Voltage Booster for Peltier Tiles

[ZiHao]

Hi all,
I am planning to install two Peltier tiles( TEC-12706 ) to an electric toothbrush which runs solely on the heat of human hand. I have tested the tile and it can generate about 150 millivolts, which is not sufficient to power a 12V DC electric motor. I think I should get a transformer or try to build a Joule Thief to amplify the voltage of the tile to 6V ( which is quite adequate to have a considerable RPM to brush your teeth ). Any recommended devices or componets to amplify the low voltage? Thanks!

 

[Borek]

It is not about voltage, it is about power. Even if you manage to convert 150 mV to 12 V (which I doubt) you probably won't be able to supply enough current to run the toothbrush.

 

[anorlunda]

You are misunderstanding basic electricity. A toothbrush needs much more power than a LED. Your tiles are probably not putting out as much power as the toothbrush needs. Voltage doubler circuits or transformers can change voltage (AC voltage for the transformer), but they do not increase the power. So the answer to your question is that amplifying voltage won't work.

If you can find the spec sheet for the Peltier tiles it may tell you how much power the tile can make. Or it might give voltage V and current I. Power P=V*I. Then find the specs for the toothbrush if possible, and see how much power it needs. The ratio of the two tells you how many tiles you need. The answer might be 10 or 30 tiles, not 2.

It may be more practical to stay with 2 tiles, and look for something to drive that needs much less power than a toothbrush. An LED is a good choice. If your purpose is to demonstrate physics rather than making useful household devices, then just making the needle on the voltmeter move shows success.

 

[ZiHao]

Or is there any energy harvesting components to work on this? Piezoelectric crystals?

 

[Rive]

I think you should try to find out the power requirements of that toothbrush first: to search for a matching source comes second.

 

[anorlunda]

Or is there any energy harvesting components to work on this? Piezoelectric crystals?

I looked it up, 2 watts for an electric toothbrush. The simplest type of energy harvesting is a solar panel. Small flexible ones designed for camping would do it. The one in the picture below says that it can produce 6.5 watts. Indoors with the lights on, it might make 2 watts.

The next step is to match the voltage and current needs of the toothbrush. The panel puts out 5v in USB format. You will have to take your toothbrush apart, disconnect its battery, and look at the motor to see what voltage and current it needs.

It would be simpler to use the panel to power a smart phone using the USB port. That doesn't need any more adaptation. If you have an older phone where you can remove the phone's battery, then the only power it has is from the panel.

 

[Borek]

Indoors with the lights on, it might make 2 watts.

I can think of several less wasteful methods of converting the grid electricity into work

 

[ZiHao]

Thanks for your information. Another idea pops in my mind, a wireless mouse with peltier tiles and piezoelectric crystals when you click on it. Is it possible? Haha.. going to do more research

 

[anorlunda]

I can think of several less wasteful methods of converting the grid electricity into work

LOL. That's true. In another thread. the OP said that his object was a science fair.

 

[Asymptotic]

How much power does an electric toothbrush require? Call it 3 watts (edit: or 2 watts; I found a different cite than @anorlunda ).

How much power is dissipated by a human hand? Seems like less than 3 watts (although 2 watts may be achievable). If a human hand isn't able to provide at least this much power, then game over.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2409965/

If we're still in the game, then:
How efficient is the peltier module? 10 to 20%?
How well does heat from a hand couple into the peltier-equipped toothbrush? For anywhere close to good coupling it would have to be held in a death grip.

How much input power would be required into a 10% efficient peltier device to power a 3 watt toothbrush? Can heat from a human hand supply it?

 

[donpacino]

You could make the tiles charge a battery that is then used to power a toothbrush? instead of holding it in your hand, make it a sock or something. Then you can have someone wear their power source so it can charge things all day

 

[russ_watters]

You could make the tiles charge a battery that is then used to power a toothbrush? instead of holding it in your hand, make it a sock or something. Then you can have someone wear their power source so it can charge things all day

I believe this would work. If you covered your entire body with peltier tiles you would probably generate enough power to charge a cell phone.

 

[willem2]

I believe this would work. If you covered your entire body with peltier tiles you would probably generate enough power to charge a cell phone.

Maybe naked in a snow storm. The problem with peltier generators, is that the efficiency is really low for low temperature differences.
The TEC12706 mentioned by ZiHao is meant as a cooler, so I can't find any data on its energy harvesting capabilities.
I've found this.
https://eu.mouser.com/ds/2/223/THR-DS-eTEG-PG37 0812-608251.pdf
The power output at a temperature difference of 10K is 1.5 mW, still with only a 10.3 mm ²surface area you could maybe even fit enough on a toothbrush handle.
I don't think you can expect more than 10K for a device uses at room temperature that shouldn't cause discomfort.
If you put it inside your shoes or under your clothes you would get even less. You should probably make clothes or shoes out of thermoelectric tiles.

The real problem is, how much heat is needed to maintain that 10K temperature difference. The termal conductance is 0.076 W/K, so you need 0.76 watt of heat to go through the tile and be rejected at the cold side to get 1.5 mW out. The generator is likely meant to be mounted to much larger cooling/heating surfaces.
The efficiency is only 0.2%, so 500 W of heat input would be needed to get one watt out.
You need 666 of those devices for 1 W., but you could fit them in 8x8 cm. (expensive toothbrush). I think a regular phone charger is about 10W. 2.5 Watt if I charge from the USB port of a computer and it takes hours.
It's of course impossible to get that much heat from a human body, and getting rid of the heat on the cold side would require water cooling. (The toothbrush would require no power cables, but 2 tubes to hook it up to the water pump and radiator).
The efficiency seems to be proportional to the temperature difference, so the power produced is proportional to the square of the temperature difference.
With a 50K temperature difference, you would need only 100W, but you probably need a strong wind and -20C to maintain this temperature difference.

 

[anorlunda]

Come on members. The OP is a high school student trying for a science contest. We should not make fun of him nor give answers too advanced for high school. We should help him.

 

[willem2]

Come on members. The OP is a high school student trying for a science contest. We should not make fun of him nor give answers too advanced for high school. We should help him.

I looked up a datasheet of a peltier device, and calculated the electric power produced, and the needed thermal power. If that is too advanced, I don't think you can say anything meaningful about this. Unfortunately the performance of a peltier generator falls short of what is needed with the low temperature difference that is available.

 

[sophiecentaur]

Come on members. The OP is a high school student trying for a science contest. We should not make fun of him nor give answers too advanced for high school. We should help him.

That's right in principle but Energy Harvesting is seldom the way to go and I wish that "Science Teachers" would do a few minimal sums (in their heads even) before encouraging students to go up a blind ally. By definition, Harvesting is making use of energy that the regular Engineers have been prepared to lose from their original designs. They have chosen to waste it because it's usually more trouble than it's worth.
The one thing that your average student lacks is experience and worldly wisdom yet they so often get given impractical projects with no apology or warning that they may not work. Milliwatts are so often presented as Watts and a factor of 1000 can't be ignored.
Perhaps students would be too embarrassed to present their tutors with links to what's been written on PF about their suggested projects but it could help those who follow them.

 

[donpacino]

This is a high school project, not a final product made by a company.
@OP. Maybe you can make a water jug as a coolant system and fill it with ice water. When you wrap your hand around it you will get a temperature gradient of ~37 C (human body is 37, ice water is zero). Let's call it 30C . according to that datasheet you will get 0.6 volts at 60 mA. 36 mW of power. If you want to get fancy with adult supervision you can try something with dry ice to experiment as well.

toothbrush batteries are typically 1.2 V 2000 mah. They consume about 3 watts and you use them for 2 minutes at a time. with each device using 36 mW of power, you would need 3/0.036=86 devices to run the toothbrush real time. of course that 43 units to charge it for 4 minutes, 22.5 units to charge it for 8 minutes, 11.25 to charge it for 16 minutes, and so on. One device would take 86 minutes to recharge the toothbrush battery.

You can use multiple devices, but to make it simple one would work. so for your science fair, you can run a test and told onto a jug for 1.5 hours, taking breaks to refill the container with ice to keep it cool. Then present your data

 

[anorlunda]

@ZiHao , you can learn by watching this video about the girl I told you about in your other thread. Study the method she used.

1. She decided to use peltier tiles to demonstrate energy harvesting; just like you did.
2. She found out how much power the human hand puts out as heat, about 5 mw according to the video.
3. She found that she needs only 0.5 mw to make an LED light
4. She tested the tiles, and found that two types made enough power, but only at 50 millivolts. The LED needed 2.5v.
5. She found a way to boost the voltage with 4 components at 50% efficiency. This article says "She did a little research and designed a four-component DC-DC converter that stepped the voltage up to 5V."
6. Her last step was to design the physical form of her flashlight.

It sounds like you started with step 1. You skipped step 2. For step 3 you chose a toothbrush without knowing how much power it really needs. You did step 4. Now you are asking about step 5.

I challenge you to re-do step 3 first. Then do your own research. Find an application that needs 0.5 mw or less, then find out how much voltage it needs. Perhaps something like powering the electronic weather station below, or powering a battery operated clock. Do your own research to find out how many mw and how many volts your application needs.

Then come back here to PF and ask for help with step 5. We have lots of smart people here. The thing to learn is that you can't skip steps. You can't do step 5 until you know what the converter is required to do.

Do you have advisers to help you with the contest? He or she might be able to help better than we can on the Internet.

electronic weather station.