How to make a brewing temperature controller
Introduction
After a couple of all-grain mashes, I got a bit sick of using my standard glass thermometer and trying to figure out an average mash temperature. It was hard to read the thing, it was hot in the bucket, and the thermometer could not be in more than one place at once.
At the same time, I was beginning to crave the fine temperature control that is possible with a recycling mash setup.
Well there is a lot of information at the fingertips
of those who can surf the web, and I thank Ken Schwarz in the USA for
the inspiration to begin this project. I did not simply copy his method
of temperature control, though. There were two good reasons to modify
his designs. Firstly, his method of calibrating transistors to measure
temperature is too fiddly in my opinion, and secondly, I wanted a simple
degrees C readout for Australian conditions using readily available Australian
parts.
What can it do?
The Brewing Temperature Controller has been designed
to keep one control temperature stable (within a few degrees C) and monitor
three other temperatures. It has been designed with both simplicity and
versatility in mind.
How it came about
I wanted to build some kind of RIMS/HERMS brewing setup. In the USA, most brewers seem to be gadget fanatics and construct incredibly complicated systems. I didn’t have the time, money or obsession to create the latest in microprocessor controlled, all stainless steel mega-gadget.
The concept for my HERMS is simple. Keep the Hot Liquor
Temperature (sparge bucket) at a set temperature and recirculate mash
liquor through a copper coil in the sparge bucket to maintain temperature.
With this idea the pump can run continuously and there is no need to re-route
plumbing depending on temperatures.
The Circuit
What I have done is constructed four digital temperature probes with one controlling a switch (240V AC). This circuit directly reads out temperatures in degrees Celsius using a digital multimeter. It will measure and display temperatures well below zero degrees to well above boiling.
The controller is designed to be powered by 12-15 V DC.
I am using a plug-pack transformer that I sourced from a second hand shop
for $2. This voltage is then regulated for the temperature calibration
part of the circuit through a 7805 regulator. The multi-turn pot is adjusted
to provide 2.73V at pin 1 of the LM324 (see fig 1).
figure 1: Schematic diagram
LM335 temperature probes are wonderful things that change voltage proportionally to changes in temperature. For every 1 degree C change, they change voltage by 10mV. It is therefore quite simple to use a digital meter to directly show a degree C reading. The slight complication is that these probes are set to read degrees Kelvin. This can actually be an advantage because the controller can be used for lagering applications where 1-2 degrees below zero C may be wanted.
The top part of the circuit diagram (based on the LM324) simply provides a reference voltage to convert between degrees Kelvin to degrees Celsius. With a 2.73V reference on one side of the meter, the LM335 probe provides a voltage that results in degrees C per 10mV. For example, if the temperature of the probe is at 0 C, the voltage output will be 2.73 V, therefore cancelling our reference voltage with the meter reading 0V. If the temperature at the probe is 50C, the probe voltage will be 3.23V. With a scale of 10mV on the meter, it will read 50.0 directly.
For the meter I have simply purchased a cheap digital multimeter. I can use the meter for other things as well. These units are around $20 normally although I picked mine up from DSE for $20 with a soldering iron thrown in. My meter will read ‘500’ when displaying 50.0 degrees.
Because I wanted to monitor several points in the brewing
process, I have included 4 probes in my circuit. This way I can monitor
the temperature of the sparge water (this is the one attached to the controller),
the inlet of the mash tun, the outlet of the mash tun, with one probe
free to monitor wherever else I choose. It would be easy to add extra
monitoring points by simply having a multi-position switch, or alternatively
simplifying the controller to just control a fridge for fermentation (one
probe controlling a 240V switch).
figure 2: PCB design
The second half of the circuit provides the switch control. It takes the voltage from one of the temperature probes and compares it to one set by a potentiometer. Essentially the output of LM324 pin 14 will go high or low depending if the set voltage is higher or lower than the probe voltage. This output will then drive the relay which provides 240V switching. The relay that suits the PCB layout is from DSE, cat P 8010. (I have not been happy with the reliability of this relay but it is compact). This switching in my application is used to control the electric element in my Hot Liquor Tun. (It is important to match the rating of your relay contacts with your switching application. I switch a 1200W/5A resistive element using a relay rated at 10A maximum). The differential resistor changes the amount of hysteresis on the switch. Mine will hover around the set temperature plus or minus a degree. Hysteresis is needed so the relay contacts are not burnt out through excessive switching.
The 240V AC wiring has a fuse included for safety. The links shown in the wiring are so that the 240V may be switched through with either the relay powered on or in its released state. The link is via a screw terminal inside the box and naturally there should not be 240V anywhere near the circuit if you do a change-over. I have included this so that the controller can be used to for either heating or cooling. The temperature set knob has two ranges for versatility. The lower range provides 0-50C, the upper 50-100C.
It is not strictly necessary to have a digital meter
to use this circuit. It would be possible to calibrate the temperature
set knob by using a marker pen and your standard thermometer, or simply
to borrow a meter for a weekend. A digital meter is very useful though,
especially in the process of setting up. I figured it was well worth the
small expense to purchase a basic model. A meter is needed if you wish
to monitor temperatures anyway.
Caution 240V
240V AC can kill. Please use caution when making this controller. If
you are not sure what you are doing - DON’T. Never expose yourself to
240V. Brewing itself can be hazardous when you mix 240V and liquid that
potentially leaks or boils over. I use a (Shock-safe) Residual Current
Device on my set-up. At only $30, there is no excuse not to protect yourself
from potential electrocution!
Making the Board
The first version I made was on experimenters breadboard. It is a simple and effective way to construct this circuit, especially if the options are kept simple. I like the reliability and clarity of a good printed circuit board so I investigated the idea of photo-etching my own. I have the computer tools to design my own circuits and enjoyed the design project.
To make a board, simply print the PCB design and use a photocopier to transfer it to an overhead transparency. (You may need to check that it prints at the right size for the components, as computers do funny things with pixels and printing resolutions.) A photo-etching kit is available from DSE for around $20 (Cat N5981). Follow the instruction from this kit and you are done. Jaycar have released a system where you print on a special transparency that then irons on to your copper board (cat HG-9980). This seems easier than the photo-etching system I began with.
The holes will need to be drilled and from there the
components added. In all it should make a comfortable rainy weekend
project. One point to note. The quality of the print will affect the
quality of the photo-etching. The lines must be sharp and dark for them
to be good when etching.
figure 3: Component overlay
The Probes
The LM335 probes were soldered on to ribbon cable using lead-free solder. I asked at DSE and they had a reel in the depths of their store but not on the shelf. There would only be a minuscule amount of lead in normal solder for this application but if you wish to go that way, do so at your own risk.
The probes and wire were protected by using heat-shrink
on them. I do not have a heat-gun, but the hairdryer belonging to SWMBO
did the job nicely. I bought some brass tube from a hobby shop and this
fitted the component and lead snugly. The brass simply provides mechanical
strength as the heatshrink has waterproofed them. I used connectors on
all external leads to the control box to simplify set up.
The Result
The circuit works quite well. I have used it to keep my Hot Liquor Tank at the right temperature quite successfully. It is not quite as simple as dial the right temperature (say 78.0 C) and have the mass of water sit at precisely this temperature. There are variances of about 3 degrees due to the functioning of the circuit (hysteresis), the variations in 20 litres of water, the positioning of the probe, and the heating lag of electric kettle elements. The system does work admirably however. I can keep the mash temperature within a degree simply by using this control box. For the most part I can set and forget.
I have also used it to control fermentation temperatures
of a fridge. With this application the temperature was more stable due
to the thermal sealing of the fridge and thermal mass of the fermenting
beer. It could also be simply used to heat a small area (maybe a cupboard)
in the winter to ale temperatures.
Should you make one?
If you simply wish to regulate fermenting temperatures and are unsure about the technical aspects of this project, it is simpler to purchase a ready made controller from good brew shops. If you wish to do a little more with your system such as monitor more temperatures and be able to work in the 50-100C range, then this project may be for you.