Recently I started a thread asking about some electrical aspects of a small portable chiller/warmer that I have.

The thing had been sitting in a cupboard for the last ten years, and during a recent clean out I decided I might as well throw it, but decided I’d muck around with it a bit first.

In the earlier thread I was trying to get it to run off mains power using some other bits and bobs I had lying around which are also destined for the rubbish bin. I didn’t manage it, but did discover this weekend that Jaycar has an adapter unit for sale specifically designed to run such 12 volt DC accessories off the mains. It cost about 40 bucks, which I couldn’t justify spending simply to achieve satisfaction.

So instead, tonight I ripped the unit apart. Turns out its an extremely simple unit. There are no tubes or cooling coils running through the walls or bottom of the main body. The body of the cooler is simply a polystyrene/plastic/metal box. The electrics consist of a fan, a heat sink, the on/off switch and another thing attached to the face of the heat sink opposite the fan, which I assume is the thing identified as a peltier cooler in the earlier thread. This peltier thingy is then further attached to a metal plate which was the only component actually inside the cool box.

I assume that the way this works is that the heat sink draws heat from the peltier cooler, the fan dissipates that heat, the peltier cooler makes the metal plate cold, and the metal plate draws heat out of the insulated box. Does that sound correct?

Two other questions:

What metal is the plate most likely made from? I think it’s stainless steel. Magnets don’t stick to it.

There is a thin layer of some kind of white paste between the peltier thing and the metal plate. What is this paste and what purpose does it serve?

esselte said:

Recently I started a thread asking about some electrical aspects of a small portable chiller/warmer that I have.

The thing had been sitting in a cupboard for the last ten years, and during a recent clean out I decided I might as well throw it, but decided I’d muck around with it a bit first.

In the earlier thread I was trying to get it to run off mains power using some other bits and bobs I had lying around which are also destined for the rubbish bin. I didn’t manage it, but did discover this weekend that Jaycar has an adapter unit for sale specifically designed to run such 12 volt DC accessories off the mains. It cost about 40 bucks, which I couldn’t justify spending simply to achieve satisfaction.

So instead, tonight I ripped the unit apart. Turns out its an extremely simple unit. There are no tubes or cooling coils running through the walls or bottom of the main body. The body of the cooler is simply a polystyrene/plastic/metal box. The electrics consist of a fan, a heat sink, the on/off switch and another thing attached to the face of the heat sink opposite the fan, which I assume is the thing identified as a peltier cooler in the earlier thread. This peltier thingy is then further attached to a metal plate which was the only component actually inside the cool box.

I assume that the way this works is that the heat sink draws heat from the peltier cooler, the fan dissipates that heat, the peltier cooler makes the metal plate cold, and the metal plate draws heat out of the insulated box. Does that sound correct?

Two other questions:

What metal is the plate most likely made from? I think it’s stainless steel. Magnets don’t stick to it.

There is a thin layer of some kind of white paste between the peltier thing and the metal plate. What is this paste and what purpose does it serve?

the white paste is something that facilitates heat transfer

esselte said:

So instead, tonight I ripped the unit apart. Turns out its an extremely simple unit. There are no tubes or cooling coils running through the walls or bottom of the main body. The body of the cooler is simply a polystyrene/plastic/metal box. The electrics consist of a fan, a heat sink, the on/off switch and another thing attached to the face of the heat sink opposite the fan, which I assume is the thing identified as a peltier cooler in the earlier thread. This peltier thingy is then further attached to a metal plate which was the only component actually inside the cool box.

I assume that the way this works is that the heat sink draws heat from the peltier cooler, the fan dissipates that heat, the peltier cooler makes the metal plate cold, and the metal plate draws heat out of the insulated box. Does that sound correct?

Yes.

esselte said:

Two other questions:

What metal is the plate most likely made from? I think it’s stainless steel. Magnets don’t stick to it.

There is a thin layer of some kind of white paste between the peltier thing and the metal plate. What is this paste and what purpose does it serve?

The metal plate is most likely to be aluminium.

The paste will be some form of heat-transferring substance, generally known as heat-sink compound … https://en.wikipedia.org/wiki/Thermal_grease

wookiemeister said:

the white paste is something that facilitates heat transfer

Yes. You used to be able to get it at Smith’s Dick, before their shops became just extensions of Big W’s TV dept.

i didn’t really know very much about them

the theory if something can sometimes be different to the practice

my take on it was that supplying the wrong power to something will normally bone it in some way

good to see whats in it though

captain_spalding said:

wookiemeister said:

the white paste is something that facilitates heat transfer

Yes. You used to be able to get it at Smith’s Dick, before their shops became just extensions of Big W’s TV dept.

i don’t think its a good idea to leave it on your hands though, i’ve heard cancer

http://en.wikipedia.org/wiki/Thermoelectric_effect

The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice-versa. A thermoelectric device creates voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference. At the atomic scale, an applied temperature gradient causes charge carriers in the material to diffuse from the hot side to the cold side.

This effect can be used to generate electricity, measure temperature or change the temperature of objects. Because the direction of heating and cooling is determined by the polarity of the applied voltage, thermoelectric devices can be used as temperature controllers.

The term “thermoelectric effect” encompasses three separately identified effects: the Seebeck effect, Peltier effect and Thomson effect. Textbooks may refer to it as the Peltier–Seebeck effect. This separation derives from the independent discoveries of French physicist Jean Charles Athanase Peltier and Baltic German physicist Thomas Johann Seebeck. Joule heating, the heat that is generated whenever a voltage is applied across a resistive material, is related though it is not generally termed a thermoelectric effect. The Peltier–Seebeck and Thomson effects are thermodynamically reversible, whereas Joule heating is not.

>The paste will be some form of heat-transferring substance, generally known as heat-sink compound … https://en.wikipedia.org/wiki/Thermal_grease

There was some of that between the cpu and the heat sink in the computer I was exploring this morning.

wookiemeister said:

i don’t think its a good idea to leave it on your hands though

Heh heh, that was the question I accidentally didn’t ask in my second post. I got some on my fingers. I washed it off, and I’m sure I’ve been exposed to worse things in my life, but I was just interested in seeing if I could find an MSDS for whatever it is.

morrie said:

>The paste will be some form of heat-transferring substance, generally known as heat-sink compound … https://en.wikipedia.org/wiki/Thermal_grease

There was some of that between the cpu and the heat sink in the computer I was exploring this morning.

most commonly seen there

you’ll normally find it under transistors that carry heavy current in solid state relays

The white paste is, as been mentioned, “heatsink compound”. It is used to facilitate the heat transfer between the peltier and the metal block. While in a perfect world you’d just use metal-to-metal contact, the real world needs this stuff to fill up the tiny imperfections in manufacturing. It will work almost as good without it, but better if you bring both mating surfaces to a flat mirror finish.

BTW, what do you think will happen if you connected two peltiers together, hot surface to cold…?

esselte said:

wookiemeister said:

i don’t think its a good idea to leave it on your hands though

Heh heh, that was the question I accidentally didn’t ask in my second post. I got some on my fingers. I washed it off, and I’m sure I’ve been exposed to worse things in my life, but I was just interested in seeing if I could find an MSDS for whatever it is.

if you’ve wiped it off as much as you can and washed your hands then i don;t feel its a problem – i’ve got it on my hands in the past and did what i could.

the msds will tell all though, i think it tells you on the side of the tube not to get it on your hands

>the msds will tell all though

Highly unlikely. It will tell you what might happen if you get massive exposure and trot out a whole lot of standard generic procedures, which will tend to make the stuff seem vastly more dangerous than it really is.

morrie said:

>the msds will tell all though

Highly unlikely. It will tell you what might happen if you get massive exposure and trot out a whole lot of standard generic procedures, which will tend to make the stuff seem vastly more dangerous than it really is.

i tend to evalaute the msds in a practical way

if it were that dangerous theres no way they would freely sell it

i don’t think benzene is commonly found in a public retail sense because it tends to kill people if they get it on their hands. mechanics were killing themselves by using it to wipe the grease off their hands

you can but 100 percent alcohol from chemical suppliers but you wouldn’t find it commonly in a public sense or you’d have thousands of people wiping themselves out

wookiemeister said:

edit :you can buy 100 percent alcohol from chemical suppliers but you wouldn’t find it commonly in a public sense or you’d have thousands of people wiping themselves out

wookiemeister said:

morrie said:

>the msds will tell all though

Highly unlikely. It will tell you what might happen if you get massive exposure and trot out a whole lot of standard generic procedures, which will tend to make the stuff seem vastly more dangerous than it really is.

i tend to evalaute the msds in a practical way

if it were that dangerous theres no way they would freely sell it

i don’t think benzene is commonly found in a public retail sense because it tends to kill people if they get it on their hands. mechanics were killing themselves by using it to wipe the grease off their hands

i have worked in a plant where blokes had been washing their hands in benzene for 20 years. While i am not saying benzene is not toxic, it serves to illustrate that getting a drop on your finger probably isn’t going to kill you.

wookiemeister said:

you can but 100 percent alcohol from chemical suppliers but you wouldn’t find it commonly in a public sense or you’d have thousands of people wiping themselves out

You can’t drink pure ethanol anyway. I have had a mouthful of it accidentally and it is extremely unpleasant. Anything more than around 50 percent is unpleasant and corrosive to consume.

morrie said:

wookiemeister said:

morrie said:

>the msds will tell all though

Highly unlikely. It will tell you what might happen if you get massive exposure and trot out a whole lot of standard generic procedures, which will tend to make the stuff seem vastly more dangerous than it really is.

i tend to evalaute the msds in a practical way

if it were that dangerous theres no way they would freely sell it

i don’t think benzene is commonly found in a public retail sense because it tends to kill people if they get it on their hands. mechanics were killing themselves by using it to wipe the grease off their hands

i have worked in a plant where blokes had been washing their hands in benzene for 20 years. While i am not saying benzene is not toxic, it serves to illustrate that getting a drop on your finger probably isn’t going to kill you.

i’m amazed, as far as i heard washing your hand sin this stuff was a death sentence

wookiemeister said:

wookiemeister said:

edit :you can buy 100 percent alcohol from chemical suppliers but you wouldn’t find it commonly in a public sense or you’d have thousands of people wiping themselves out

I tried to buy ethyl alcohol for extracting essential oils from plants.

morrie said:

wookiemeister said:

you can but 100 percent alcohol from chemical suppliers but you wouldn’t find it commonly in a public sense or you’d have thousands of people wiping themselves out

You can’t drink pure ethanol anyway. I have had a mouthful of it accidentally and it is extremely unpleasant. Anything more than around 50 percent is unpleasant and corrosive to consume.

you’d get people diluting it with water/lemonade/flavour

i’ve mentioned before i had warned a young person cleaning the workshop area not to be tempted to drink this stuff

lower levels might allow you to consume it easily and end up killing you. i suspect the gov tax the hell out of the stronger stuff to discourage drinks manufacturers from killing their customers

i think you before any chemical from a supplier you should read and evalaute the msds thoroughly

wookiemeister said:

morrie said:

wookiemeister said:

you can but 100 percent alcohol from chemical suppliers but you wouldn’t find it commonly in a public sense or you’d have thousands of people wiping themselves out

You can’t drink pure ethanol anyway. I have had a mouthful of it accidentally and it is extremely unpleasant. Anything more than around 50 percent is unpleasant and corrosive to consume.

you’d get people diluting it with water/lemonade/flavour

i’ve mentioned before i had warned a young person cleaning the workshop area not to be tempted to drink this stuff

lower levels might allow you to consume it easily and end up killing you. i suspect the gov tax the hell out of the stronger stuff to discourage drinks manufacturers from killing their customers

When I was young and silly, one of my mates bought a bottle of cane spirit(190proof). We tipped some into a can of coke and it stripped the paint off the side. We drank it anyway. He tipped some in a puddle onto the road and lit it up. It burned well. So did his arm, as he had accidentally spilled it in the process.

I don’t remember much after that.

Carmen_Sandiego said:

The white paste is, as been mentioned, “heatsink compound”. It is used to facilitate the heat transfer between the peltier and the metal block. While in a perfect world you’d just use metal-to-metal contact, the real world needs this stuff to fill up the tiny imperfections in manufacturing. It will work almost as good without it, but better if you bring both mating surfaces to a flat mirror finish.

BTW, what do you think will happen if you connected two peltiers together, hot surface to cold…?

it would just transfer the heat from one peltier unit to the cold face, unless theres some operating range for the unit which means beyond a certain temp it doesn’t operate and starts generating voltage?

>i suspect the gov tax the hell out of the stronger stuff to discourage drinks manufacturers from killing their customers

It is taxed at $66 per litre when made up into drinks, independent of the composition. (that number is from a few years ago, it might have gone up)

Skunkworks said:

wookiemeister said:

wookiemeister said:

edit :you can buy 100 percent alcohol from chemical suppliers but you wouldn’t find it commonly in a public sense or you’d have thousands of people wiping themselves out

I tried to buy ethyl alcohol for extracting essential oils from plants.

I suspect the isopropanol might have served your purpose better. Available from hardware stores. Don’t drink it though.

morrie said:

I suspect the isopropanol might have served your purpose better. Available from hardware stores. Don’t drink it though.

ok, might check that out. There is a method of extraction that uses butane gas but the extract must? needs to be smoked which is not my deal.

wookiemeister said:

i think you before any chemical from a supplier you should read and evalaute the msds thoroughly

Yeah, I agree. I used to use Dihydrogen Monoxide for all sorts of things until I read the MSDS.

Stealth said:

wookiemeister said:

i think you before any chemical from a supplier you should read and evalaute the msds thoroughly

Yeah, I agree. I used to use Dihydrogen Monoxide for all sorts of things until I read the MSDS.

meh, that is whack. If someone on a street stops you and asks you a series of questions that seem to reveal a deadly product that is uncontrolled by the govt and used freely by manufacturers I think it fair to impose some controls. But when it is revealed to be water along with a laugh track I think it reveals more about the motives of those surveying than people being stupid.

And as an aside I think it fairer to think that if someone cannot spell it is better and safer to estimate them as under or uneducated than stupid. Figuring other people are stupid based on spelling is stupid in itself and likely to leave one with egg on your face and out smarted.

But I see it a lot on the net, I think people imagine if they can point at other people and label the stupid because they do not know what Dihydrogen Monoxide is or cannot spell then it must mean they are then smarter than the person they are dissing.

the other thing is that you have to think what kind of environment you might be using it in

using alcohol in an unventilated area means you’ll start breathing the fumes in and the fumes might create an explosive environment

Skunkworks said:

morrie said:

I suspect the isopropanol might have served your purpose better. Available from hardware stores. Don’t drink it though.

ok, might check that out. There is a method of extraction that uses butane gas but the extract must? needs to be smoked which is not my deal.

I’d be surprised if the extract made using butane isn’t soluble in butter.

As Morrie said, it’s not advisable to consume isopropanol. Your body can cope with small amounts of it: it’s used as a base for aftershave, it’s sold as rubbing alcohol (you can find it in your supermarket under the brand name Isocol); some people find it’s great for treating acne. It’s commonly used as the alcohol in those alcohol hand wipe things and the swabs they use when the give you an injection, and in various alcohol hand sanitisers. OTOH, some people find it irritating to the skin.

Although it’s far less toxic than methanol, it metabolises to acetone, which is nasty on the liver and a known carcinogen, so you definitely wouldn’t want to try & get drunk on it (although I have heard urban legends of people in gaol getting drunk on aftershave). Wikipedia says

Toxicology

Isopropyl alcohol and its metabolite, acetone, act as central nervous system (CNS) depressants. Symptoms of isopropyl alcohol poisoning include flushing, headache, dizziness, CNS depression, nausea, vomiting, anesthesia, and coma. Poisoning can occur from ingestion, inhalation, or absorption; therefore, well-ventilated areas and protective gloves are recommended. Around 15 g of isopropyl alcohol can have a toxic effect on a 70 kg human if left untreated.

However, it is not nearly as toxic as methanol or ethylene glycol. Isopropyl alcohol does not cause an anion gap acidosis (in which a lowered blood serum pH causes depletion of bicarbonate anion) unlike ethanol and methanol. Isopropyl alcohol does however, produce an osmolal gap between the calculated and measured osmolalities of serum, as do the other alcohols.

Overdoses may cause a fruity odor on the breath as a result of its metabolism to acetone, which is further metabolized to produce the nutrients acetate and glucose. Isopropyl alcohol is oxidized to form acetone by alcohol dehydrogenase in the liver.

http://en.wikipedia.org/wiki/Isopropyl_alcohol#Toxicology

PM 2Ring said:

As Morrie said, it’s not advisable to consume isopropanol. Your body can cope with small amounts of it: it’s used as a base for aftershave, it’s sold as rubbing alcohol (you can find it in your supermarket under the brand name Isocol); some people find it’s great for treating acne. It’s commonly used as the alcohol in those alcohol hand wipe things and the swabs they use when the give you an injection, and in various alcohol hand sanitisers. OTOH, some people find it irritating to the skin.

Not to be drunk, the alcohol gets evaporated off.

Isocol contains other additives, probably to stop people drinking it. I recall pure alcohol that would evaporate away completely and it used to be used as a solvent to clean electrical contacts/radio equipment and it leaves no residue.

Skunkworks said:

Not to be drunk, the alcohol gets evaporated off.

Sure, but it’s hard to get all the alcohol out, especially once the extract thickens up, so there’ll probably be some isopropanol left behind, even if you use a vacuum extractor.

Isopropanol has a fairly distinctive odour, but it may not be easy to smell on top of all the other godies in your extract.

When chemists use toxic solvents to extract stuff that’s going to be consumed they generally do it in stages with multiple solvents, using a relatively safe solvent like ethanol for the final step.

Skunkworks said:

Isocol contains other additives, probably to stop people drinking it.

And to stop people doing what you want to do with it. :)

I suppose it may contain a perfume, but it smells a lot like straight isopropanol to me… not that my olfactory sensitivity is that fantastic. :)