose a certain amount of risk) but when you're starting at ground level with a device that gets scorching hot as a part of its normal function.... wow. i hope none of you guys ever get a design job. on second thought i guess this partially explains why 90% of you work glorified tech support"

You know how those little water coolers chill the water right?

Or I guess you dont.

12/2/2007 9:54:49 PM

You know those little water coolers are UL approved right?

Or I guess you don't.


[Edited on December 2, 2007 at 9:58 PM. Reason : s]

12/2/2007 9:57:53 PM

They get so scorching hot the paper cups on the side sometimes catch fire

12/2/2007 9:59:20 PM

yea you're right, they do in the UL lab and then the engineers modify their design to improve safety.

unfortunately for muddbubble, he doesn't have the equipment or resources to hire someone with enough experience to test the myriad ways in which the device could fail and cause a fire.

12/2/2007 10:08:36 PM

Yeah youre right, I've never seen something UL listed that couldnt burn down a house.

Oh wait!

12/2/2007 10:12:32 PM

omfg a bridge fell down in minnesota ergo all civil engineering is a total crock!

12/2/2007 10:14:22 PM

Sorry I just put out another fire in the break room

12/2/2007 10:16:00 PM

my brother only narrowly avoided driving across an overpass after I called him and warned about how bridges were falling down everywhere

12/2/2007 10:22:38 PM

Solinari is the biggest disgrace to an ECE degree that NCSU has ever seen. It's Matthew right? The guy that rolls to legends, and cries to professors that didn't teach him shit and he only got a B+? That's you right?

12/2/2007 10:58:41 PM

yea, sorry for busting your curve that one time

i guess that's probably what sent you into an academic slump leading to your tech support job


BTW, I guess you two, Chance and Quinn should team up and actually design this P.O.S. scheme if you think its going to be so failsafe and easy.

Unless of course, you know I'm right and you're just trolling.

[Edited on December 3, 2007 at 7:57 AM. Reason : s]

12/3/2007 7:32:48 AM

You sound just like TreeTwista, which is extra extra scary.

12/3/2007 9:46:31 AM

boiling down all the hyperbole, looks like this is where we'll always remain.

Chance:
Designing this project is easy and essentially risk-free as long as a few simple guidelines are adhered to

Quinn:
Jumping in opportunisitically

Solinari:
Designing this project is relatively easy, but large amounts of time and experience are needed to fully validate its safety for everyday use in a home




No sense in arguing beyond this. Its more of a philosophical disagreement than any other. I am much more cautious than any of you guys, apparently.

12/3/2007 12:12:00 PM

You still haven't said shit in this entire thread. You haven't done one thing...ever...in Tech Talk to prove you have any sort of credibility in regards to reading a data sheet.

Lets start with this which you failed to bother addressing:

Quote :

"anybody who uses a solid state heat-exchanger in a non-UL approved device is just asking for trouble"

Tell us what experience you have in this regards. Sure they aren't efficient, but that's pretty generic. That doesn't automatically exclude it's use from this application. It also doesn't imply that it will get "scoring hot" in this application.

Quote :

"i'm not being snarky. go spend $10 on one of those bad-boys and come back to the thread once you've applied 12V to it"

I'm asking you again, or get the hell out of this thread, tell me what experience you have other than "it gets hot"? What application do you have experience using a TEC? I know it isn't OC'ing CPUs, because you're the guy that made it his mission to lambaste overclockers every time they posted a thread in here. I'd LOVE to have an engineering discussion with you about this device, but before we can do that, we need to have some sort of a basis to work from. Something a little more substantive than "it gets hot".

Quote :

" its an engineer's job to be pessimistic. only a fool would hire an optimistic engineer. "

That's quite a leap you made there. Did you invent that yourself? I like how your pessimism is based in "it gets hot"...and that's it...and my 'optimism' is based in "I read some of the documentation, considered the application, and feel like it will be an acceptable" solution.

After you have completely shirked any real qualifications or responsibilities in this thread, you shifted over to just pure trolling.

He asked for "practical EE or CE". So far, you haven't proven to be that person yet.

12/3/2007 2:36:08 PM

Well, like I said - our differences can't be resolved. We're approaching the problem from irreconcilable positions.

My position is one of admitted ignorance - I don't know all the possible paths to failure and wouldn't feel comfortable enclosing it in a wooden structure until I'd rigorously and exhaustively tested it.

Your position is one of admitted optimism - you've read a few data sheets and feel like you have enough information to state that it doesn't run the risk of causing a fire.



EDIT:

You know what, I finally broke down and decided to read the data sheet that you keep crowing about. It didn't seem relevant to me up until this point, because of my past experience with Peltier devices and because of my natural cautiousness regarding product safety, and my experience with how difficult it is to guarantee good reliability

Guess what I found on PAGE 2 (TWO!!)....

Quote :

"General Safety Warnings This manual is available in English only. It must be read and followed carefully before installation and operation. The TC-48-20 should only be used for its intended purpose of providing temperature control of thermoelectric devices or purely resistive devices only. The controller is intended for light industrial, laboratory, or similar use. It is not intended for household use or medical use."

/thread

/chance credibility

[Edited on December 3, 2007 at 3:33 PM. Reason : s]

[Edited on December 3, 2007 at 3:35 PM. Reason : s]

12/3/2007 3:23:32 PM

Quote :

"Well, like I said - our differences can't be resolved. We're approaching the problem from irreconcilable positions."

I think you must be TreeTwista? Because this is exactly how he trolls TSB.

Our position can't be resolved? OF COURSE IT CAN. What kind of clever trolling is this?

I'm asking you to change my mind. It's changeable. I'm convinced that this thing won't get as hot as you think it will based on what I read in the data sheets and considering it's target application.

You're convinced it will get scorching hot...but you don't provide any sort of information as to how you arrive at this conclusion. You don't say what experience you have with a TEC, probably because you have none and are rather enjoying yourself trolling this thread. So, I'll ask for a 3rd (or is it 4th?) time now, what experience do you have that allows you to have the opinion it will get scorching hot? Anything else other than this answer is trolling and you know it. You know it because thats all you ever do in this section.

You're a pseduo-intellect feeling entitled to rile the "noobs" and other people you deem inferior in this section. You've done it for years, you're doing it in this thread, and you'll keep doing it.

You can keep your busted curve, your book knowledge, your crying to professors, and trolling, I'll keep my practical knowledge and paycheck bigger than yours!

Have fun at Legends!

12/3/2007 3:36:05 PM

well, like I quoted previously, the damn product's own manufacturer agree with me. what are ya gonna do now, accuse them of trolling their own marketspace?

...on PAGE 2 (TWO!!)....

Quote :

"General Safety Warnings This manual is available in English only. It must be read and followed carefully before installation and operation. The TC-48-20 should only be used for its intended purpose of providing temperature control of thermoelectric devices or purely resistive devices only. The controller is intended for light industrial, laboratory, or similar use. It is not intended for household use or medical use."

pwn! in your face. with your own damn datasheet

[Edited on December 3, 2007 at 3:46 PM. Reason : s]

12/3/2007 3:42:34 PM

That doesn't mean it's going to get too hot or be any type of fire hazzard

12/3/2007 3:56:56 PM

well, thats why I said that I'm apparently the most cautious person in the thread

and apparently the manufacturer agrees with me.


must have to do with a learned appreciation for the responsibilities that an engineer incurs when he provides a product to someone else, particularly when its an in-home application.

I wouldn't have a problem disregarding some types of product safety when it came to myself and my own hobby projects, but you young grasshoppers must learn the difference between real engineering and your hobbies.

[Edited on December 3, 2007 at 4:00 PM. Reason : s]

12/3/2007 3:59:32 PM

^ That thing you posted is not a safety warning.

They're saying it's not intended for joe blow consumer to buy it and use it to see when their bath is warm enough.

And they aren't willing to warrant it against failure in a medical situation where someone's life might be at risk. It's kind of like how the license agreements for software says "not to be used at a nuclear power plant" and stuff like that. They're not saying it can't be used like that, they're saying they don't want their lawyers and insurance to be liable for a nuclear power accident.

12/3/2007 4:05:28 PM

ding ding ding

12/3/2007 4:07:38 PM

Quote :

"well, like I quoted previously, the damn product's own manufacturer agree with me."

This CYA statement says NOTHING about the temperature of a thermoelectric cooler, which is what your assertions have been up to this point. I mean, you aren't a lawyer, so I can understand why you'd attempt to interpret this legalese in this way. Should this final product be UL certified if it is intended to be sold as a finished product, probably, and you made the point that 15hrs probably isn't enough if this route is taken, but we aren't arguing that.

In short, just stop trolling this section, guy. You're EE ability isn't even up to the laughable level yet, it's downright pathetic and I am saddened you're killing the academics credentials of the University I attended.

12/3/2007 4:09:28 PM