6 February 2015

DIY Sous-Vide Machine

This machine will make you the most perfect medium-rare steak you've ever dreamt of.

By In Make 16 min read

This article starts off with some background on my own first experiences with sous-vide, so if you just want help creating your own Rex-C100 PID based sous-vide machine keep scrolling down until you hit the halfway point!

The problem of cooking large pieces of food in a pan is that heat is not transferred equally to every part. Everyone has had that strip of meat that is just the perfect medium-rare on the inside, but scorched black on the outside. Or the fish filet that has the perfect crust, but is still frozen solid when you cut it open. Sous-vide, French for ‘under vacuum’, is a method that tries to solve this problem. Using sous-vide your food is sealed in a vacuum bag and submerged in water. The water is set to a specific temperature and the food is kept there until it reaches that same temperature. Using this method your food reaches its perfect level of doneness without any burnt parts, while the vacuum bag keeps any of the taste from being lost to the water. According to some top chefs you’ll get the perfect steak if you leave it in a sous-vide machine for 2 hours at an ideal 55 degrees Centigrade.

Screenshot 2015-01-09 03.51.10

I’d tried something like that before: Timothy Ferris’ book 4 Hour Chef has a sous-vide recipe, where you spend one and a half hour next to a stove with a thermometer in a pan of water. The water contains a freezerbag filled with chicken that needs to be kept to 63 degrees Centigrade. If the temperature drops below 63, turn up the stove. If it rises above 63, turn it down. A great idea, until you spend the next one and a half hour being extremely OCD afflicted. Wasn’t planning on doing that again.

Anova_2013 0264_v1

Instead of staring at a stove you can pick a pre-built sous-vide machine, like the much praised Anova One. It doesn’t get simpler than this all-in-one device: fill a pan with water, put the Anova in, set the temperature – done! The Anova regulates everything without you ever having to touch it again. That ease just comes at a cost of about 200 dollars…


And that’s when I saw this article in the Volkskrant. Creating your own sous-vide machine by combining a PID (Proportional-Integral-Derivative) controller with a heatsource like a watercooker. The PID, an industrial thermostat, learns how turning the cooker on and off influences the temperature over time. For example, when you normally turn a cooker off the heating element will remain warm and keep heating the water for a while. The PID can learn from this overshoot behaviour and compensate for it in the future, turning the cooker off early so the remaining heat brings the water up to the desired temperature instead. By compensating constantly the PID can keep the temperature within a very precise band. And any heatsource can be used instead of a watercooker – rice cookers and deep fryers are popular too – as long as the PID learns to compensate for the specific behaviours of your setup.


The PID the Volkskrant uses is the Chinese Rex-C100, available at Amazon for 30 euro according to the newspaper. For that money you don’t just get the PID, it includes a thermocouple (the thermometer) and a solid state relay (the switch that turns your heatsource on and off) that are also necessary for the project. That might sound cheap, but it’s actually twice as much as they would’ve paid if they had just bought it directly from China: Banggood sells the same kit for 14 euro. So of course I had to try it out.

‘Try’ being the operative word, as it turned out to be a bit harder than I expected. What should’ve been a 1 hour project stretched to a few days I spent reading the indiscernible Chinese manual, trawling through conflicting online guides and scouring for a few missing parts. Suffice to say it was worth it, because my efforts resulted in this majestic creation:


Uh, yeah, so that’s a bit of an anticlimax. But believe me, it works better than it looks. The ugly plastic storage box still keeps the parts dry, which is kinda nice considering there’s 230 volts running through them, and because I used a standard outlet I can plug in any heatsource I want. Sure, I could have used an actual project box, I could have used a nice built-in power connector, but really – what would’ve been the fun of that?


So what’s the first thing we’re gonna try? Eggs!

Not just because that’s what the original Volkskrant article was about, but also because it’s a standard test for any DIY sous-vide machine. By setting it to the perfect temperature you can make eggs where the yolk has this custard structure – not hardboiled, not soft, something in between that’s not attainable in any other way. But it’s a very precise temperature, much more precise than in any other sous-vide recipe. If your sous-vide machine deviates from the set temperature too much you’ll get a regular hard or soft egg, which would be kind of shit for all the effort you put in. Serious Eats has a lengthy article that I would recommend to everyone.

I set the PID for 64 degrees Centigrade, because according to this video from a sous-vide machine brand that’s the perfect temperature to create custard eggs. After a brief heating period the cooker was at the desired temperature – but was the PID right? For an extra quick check I used my cooking thermometer.


Hmmm, 63, not bad. One degree lower than the PID says it is. Of course the problem is that I don’t know if my cooking thermometer is right either. And more importantly, both are rounding the temperature down to whole degrees. Maybe the cooking thermometer thinks it’s 62,5 degrees, while the PID thinks it’s 64,4. Or maybe the thermometer thinks it’s 63,4 degrees and the PID 63,5. No clue.

But that can wait. After the recommended 55 minutes I took out my egg, peeled it and cut it in half…


Okay, that was not what I expected. According to the online guides this should be safe to eat, even though it looks like liquid salmonella. After the first few cautious bites it turned out to be quite tasty, like an extremely soft egg. But not the custard egg I was promised.

Serious Eats says time is also a factor. Maybe 55 minutes in my DIY setup wasn’t long enough? To test that I kept the next egg in the cooker for 2 and a half hours. So after more waiting, peeling and cutting I got…


Better I guess, but still very liquid. Tasted good and the yolk was creamier, it could even be spread on toast like suggested in the video. But this still looks too much like liquid salmonella for my tastes.

I did one last attempt with an egg, but now at 66 degrees instead of 64. In the Serious Eats article that was the temperature at which the picture of their test eggs looked most like the description of a custard egg. 55 minutes later I cracked it open and…


Wow. It’s just 2 degrees of difference, but suddenly the yolk has this custard-like appearance and the white actually retains an egg-shape after cutting. This is kinda cool.


But a test with eggs is not a true test. Meat is the only true test! A nice piece of steak, to be exact. Serious Eats has another lengthy article you should read. According to them 45 minutes at 55 degrees should be sufficient to get the perfect medium-rare piece of cow on your plate. But because I’m becoming a bit wary of my PID, it might be reading higher temperatures than I’m actually getting, I decide to make it 1 hour at 57 degrees just in case.


I had a piece of steak still lying in the freezer, and the plastic it was already vacuumsealed in was fine to use for sous-vide. This did mean that I couldn’t add salt and pepper or other spices to the steak, but it’d be fine for a first test. After defrosting in the fridge the steak went into the cooker and an hour later…


Okay, that doesn’t look very tempting, but hey, it’s a work in progress. Maybe it’s better if we take it out of the bag.


No. That’s definitely not better.


Luckily I’d read beforehand that you need to finish any sous-vide meat in the pan, so I knew what I was getting into. 1 minute at your highest scorching heat on both sides will give you enough maillard reaction to get you that nice traditional brown steak crust. After that I sliced it open to take a look…


Goddamn, nice. I’m drooling just seeing these pictures again.


So tender. So tasty. So unexpectedly good for a first test. So worth getting redflagged as a bombmaker on the internet over.

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 😀

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