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:
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.
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).
High effect thermoelectric modules are expensive. If you would like to see more of those experiments in the future, please consider a small donation.
Bitcoin address: 1BouwowuprgQrtUYgyzYnNvHyRYbLceqHg
Step 1: Materials and Tools
I bought the TEP1-1264-1.5 at http://termo-gen.com/
Tested at 230ºC (hot side) and 50ºC (cold side) with:
U (load): 4.2V
I (load): 1.4A
P (match): 5.9W
Step 2: Construction (Plate)
See drawings for all measurements.
Step 3: Construction (Base)
I used a cut in half fire wood.
Step 4: 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.
Step 5: Assemble (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)
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.
Step 7: Assemble (rod and base plate)
Step 8: Assemble (motor, candle hanger and counter weight)
Step 9: 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.
RPM="motor revolutions per minute"
mF()="motor characteristics formula"
A="air resistance + motor friction constant"
mod()="thermoelectric module characteristics formula"
sink()="heat sink characteristics formula based on air velocity"
fire()="candle fire efficiency formula based on air velocity"
Alternative Solutions (Feel free to make suggestions):