Last time I posted I discussed the parameters in which I can use this thermo-electric generator. In this post I will go over what I have made thus far, what it’s capable of, and what I would like to do next.
The TEG module that I am using is labeled as TEG2-126LDT
It’s the only TEG module designed specifically for Low delta temperature (D.T.) operations primarily because,
- It has no seal around the perimeter to prevent thermal bridging.
- It’s twice as thick which slows heat transfer (allowing a larger D.T. for a longer period of time.
The next item that is recquired to accompany the TEG module is a LTC3108 chip. It can be setup as follows,
But luckily there is a breakout board, so it’s not necessary to construct said circuit. Unfortunately it’s rather pricey at ~$40. It would be better to make your own circuit as the chip itself only costs $5, but it’s hard to find a distributor. The only one I found required a minimum purchase of 100 units…. So back to the breakout board
I then tested the setup with a breadboard to see if the concept works
In the top left picture you can see the LED lit up. This was caused by pressing my wrist on the labeled “hot side” of the TEG module.
So it seems to work..!! What I can do instead of light an LED, is charge a capacitor. The device can then be used for a large variety of applications that would need quick bursts of energy, and then can rest dormant until the capacitor recharges.
I can choose a few different voltages based on the following diagram:
To operate this diagram, look at Pin_10 & Pin_9. Those are your selection pins that need to either be shorted to GND or Vset. Looking at the table on the right, you select from 4 different desired voltages. I currently have mine set to 3.3v. I should note that to store energy in a capacitor as mentioned before, you can use Pin_3. This “Vstr” in my application will use either a 0.1F or 0.47F capacitor. I’m still experimenting with the options.
So next on my agenda was to make this setup wearable on my wrist. I went to JoAnne’s, bought some fabric, velcro, and learned how to sew. I also converted the breadboard circuit to a perfboard, and added an LED with a switch. I unfortunately made a mistake and swapped my two capacitors. The large 0.47F capacitor is where the 1000uF capacitor is supposed to go. A new rendition is in order to correct this mistake!
I was unable to see the full potential because of this dilema, which made it hard to make use of the LED that I mounted on this system due to an excessive amount of time it took to charge the super capacitor. This may be resolved by placing the super capacitor on the Vstr pin, or by using a smaller 0.1F capacitor. In my next design, I’d like to make this swappable as the capacitor in question may be entirely application dependant. The reason that it prevented the LED from lighting up is because the capacitor would soak all of the voltage and current away until it was charged. The LTC3108 chip is meant to drive Vout first, and then with excess energy it can charge Vstr. I had placed the large capacitor on Vout on accident. If I had placed it on Vstr instead, the LED would be able to light up regardless of the super cap’s charge level. The purpose of Vstr is to supply energy should the TEG module not be producing enough energy. I hope that made sense.
Here’s the LED turned on after given a day of charging. I could get about 0.1 volts for every 10 to 15 minutes I spent outside. I was not able to get much of a charge whilst sitting indoors. I believe there’s not enough air to cool the “cold side” of the TEG module. If one was skiing on a cold mountain, a lot more energy could be produced. With more energy, comes more possibilities
An LED is cool and all, but I want something that’s more interesting. I’m thinking an FM transmitter (to transmit your voice) or some kind of wilderness survival application. The point of this assembly is that it is 100% maintenance free. It’s something that could be pulled out 30 years from now and still work. That can not be done with a battery as the chemistry in those eventually fouls.
This is an extremely small FM transmitter. Given my circuit, I should be able to transmit ~50m with this. I tried acquiring some small low power FM receivers but it’s been over 5 weeks now. This transmitter uses only ~9mA. I at least already have the transmitter.
So what I’d like to do in the future is make a better wrist mounting fabric. Oddly enough, this seems harder to do than making some kind of a circuit so that may take the back burner for now. Other than that, I’m going to fix the capacitor swap issue, and test out using the FM transmitter. After that, I am thinking a heart rate monitor may be interesting. I’ve looked extensively into using a low power arduino and it may prove to be an excellent exercise to learn how to create a sleeping arduino in the realm of ultra low power electronics. Unless there’s a new, better idea lurking around the corner 😉