Sous vide: a DIY guide (part 2)

  • Now I bet you want to make your own sous-vide machine after seeing these pics.

    I’m gonna start you off with a warning: if you’ve never played around with electricity before, find someone who has. This isn’t a hard project at all, but you’re still working with 230 volts. That’s kinda different than the 5 or 12 volts you’re used to fucking around with inside your computer. And because this machine will help you cook it’ll always be near large reservoirs of water. Water and electricity: not best friends.

    Sous-vide machine van binnen. Don't mention the wiring...

    I refrained from making an actual tutorial because my version takes a few shortcuts that would probably get noobs zapped. You can definitely build a safe version with the information I provide, but if you’re unsure ask someone with more experience. I am, after all, an electrical engineering dropout. You really shouldn’t trust me on this.

    Also: I’m not responsible for any self-electrocution, house-burnings or other creative ways in which you’ll win a Darwin award. There are more stupid things to die over than the perfect steak, but I’m pretty sure it ranks up there.

    Now that that’s out of the way…


    The set you buy at Banggood contains a Rex-C100 PID, a type K thermocouple and a Fotek 40A solid state relay (SSR). Though the SSR and PID do not have ground connections you can set the rest of the wiring up with a ground, which would be a good idea considering the amount of water this thing will be near.


    The SSR needs a fuse and a heatsink according to the specs to handle more than 5A, which are not supplied in the set. Fotek makes a fitting heatsink with the right dimensions and pre-drilled holes, but any heatsink with sufficient surface would be enough to handle the heat. So I just went to my local electronics shop and bought the first heatsink that was bigger than the SSR and had holes in the right places. Cleaned them up with some 96% cleaning alcohol and used thermal paste to connect the SSR to the sink. I kinda forgot about the fuse, you probably shouldn’t.


    Yeah, the drilled holes weren’t quite in the right place for this SSR. Not optimal, but meh.


    The thermocouple in this set is a type K and can be used to measure temperatures from 0 to 400 degrees Centigrade according to the specs. I was surprised to find that the thermocouple was actually waterproof and usable for my sous-vide project, though in the future it might make more sense to get a better thermometer. An RTD type for example could measure the temperature to a decimal. It’s important to know that you can’t extend thermocouple cables with any other wiring, because you’d be changing the voltage differential that’s used to measure temperatures. The maximum distance between your PID and your water reservoir is the length of the thermocouple cable.


    The Rex PID series is officially a product of the Japanese RKC Instruments, but I have the feeling that this version from China is a cheap knockoff. On eBay you can get the cheapest version of the Rex for $1.99. No problem, knockoff or not, it still does what it’s supposed to. The manual you get in the set is in useless Chinese and the English manuals you find online are extremely confusing. There are multiple versions which differ per reseller, and they appear to be describing alternate versions of the C100 with different menus and settings. The only manual I found that seems to describe the C100 I have is this one. There’s a few strange translations in there, but for the most part it’s perfectly understandable.

    The C100 has a sticker on the side that will tell you the specific model. Because there are many variants of the C100 and it’s unclear if Banggood always puts the same one in every set it’s actually quite important to check this number. The meaning of every symbol is explained in the previously linked manual. My C100 is model REX-C100FK02-V*NN, where the -V is the important part. If you have an -M instead of a -V model the C100 has an internal relay built into the PID. The problem is that this internal relay can’t handle the power we’ll be running through it and is bound to fail, sooner rather than later. That’s why we use the external SSR with a -V model. If you accidentally acquired an -M model, you can modify it yourself.

    Interesting detail: all of the online manuals, except the one I linked, have a wrong pinout. The pinout on the sticker on the side of your C100 is correct. The manuals tell you to hook up the power to pin 6 and 7, while in reality it needs to go on pin 1 and 2. Pin 6 and 7 are alarm pins and hooking up 230 volts to it would be a fine way to blow up your PID. Luckily, my version of the C100 has no alarm and has no pin 6 or 7, so I really couldn’t make that mistake.

    As a heatsource I’m using a watercooker, so my heatsource and my water reservoir are combined, which would also be the case with a rice cooker or a deep fryer. But you could also use an immersion heater, or several of them in parallel, in a separate reservoir. Some people use immersion heaters and insulated iceboxes to retain as much heat as possible.

    Wire it all up like this:

    Wiring diagram Rex-C100 PID for sous vide use

    Considering I’m not using a metal case I’m grounding the heatsink in this build, as it’s the only metal object I might accidentally touch. But if you’re using a metal case, I’d just bolt the heatsink to that (for better heat dissipation too) and ground the case instead.

    Plug in the device and the PID will boot – you’ll see the the type of thermometer, the min and max temperature, followed by the standard PV/SV view. The upper number, the PV, is the measured temperature. If this says Err, oooo or uuuu something is wrong with (the wiring of) your thermocouple. The lower number, the SV, is your desired temperature value. The four buttons beneath that are the SET, SHIFT, DOWN and UP buttons. Press SET once to change the SV value. Use SHIFT to pick the number to change with UP and DOWN. Press SET again to save this value. That’s important: the PID will not save any changed settings, here or in the menus, until you hit SET again. If you picked an SV higher than your current PV the PID will start trying to turn on the heatsource. You’ll see OUT1 light up on the PID and the red relay light on the SSR turn on.

    Screenshot 2015-01-19 23.12.35

    The other settings of the PID are spread over 3 menus: the Parameters menu you get when you hold SET down for 3 seconds, the Functions menu (COD 0) that you get when you hold down SET and SHIFT both for 3 seconds, and the Constants menu (COD 1) that you get when you change COD to 0001 in the Functions menu. According to the manual there should be a COD 2 menu too, but that one is missing on my C100. It’s possible that you can’t enter the COD menus on your C100 at first. In that case you need to switch the data lock function, LCK in the Parameters menu. Set it to 1000 to access all menus.

    Check and set the following values in the COD menus:

    Define input as a type K thermocouple.
    COD0 menu, SL1 set to 0000

    Define input unit as degrees Celcius.
    COD0 menu, SL2 set to 0000

    Turn off all alarm functions.
    COD0 menu, SL4 set to 0000
    COD0 menu, SL5 set to 0000
    COD0 menu, SL7 set to 0000

    Set function to heating.
    COD0 menu, SL6 set to 0001

    Set max temperature to 400.
    COD1 menu, SLH set to 0400

    Set min temperature to 0.
    COD1 menu, SLL set to 0000

    Turn off Digital Filtering.
    COD1 menu, DF set to 0000

    This is important: the purpose of Digital Filtering is to remove small fluctuations from the measured temperature, but the function is built so badly in the C100 that it actually filters out large temperature deviations. Once reached the PV temperature shown will remain equal to the desired SV temperature, even though the actual temperature of the water is unstable. This means the system looks perfectly accurate when in fact you’ll be drifting many degrees. That’s unacceptable for sous-vide cooking, of course.


    Finally you need to let the PID automatically tune itself for your setup, which needs to be repeated any time you change heatsource or water reservoir. By using the autotune procedure the PID will turn your heatsource on and off repeatedly, so it can learn how your setup warms up and cools down over time. When it’s done the options in the Parameters menu will be automatically set. If you’re unhappy with the results you can override the parameters manually, but it worked perfectly for me. And I have no clue what the PID parameters actually do, so there’s that.

    To start the autotune procedure: fill your reservoir with water, turn on the heatsource and place the thermocouple in the water. Set the SV to a sous-vide temperature like 60 degrees Centigrade. Go to the Parameters menu and set ATU to 0001. This will start the procedure when you exit the menu. The AT light will start blinking while tuning, the length of the procedure depends on your heatsource and reservoir. For me the PID was done in 15 minutes while using a 1,7 liter watercooker. When the procedure is finished the AT light will go out and the PV and SV should be at the same temperature. Congratulations, your DIY sous-vide machine is ready for use! Better start here to find out what you’ll be cooking tonight 😀

    This article was originally published on Style.over Substance.

    • Guy naively wrote his master's thesis on the subject of authenticity and in doing so unwittingly doomed himself to life as a hipster. Now he writes about the eternal struggle to find the purest expressions of heritage and craftsmanship in products, and the burning hole in his wallet.

    • Show Comments

    Leave a Reply

    You May Also Like

    Every cut of beef explained

    One thing I’ve learned from sous vide cooking: I have no clue where any ...

    25 Knives, 47 Knife Skills

    A master chef with impeccable knife skills is presented with a series of knives ...

    Sous vide: a DIY guide (part 1)

    The problem of cooking large pieces of food in a pan is that heat ...