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Lambda-Eyde
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[*] posted on 24-5-2012 at 15:20
Making a domestic refrigerator suitable for lab use


This is something I've been thinking about for a time, I'd like some input on the matter.

I've considered getting a small refrigerator for my lab (with a built-in fridge) for ages now, but I still haven't done it. It'd be nice to have for storing such things as bromine, hydrogen peroxide, sulfuric acid and using it when doing crystallisations. But I'd also like to keep things such as bromoethane and other flammable chemicals with low boiling points, or flammable reagents that for other reasons need to be stored cold, such as certain organometallic reagents.

Seeing as buying a (new) lab fridge is out of the question, I've been thinking about how to render a domestic refrigerator safe for use with flammable reagents. I understand that it is the thermostat that can produce sparks, is this all there is to be aware of? Also, how could one render it spark-free? Replace it with something that doesn't spark? Put a piece of tape over it? I don't know a lot about refrigerators, plumbing or electronics, so any input from the more knowledgeable members would be highly appreciated. Also, I think this topic would be interesting to other members as well - hopefully we could produce something interesting here!




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[*] posted on 24-5-2012 at 16:05


I have often wished I had such a small refrigerator for my lab. In regard to potential explosions have you read chemoleo's story about an ether explosion in a lab fridge? It's very entertaining and definitely food for thought.

I don't know why a thermostat should be a source of sparking. I would think that all that should be needed is a thermocouple penetration into the refrigerator. What spark would that produce? - none.

I presently keep my 30% H2O2 in my kitchen fridge. I keep my bromine as well as my flammable solvents in an outside storage shed that has no temperature control. Not the best, but it seems to be OK.

I still think that an ice chest, buried 2 feet below grade, and covered with an insulated cover, would be quite adequate. It would cost little, have no risk of explosion or contamination of your living space, and would be under automatic temperature control immune to power failures.




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[*] posted on 24-5-2012 at 16:28


Install a system which would inject few liters of argon into the fridge after the doors are closed. :):):)

I don't believe that fridges could explode just like that. Properly closed containers do not leak enough vapors to make an explosive mixture.
The only reason flammable solvents should be kept in a separate room is because of the fire. They're not the source of the fire, but if they're caught in one, they burst and make a fiery mess.




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[*] posted on 24-5-2012 at 16:29


http://www.tovatech.com/blog/2215/lab-refrigerator/safety-tips-for-lab-refrigerators-and-lab-freezers

Quote:

Sources that can cause internal ignition of vapors include lighting, timer housings for defrosters, thermostats and compressors.






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[*] posted on 24-5-2012 at 17:37


from entropy51:
Quote:

One particularly memorable episode involved an ether explosion in the kitichen that literally propelled the refrigerator into the backyard.


Now I understand. Leaking solvent vapors creep around, or go through wall penetrations, to the back of the fridge. There they are exposed to a sparking component such as a thermostat switch and/or a compressor motor.




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[*] posted on 24-5-2012 at 19:14


Quote: Originally posted by Magpie  
I have often wished I had such a small refrigerator for my lab. In regard to potential explosions have you read chemoleo's story about an ether explosion in a lab fridge? It's very entertaining and definitely food for thought.

No, I haven't. I didn't find it using the search function either, so I'd appreciate a link.

Quote: Originally posted by Magpie  
I don't know why a thermostat should be a source of sparking. I would think that all that should be needed is a thermocouple penetration into the refrigerator. What spark would that produce? - none.

Well, it just shows how much I know about thermostats, which is why I created this topic. :P

Quote: Originally posted by Magpie  
I presently keep my 30% H2O2 in my kitchen fridge. I keep my bromine as well as my flammable solvents in an outside storage shed that has no temperature control. Not the best, but it seems to be OK.

I used to keep my 1L bottles of sulfuric acid and 35% hydrogen peroxide in the kitchen refrigerator, until the shelf came loose and the bottles smashed in the ground. It had to happen two times (miraculously without breakages) before I brought them down to my lab for room-temperature storage. Concentrated sulfuric acid and 35% hydrogen peroxide smashing onto the kitchen floor as my 10 year old brother goes in there to find a snack is something I'd like to avoid... And yes, I know it was stupid to store them together like that. The sulfuric acid has its own tray now.

All my chemicals are stored in my lab in two separate cupboards: One for flammables (in an actual cupboard designed for flammables) and the rest in another metal cupboard. In the long run I intend to add a cupboard specifically for oxidizers as well as one for corrosives. Some of the more innocious chemicals I store on shelves; I also plan to use that option more actively (read: get my lazy ass to put up some more shelves).

Quote: Originally posted by Magpie  
I still think that an ice chest, buried 2 feet below grade, and covered with an insulated cover, would be quite adequate. It would cost little, have no risk of explosion or contamination of your living space, and would be under automatic temperature control immune to power failures.

An ice chest, as in those insulated thingies you put your beer in when you go to the beach? Seeing as I don't live near the lab anymore I'd like something more maintenance-free (refilling cold packs) and something a bit more... Professional :P The cost factor isn't much of issue either; an old, used refrigerator can be had for a song (people are always looking to get rid of such stuff), and I'm not the one paying for the electricity anyways. ;) Power failures are to be expected a few times a year, but I don't intend to store anything that would go haywire above 10 degrees, mostly chemicals that are simply more pleasant to store at lower temperatures. Bromine, ethyl bromide and acetaldehyde spring to mind. Also, the freezer on top would be nice to have; useful for recrystallizations, cooling reagents before using them etc. as well as having a steady supply of ice cubes of course.

Quote: Originally posted by Endimion17  

I don't believe that fridges could explode just like that. Properly closed containers do not leak enough vapors to make an explosive mixture.

Well... They have exploded like that, and I don't want to take that risk in my parent's house.

Quote: Originally posted by Magpie  

Now I understand. Leaking solvent vapors creep around, or go through wall penetrations, to the back of the fridge. There they are exposed to a sparking component such as a thermostat switch and/or a compressor motor.

That's a scenario I didn't consider. But aren't there any sources of ignition inside the refrigerator that would pose a more immediate risk? My flammables cabinet has a 100 mm vent on top, designed for attaching flexible ducting and a fan. I've been thinking about putting it to use, but having a 1 hp fan grinding away constantly would obviously be a waste. I'll have to think of something for that.




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[*] posted on 24-5-2012 at 19:51


The thermostat is just a switch, and will make a spark when it comes on or off. It must be moved outside of the refridgerator to make it safe. Also auto defrost switches are bad for sparks, so manual defrost are better. So if you can mount the temp controller outside and run the temp sensor in through a resealed sealed hole, then it can be safe. It has been done to ref's before for lab use. You also might be able to find a used one for sale, believe it or not, there are a lot of small ones used and there used to be a bunch on the market a while back.

But flammable liquids and air WILL make explosive mixtures, especially in a sealed space with time for the vapors to saturate the air. Some chemicals have very wide ranges of mixtures in air that are flammable. You can use a manual defrost refrig. for non-flammable chemicals easily, but for flammable chemicals, you are better to store in a flammable cabinet or in a sealed container or paint can inside a non sparking refrig. There may be a low chance of a fire, but given a chance, Murphy can really make a mess.
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[*] posted on 24-5-2012 at 20:25


Quote: Originally posted by Lambda-Eyde  
Quote: Originally posted by Magpie  
... In regard to potential explosions have you read chemoleo's story about an ether explosion in a lab fridge? It's very entertaining and definitely food for thought.

No, I haven't. I didn't find it using the search function either, so I'd appreciate a link.

Quote: Originally posted by Magpie  
I don't know why a thermostat should be a source of sparking. I would think that all that should be needed is a thermocouple penetration into the refrigerator. What spark would that produce? - none.



Quote: Originally posted by Magpie  
I still think that an ice chest, buried 2 feet below grade, and covered with an insulated cover, would be quite adequate. It would cost little, have no risk of explosion or contamination of your living space, and would be under automatic temperature control immune to power failures.

An ice chest, as in those insulated thingies you put your beer in when you go to the beach? Seeing as I don't live near the lab anymore I'd like something more maintenance-free.


I couldn't find chemoleo's story about the exploding lab fridge either. All I can remember is that a female chemist was opening a lab fridge in which a bottle of ether was stored and it exploded sending the fridge door through a nearby hood. The woman, terrified, ran out of the lab never to return. Maybe it wasn't chemoleo's story, but it is on this forum.

Although I don't know how the common garden variety fridge is constructed it seems illogical that a manufacturer would put the thermostat switch inside the fridge when all that is needed inside is the sensor which is a passive element inside a thermowell. But I'm just guessing here.

Edit- I think I've found out why the thermostat is located inside the common domestic fridge: So it can be adjusted by the user - duh.

The ice-chest I'm referring to is nothing more than an insulated plastic box with a hinged cover. Nothing could be more maintenance free. There would be no need for ice-packs as the ground stays a uniform temperature year round, once you get deep enough. I agree that it would be unprofessional looking and inconvenient to access.



[Edited on 25-5-2012 by Magpie]




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[*] posted on 25-5-2012 at 06:23


Quote: Originally posted by Lambda-Eyde  
Seeing as buying a (new) lab fridge is out of the question, I've been thinking about how to render a domestic refrigerator safe for use with flammable reagents
For maximum paranoia, there are three electrical systems with potentially sparking contacts that must be replaced: thermostat, compressor, lighting.

The simplest thermostat, mechanically reliable and cheap, is a bimetallic strip. Replace it with a thermocouple or RTD. You'll need an adequate signal conditioning unit, such as the one in a PID controller, though other options are around. While a PID controller might seem like overkill, the Asian import ones are cheap and no more expensive than a simple thermostat control. You want a fairly low duty cycle for the compressor in any case, and all these PID controllers can be programmed with adequately long turn-on/turn-off cycles.

The compressor in a refrigeration system is generally sealed, so even though it's an electric motor, the motor isn't the risk. It's the mechanical relay that operates the motor that has the sparking contacts. Replace the relay with a solid-state version (SSR = solid state relay).

The lighting system has two sources of spark: the door switch and the light socket. I'd have to guess that the ether explosion mentioned here was trigger by a spark in the door switch, a hazard pretty much guaranteed to manifest exactly when some person is right in front of the refrigerator. Replace the door switch with a Hall effect sensor and a little magnet in the door. Alternately a mechanical switch and an opto-interrupter could be used. These are just sensors; you'll likely need another SSR to switch the current.

The typical bayonet socket for a light bulb is subject to corrosion and thermal cycling and subsequent loose and/or high-resistance connection leading to spark. It's why you see glassed-and-armored lamp fixtures when explosion resistance is required. For a refrigerator, perhaps the easiest thing to do is to replace the lamp with LED strips. Don't use a push-in mechanical connection; make sure all connections are screwed down or soldered.
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[*] posted on 25-5-2012 at 08:02


Or, you can make sure:
- your containers aren't a million years old and cracking
- aren't plugged with corks with pores the size of the Moon
- you don't store a cubic metre of ether in the fridge
- you don't put them in the fridge immediately after pouring when they're all wet close to the top

I'm sure those rare accidents are due to the extreme sloppiness and careless behaviour of the people working in the lab.
If the danger was so severe, most of the sheds around the world would explode every now and then. But it doesn't happen.

Be sensible and use standard laboratory precautions and nothing bad will happen. If a containes has a leaky top, reinforce its neck with teflon tape.
Use the money for pimping the fridge to buy more chemicals or... candy, I don't know.




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[*] posted on 25-5-2012 at 08:50


Alternatively, one can apply conductive grease on light bulb sockets to reduce corrosion :) One can also use the principle of the Davy lamp to reduce the risk of sparks igniting vapors:

http://www.sciencemadness.org/talk/viewthread.php?tid=5498#p...

http://www.sciencemadness.org/talk/viewthread.php?tid=6707#p...

:cool:




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[*] posted on 25-5-2012 at 10:54


Perhaps you could replace the conventional internal thermostat with a unit like this:

http://www.northernbrewer.com/shop/johnson-refrigerator-ther...




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[*] posted on 25-5-2012 at 13:08


I'm just wondering, isn't a refrigerator (regardless of the thermostat's hazards) better than nothing at all? I don't own too many flammable liquids, but I find that storing things in a basement or some kind of cave is more than adequate. The ground stays at 15 degrees centigrade all year round, which is perfectly adequate for storing hydrogen peroxide and other goodies.



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[*] posted on 25-5-2012 at 16:40


Quote: Originally posted by Dr.Bob  
The thermostat is just a switch, and will make a spark when it comes on or off. It must be moved outside of the refridgerator to make it safe. Also auto defrost switches are bad for sparks, so manual defrost are better. So if you can mount the temp controller outside and run the temp sensor in through a resealed sealed hole, then it can be safe. It has been done to ref's before for lab use.

An older refrigerator shouldn't have an automatic defrost function, I reckon. Do you know of any laboratory refs that you could point me to?

Quote: Originally posted by Dr.Bob  
You also might be able to find a used one for sale, believe it or not, there are a lot of small ones used and there used to be a bunch on the market a while back.

In a country with 5 million inhabitants, the market for used lab equipment is practically non-existent. Buying a refrigerator from abroad is out of the question.

Quote: Originally posted by Dr.Bob  
But flammable liquids and air WILL make explosive mixtures, especially in a sealed space with time for the vapors to saturate the air. Some chemicals have very wide ranges of mixtures in air that are flammable. You can use a manual defrost refrig. for non-flammable chemicals easily, but for flammable chemicals, you are better to store in a flammable cabinet or in a sealed container or paint can inside a non sparking refrig. There may be a low chance of a fire, but given a chance, Murphy can really make a mess.

Yes, it's mr. Murphy I'm afraid of. I wouldn't like having him visit my lab. I'm more concerned about sparks inside the refrigerator (where fumes can build up over months) than outside. Although my lab isn't that big, I doubt explosive mixtures would form unless I left a bucket of gasoline open on the floor for an extended period.

Quote: Originally posted by watson.fawkes  
For maximum paranoia, there are three electrical systems with potentially sparking contacts that must be replaced: thermostat, compressor, lighting.

I was waiting for you to reply, watson.fawkes. :D Thank you for an informative and helpful answer as always. Yes, "maximum paranoia" is what I'm going for - though, within the limits of sanity. I didn't consider the lighting, which in retrospect is kinda obvious.

Quote: Originally posted by watson.fawkes  
The simplest thermostat, mechanically reliable and cheap, is a bimetallic strip. Replace it with a thermocouple or RTD. You'll need an adequate signal conditioning unit, such as the one in a PID controller, though other options are around. While a PID controller might seem like overkill, the Asian import ones are cheap and no more expensive than a simple thermostat control. You want a fairly low duty cycle for the compressor in any case, and all these PID controllers can be programmed with adequately long turn-on/turn-off cycles.

PIDs are relatively cheap, that's a good idea. But I would need two, right? One for the freezer and one for the refrigerator? Then the cost is doubled, but it's not more than I'd like to spend. Also, PIDs look cool - that's a neat bonus. Problem is that I have no idea about how to wire them and operate/program one. I have no formal training in practical electronics, only what the high school physics curriculum teaches - i.e. current and voltage laws, how semiconductors work, flux density calculations and induction. Sadly, they didn't teach us how to make a functional, useful circuit with a soldering iron and components...

Quote: Originally posted by watson.fawkes  
The compressor in a refrigeration system is generally sealed, so even though it's an electric motor, the motor isn't the risk. It's the mechanical relay that operates the motor that has the sparking contacts. Replace the relay with a solid-state version (SSR = solid state relay).

I take it that swapping the mechanical relay for an SSR is easy? From a cursory eBay search, they seem to be dirt cheap - but how do I know which one to pick? Just make sure they're inside the voltage and current specifications?

Quote: Originally posted by watson.fawkes  
The lighting system has two sources of spark: the door switch and the light socket. I'd have to guess that the ether explosion mentioned here was trigger by a spark in the door switch, a hazard pretty much guaranteed to manifest exactly when some person is right in front of the refrigerator. Replace the door switch with a Hall effect sensor and a little magnet in the door. Alternately a mechanical switch and an opto-interrupter could be used. These are just sensors; you'll likely need another SSR to switch the current.

The Hall effect sensor seems like a neat thing, thanks for the idea.

Quote: Originally posted by watson.fawkes  
The typical bayonet socket for a light bulb is subject to corrosion and thermal cycling and subsequent loose and/or high-resistance connection leading to spark. It's why you see glassed-and-armored lamp fixtures when explosion resistance is required. For a refrigerator, perhaps the easiest thing to do is to replace the lamp with LED strips. Don't use a push-in mechanical connection; make sure all connections are screwed down or soldered.

No doubt a standard light bulb connection would corrode inside a refrigerator with bromine and friends. The LED strips seems like a good idea, but that poses another problem as the standard light bulbs run on the net voltage, while LEDs require lower voltages and DC. Mixing a transformer and rectifier into this whole mess would be cumbersome and kind of over-the-top. Maybe I could make the housing for the lamp hermetically sealed? Then there's the problem on how to do that while still keeping in mind it has to be changed every few years.


Quote: Originally posted by Endimion17  
Or, you can make sure:
- your containers aren't a million years old and cracking
- aren't plugged with corks with pores the size of the Moon
- you don't store a cubic metre of ether in the fridge
- you don't put them in the fridge immediately after pouring when they're all wet close to the top

Have you ever been in the stockroom of a university lab? You can certainly smell all the different solvents and other goodies, even though the containers aren't faulty. The flammables cupboard at my high school also had a distinct smell. It is to be expected. Storing a cubic meter of ether in the fridge isn't really relevant. In such a small space you don't really need large amounts before significant fumes can build up. However, making sure the containers are dry before you put them inside is a good tip, thanks.

Quote: Originally posted by Endimion17  
I'm sure those rare accidents are due to the extreme sloppiness and careless behaviour of the people working in the lab.
If the danger was so severe, most of the sheds around the world would explode every now and then. But it doesn't happen.

It may be due to sloppiness, it may be honest accidents. Nevertheless, I'm not willing to risk a devastating fire in my parent's house, taking my lab with it. Who knows, even I may become sloppy in a moment of whimsyness.

Quote: Originally posted by Magpie  
Perhaps you could replace the conventional internal thermostat with a unit like this:

http://www.northernbrewer.com/shop/johnson-refrigerator-ther...

That would be an option, yes. But it's significantly more expensive than a PID (and less cool, of course).

Quote: Originally posted by White Yeti  
I'm just wondering, isn't a refrigerator (regardless of the thermostat's hazards) better than nothing at all? I don't own too many flammable liquids, but I find that storing things in a basement or some kind of cave is more than adequate. The ground stays at 15 degrees centigrade all year round, which is perfectly adequate for storing hydrogen peroxide and other goodies.

I'm not sure whether you're arguing for or against getting a lab fridge here. But anyways, in time I will buy one regardless of whether I decide to make it explosion proof or not. It would be nice for storing bromine, ammonia and other non-flammable nasties, as well as having ice cubes on hand at all times. The problem is that some flammable reagents really need to be stored cold, such as acetaldehyde and ethyl bromide. It's this kind of stuff I'm worried about storing in a domestic fridge. My lab in the basement is 10-15 C most of the time anyways.


Sort of unrelated, but can someone recommend a good textbook on practical circuitry? My girlfriend has a book called "Electric Circuits" by Nilsson and Riedel (she's studying to become a computer engineer), but it's not really what I'm looking for - it's just another calculus textbook with the wrong cover. :P What I want is a more practical and basic approach to designing simple circuits, soldering etc. as well as explaining what certain components do. I know what resistors and transistors do, but I'd also like to know how SSRs, PIDs, capacitors, transformers, microcontrollers, sensors and diodes work - and most of all, how to implement them in a circuit to do what I want. What I'm not looking for is a theoretical treatise on transistor designs with tens of pages on PNP layers complete with differential equations to describe ~everything they do...




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[*] posted on 25-5-2012 at 17:44


Quote: Originally posted by Lambda-Eyde  
PIDs are relatively cheap, that's a good idea. But I would need two, right? One for the freezer and one for the refrigerator? Then the cost is doubled, but it's not more than I'd like to spend. Also, PIDs look cool - that's a neat bonus. Problem is that I have no idea about how to wire them and operate/program one.
[...]
I take it that swapping the mechanical relay for an SSR is easy? From a cursory eBay search, they seem to be dirt cheap - but how do I know which one to pick? Just make sure they're inside the voltage and current specifications?
[...]
No doubt a standard light bulb connection would corrode inside a refrigerator with bromine and friends. The LED strips seems like a good idea, but that poses another problem as the standard light bulbs run on the net voltage, while LEDs require lower voltages and DC
Running a two-zone control with a single compressor and good temperature control in both zones is more than I'd care to take on in modifying a residential style refrigerator-freezer combo. The way these work is that the freezer cools the refrigerator by modulating the heat exchange between them. The temperatures in these two zones are not actually independent. That's OK if all you need for the freezer is to keep water solid. Personally, I think the easiest way to get two zones is to start with two refrigerators (or freezers) and set each to its own temperature.

Wiring up PID's is a good beginner project. It's mostly wiring; there's not a lot of electronics proper to it except for some component selection. SSR's are more-or-less a drop-in replacement for mechanical relays; they're better in many ways, because the tend to have a fairly wide range for their input signals. There an output on every PID I've seen that can trigger an SSR without any other interface but the wire. As for the outputs, just be sure the rated voltage and current are larger than what you need.

The only even partly tricky thing it so specify the SSR for the inrush current for the compressor, not its ordinary operating current, which is lower. On the nameplate of the compressor, there should be two current ratings. For the one in a residential refrigerator, you might need to find a spec sheet. Just pick the larger of the two values as the minimum for the SSR capacity.

Chemical compatibility for lighting is going to be a problem no matter what you do. For that matter, chemical compatibility for even the interior plastic lining of the refrigerator might be a problem, depending on what you're storing. There's a reason why a lot of lab refrigerators have sheet metal linings. For LED's, though, you can just stick them inside glass tubes. The only glassworking is cutting and polishing, well within the capacity of a complete novice (and you could skip the polishing, even). You could use a standard explosion-proof fixture, but they are bulky and expensive. Using LED's and glass tubing seems a better way to go.

The easiest way to power the LED's is to use an AC power supply, the moral equivalent of a wall wart, and use an SSR to switch the AC power into the adapter.
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[*] posted on 25-5-2012 at 23:28


There seem to be some mutual misunderstandings here, watson.fawkes. Correct me if I'm wrong.

Quote: Originally posted by watson.fawkes  
Running a two-zone control with a single compressor and good temperature control in both zones is more than I'd care to take on in modifying a residential style refrigerator-freezer combo. The way these work is that the freezer cools the refrigerator by modulating the heat exchange between them. The temperatures in these two zones are not actually independent. That's OK if all you need for the freezer is to keep water solid.

I thought they were independent and driven by two separate compressors, thus leading me to believe two separate PIDs were needed. I realize that controlling two temperature zones with two PIDs and one compressor is way out my league, and would probably deserve its own prepublication topic if it were to be carried out.

Then, let's go back a little bit: What if I want to control a refrigerator/freezer combo with only one PID? Then I would have the PID control the temperature in the fridge (as the freezer wouldn't need to do anything but keep water solid, as you said), would that work? I don't see how substituting the thermostat for a PID/thermocouple combination would involve any changes that would alter the way in which heat (or rather, cold) is distributed between the two zones. In principle it should be the same, just with a different gadget controlling the compressor's duty cycles. Right?

Quote: Originally posted by watson.fawkes  

The only even partly tricky thing it so specify the SSR for the inrush current for the compressor, not its ordinary operating current, which is lower. On the nameplate of the compressor, there should be two current ratings. For the one in a residential refrigerator, you might need to find a spec sheet. Just pick the larger of the two values as the minimum for the SSR capacity.

If those values aren't on the compressor, then finding the spec sheet for a fridge that's older than me might prove a challenge.

Quote: Originally posted by watson.fawkes  
Chemical compatibility for lighting is going to be a problem no matter what you do. For that matter, chemical compatibility for even the interior plastic lining of the refrigerator might be a problem, depending on what you're storing. There's a reason why a lot of lab refrigerators have sheet metal linings.

I'm not really concerned about that. There would have to be rather high concentrations of quite obnoxious chemicals before there would be anything but cosmetic damage to the plastic insides of the fridge.

Quote: Originally posted by watson.fawkes  
For LED's, though, you can just stick them inside glass tubes. The only glassworking is cutting and polishing, well within the capacity of a complete novice (and you could skip the polishing, even). You could use a standard explosion-proof fixture, but they are bulky and expensive. Using LED's and glass tubing seems a better way to go.

Would that even be nescessary? I can't imagine LEDs setting fire to anything. The intent of my previous post was to discuss the possibilities of sealing the original light housing without replacing it, thus avoiding the added trouble of installing a low voltage DC source for driving the LEDs.

Quote: Originally posted by watson.fawkes  
The easiest way to power the LED's is to use an AC power supply, the moral equivalent of a wall wart, and use an SSR to switch the AC power into the adapter.

You lost me right there. Don't you mean DC? And where does the SSR come into play, would it wired up to the Hall effect sensor?

[Edited on 26-5-2012 by Lambda-Eyde]




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[*] posted on 26-5-2012 at 04:51


Quote: Originally posted by Lambda-Eyde  
Have you ever been in the stockroom of a university lab? You can certainly smell all the different solvents and other goodies, even though the containers aren't faulty. The flammables cupboard at my high school also had a distinct smell. It is to be expected. Storing a cubic meter of ether in the fridge isn't really relevant. In such a small space you don't really need large amounts before significant fumes can build up. However, making sure the containers are dry before you put them inside is a good tip, thanks.


Of course, all the time. Even the places piled up and without adequate ventilation. The smell inside, although sometimes headache-inducing, is the smell in the range of ppm. If there was an actual combustible air mixture inside, you couldn't breathe. You'd suffocate. Laryngospasm. ;)
Depending on the solvent, the speed of gradual fall from narcosis to a coma and death would vary.

Quote:

It may be due to sloppiness, it may be honest accidents. Nevertheless, I'm not willing to risk a devastating fire in my parent's house, taking my lab with it. Who knows, even I may become sloppy in a moment of whimsyness.


Judging by the conditions I saw at universities and few laboratories, such explosions should've happened many times so far. People that do laboratory work for a living are generally a bit sloppy. It comes with years of work.
I'm just saying that measures you're discussing here are measures used for large refrigerators intended to be stuffed with solvents and rarely opened. The ones in research labs, in basements, serving as a backup and rarely opened. I'm sure you're going to open your fridge at least once a week.



Quote:

I'm not sure whether you're arguing for or against getting a lab fridge here. But anyways, in time I will buy one regardless of whether I decide to make it explosion proof or not. It would be nice for storing bromine, ammonia and other non-flammable nasties, as well as having ice cubes on hand at all times. The problem is that some flammable reagents really need to be stored cold, such as acetaldehyde and ethyl bromide. It's this kind of stuff I'm worried about storing in a domestic fridge. My lab in the basement is 10-15 C most of the time anyways.


Fridge is a cool thing, but have you considered just ampouling those liquids? Bromine should be stored in ampoules. If you store it in a nonsealed bottle, such as those with borosilicate glass with a plastic screw-on top, you'll mess up your fridge. You'll fuck up every piece of metal inside, for example the evaporator. Seems like a waste of money, if you ask me. And if you seal it in an ampoule, it doesn't have to stay in the fridge.
Ammonia doesn't have to stay in the fridge...

I hope you're not planning to cram the fridge with various chemicals, because some of them aren't compatible. If you're going to use the fridge for organic solvents such as ether, benzene, toluene, don't put stuff like nitric acid, which is far more notorious for its seeping from the bottle.

Therefore, I'm asking you - how much of those solvent are you planning to cram into the fridge, and what chemicals are we talking about?




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[*] posted on 26-5-2012 at 06:21


Quote: Originally posted by Endimion17  

Of course, all the time. Even the places piled up and without adequate ventilation. The smell inside, although sometimes headache-inducing, is the smell in the range of ppm. If there was an actual combustible air mixture inside, you couldn't breathe.

Alright, that was a really bad example. What I was getting at is that containers leak nonetheless, which can be a problem in a confined space. Think a quarter of a cubic meter compared to a stockroom.

Quote: Originally posted by Endimion17  
I'm just saying that measures you're discussing here are measures used for large refrigerators intended to be stuffed with solvents and rarely opened. The ones in research labs, in basements, serving as a backup and rarely opened. I'm sure you're going to open your fridge at least once a week.

No, in fact I'll be opening it rather rarely. I live away from my lab to attend university. I haven't been home for almost two months, and then I didn't even do anything in the lab. So my fridge will be closed for months on end until I return, and even then I might not even use something in it - then another three months pass, and so on.

Quote: Originally posted by Endimion17  
Fridge is a cool thing, but have you considered just ampouling those liquids? Bromine should be stored in ampoules. If you store it in a nonsealed bottle, such as those with borosilicate glass with a plastic screw-on top, you'll mess up your fridge. You'll fuck up every piece of metal inside, for example the evaporator. Seems like a waste of money, if you ask me. And if you seal it in an ampoule, it doesn't have to stay in the fridge.
Ammonia doesn't have to stay in the fridge...

I described the way in which I store bromine in this thread. What I didn't mention is that the threads also have a few windings of teflon tape around them. I can only smell the bromine by sticking my nose to the bottle. It has been in one of my metal cabinets for (I think) two years now, without any visible damage around it to labels, plastics or the sheet metal in the cabinet. My hydrochloric acid is a much bigger problem in that regard; it has caused my stands and clamps to become covered in thick layers of rust. Anyways, I think ampoules are impractical for a chemical I plan to store relatively large amounts of and use quite often.

I know ammonia doesn't have to stay in a fridge, but the 25% variety is unbearable to handle at room temperature, even outside on a windy day. I know, I know - "FUMEHOOD", you say. :P

Quote: Originally posted by Endimion17  
I hope you're not planning to cram the fridge with various chemicals, because some of them aren't compatible. If you're going to use the fridge for organic solvents such as ether, benzene, toluene, don't put stuff like nitric acid, which is far more notorious for its seeping from the bottle.

Yes, I know how to store chemicals properly - although I would have to be slightly less strict with the refrigerator. To make up for it (to some degree) I would group them strictly and be generous with the spill trays.

Quote: Originally posted by Endimion17  
Therefore, I'm asking you - how much of those solvent are you planning to cram into the fridge, and what chemicals are we talking about?

I saved this for the last quote: In which post did I mention anything about storing solvents in the fridge? I didn't. It's an important distinction to make: Solvents come in 1 liter bottles, I have several of them, and I will get even more solvents as time progresses. I think I have about 10 L of solvents at the moment. They are stored inside a flammables cabinet, as all but a few are highly flammable. What I want to store in the fridge, in addition to a buttload of non-flammable reagents, are flammable reagents that for some reason have to be kept cold, such as ethyl bromide, acetaldehyde and styrene. The only flammable reagents that would be kept in the fridge are those that a) have low boiling points, b) are prone to polymerisation, which is slowed by colder temperatures or c) would otherwise decompose/degrade faster at room temperature. Most, if not all of these, would be made by myself. We're speaking quantities in the range of anything from a few mL to a maximum 250 mL, and we're dealing with a small group of chemicals - not my whole solvent repertoire.

I don't know if you're indirectly accusing me of being an idiot, but why would I store such things as benzene and toluene in a fridge? That's just... Stupid. :P



(I'm only kidding with you :D)

Edit: Was that pun intended? ;)

[Edited on 26-5-2012 by Lambda-Eyde]




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[*] posted on 26-5-2012 at 08:54


Quote: Originally posted by Lambda-Eyde  
Alright, that was a really bad example. What I was getting at is that containers leak nonetheless, which can be a problem in a confined space. Think a quarter of a cubic meter compared to a stockroom.


Well, yeah, that's is a valid argument.


Quote:
No, in fact I'll be opening it rather rarely. I live away from my lab to attend university. I haven't been home for almost two months, and then I didn't even do anything in the lab. So my fridge will be closed for months on end until I return, and even then I might not even use something in it - then another three months pass, and so on.


Several months? :o
Well, in that case, go for it. But, what about the electric bills? Are your parents (or whoever you're living with) ok with one additional money-sucking appliance? I sincerely recommend one of those small fridges we usually see in bars. I know they're promotional, and that the bar doesn't really own them, but try to get hands on the smallest fridge you can find.


Quote:
I described the way in which I store bromine in this thread. What I didn't mention is that the threads also have a few windings of teflon tape around them. I can only smell the bromine by sticking my nose to the bottle. It has been in one of my metal cabinets for (I think) two years now, without any visible damage around it to labels, plastics or the sheet metal in the cabinet. My hydrochloric acid is a much bigger problem in that regard; it has caused my stands and clamps to become covered in thick layers of rust. Anyways, I think ampoules are impractical for a chemical I plan to store relatively large amounts of and use quite often.


Yup, those bottles. Teflon is a must. However, bromine is best kept sealed. It's usually sold sealed. For long term storage, consider storing it in few sealed test tubes, or real ampoules.
Fridge evaporators are made of aluminium, and though cold, there's moisture around them. Small amounts of bromine vapors, together with moisture, sealed for months... That's a neat way to screw up the evaporator in a few years. Just saying...


Quote:
I know ammonia doesn't have to stay in a fridge, but the 25% variety is unbearable to handle at room temperature, even outside on a windy day. I know, I know - "FUMEHOOD", you say. :P


You've mentioned 10-15 °C in your basement. That's ok.
My room conditions are pretty much the same. I don't have a fumehood because there's no space for it. I have a forced electric ventilation and if I sense a too powerful whiff, I stop breathing. :D
I've learned to breathe calmly. Laboratories aren't a place for excercise. :D
If I have to work with dangerous amounts of choking material, which is like hardly ever, I do it outside.
To prevent bad scenarios, keep a small bottle of ammonia at hand, and keep the main container in storage.


Quote:
Yes, I know how to store chemicals properly - although I would have to be slightly less strict with the refrigerator. To make up for it (to some degree) I would group them strictly and be generous with the spill trays.


I'd be more strict with the fridge because of the possible effects on the equipment.
All my corrosive liquid reagents are on shelves. Each compatible group or sometimes several identical compounds share one separate spill tray. The flammambles are in the cupboard on the floor. No trays. The lab is locked and inaccessible to pets.


Quote:
I saved this for the last quote: In which post did I mention anything about storing solvents in the fridge? I didn't. It's an important distinction to make: Solvents come in 1 liter bottles, I have several of them, and I will get even more solvents as time progresses. I think I have about 10 L of solvents at the moment. They are stored inside a flammables cabinet, as all but a few are highly flammable. What I want to store in the fridge, in addition to a buttload of non-flammable reagents, are flammable reagents that for some reason have to be kept cold, such as ethyl bromide, acetaldehyde and styrene. The only flammable reagents that would be kept in the fridge are those that a) have low boiling points, b) are prone to polymerisation, which is slowed by colder temperatures or c) would otherwise decompose/degrade faster at room temperature. Most, if not all of these, would be made by myself. We're speaking quantities in the range of anything from a few mL to a maximum 250 mL, and we're dealing with a small group of chemicals - not my whole solvent repertoire.I don't know if you're indirectly accusing me of being an idiot, but why would I store such things as benzene and toluene in a fridge? That's just... Stupid. :P (I'm only kidding with you :D)Edit: Was that pun intended? ;)


Seems I skipped that part, sorry.
Well, if those are the chemicals you're concerned about, then a fridge is a nice add-on, though cold basements work just as fine. Not for the ones prone to polymerisation, though. But things like styrene generally have a low shelf life and are bought fresh.
I mentioned common solvents because people do store them in fridges, and there was some solvent-talk here.

How about just not using the lamp in the fridge, and hot-gluing any spark-prone things? Who needs a fancy light? Fridges in universities rarely have them.

You could also seal every bottle in its own plastic bag, if the fumes don't attack the paper label on the bottle. That would slow down the vapors, too.




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[*] posted on 26-5-2012 at 11:17


Quote: Originally posted by Lambda-Eyde  
I thought they were independent and driven by two separate compressors, thus leading me to believe two separate PIDs were needed.
[...]
Then, let's go back a little bit: What if I want to control a refrigerator/freezer combo with only one PID? Then I would have the PID control the temperature in the fridge (as the freezer wouldn't need to do anything but keep water solid, as you said), would that work? [...] In principle it should be the same, just with a different gadget controlling the compressor's duty cycles.
[...]
If those values aren't on the compressor, then finding the spec sheet for a fridge that's older than me might prove a challenge.
[...]
Would that even be nescessary? I can't imagine LEDs setting fire to anything. The intent of my previous post was to discuss the possibilities of sealing the original light housing without replacing it, thus avoiding the added trouble of installing a low voltage DC source for driving the LEDs.

Quote: Originally posted by watson.fawkes  
The easiest way to power the LED's is to use an AC power supply, the moral equivalent of a wall wart, and use an SSR to switch the AC power into the adapter.

You lost me right there. Don't you mean DC? And where does the SSR come into play, would it wired up to the Hall effect sensor?
Standard residential refrigerators have only a single compressor. If you can find one with two, go for it and just use two PID controllers.

As I recall, the thermostat switch in these units is in the refrigerator compartment, but evaporator (the cold plate) is in the freezer. It doesn't matter a whole lot where you put the thermocouple, be it the freezer or refrigerator side; the controller will work adequately. What you will likely want, though, is a thermometer for the other side. Since it's passively regulated, it would still be a good idea to know.

If you can't find a spec sheet, just measure the ordinary operating current of the compressor. To estimate the inrush current, multiply by 8. That's slightly conservative as an estimate to spec your PID. I'd guess you're going to end up with either a 20 A or a 30 A unit, and there's not a huge price differential between these.

The reason to encapsulate LED lighting strips to protect the LED's. It's not for fire safety. If you don't think it will be a problem, don't do it. If it is a problem and your LED's fail, then retrofit.

Power supplies for the easiest-to-find LED lighting strips are an AC adapter at mains power level with a 24 V DC output. It's easier to switch the AC input to such an adapter than to switch the DC output. It also saves energy by eliminating the phantom power draw of an adapter operating without load.

I can't recommend an off-the-shelf Hall effect sensor, though I imagine there exists such products. Just make sure the output can be fed directly into an SSR. I have to figure that such products exist. You could also just use a manual switch, if you want to save the expense.

Since you mentioned that this will be largely a dead-storage refrigerator, there are a couple of things you can do to decrease the energy draw. The first is just to put extra insulation on it. In the US, you can get 2" polyurethane foam sheets in standard building dimensions. I don't know the situation in Europe, but I imagine there a 50 mm product equivalent. Just clad your refrigerator with that. The second thing to do is to reconfigure the coolant piping to make what's called a "split system". All that means is that the compressor and radiator are not physically part of the same case as the chilled chamber. This allows you to insulate one face of the refrigerator better and moves the hot radiator away from the cold chamber, for less heat flow. The only extra thing you need to make a split system is to braze on some extra copper tubing to the coolant lines, and then insulate them (foam-in-place polyurethane is good for that).
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