1 Analog pot to set the target temperature or fan speed
1 Switch for manual/automatic mode
Charging shield for the batteries, i.e. charging should only take place if there is enough heat/energy. Empty batteries would otherwise suck all the available power. Charging should be current limited and pulsed. The Arduino has such few things to do, a current limited SMPS with a hardware interrupt should be possible. Hardware needed: shunt resistor, opamp, mosfet, …
Code: PID- or P-controller. LCD for displaying the temperature and battery charging state.
I would leave out the switch and just define the upper range of the pot value to full power, regardless of temperature, and the lowest setting to full-stop.
I have țhe pot, display and also an atmega 328pu with arduino bootloader.
I also have some n channel mosfets for controlling the fan and the charging circuit. I don’t have any rail2rail opamps left, but normal ones.
Shunt resistor of 3R3 SMD is also present.
I have a fan at hand and also a temperature probe, so I don’t need those if they are approximately the same kind. Yes I could do that and developing the controller shouldn’t be a big deal. But I have this other Open Source micro controller project on my list, the open source timekeeping system which I first want to finish. We already talked about that, I will get to it in 2 weeks and maybe you can help with the web interface
Is the fan out of metal? What is the temperature down there? The fan should be kept in a cool environment so one could use cheap computer fans. But maybe it’s cold enough at the current location.
What voltage and current does the fan run on? And I need a data sheet of the sensor, then I can have a look for suitable parts.
But I guess a small computer fan has too bad performance for this use case.
Imagine that we want to cool a TEG element which gets very hot (200°C - 250°C on warm side - maybe we can reduce this or need to since we need to find a TEG that is heat resistent enough) and also push the cold air upwards in the secondary air flow (burn chamber, gas combustion at the top)
I guess the average 80mm or 120mm computer fan is really enough if you don’t want to melt down metal
200°C on the warm side should still be okay if the other side is cooled down. Anything above is starting to make trouble, as the peltier elements are usually soldered and mostly silicon semiconductors. A CPU heat sink should be fine. Maybe we can incorporate a retention module at the burning chamber and have it made modular for different heat sinks.
quick note: A 5V fan could be used more efficiently, however, most fans are 12VDC and turn very slow or don’t even start at 5V. Thus we have to incorporate a dc-dc step-up controller to power the fan, at least I have only 12V fans at hand.
I now have an 80mm 12V fan running from a LM2577 step-up DC-DC swtich mode power supply with 4 NiMH cells.
Next step will be to test a TEC (Thermo-electric cooler, Peltier element) or a TEG (Thermo-electric generator), I don’t have any of the latter. I will hook up some LM335 temperature sensors to a TEC element and characterize it for MPPT purposes. (MPPT = maximum power point tracking)
Deal? 