instructables.com - make a cloud chamber using peltier coolers

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Make a Cloud Chamber using Peltier Coolersby nothinglabs on March 19, 2010

License: Attribution Non-commercial Share Alike (by-nc-sa)

Intro: Make a Cloud Chamber using Peltier Coolers

Cloud chambers let you see vapor trails left by radioactive particles!

Note: The suggested peltier coolers for use with this project have been updated. See step 1 for details.

They work by creating a supersaturation of alcohol vapor. Vapor trails are then formed when the radiation ionizes the alcohol.

Cloud chambers need to be very cold (about -15f) - so most designs require dry ice.

This design uses inexpensive electrical "Peltier" coolers instead! No need to buy / store dry ice!

It's fairly easy to construct - and should only cost about $100.

This chamber design cools down very quickly - you can see vapor trails within a few minutes.

On the downside - it's not as cold as a dry ice chamber - so the supersaturated area isn't as thick.

step 1: Stuff You'll Need (Part 1)Peltier Coolers (need 2)- Tec1-12709 for "top" cooler ($8 on ebay)- Tec1-12710 for "bottom" cooler (might be listed as CP1-12710 - also $8 on ebay)- Search ebay -descriptions- to find specific models- Coolers look identical - put a piece of tape on a wire of the Tec1-12710 so you can identify it later- Larger coolers are not necessarily better- Using more than 2 coolers will not measurably improve performance- Fragile wires tend to break - avoid bending (might want to buy a spare or two)- Do -NOT- connect a peltier to power backwards or without a heatsink!

Note: This article originally suggested Tec1-12709's top and bottom - further testing indicated that using the Tec1-12710 on the bottom produces -significantly- betterresults.

Power Supply #1

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- 12v and at least 8 amps (good results between about 11v and 15v)- Used to power 'bottom' peltier cooler- www.allelectronics.com part # PS-1512 is a good option for $25

Power Supply #2- 5 volts and at least 2.5 amps (good results between about 4v and 8v)- Used to power 'top' peltier cooler- D-Link JTA0302C power supply on ebay for about $10- Alternative: Use a PC ATX power supply for both 12v and 5v sources (Google for more info)

CPU Cooler / Fan- Look for "heat pipes"- Design that can be run "upside down" with good airflow- Good results with Kingwin HTC series (under $30 on ebay)- Water-cooling system may work even better

step 2: Stuff You'll Need (Part 2)Small Plastic Container- Relatively flat bottom (doesn't need to be perfect)- Fairly thin plastic (1/16th" or less)- Good Transparency- Good results with Rubbermaid Premier 473ml (about $5)

Arctic Silver 5 Thermal Compound- $10 at Radio Shack for 3.5 grams- Should probably get 2 tubes (if you're efficient you may get away with 1)- Arctic Silver "Ceramique" provides good results for less money (22 grams for about $10 at Fry's)- Other thermal compounds / paste can work- Have -not- had good luck with Radio Shack's "house brand" thermal paste

Alcohol- 99% rubbing (isopropyl) alcohol works best ($5 at drug store)- 91% rubbing alcohol also works


- Denatured ethyl alcohol is another option (hardware store paint section)

Misc. electrical connectors to hook stuff up- Soldering is another option- Don't use thin-wired gator clips - they'll melt

LED flashlight (the cheap 9-LED ones work well)

Black Sharpie felt pen

step 3: Stuff You'll Need (Part 3)1/4" x 1" nut + bolt (size doesn't really matter)

1" x 1" piece of kitchen sponge

Styrofoam cup (or any other static source)

Infrared / non-contact thermometer (optional)- Optimally can read to at least -28f- Cen-tech Pocket Thermometer goes for about $20 on ebay- Cheaper ones may give erratic results

Multimeter (optional)- For verifying power supply polarity / troubleshooting


step 4: Obtaining a Radioactive SourceThere are many easily obtained inexpensive (and legal) radioactive sources available online.

Small Autunite samples commonly sell for about $20 on ebay (contains uranium).

Try seaching ebay descriptions for "geiger" and "cpm" to see other possibilities.

Alternately - the cloud chamber can be used without a radiation source to view cosmic rays. They typically appear once every 1-2 minutes.

Take precautions appropriate for your sample! The provider of your specimen may be able to provide further information on its safety.

To be extra safe - use gloves when handling. Wash your hands after if you should touch it.

step 5: Add Thermal Paste to the HeatsinkPosition the CPU cooler with the heatsink surface facing up.

Spread a small amount of Arctic Silver on top of the heatsink using a credit card or thin piece of plastic.

Spread it thinly and evenly (thinner is better). Cover an area the size of a peltier cooler.


step 6: Mount the Bottom Peltier CoolerPlace the Tec1-12710 peltier cooler on top of the heatsink.

Important: The wires should be facing you and the red wire should be on your right.

This should assure that the peltier is positioned with the cold side up.

Push the peltier down - and move it around slightly to assure good contact with the thermal paste.

step 7: Connect the Bottom Peltier and Fan to PowerFirst - Make sure the 12v power supply is unplugged!

Electrically connect the CPU cooler's fan and the peltier to the 12v power supply.

Red goes to positive, black to negative.

Ignore any unused connections for the fan.


step 8: Test the Fan and Bottom PeltierThese steps need to be performed quickly! If the peltier is connected backwards or is upside down - it'll burn up in a very short period unless it's disconnected.

1. Plug in the 12v power supply (fan should spin up)

2. Quickly touch the top of the peltier (or measure it with a thermometer)

3. Is it warm? UNPLUG THE POWER NOW! (peltier is backwards or upside down)

4. Is it cold? Good! (unplug the power)

step 9: Spread Thermal Paste, Attach the Second Peltier and Connect itThinly spread a small amount of Arctic Silver over the top of the peltier you've already placed on the heatsink.

Place the other peltier (Tec1-12709) on top of the existing one. Push it down a bit to assure good contact.

Important: The wires should be facing you and the red wire should be on your right.

Connect the top peltier to the 5v power supply (leave power supply unplugged).


step 10: Test the Top PeltierSame drill as before - these steps need to be performed quickly!

1. Plug in the 5v power supply

2. Quickly touch the top of the peltier (or measure it with a thermometer)

3. Is it warm? UNPLUG THE POWER NOW! (peltier is backwards or upside down)

4. Is it cold? Good! (unplug the power)

step 11: Test Both Peltiers SimultaneouslyPlug in the 5v and 12v power supplies.

Marvel at how cold the top peltier gets!

If you have a thermometer - hopefully it reads -18f or colder!

If not - something might be wrong - or it could just be your thermometer isn't that accurate (this is common).

Unplug both power supplies. If any condensation has formed on the top peltier - wipe it off.


step 12: Black Out the Bottom of the Cloud ChamberUse the Sharpie to black out the -outside- bottom of the plastic container.

This will help the vapor trails appear more clearly.

step 13: Attach the Sponge to the Container's TopDrill a hole in the top of the container for the bolt.

Poke a small hole in the sponge using a pencil.

Use the nut and bolt to attach the sponge to the inside top of the container.

Don't worry about the seal not being perfect. A small leak at the top of the chamber won't hurt performance.


step 14: Apply Thermal Compound to the Top PeltierApply Arctic Silver to the top of the top peltier.

This time - apply it fairly liberally. Use enough so that good contact can be made with the bottom of the container (accounting for any imperfections like raised text).

Yes - normally less is better with thermal paste - but this is an exception.

This may be the point where you have to run to Radio Shack to buy another tube of Arctic Silver.

step 15: Attach the Container to the Top Peltier CoolerPlace the container on top of the top peltier. Push it down - and squish things around a little.

If it doesn't seem to be making good contact - try adding more Arctic Silver.

Try to make a tight seal - you don't want condensation getting between the container and the peltier.


step 16: Test Everything with Container Attached / TroubleshootingPlug both power supplies in.

The bottom of the container should get very could within several minutes minutes.

If you have a thermometer - hopefully it reads -14f or better! (Don't worry if the entire surface doesn't read this cold.)

If so - your cloud chamber is now ready for use!

If you aren't getting this cold:

- Don't place too much faith in your thermometer - if you're getting significantly below 0f - it may make sense to proceed and see if things work

- This article originally suggested Tec1-12709's top and bottom - this will work - but using a Tec1-12710 on the bottom works better. If you're using two Tec1-12709's andhaving poor results - you may want to switch out the bottom one with the 12710.

- Check your thermal paste application - this is probably the most common issue. The layers between the peltiers and the heatsink should be thin. The final layerbetween the top peltier and the chamber may need to be fairly thick to make good contact. As a last resort - you may find that removing all thermal paste using alcohol -and then re-applying solves the issue.

- Are the peltier coolers and container all centered over the middle of the heatsink?

- Is your heatsink getting even a little warm? If so - it may not be good enough.

- Verify your electrical connections are good (warm wires indicate they are too thin).

- Try applying a small amount of weight / pressure to the top of the chamber - this might help close up any gaps in the thermal paste.

- Re-test the peltiers. You can also check them against their specified resistance values using your multimeter (they shouldn't read any higher than 4 ohms).

- Try waiting a few hours - some thermal pastes will "set up" and become more conductive over time


step 17: Using the ChamberPlace your radioactive sample inside the cloud chamber.

Add about 1 teaspoon of alcohol to the sponge.

Put the top on the container.

Plug in both power supplies.

Hold the LED flashlight behind the chamber.

Within a minute or two you should be able to see a fine mist covering the bottom 1/8th inch or so of the container.

Try changing your viewing angle / flashlight position to best see the mist.

Within 2-10 minutes - you should start seeing vapor trails from the radiation!

Performance may improve as things cool.

step 18: TipsImportant: Periodically check to make sure the peltiers / chamber aren't sliding away from the center of the heatsink (this is bad). Gently reposition them if this happens.

Without a radiation source - you'll be able to see cosmic rays every few minutes. Definitely try this!

Try rubbing the styrofoam cup (or other static thingy) in your hair - then place it over the container. This rounds up ions / dust and may help performance. Experimentwith this!

It's possible to run the chamber with the top slightly off. This can be great for shooting photos and video.

If too much alcohol builds up on the bottom of the container - it may hurt performance (wick it up with a paper towel).

If your sample becomes wet with alcohol - some radiation will get blocked (again - a paper towel can solve this issue).

The rubbing alcohol on the sponge should last a long time - but if you stop seeing trails - it may be time to add more.

If you only see trails / mist over a small portion of the container - you may want to try applying more thermal paste between the container and top peltier.

Other directional light sources besides LEDs (like spotlights) can also provide good lighting results. Standard incandescent or florescent bulbs may even work at certainangles (especially if in a desk lamp or other fixture)- experiment!

Depending on a number of variables you may find that increasing / decreasing the voltage for either cooler may improve results.

However - do -not- try running the top peltier at 12v instead of 5v. It won't work (at least not well) - trust me.

The quick explanation is that each peltier needs to pump all the heat pumped by the one above it -plus- any heat the upper peltier generated itself. Since peltiers are notvery efficient - this head adds up pretty quickly - and becomes a problem. Trying to stack two peltiers running at the same total power level will result in -less- coolingthan a single peltier at the same power.

instructables.com - make a cloud chamber using peltier coolers

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