Part 4 of the previous heat sink post.
To recap…..
We have built the aluminium bar into a heat sink with peltiers and heat sinks and fans, we have been able to fit it to our fermentation cabinet, now it is time to wire it all up for control.
Below you can see what we are building today.
More after the break
Index
Step 1 – Build a top for your Cabinet
Step 2 – Wire up a socket and attach all 240v devices
Step 3 – Fit the peltiers and heat sinks
Step 4 – Connect the peltiers
Step 5 – Fit and wire the relays
Step 6 – Bridge Rectifier
Step 7 – Fan Power Circuit
Step 8 – Add the other components
Tools Required
Electric hand drill
Screwdriver
Jigsaw
Soldering Iron and solder
Parts List
Assembled aluminium block from part 2
8 x self tapping screws with flat head
Wood screws
Blue LED
Red LED
Electronic temperature controller
2 x computer case fans
2 x 15v 8A power supplies
IEC 3 prong socket with switch
Numerous screw terminal strips
Bridge Rectifyer
1mm Copper Cable in black and red x 5m
Heat shrink
Optional
Vero strip
4 x 3 pin computer fan headers
Step 1 – Build a top to your Cabinet
At the moment the top of my cabinet is flat. It will be difficult to contain everything the way that it is, so I want to have a top added that will contain all the electronics in a separate compartment.
Above you can see that I have cut 4 pieces of MDF and fixed them to the cabinet with 10mm square battons and screws. I intend to paint this cabinet at some stage, so keeping everything as flat and as square as possible is preferable to keep the Wife Approval Factor as high as possible.
The temperature controller mounted to the left hand side of the cabinet top. I picked this location as it seemed to be the most appropriate place for me, but yours may be totally different of course.
In order to know what is happening with the fermentation cabinet at a glance, I have fitter a bright blue LED and red LED to the right hand side of the cabinet top. I dont have a tutorial on how to use LED’s but basically you need to wire up a resister inline with the LED to ensure the correct voltage. The specific resister needed will vary based on what LED you have, but generally a 300ohm resister will suffice. I found these neat little mounting caps that made it real easy to mount them in the MDF. Just drill a hole and clip the in.
In oder to shift the heat form the power supplies and the heat sinks, we better have a few case fans in the cabinet. I chose two fans that I already had for the job.
Step 2 – Wire up a socket and attach all 240v devices
NOTE: In some countries using 240v (or 110v or whatever your local mains voltage is) in a project like this, without appropriate electrical qualifications is illegal.
Regardless of that fact, you should not undertake any mains voltage work without the proper know how or precautions. I cant teach you these, but this step in the process is unnecessary, I wanted to tidy it up a little. If you are not comfortable or have no knowledge in this area, then just use a power strip and plug in your mains voltage components to that and save yourself some potential grief.
Warnings out of the way, lets get on with it!
I found this neat fused, switched IEC chassis that takes a standard 3 pin machine plug.
Here is the back. You can see the ground, active and neutral pins on the right, and the switch on the left.
Due to my warnings at the top of this step, I am not going to show an in progress shot of this step, but suffice to say, solder on the neutral and ground of each connected device is connected to the relevant posts on the back of the socket and the active is switched.
Take your plug and cut the mains connector off.
Strip the end to reveal the active, neutral and ground cables.
Connect the cables and heat shrink the back to make it as safe as possible.
You are left with the temperature controller wired in, and two power pack plugs ready to plug in the transformers.
The switch ends up on the outside with the socket.
Step 3 – Fit the peltiers and heat sinks
Simple step. Use your heat sink compound and smear onto the bottom face of one peltier.
Use your finger or another appropriate device to get an even coating over the entire surface that is a regular thickness.
Press the peltier to the face of the aluminium block heat sink, being careful to ensure that you have it the right way up. (there is no actual right way up , they are both identical, but you want to ensure that they are both the same direction) Smear the top side of the peltier and smooth out as you did on the under side.
Repeat this step with the second peltier, being careful to ensure that they are both the same way up.
Fit the heat sinks then the fans to the heat sinks. Be careful not to over tighten the screws.
Step 4 – Connect the peltiers
Now, this step is going to seem complicated for the uninitiated in electronics, but bear with me, and dont be afraid to ask any questions.
Cut 4 terminals off your strip of terminal connectors, and screw it to the cabinet near the peltiers. This is where we connect the cables coming out of the peltiers. The cables will be black and red, and you should connect them as I have above. Push the stripped end of the cable into the connector and screw the terminal down until it is tight. NOTE: dont over tighten them, just a nip up from being finger tight.
The terminal strip that we just connected is on the right of this image above.
In order to do our magic swapping of the polarity we need to built the configuration as showed above. What we are doing is taking the black from one side of another 4 way terminal strip and connecting it to the red from the other side, and visa versa.
Now add in the second side, which is a duplicate of the first. This gives us separated circuits for each peltier. This is important as seeing as the peltiers are 6A and our power supplies are 8A, we need to power each peltier separately,
Step 5 – Fit and wire the relays
Now that we have the peltiers taken care of, including out tricky polatiry swapper, we need to install the relays that will drive the polarity swapper and the peltiers. The relays are activated (energised) buy the power supplies and the temperature controller and will supply the appropriate polarity to the peltiers dependent on whether heating or cooling is needed.
I chose to use relay bases, but you dont have to, it just made prototyping easier for me and the connections are much nicer to make.
Fit the relays. These are 12v-15v Double Throw, Double Pole relays.
The relays are driven by the temperature controller, so a common positive lead needs to come from the power supply and go to a pair of relays and the temperature controller. In the image above you can see that I have used a pair of terminal strips and joined them together so that the positive power connection will be plit to 3 different wires. One goes to the common connector on the temperature controller and the two others go to the two relays on one terminal of the coil each. ie this is going to power the relay to cause it to latch.
We now repeat the terminal strip pair with another one for the negative. This 4 wires coming out, that go to the pole on each relay that will be be switched and to the top of the connector to energise the relay. The heating and cooling contact points on the temperature controller are connected to the relays, one goes to the switched connector on each.
This is reasonably important as you might have to swap these if your system heats instead of cools at the appropriate time.
We now can connect the right hand side output of the relay that matches the switched inputs that we just connected. These are connected to the terminal strip that we connected previously that goes to the peltiers.
Now, we have to repeat the process for the second set of relays. It is exactly the same process and in order to accomplish it you will have to add an extra cable to the connectors in the temperature controller.
Step 6 – Bridge Rectifier
OK, we now have done the heavy lifting, but we need to connect the fans so that they will run whenever we are heating or cooling. This should be pretty easy and just a matter of connecting the fans inline with the peltier output. There is an issue with this though, we need to have the fans the spin the same way regardless of the polarity of the output, and that computer fans will only run on one polarity in any case.
To accomplish this we need to use a small IC device called a bridge rectifier. What this does is take any polarity input and rectify it to always be the same polarity output. Super easy! just connect one to the output of one relay as it goes to the peltier and the fans to the other side. The rectifier has two pins that are marked as ‘~’ these are the input and it doesnt matter how you connect them, the output pins are mared ‘+’ and ‘-’ and should be connected to your fans in the correct polarity.
Step 7 – Fan power circuit
I wanted to have a reasonably modular setup, so I built this little board and put fan headers on it so that I could plug and unplug the fans. You could just solder them all together however, it is up to you.
Step 8 – Add the other components
So we are basically done at this point. Add your transformers and be sure to wire them up to the same polarity. Route your cables and make it all nice and tidy. If you want to use the coloured LED’s then they are wired up to one pair of outputs from each of the relay outputs for one set. You can see them in the image below in the lower right.
You can now turn the system on and see what is going on. Set your temperature controller to be heating. You want to see a red LED on and the internal heat sink should get hot. If this is the case then everything is setup as it should be. If the LED is wrong, but the heat sink is right, then swap the relay that the LED is connected to. If the peltiers are wrong, ie the temp controller is set to heat, but the internal heat sink is getting cold, then you need to swap the cables that are coming out of the temperature controller.
That is the end of our wiring tutorial.
After building this iteration of the fermentation temperature control system, it became apparent that I had inadvertently stumbled upon a bad design. In order for a peltier system like this to operate in the best way, there needs to be an imbalance in the heat sinks in order to let the inside cool the most.
The outside heat sinks need to be much bigger than the inside heat sinks to allow for the best dissipation of the heat that is generated. In my earlier versions I had had BIG outside heat sinks by luck, and this version I was going for good looks and a low profile. In actuality, the heat sinks that I used on the top were not big enough, not letting enough heat dissipate. As a result the internal heat sinks didnt get cold enough.
The answer was to just allow for much more cooling on the top. I could have used bigger heat sinks, but wasnt interested in a big trial and error experiment, so I opted to go for water cooling. I had water cooled a single peltier in the past and knew that it would work wonderfully, so I had to come up with a plan to water cool two peltiers.
Stay tuned in the next post where I build a water cooling unit to replace the outside heat sinks.
