Peltier pads / thermal paste and headsinks

[AlpacasSayQuack]

To start off, please don't argue about "transferring cold." I did well in science so I know there isn't actually a thing as "transferring cold." This is just the easiest way to word what I'm doing. 

Anyway, I'm building a humidor for my cigars. I live in northern Idaho and my house doesn't have central AC so parts of my house get too hot (almost 80 degrees during the hot summer) for cigars. I need to keep my cigars around 70 degrees. I need more storage than a box so I'm turning an endtable into a humidor. 

My plan:

Arduino to control temperature from a peltier pad. I'll build the pad into the back of the endtable with the hot side out of the table and the cold side inside with a fan. 

I picked up some junk heatsinks. One was a solid aluminum heatsink with fins, and the other was one with heatpipes. Real junk. I found it in a box with a Celeron processor from 1998. 

First off, does thermal paste work for "transferring the cold" from the cold side of the peltier pad? 

Second, which heatsink should I use on the cold side? Will heatpipes work transferring the cold to the humidor/endtable or should I use the solid heatsink for the cold side? 

[Hackentosher]

Cold is the absence of heat, so effectively you're transferring the heat from your cigars to the cold side of the peltier, with the thermal paste as an interface between your heatsink and the TEC. 

[AlpacasSayQuack]

1 minute ago, Hackentosher said:

Cold is the absence of heat, so effectively you're transferring the heat from your cigars to the cold side of the peltier, with the thermal paste as an interface between your heatsink and the TEC. 

I know that. These are the answers to my question that I was trying to weed out. This helps me none. 

If i need to reword my question:

Is thermal paste good at transferring the heat from a heatsink in the 80 degree air to a cold peltier pad? 

Furthermore, would a solid aluminum heatsink or one with heatpipes be better at transferring heat from the ambient air to the cold side of the peltier pad?

There. I reworded it and now I may be able to get answers.

[MedievalMatt]

16 minutes ago, AlpacasSayQuack said:

I know that. These are the answers to my question that I was trying to weed out. This helps me none. 

If i need to reword my question:

Is thermal paste good at transferring the heat from a heatsink in the 80 degree air to a cold peltier pad? 

Furthermore, would a solid aluminum heatsink or one with heatpipes be better at transferring heat from the ambient air to the cold side of the peltier pad?

There. I reworded it and now I may be able to get answers.

the purpose of thermal paste is not necessarily heat transfer.

 

While yes, it is exception at heat transfer.  the main purpose is to fill in the tiny microscopic imperfections in two surfaces to facilitate a better interface between the two.

 

not sure exactly what you are going for.

 

but you would have Hot-thing -> thermal paste(could be a thermal pad, whatever) -> heatsink of some kind -> ambeint air.

 

If im understanding you right.  you want to replace ambient air with the cold side of a peltier cooler?

 

if you are doing that just do this hot-thing -> thermal paste -> cold-side-of-peltier.

 

 

[AlpacasSayQuack]

7 minutes ago, MedievalMatt said:

the purpose of thermal paste is not necessarily heat transfer.

 

While yes, it is exception at heat transfer.  the main purpose is to fill in the tiny microscopic imperfections in two surfaces to facilitate a better interface between the two.

 

not sure exactly what you are going for.

 

but you would have Hot-thing -> thermal paste(could be a thermal pad, whatever) -> heatsink of some kind -> ambeint air.

 

If im understanding you right.  you want to replace ambient air with the cold side of a peltier cooler?

 

if you are doing that just do this hot-thing -> thermal paste -> cold-side-of-peltier.

 

 

No.

Coldside of peltier > thermal paste > heatsink (which would be cold) . 

Would thermal paste be efficient when it is attached to a cold surface vs. a hot CPU lid?

Secondly, which heatsink would work better when cold, heatpiped one or a solid aluminum?
I'm making a wine cooler basically. Instead of running a compressor, rad, refrigerant etc, i'm running a peltier pad. 

[MedievalMatt]

1 minute ago, AlpacasSayQuack said:

No.

Coldside of peltier > thermal paste > heatsink (which would be cold) . 

Would thermal paste be efficient when it is attached to a cold surface vs. a hot CPU lid?

Secondly, which heatsink would work better when cold, heatpiped one or a solid aluminum?
I'm making a wine cooler basically. Instead of running a compressor, rad, refrigerant etc, i'm running a peltier pad. 

 

Ah, I see.

 

Thermal paste typically looses efficiency as it cools.  there are exceptions.  Thermal Grizzly cryonaught is designed for LN2 overclockers, and therefore sub zero temps.

 

Heatpipes are designed (at least the ones on CPU coolers) so that the flat mounting surface is at the bottom, and the liquid evaporates up.  they wont work well when cold (if at all).

 

Assuming there will be airflow, you want to increase the surface area of the cold side as much as possible.  Probably using copper, or aluminum with some fins.  Without airflow your not going to be able to cool the entire area effectively, there will be cold spots and hot spots.

 

if you have the ability, take a chunk of aluminum, cut out some fins, that will be about as good as you could get AFAIK.

 

youll also need something on the hot side to help the cold side out, and your heatpiped cooler will be very effective at that.

[AngryBeaver]

or realize you have thought too much on this already and spend about $200 on something like this https://www.amazon.com/NewAir-CC-100-Count-Cigar-Cooler/dp/B00N1XAVFC/ref=asc_df_B00N1XAVFC/?tag=hyprod-20&linkCode=df0&hvadid=167135453740&hvpos=1o1&hvnetw=g&hvrand=13731954379176832998&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9060340&hvtargid=pla-273305811979&psc=1

 

or for 300 a 400 count cooler

 

https://www.amazon.com/NewAir-CC-100-Count-Cigar-Cooler/dp/B00N1XAVDY/ref=asc_df_B00N1XAVFC/?tag=hyprod-20&linkCode=df0&hvadid=167135453740&hvpos=1o1&hvnetw=g&hvrand=13731954379176832998&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9060340&hvtargid=pla-273305811979&th=1

[AlpacasSayQuack]

33 minutes ago, MedievalMatt said:

 

Ah, I see.

 

Thermal paste typically looses efficiency as it cools.  there are exceptions.  Thermal Grizzly cryonaught is designed for LN2 overclockers, and therefore sub zero temps.

 

Heatpipes are designed (at least the ones on CPU coolers) so that the flat mounting surface is at the bottom, and the liquid evaporates up.  they wont work well when cold (if at all).

 

Assuming there will be airflow, you want to increase the surface area of the cold side as much as possible.  Probably using copper, or aluminum with some fins.  Without airflow your not going to be able to cool the entire area effectively, there will be cold spots and hot spots.

 

if you have the ability, take a chunk of aluminum, cut out some fins, that will be about as good as you could get AFAIK.

 

youll also need something on the hot side to help the cold side out, and your heatpiped cooler will be very effective at that.

Great. This answers my questions fully! One of my junk heatsinks I found is just that: Solid piece of aluminum with big fins. Thanks for the cryo paste! I'll use it. Heatpipe heatsink for hotside outside of endtable and the solid aluminum with fans for airflow on the inside. 

[AlpacasSayQuack]

27 minutes ago, AngryBeaver said:

or realize you have thought too much on this already and spend about $200 on something like this https://www.amazon.com/NewAir-CC-100-Count-Cigar-Cooler/dp/B00N1XAVFC/ref=asc_df_B00N1XAVFC/?tag=hyprod-20&linkCode=df0&hvadid=167135453740&hvpos=1o1&hvnetw=g&hvrand=13731954379176832998&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9060340&hvtargid=pla-273305811979&psc=1

 

or for 300 a 400 count cooler

 

https://www.amazon.com/NewAir-CC-100-Count-Cigar-Cooler/dp/B00N1XAVDY/ref=asc_df_B00N1XAVFC/?tag=hyprod-20&linkCode=df0&hvadid=167135453740&hvpos=1o1&hvnetw=g&hvrand=13731954379176832998&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9060340&hvtargid=pla-273305811979&th=1

This is actually a simple setup. Super simple, and cheap.

This will cost me less than $30 dollars.

 

I have endtable FREE

I have cedar and other building materials already FREE

I have spare arduinos, PCBs, LCDs, and temp sensors. FREE

PSU laying around: Free 
Peltier pad $2.00

Breakout Board for PSU $10.00

Spare fans laying around: FREE

Heatsinks: FREE 

thermal paste: $15

 

[AngryBeaver]

7 minutes ago, AlpacasSayQuack said:

This is actually a simple setup. Super simple, and cheap.

This will cost me less than $30 dollars.

 

I have endtable FREE

I have cedar and other building materials already FREE

I have spare arduinos, PCBs, LCDs, and temp sensors. FREE

PSU laying around: Free 
Peltier pad $2.00

Breakout Board for PSU $10.00

Spare fans laying around: FREE

Heatsinks: FREE 

thermal paste: $15

 

it will also perform and look like it was mostly free. If you invest money in a lot of cigars than this not working out properly can cost you much more than the price of that unit.

[AlpacasSayQuack]

All of the innards will be in the back, and unseen. It's a nice table so it will look fine. It doesn't matter how it looks. I can spend my $300 I'm saving on top-shelf cigars. 

[AlpacasSayQuack]

1 hour ago, Pangea2017 said:

No plan what 70 degree is.

It depends. For sub zero and similar some tim start getting bad and for the heat pipe check the datasheet since they are filled with water and sub zero can be a problem even at lower pressure.

To get a reading use  either thermocouples or I2C/SPI ones like the BME280.

For driving the TEC you need some mosfet (calculate how much heat they generate) and read the 4 pin pwm specs. for the fans.

21 degrees Celsius = 70 degrees Fahrenheit. 

I never knew what liquid was in heat pipes. I thought many were a lower freezing refrigerant or something. With these comments, I'll be putting the heat pipe heat sink on the hot exterior side of the pad, and the interior side will be the solid aluminum heat sink. 

[LinuxTek]

Arduino to control a Peltier module....interesting project.

 

Using an L298 Bridge IC to power the Peltier?

 

 

Will you unveil that a Peltier module will become more efficient with digital pulses of DC instead of straight DC with a mere Cigar Box project....I have weird thoughts this late at night.

 

 

 

 

 

[AlpacasSayQuack]

14 hours ago, LinuxTek said:

Arduino to control a Peltier module....interesting project.

 

Using an L298 Bridge IC to power the Peltier?

 

 

Will you unveil that a Peltier module will become more efficient with digital pulses of DC instead of straight DC with a mere Cigar Box project....I have weird thoughts this late at night.

 

 

 

 

 

Disclosure: I'm not sure how much power it will take to regulate the temp in my humidor, but I'm worried the l298 IC can't run it. 

The peltier pads have max powers starting about 60 w. The l298 has a max power of 25 watts and a current of 2amps. Considering the pad runs 12v, i'm looking at 24w at most. I'm thinking of running an arduino controlled relay. I'll use an ATX PSU breakout board (or really print my own) and run the 5V to power the arduino, and run the 12v to the peltier pads through the relay controlled by the arduino.

What do you think about the build?

 

[mariushm]

You can buy various peltier elements, with various operating voltages, it would be easier to just get one that you can power directly.

 

I'd suggest powering your project from a 5v 2A usb adapter  power supply thing, and use a dc-dc converter with enable pin to turn on or off the power to the peltier element (use a io pin on your arduino to control the voltage regulator)

 

Here's some suggestions: https://www.digikey.com/short/j274br

 

You don't need a huge peltier element, since you're only planning to cool a small box by just a few degrees, so you either run the peltier element for longer periods of time, or you'll have a powerful peltier element that you'll constantly turn on and off

[AlpacasSayQuack]

13 minutes ago, mariushm said:

You can buy various peltier elements, with various operating voltages, it would be easier to just get one that you can power directly.

 

I'd suggest powering your project from a 5v 2A usb adapter  power supply thing, and use a dc-dc converter with enable pin to turn on or off the power to the peltier element (use a io pin on your arduino to control the voltage regulator)

 

Here's some suggestions: https://www.digikey.com/short/j274br

 

You don't need a huge peltier element, since you're only planning to cool a small box by just a few degrees, so you either run the peltier element for longer periods of time, or you'll have a powerful peltier element that you'll constantly turn on and off

Thanks for the link. My ali 12v peltiers are 1-2 bucks a piece instead of $17 so I may stay with that. Thanks again for that btw though. Also, I have a lot of 12v fans laying around so I'll be running 12v for those anyway. 

[AlpacasSayQuack]

12 hours ago, James Evens said:

Use mosefets instead of a h bridge. Keep in mind that they might need a heatsink.

Ooo. Thanks for the tip! I have spare small heatsinks from junk boards and things laying around.

[MineSwiss]

Soo i built a peltier-fridge as a school project once and i now changed up the schematic language to english real quick witch might help you quite a bit.

 

Peltier-Fridge_2.0.pdf

 

Edit:

And in terms of ventilation you might want to watch out because by messing with the temperature and ventilation you might have some unwanted effects on the cigars since cooling drastically rises the relative humidity and ventilation causes the humidity to interact faster.

 

Of course the cooling is much more efficient when you use ventilation but you might consider passive elements on the cooling side so the heat exits slowly and well controlled.

 

The temperature sensor should be placed as close to the cigars as possible and there should be a decent amount of space between the cooling element and the cigars so there is not too big of a heat spectrum between seperate cigars. Mount the heat sink on the lid if possible in order for the cold air to flow down and the warm air to rise against the cooling surface (convection).

 

You could also use a mosfet-half-bridge so you can heat the cigars as well if needed.

Edited September 12, 2018 by MineSwiss

[AlpacasSayQuack]

Thanks a lot for the tip and design! Very informative