I am working on an idea with peltier modules. My understanding is this: material attached to one side of the module is heated, the material attached on the other side is kept stable(y) cooler than the heated side. The energy transfer across the module is gathered and converted to a usuable flow of electricity. If the side being warmed is being radiantly heated from a flame, what would be the best practice for cooling the other side? How many mA could be generated? Would it make sense to siphon some power away from the usable output and run a small cooling fan blowing inward toward an attached heatsink? I know peltiers are very inefficient, this is more of a test in plausibility. Trying to produce a steady 5v output at 1000mA. Thanks for any help!
Hello @livedifferent1,
You seem to have the idea behind using a peltier module for energy generation right. The idea that you are going to get a steady 5V 1A out of a unit is the hard part when you are dealing with a flame for a heat source and trying to cool the opposite side properly. I am not saying it can’t be done, however you will find that as the hot side begins to heat you will have a small energy generation. As it gets hot that will rise and then as the heat transfers to the cold side the cold side warms the power will diminish. Then there is how to cool the cold side as it heats from the flame. This will not be an easy task as you need to remove all of the heat from the flame. (Imagine heating a frying pan on one side and what it takes to cool the other side so you can still touch it.)
There is a post on Hackaday from Mike Szczys. He built a campfire generator the sort of does 14W. I would take a look at what he is doing and it will give you some ideas. He uses a stove and liquid cooling for the peltier and then a need relay setup to help regulate the voltage as it fluctuates. Here is a link.
I took a look at the project you referenced, I think part of his cooling dilemma is the orientation of his apparatus. I may be wrong here, but it would seem that if his plate was turned sideways or even at a >90° angle it would help some heat move away rather than having it on top where heat rises. In addition if it was moved away from the heat source slightly (couple feet in a campfire situation) and had a double wall on the heat side to stabilize temperature it may help as well. Or even a thermocouple placed in the heat? But the cooling is still tricky, what about a heatsink with a fan running off of the peltiers? Would this accomplish anything? I know that water holds temps much much better than air but maybe this would work. My other thought was alum ground rods, and build it entirely upside down in comparison to his model. You would have to have ground soft enough to drive the rods in of course. But then you could use the stable ground temp to help keep the peltiers cool. Again you would need an air gap between the heat source and the hot side of the peltiers. Has anyone tried it like this? Peltiers are inefficient but if you already have the energy source (fire) why not try to harness it??
It is true if turned there would be less heat rising to the cold side, however in this instance there would also be a lot less heat on the hot side if turned.
In theory your idea can be done, however you would need to find an efficient fan if you are going to try to run it to cool your Peltier unit(s). Efficiency will also be affected depending on the ambient air temp. The colder the air you are blowing across your heat sinks the more efficient it will be.
I think you have a lot of trial and error ahead of you. First to find the temp that you can evenly heat the hot side of your units at. The temp you need to keep the cold side of your units at to produce the power you need.
Then you need to calculate the airflow that is needed to cool the heatsinks to that temperature depending on the wide variety of ambient temperatures that you may be operating in. You will then need to calculate the fan and fixture that you need to deliver that amount of air evenly over the heat sink.
With all of those you should be able to tell yourself if the power supplied in ideal situation will power the fan and still provide the power that you are hoping to get to start with. Of course, you will have some loses and inefficiencies as the flame will not be 100% all the time so you will need to factory variances in output power and how to regulate the control of your fan and other devices much like mentioned in the Hockaday post.
-Robert
@AmyYoung I am not sure I understand your question. If you are looking for some Peltier Modules here is a link to the available options. https://www.digikey.com/short/z934bz
-Robert
To answer the original question, and Amy’s question, from personal experience regular peltier modules made to generate cold/heat with a voltage input do not work well for Thermoelectric Generators (TEG) /Seebeck Generators, otherwise known as Thermo-Electric Modules (TEM)
Based on experiments, a regular peltier, if you drive the cold side with another peltier, and drive the hot side with a third pelter, in a peltier sandwich will not even produce enough voltage to light up an LED and the current is in the less than 20mA range. We were also cooling the cold side actively with icewater to reduce thermal breakthrough.
There are Thermoelectric modules specially made that use a different sintering material/process that can withstand higher operating temperatures, up to 200 degrees C. Some of these are made to get up to an Amp or higher given ideal conditions.
Here’s a link to purpose built ThermoElectric Modules made for generating power provided there is a differential available between hot and cold, the greater the differential, the greater the output.
Click Here for ThermoElectric Modules (Generators) from Marlow Industries