Powering Peltier TEC for Beer Brewing

[numbfx]

Hello,

This is my first go at EE and programming, and I'm working on a system to control fermentation temperature during beer brewing. I am doing this in a small space, so I am using Peltier TEC plates.

I found that I can program an Arduino to run PID temperature control and power the TEC with PWM. Although, I've read that PWM with a Peltier severely reduces efficiency, so I have attempted to design a power system that will take the PWM signal and supply a proportional smooth current/voltage to the TEC. Since this is my first attempt I am posting the schematic in hopes that anyone may provide input to help with the power part of the system.

R1, R2, and R3 are the Peltier plates. They are TEC1-12715, rated as 15A each, and are surrounded by a Buck converter system.

The MOSFETs are IRFB3207. I picked these because they are fast switching and have a high current limit.

The MOSFET driver is MCP1407. I am using this because the Arduino does not give out a nice square wave at high frequency, and thought it would cause problems driving multiple MOSFETs in parallel at the same time.

I've put decoupling capacitors between Vcc and GND on the driver, as per the data sheet. I've also added a pulldown resistor between the Arduino and and driver.

Resistors between the Arduino- driver, and driver- MOSFETs because I've seen it mentioned elsewhere. Likely to limit the current, at least for the Driver-Mosfet connection because that has a max current of 6A. Although I'm not sure if a resistor is necessary between the Arduino and driver.

Any help is appreciated!

 

[Minder]

Small space? What size are your tanks or carboys?
If this is small batch's, I simply have a enclosure just the size of the carboys and use a small office under desk foot warmer thermostatically controlled.
Does the job as it keeps the enclosure at a constant temp.
M.

 

[numbfx]

I'm using a 7 gallon bucket, my current batch going now is 5.5 gal of Hefeweizen sitting in a swamp cooler that I am cycling out bottles of ice to maintain a temperature of 60-64 deg F.

I live in an apartment and don't have space for a second refrigerator and don't want to deal with the maintenance or temperature fluctuation of the swamp cooler.

I really just need cooling, no heating for fermentation, as the room temperature is higher than ideal fermentation temp. Plus I would like the ability to control a Setpoint which may allow for lagering or cooler brews.

 

[Bluejets]

I see the guys over on Arduino have given you some solid advice.
Assume you don't agree with their findings..??

 

[numbfx]

https://forum.arduino.cc/index.php?topic=604731.0

What solid advice? Give up? No way. Maybe I didn't start out by asking specific questions, so people are just picking at the project.

I'm just asking if the schematic looks sufficient to drive the MOSFETS from the Arduino and smooth the PWM.

Also, I was wondering how a single MOSFET can handle 15A, the pins are so small. Will I need a heatsink? Should I use more of them?

Will there be power supply issues if they are all wired together? I was thinking of taking a 50A 12V power supply and wiring everything to that.

Is there any way I should wire the grounds? Are the values for components I chose reasonable?

I've never made a PCB before so I'm trying to figure this out.

Also, I posted here because a friend suggested this website to me after he saw the replies on Arduino.

 

[Harald Kapp]

The circuit may work (I haven't analyzed it in detail) but it is imho way too complex.
The TEC1-12715 are rated for 12 V operation, so there is no need for a buck-converter type of driving. Simply turn them on and off using the arduino as a bang-bang controller. The thermal inertia of the bucket full of broth will smooth out the fluctuations, working effectively as a low pass filter.

 

[Harald Kapp]

Also, I was wondering how a single MOSFET can handle 15A, the pins are so small. Will I need a heatsink? Should I use more of them?

If the MOSFET is rated for 15 A or more, it will handle them. You need to calculate the power dissipation (V_DSD*I_DS and use the thermal resistance of the MOSFET's case vs. ambient to find out whether you need a heatsink (link to theory, link to online calculator). My gut feeling is that you will need a heatsink - do the math.
15 A is a manageable current. While it is possible to use MOSFETs in parallel I recommend to avoid this as long as it is not absolutely necessary as you can find MOSFETs that can easily handle that current.

With respect to the buck converter circuit: That will even increase the power dissipation of the MOSFETs due to switching losses (those can be ignored at the very low switching frequencies of a bang-bang controller).

Is there any way I should wire the grounds?

Yes. Make ground as electrically "solid" as possible. When you create a PCB, use a ground plane, but keep the grounds for power (MOSFETs) and logic (Arduino) separate as good as possible. Ensure a single star-point connection at e.g. the Arduino's GND pin. This will help to keep noise from the switching of the MOSFETs away from the logic.
You may even need to increase the current carrying capability of the PCB in th epower area by adding an additional layer of tinning (only for the power part) or even soldering wires on top of the PCB traces.