Posted by: ohmypuddin | April 20, 2011

Building Your Own Sous Vide Machine – Part 2

Heating Element Selection and Assembly

Editor’s Note: Confused? Read Part 1 of Building Your Own Sous Vide Machine for the intro, parts list, and blog post that sparked the inspiration for this project.

Instead of the three immersion heaters that Scott linked in parallel, I chose to use a 1500 watt 120v water heater element. This part will set you back less than $10 at a Home Depot or a Lowes.  I know because I bought one at each throughout the course of this adventure.  The one at Lowes is about an inch longer, but other than that, they’re pretty much the same.

I wanted more power than what was offered by the coffee cup heaters, and I thought that because the element was threaded I could just screw it into the bottom of my enclosure. The heating element selection turned out to be the direct cause of the failures of both versions 1 and 2.

In version 1 I did as I had planned and screwed the heating element into the bottom of the acrylic enclosure. As I was testing the machine for the first time, the PID was controlling the element, and the water was heating, but I hadn’t had the machine on for very long before I smelled melting plastic. I shut the machine off before there was any damage, but I knew at that point, that I needed something to mount the element on besides the plastic.

It was back to the hardware store to find some way that I could mount the element without it touching plastic. At the hardware store I happened upon a steel floor flange. The flange had a center hole that was threaded for a 1″ pipe. It also had four bolt holes spaced around the edge. I thought that this would be just what I needed. So in version 2, instead of mounting the heating element directly against the plastic, I mounted the flange up on rubber grommets within the enclosure, and then threaded the element into the flange. This left the element so that only about half the element was submerged in water once the water was filled and the circulator was mounted over the water.

Version 2 was a disaster. In the next test, I left the machine on long enough for the water to come up to 130 (Fahrenheit…come on this is America people) and hold temperature. At first, it seemed like everything was working, but then I realized that the flange was melting through the bottom of the enclosure. By the time I noticed and shut the machine off, not only had it melted partially through the bottom, but it had turned the inside of the enclosure into an oven, partially melting some of my other components. The heating element itself was actually beginning to melt at the top as it entered the first stage of burning out. I learned two lessons out of this:

  • Lesson 1: Water heater elements must be submerged almost entirely when in use.  Anything less and you’re flirting with a meltdown.
  • Lesson 2: Never ever put a heat sink (e.g. steel floor flange) inside an airtight plastic case. Man and I even had a class on thermodynamics in college – you would think I would know better. To be fair to my thermodynamics teacher, I did sleep a lot in that class.

This led me to the third and final version of the heating element mounting assembly (yes, I know there’s a version 4 of the circulator, but it’s still using the same heating element mounting assembly from version 3, if it ain’t broke, don’t fix it).  In version 3, I bought a sheet of aluminum from the hardware store and 4 2 inch long nylon bolts with 3 times as many matching nuts and a set of nylon washers.  I also reused the rubber grommets that I purchased for version 2.  Following are the instructions to make the mounting assembly for the heating element:

  1. On the sheet aluminum using a carpenter’s square, draw a 3’’ x 3’’ square.
  2. In the center of the square draw a 1 inch circle.
  3. Evenly spaced on the four corners of the square make marks for 4 bolt holes spaced far enough from the edge that the holes can be drilled safely.  What you end up with should be a square of aluminum that looks something like this…only bigger.
  4. Once you have the design traced into the aluminum you’ll need to cut it out. I used a Dremel and with a circle cutting attachment for the one inch hole.  For the bolt holes you should just be able to use the normal metal cutting bit and eyeball it.
  5. With your square cut out, attach your rubber grommets to the bolt holes. If you cut your holes correctly you should be able to pinch and slide them into place.
  6. Slide the four nylon bolts through the grommets and tighten one nylon nut onto each bolt all the way until the nut and bolt head are snug against the rubber grommet. You should end up with something like a tiny table with a huge hole in the top.
  7. Next, thread your heating element into your assembly. The heating element should be coming out opposite the side that the bolts are facing. Back to the table metaphor, the heating element should be coming out of your table top like a giant center piece.
  8. That’s it.  Your heating element assembly is complete. On your enclosure, you’ll need to cut four corresponding bolt holes to mount the assembly with one small center hole to thread wires to power the element. These 4 bolt holes and one center hole will take the place of the three holes that are cut for the immersion heaters in Scott’s original design.
     

Next time, relays!

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  1. […] Part 1 Part 2 […]

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  4. […] How to build your own sous vide machine part 2 […]

  5. There are heater elements on Amazon with a flange. This makes it so you don’t have to fabricate the aluminum mounts.

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  7. Nice idea and execution. The only thing that I would change is insulating the wires at the top of the waterbath similar to the way people that use them for heat sticks making home brew do. They use a one inch coupling that is almost the exact size to fit over the electrical end of the element and completely submerge the wires and connectors with epoxy (j b weld) then they cut the coupling off. I would cut it first in your case to a length that will be just a little taller then the connections. This way there is no chance of getting water up there or electricuting yourself if it somehow wound up in the water. This upgrade will only cost you about $5 for the jb weld and coupling. Here is a link so you can see what i mean. http://www.homebrewtalk.com/f170/my-method-sealing-heatstick-220198/

    On a side note, do you feel your 1500w element is too much for your bath or can the controller keep it at .1F accuracy? I was planing on doing this but only using a 1000w element since the 3 immersion ones people usually use are only 300w each but if the 1500w isn’t a problem, i will just buy one in town and do a similar setup to what you did. I thought that a 1500 might be hard for it to keep from over shooting, and I also thought it was longer.

    Also, how submerged to you keep the rod, right up to the bottom threads or is it ok to have a little uncovered with water? I was actually planing on fully submerging it like what they did on the website above for the heat sticks, but vertically it takes up less space like you did. I just didn’t want to risk burning it out or have a heat problem, but i see your solution for that so that is not a concern.

    Thanks

    • Hey Rob, I asked John to answer your questions, and here he is:

      Good tip on sealing the wires, I hadn’t thought of that.

      I don’t think that the 1500 W heating element is overkill. I started with a 1000W one, unfortunately it got burned out in one of my early versions, and a 1500W was the closest they had at the hardware store. It is slightly longer than the 1000W, but not by much, maybe an inch or so. With the 1500W it can take about half an hour or so for it to bring my water bath up to my cooking temperature depending on what it is I’m cooking.

      I think that if you’re worried about accuracy, it’s going to be more about what thermocouple and PID controller you get. The cheaper PIDs don’t guarantee that degree of accuracy, you’d also probably want to insulate your water bath and make sure that the pump you have circulating was pretty powerful. With mine, I probably have +/- 1degree F accuracy and that’s plenty for me, but I don’t think it’s due to the 1500 W supply. My Auber instruments PID doesn’t even display decimals for Fahrenheit, so it’s definitely not going to control to that degree of accuracy.

      I try to keep the heating element submerged up to the threads whenever possible. I’m not sure where exactly the breaking point is, but I don’t want to find out.

      • Thanks a lot. I am going with the 1500w element and see how it goes. I am using a 10 gallon water bath so it should be fine then. I am using the JLD612 PID from lightobject.com and it does support 0.1F resolution if you use a PT100 thermocouple (and select the PT10.0 setting in the probe type selection) so I’ll see if it can really hold it stable or not. It probably is overkill, but if it can keep it within +-0.5F I’d be happy. I like your setup for the probe but I think I am going to go with more of the heat stick approach and cut a 1 1/2″ hole in the acrylic for the J pipe to stick up through so I’ll be able to get the probe fully submerged for sure (and not worry so much about water level if I am going to let it run 24 hrs+) since I can put the whole thing about 1″ off the bottom of the tub since it will be in a j pipe. I will leave it so I can slide it up or down in my 1 1/2″ hole for if I move the head unit to another water bath If I need a deeper vessel. I can also play with different depths to see if it will affect the stability of the water bath temperature. BTW, if you don’t know what the J pipe is, that is the chrome pipe that runs from the bottom of your kitchen sink and connects in the middle to the t connector so it will be long enough to move it up or down up to a foot or so.

        If you are keeping it submerged to the threads, which i think you should from what i have read, you really should think about sealing up your electrical connections. If you decide to do the 1″ coupling to make yours water proof it was 40 cents for the coupling and $4 for the jb weld from walmart. I did my element last night and it turned out good. It fills the coupling 1/2 way up using both full tubes of jb weld so you could just cut the coupling in half before you start to make it easier. Another thing you could do instead would be to leave the whole thing there, then after it sets up 24 hrs, you could cut the whole coupling off using a dermel. They basically split down both sides of the coupling cutting it in half length wise then just split it apart. The only reason they leave any on it is for a tight fit into the j-pipe, you could just use it for a mold. Just some food for thought.

        Thanks for the good blog. You gave me me some new ideas and got me researching different setups with water heater elements and changed my mind about using the cheesy NORPRO 559 Immersion Heater that so many people use for this. After testing my first norpro and it burning out in 5 mins, I can’t see putting up with that hassle or quality. Sent it and my other 2 back for a refund and built this much more industrial setup for only about $10 more. Plus I get an extra 600w of heating power then I was going to have with the 3 – 300w norpros. Water heating elements last 10 years+ in a water heater so that seems like the smart move to me.

        Robert

      • From John:

        If you sealed your electrical connections and threads of your heating element, it will definitely last a good long time. You can clean your heating element after a few uses with distilled vinegar unlike when you have it in an actual water heater. After you clean it it removes all the build up and looks as good as new except for som rust at the top.

        Be careful with JLD612. That’s the PID I used first. It had a real tendency to over shoot it’s temperature and never cut off. I believe that it was responsible for one of my major melt downs. Not sure if I got a faulty one or what. It had a way to trigger a recalibration that seemed to help, but I had to do it every time I turned it on and set the temperature, again, I might have just had a faulty one. I’ve the auber intsraments pid much easier to use and and it has never overshot by more than a degree on me and I don’t have to do any sort of auto calibration, I just turn it on and it works. I think the auber is a favorite of a lot of home brewers. The company is based in the US and the PID is designed here but built overseas.

        Also, I just remembered. I’m pretty sure that the .1 degree resolution on the JLD612 might only apply to degrees Celsius not Fahrenheit, I could be wrong about that but I’m pretty sure when I got my hands on the actual docs for it that was the case.

      • So far I have used it 3 times since i put it all together. It has worked awesome so far. It can go to .1F if you set the PT100 probe to the right setting in the setup, P10.1
        I have found the auto calibration to be worthless. I did some searches online and found some manual settings that people have used online and used that as a starting point. I read though the manual that explained what all the setting did and after a few minor tweaks, I have it within .1F variance over a 24 hr period. I had it set on 137.2F and it was bouncing between 137.3 and 137.2. I am very happy with it. Before I ran the calibration or changed any setting manually using the default settings, it was bouncing almost a full degree and was not very responsive. When i first put it together it would vary as far as 134.1-136.1 when it was set to 135F. Still not terrible, but not good enough for me. I auto calibrated it and it was not much better, still bounce more than a full degree and had slow response time. Since I manually tweaked it, it am happy with it only bouncing .1F and I’m glad that I can read the temp to the .1F accuracy to see how it is really doing, although I know it is not that important.

        I am using about 7 gallons of water and a Rio brand aquarium pump that is rated at 90gph that seems to be working fine so far. It sounded a little labored at 150F so I don’t think I will try getting it up to the temp to do vegetables unless i’m really ready stress test my pump. I tested the bath in various places with my thermapen instant probe it was exactly the same everywhere.

        I cooked a 4.5 lb bottom round roast in it for 26 Hrs at a water bath temp of 137F and it turned out awesome. Very tender and still very pink. Still had a very good steak texture, not quite as tender as filet, but not close, i’d say about almost as good as a good prime rib.

        I don’t like how the water heater element is showing rust in the threads and the flat part the element actually comes out of (the part that would normally be inside of a water heater) I have been using about a 1/4 cup of vinegar in the 7 gal of water to try to keep the scale down. Is this causing the rusting? The element has turned to the copper color now after using the vinegar. After just one use i had a little build up when i wasn’t using the vinegar, so I read someone talk about that to keep the scale down. Any ideas on why it’s rusting? I guess maybe it does inside of a water heater too but you just don’t see it?

        Rob


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