Background:
I study physics at uni so have an idea of the principles behind some basic circuits and I've had some minor practical experience with circuitry- I'm no stranger to a soldering iron. However, I have never done any projects involving any form of chip based circuits. Also, the only coding experience I've had is dipping my toe into matlab and labview. I'm keen to learn and any books/ resources that people know of that'd be worth reading would be much appreciated.
The project:
I want to make a circuit that can control and regulate the temperature of a water body via thermal exchange that include a cooling mechanism, a heating mechanics and a series of temperature sensors. I'd also like to incorporate some form of screen that can provide readouts for temp of input and output + various other thermodynamic properties (efficiency etc).
One idea I have with regards to cooling the water is to use a series of 9 computer fans that will cool a heatsink in contact with a water system. The cool water will then be pumped into a countercurrent coil so it can thermally exchange with the system that is being regulated. The benefit I can see from this system is that with 9 fans it wouldn't be all that difficult (would it?!) to vary the motor speed on them to alter the cooling. Downside, probably quite energy intensive + a heatsink of that size would be expensive to make.
The other idea is to gut a small refrigerator that has a circuit controlled pad and replace that with the arduino control. I know I could leave it in situe and use the arduino for sensors but I want the cooling to react to readings taken by the sensors and proportional integral derivative mathematics to regulate it.
So, what are peoples thoughts, red flags, potential pitfalls and general advice?
TLDR:
I'm looking to start a project where I use a computer controller to cool a body of water (~25 litres) by using either a mixture of computer fans and a heatsink, or the innards of a refrigerator (compressor etc.)
Sorry, more questions.
What temperatures are expecting to heat/cool the liquid to/from.
How fast do you expect to heat/cool the body of liquid.
Is it a closed or open system.
Does it need to be self contained or will it be able to use external resources.
You can use these devices to do controlled cooling, you can reverse the current and heat instead.
Also if you re-arrange the principle you can generate electricity off 2 surfaces differing in temperature.
Using PWM you can have fine control over the device.
PID may not be the ideal choice if you use refrigerator parts for your cooling. PID is at its best if you have proportional control of your output. In this case, you don't - it's on or off. You can still use PID in this circumstance - you use the PID output value to tell you what proportion of the time to run the cooler, a kind of ersatz long timeframe PWM. The trouble with this though is that it means your compressor is being turned on and off relatively frequently, which tends to reduce its life.
Better perhaps to just turn the cooler on when the water is too hot and make sure that you have a sufficient deadzone around the setpoint that it isn't switching on and off rapidly.
Riva:
Sorry, more questions.
What temperatures are expecting to heat/cool the liquid to/from.
How fast do you expect to heat/cool the body of liquid.
Is it a closed or open system.
Does it need to be self contained or will it be able to use external resources.
The initial idea would be to have a system that regulates near body temperature (~37.5c) but I think it'd be more fun to create a system that will need to be more intensively cooled so would be looking to cool to roughly 10-15c (not really set on a particular temp yet)
How fast? Ideally I'd like it to adapt as soon as physically possible. This is another factor in making the type of cooling pretty intense (having a look a TEC modules, they look like they could be pretty cool to play with)
The system would be sealed, both the system that is being cooled and the cooling system. So there has to be an effective way of dissipating heat into the environment.
You can use these devices to do controlled cooling, you can reverse the current and heat instead.
Also if you re-arrange the principle you can generate electricity off 2 surfaces differing in temperature.
Using PWM you can have fine control over the device.
I briefly looked at these, but glossed over them because of the small size of the actual module. What sort of area would each one effectively be able to cool if in contact with the cooling fluid? Are they easy to use many in tandem with each other?
wildbill:
PID may not be the ideal choice if you use refrigerator parts for your cooling. PID is at its best if you have proportional control of your output. In this case, you don't - it's on or off. You can still use PID in this circumstance - you use the PID output value to tell you what proportion of the time to run the cooler, a kind of ersatz long timeframe PWM. The trouble with this though is that it means your compressor is being turned on and off relatively frequently, which tends to reduce its life.
Better perhaps to just turn the cooler on when the water is too hot and make sure that you have a sufficient deadzone around the setpoint that it isn't switching on and off rapidly.
I had initially considered dead zone reference points, but I don't know I just kinda find it a bit of a "clunky" way of regulating, but I do understand it has it's advantages with and on/off mechanism
AmbiLobe:
That is safe because the spec for IRFS3107 is 370 watts maximum power dissipation using a big heat sink.
It might need enough PCB area, if not available then d2pak heatsink.
further more we could use air cooling(fan), water cooling, ice-water cooling, peltiers, dry ice, liquid nitrogen, mini air conditioner, other type heat pump...
With any project the first thing to do is to define exactly want you want. This is a requirement spec. From there you develop into implementation. For a first project keep it very simple. Reality has a habit of making things much more difficult than they appear. You need to define the tempeerature range that you are going to work within, and the controlled temperature and the desired accuracy and range.25L of water will involve a lot of temperature gradients and a lot of power to be handled. Control theory is complex.
Once you have a requirement you can construct a system block diagram and estimate how much and how long it will take. You can then look at the individual blocks and develop test specifications and detailed implementation.