Introduction: Thermoelectric Rotational Ornament

Picture of Thermoelectric Rotational Ornament

Background:

This is another thermoelectric experiment/ornament where the whole construction (candle, hot side, module and cool side) is rotating and both heating and cooling itself with a perfect balance between module output power, motor torque & rpm, candle efficiency, heat transfer, cooling efficiency, air flow and friction. A lot of physics are going on here but with a very simple construction. I hope you enjoy this project!

See videos for final result:
Youtube Video 1
Youtube Video 2
Youtube Video 3

Some other of my thermoelectric projects can be found here:

Thermoelectric Fan
Smarthphone Charger
Emergency LED


Concept:

The heart of the construction, the thermoelectric module, is also called a peltier element and when you use it as a generator it's called seebeck effect. It has one hot side and one cold. The module generates power to drive a motor which axis is attached to the base. Everything will turn and the air flow will cool the upper heat sink faster than the aluminium plate below. Higher temperature difference => increased output power => increased motor RPM => increased air flow => increased temperature difference but decreased candle power. As the candle also follows the rotation the heat will be less efficient with increased speed and this will balance the RPM to a nice slow rotation. It cannot go too fast to put out the fire itself and it can't stop until the candle runs out of fuel.

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


Result:

My original plan was to have stationary candles (see video) but I found this construction was both more advanced and fun. You could run this with stationary candles but it will require 4 of them if you don't use two modules or larger aluminium heat area.

The speed is between 0.25 and 1 revolution per second. Not too slow and not too fast. It will never stop and the fire will burn until candle runs empty. The heat sink will be quite hot over time. I used a high temperature TEG module for this and I cannot promise a cheaper TEC (peltier module) will make it. Please be aware if temperature exceed the specification of the module it will be damaged! I don't know how to measure the temp but I cannot touch it with my fingers so I guess it´s somewhere between 50-100C (on the cold side).

Step 1: Materials and Tools

Picture of Materials and Tools

Materials:

  • Aluminium plate: 140x45x5mm
  • Plastic rod: 60x8mm [from a venetian blind]
  • Electric motor: Tamiya 76005 Solar Motor 02 (Mabuchi RF-500TB). [Ebay].
  • Thermoelectric module (hight temp TEG): TEP1-1264-1.5 [from my other project, see below]
  • Heat sink: Aluminium 42x42x30mm (single directional air channels) [from an old computer]
  • 2x Screws + 4 washers for motor: 10x2.5mm (not sure about threading)
  • 2x nails for heat sink attachment: 2x14mm (cut)
  • 2x springs for heat sink attachment
  • Counter weight: M10 bolt+2 nuts+2 washers+magnet for fine adjustment
  • Thermal paste: KERATHERM KP92 (10 W/mK, 200C max temp) [conrad.com]
  • Steel wire: 0.5mm
  • Wood (birch) (final base is 90x45x25mm)

TEG spec:

I bought the TEP1-1264-1.5 at http://termo-gen.com/
Tested at 230ºC (hot side) and 50ºC (cold side) with:

Uoc: 8.7V
Ri: 3Ω
U (load): 4.2V
I (load): 1.4A
P (match): 5.9W
Heat: 8.8W/cm2
Size: 40x40mm

Tools:

  • Drills: 1.5, 2, 2.5, 6, 8 and 8.5mm
  • Hacksaw
  • File (metal+wood)
  • Wire brush
  • Steel wool
  • Screwdriver
  • Abrasive paper
  • (Soldering iron)

Step 2: Construction (Plate)

Picture of Construction (Plate)

See drawings for all measurements.

  1. Draw on the aluminium plate or use a template.
  2. Use hacksaw to cut out the piece.
  3. Use file to fine adjust
  4. Drill two 2.5mm holes for motor (22mm between) plus 6mm hole for motor center
  5. Drill two 2mm holes where the nails will be (for heat sink attachment)
  6. Drill one 8.5mm hole for counter weight (will be threaded as M10)
  7. Finish the surfaces with wire brush and wool

Step 3: Construction (Base)

Picture of Construction (Base)

I used a cut in half fire wood.

  1. Use file and abrasive paper before cutting it (easier to fixate)
  2. Drill a 8mm hole in the top center for the rod (20mm depth, not all the way through)
  3. Cut the piece at 90mm length
  4. Finish the surface
  5. Use oil or wood stain for nice surface color (I applied dark wood stain after all photographs for better look)

Step 4: Construction (candle Hanger)

Picture of Construction (candle Hanger)

This is the most tricky part i guess. Maybe easier if you do this at the end when everything is finished and working. I used a thin wire to bend it by using just two pieces. It was difficult to photo all angles. This part will hold the candle beneath the thermoelectric module at a distance so the flame does not touch the aluminium plate.

  1. Bend two identical parts to fit the candle
  2. Glue the two parts together

Step 5: Assemble (motor)

Picture of Assemble (motor)
  1. Use one washer at each side of the plate
  2. Make sure the screws are correct length (to long will damage the motor)
  3. Screw the motor

The washers will separate the motor a little from the plate and make sure it doesn't get overheated later on.

Step 6: Assemble (TEG Module)

Picture of Assemble (TEG Module)

It's a critical part to use thermal paste in order to get a good heat transfer between the parts. I used high temperature (200C) thermal paste but it "might" work with regular CPU thermal paste. They can usually take between 100-150C.

  1. Make sure the surfaces of the plate, module and heat sink and clean from dirt (must be good contact)
  2. Apply thermal paste on the "hot side" of the module
  3. Attach module hot side to the plate
  4. Apply thermal paste on the "cold side" of module
  5. Attach heat sink on top of the module
  6. Attach springs to hold the heat sink steady (high pressure results in better heat transfer)

Step 7: Assemble (rod and Base Plate)

Picture of Assemble (rod and Base Plate)
  1. Drill 1.5mm hole in the rod (3mm depth)
  2. Attach motor axis to the rod
  3. Attach rod to the base wood

Step 8: Assemble (motor, Candle Hanger and Counter Weight)

Picture of Assemble (motor, Candle Hanger and Counter Weight)
  1. Attach module cables to the motor (soldering iron is good)
  2. Attach candle hanger to the same nails as the heat sink springs are attached to
  3. Place a candle in the hanger
  4. Mount counter weight and tilt the construction to make sure you have right balance

Step 9: Final

Picture of Final

Please be aware that the heat from the candle can damage your module if the specification has low max temp. Even the cold side will be pretty hot! Another step that you might want to do is to prepare the heat sink with electrical tape and fill it with water. That make sure the cold side will never reach over 100C! My planB was to do this but I didn't need it.

  1. Lit the candle (detached)
  2. Place the candle
  3. Wait 10sec and maybe try to help it spin to get it started before the cold side gets overheated
  4. Enjoy!

Main formula:
Energy=Energy+fun

Detailed formula:
RPM=mF(tegP)-A*(RPM^2)

RPM="motor revolutions per minute"
mF()="motor characteristics formula"
tegP="module power"
A="air resistance + motor friction constant"

tegP=mod(Tdiff)
mod()="thermoelectric module characteristics formula"
Tdiff="temp difference"

Tdiff=sink(RPM)-fire(RPM)
sink()="heat sink characteristics formula based on air velocity"
fire()="candle fire efficiency formula based on air velocity"

Finally:
RPM=mF(mod(sink(RPM)-fire(RPM)))-A*(RPM^2)


Alternative Solutions (Feel free to make suggestions):

  1. Two modules and heat sinks (symetrically) on each side of the motor for more power
    • Connect the modules in parallel or in series with the motor (stronger vs. faster)
  2. Use stationary candles on the ground or fixed in the base
    • I had to use 4 candles to get sufficient power
    • See vid

Comments

CrazeUK (author)2016-10-04

I love these projects. And your work is so neat. If you see mine its a little.. err messy.

I have a fascination with all things peltier and LED. lol

I would definitely say where you have the candle under the peltier, have a glass tube so the candle can breath, we get the warmth of the flame, but as much heat as possible is captured (obviously there will be loss through heating the glass, and to the air surrounding it.

I would have thought a protected candle under the peltier would be more efficient and powerful than 4 candles with gaps?

What did you find the difference was between the two?

Without complecating it all, have you tried to get ther average number of spins per candle?

FreeBaseBuzz (author)2014-04-03

Nice Instructable.

Similar idea to mine, I used solar panels though, and no DC motor

https://www.instructables.com/id/Solar-Spinner/

Joohansson (author)FreeBaseBuzz2014-04-03

Nice project!

askjerry (author)2014-03-28

Brilliant! And by rotating, the cooling is more effective, so it generates more power. Very clever... very clever indeed!

Two thumbs up!!

armored bore (author)2014-03-28

Witchcraft!

robomaniac (author)2014-03-27

This is amazing! You should make sure your youtube video can be seen at the very top. Right now, you have to click "show all 6 items" to see that you have youtube video OR read the first paragrah. By placing one great picture, then the youtube video, this will prevent user to search/read or click "show all 6 items"

Joohansson (author)robomaniac2014-03-27

I guess it depend of what platform you are on, but I've change it as you said. Thanks.

robomaniac (author)Joohansson2014-03-28

yes that works for me! Now, the number of views on your youtube video should go up!

I saw that is what you normally do that in your other instructables. Keep up the great work!

cchubb (author)2014-03-27

Maybe build the candle hanger to hold the candle just ahead of the edge of the plate so that while it rotates the heat rises and hits the center of the aluminum plate. How far depends on RPM I guess, but then you wouldn't be outrunning the rising heat.

Joohansson (author)cchubb2014-03-27

Yes that would probably increase the rpm a little bit. Much can be optimized here =)

protonguitar (author)Joohansson2014-03-27

Just put a guard around the flame to prevent loss of rising heat energy during rotation.

protonguitar (author)2014-03-27

Cool project! You could probably boost its efficiency dramatically by enclosing the flame between the candle "tin" and the bottom of the peltier assembly....maybe a metallic cylinder (maintaining access to oxygen, of course).

Joohansson (author)2014-03-27

Thanks for some nice ideas. I've been thinking about that wind break myself. I might try that but I don't think I want it to go any faster as it´s decorating light when I watch TV =) If I would do any major changes to the design it would be a better artistic looking counter weight and candle hanger.

agis68 (author)2014-03-27

very amuzing technology!!!! I love peltiers !

Chelwy (author)2014-03-27

Please be kind to tell us how to make it from 0 to the end :) thanks anyway :)

Joohansson (author)Chelwy2014-03-27

Just to make sure, did you see there is 9 additional pages?

hardwarejunkie (author)2014-03-25

I like It!

What about replacing the counterweight with something like a crystal or lens on the bottom to catch and throw the candlelight? Mirrors maybe?

Thanks, yes that could be something to try. A glass cylinder maybe. I did actually modify my construction a bit by polishing the counterweight nuts and placed them beneath the aluminium plate. It gives some reflections.

Antzy Carmasaic (author)2014-03-25

Nice idea. I like how it's always at equilibrium between all those variables.

bobiebob (author)2014-03-25

Looks awesome! would it be possible to to make it symetrical? so with two candle lights, two thermoelectric elements and heat sinks, but with one motor?

Joohansson (author)bobiebob2014-03-25

Thank you! Yes that was my backup plan if this didn't work (that is why the plate is symetrical). You can either connect the modules in parallell or in serie with the motor (what works best). Parallell makes the motor stronger and serie makes it faster.

Kiteman (author)2014-03-25

How sensitive is the balance? As the candle burns, it will lose mass - does that affect the motion at all?

Joohansson (author)Kiteman2014-03-25

The counter weight is slightly lighter than full candle to compensate for that. I let it burn out and the speed does not seem to be affected. The friction at the start in the movie should be the same as when it´s almost empty. That motor seems to have good bearings in all directions, not all motors can take axial force for example (only radial).

Akdil (author)2014-03-25

Impressive but the wax doesn't fall with the circular motion?

Joohansson (author)Akdil2014-03-25

Thanks. No it´s too slow for that, no problem.

mahesh_jo (author)2014-03-24

Very nice project. What I found amazing is TEG module is generating enough current to drive the solar motor!

jessyratfink (author)2014-03-24

This is fantastic! Really beautifully documented too. :)

About This Instructable

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Bio: I like to design, construct and experiment with both old and new technology, especially when it includes mechatronics. I'm also devoted to photography, computers ... More »
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