Idea for thermowell

Hello. This is my first post here. I am interested in BrewPi and I have started gathering parts. I live in Korea, so the heat of the summer makes it difficult to homebrew without some sort of temperature control, but I don’t want to leave the a/c on all day just to keep the beer cool. No problem in winter though. If you stay indoors.

Anyway, I had an idea about thermowells for the beer temperature sensor. I have searched but I have not seen a similar suggestion, so either it’s very innovative and cool, or it’s really dumb. I’d like a few opinions either way before I continue.

Basically, the common “waterproof” DS18B20 sensors we find on ebay, Amazon, or other sites such as this:

…are housed in a sealed stainless steel tube. The sensor is its own thermowell.

I have found that on the one that I have the heatshrink tube covering the joint between the stainless steel tube and the cable is not a tight fit and it would slide off, but that’s not a problem as I don’t intend to immerse the whole thing.

So, here’s the idea. The sensor is housed in a 50mm long 6mm diameter stainless tube with a sealed end. I am thinking of cutting a 30mm piece of silicone tube with 6mm internal diameter (ID) and 8mm or more outside diameter (OD). I would slide the silicone tube over the stainless tube at the heatshrink end, leaving 20mm of stainless tube protruding. Next, I’d drill a hole in my plastic brewing vessel slightly smaller than the OD of the silicone tube about half-way up the side. Finally, I’d push the sensor into the hole, maybe protruding about 30mm into the vessel (20mm stainless and 10mm silicone). The silicone material and stainless tube should be safe in the beer, and the silicone would be slightly compressed in the hole to make a good seal.

I have immersed the sensor in water for two weeks to see that it didn’t corrode (it didn’t), and a thermowell is made from stainless steel in the same way as the housing of this sensor, so putting one of these sensors inside a thermowell seems redundant.

Has anyone else tried this? Thoughts, opinions, and empirical evidence welcome.

Thank you.

1 Like

This sounds like a pretty good solution for the cheap eBay sensors with heat shrink, but the ones in our store are actually 100% waterproof. They use epoxy to seal instead of heat shrink. I think it is just wrong that they are selling the shrink wrapped ones as waterproof.

I am trying to get them entirely made from food safe materials for the next batch, the silicone cable used now does not have a food safety rating.

Thanks. I just wondered if anyone else had left the cheap sensors in contact with the beer.

My other idea was to get a longer silicone tube, maybe 40cm long, with 6mm ID, and use it to cover the 5cm stainless tube and the cable, and drop it down from the lid. The silicone tube would cover about 3cm of the stainless tube, and the joint, and the cable, and it would make a good seal through a hole in the lid. It would essentially form a flexible thermowell inside the vessel, but the end would be 20mm of the sealed stainless tube.

At the moment I only have a small piece of silicone tubing, which will only work with my first idea.

I did peel back the heatshrink covering the joint on my sensor, and it’s hard to see what’s inside the steel tube. The cable and its sheath enters the tube, but I can’t see if there is a seal around it, or if the sensor itself is potted or something.

Thank you for your comments.

Silicone is a good thermal isolator, I don’t think you’ll want to cover the tubes. With the heat shrink sensors I had it was easy to pull the bare sensor out of the stainless tube, inside was just a small blob of glue.

Right. I would leave 20mm of the stainless steel exposed at the end of the tube.

I’ll try pulling on the waterproof sensor I have, to see if the bare sensor will come out.

I played around with these à while ago. The sensor diameter of the ss is 6mm and thermowell i am using is made from a 300mm long piece of stainless steel that is 12.5mm od and 10mm id so there is a bit of play between the sensor and the sides of the the thermowell. It works fine when fermenting but is not so good if using the same setup for mashing. For mashing i stripped the shrink tube off the ss probe and slipped it inside a 6mm id copper tube with 20mm of the ss probe extending out of the tube. I sealed the probe to the tube with some aquarium silicone and it works a lot better. I found the lag of the probe reduced from 6 min when inside the loose ss to 1min when the probe is directly in contact with the liquid…
I dont use the copper tube probe in the fermentor, only for mash temps. I was going to do a similar thing for the fermentor using 6mm id beer line and have the ss probe hanging 20mm out the end much like you described but havent had to do this yet.

I just purchased a stainless steel thermowell from Brewers Hardware item #: WLFTW12

I’m very happy with it. It attaches like a bulkhead fitting to my flat top fermenter lid.

I purchased my thermocouples with my Brewpi. I used it immersed in the wort/beer. While removing it after a brew one of the silicone to stainless joints failed and it shorted my thermocouple.

Hi Greg, was this one of the newer RJ11 probes?

Sorry, I was supposed to look at my sensor and report back. The heatshrink covering the joint between the cable and the stainless cap can be slid up the cable a little. I did that and took a look, but the cable is glued into the cap and does not come out if I pull on it. There is evidence of some white glue (epoxy?) at the joint.

Incidentally, there are two types of heatshrink. Regular, and adhesive-lined. I guess the adhesive-lined type would make a good job here.

I have ordered 5 metres of 6mm ID silicone tube. When it gets here I will cut about 40 cm from it to make a silicone ‘thermowell’. I decided my first idea (cutting a hole in the side of the brewing vessel) was not as good as cutting a hole in the lid of the vessel.

I don’t think so, it was order 209: Waterproof OneWire digital temperature sensor (DS18B20)

Ah, good. The shrink wrap sensors are not really waterproof, they do tend to fail under the shrink wrap. Because of this I found a new supplier and are now selling much better sensors.

If I was to cover your temperature sensors with food grade heat shrink tubing (like shown in picture #3), covering all the cable and only leaving some of the probe exposed would it be ok to just have it “dipped” into the wort and bypass the need of a thermowell? Provided I got a tight fit from the heat shrink.

Thanks in advance,

I think it would probably be okay. It’s the same idea I had of slipping silicone tubing over the sensor. Your problem might be at the other end, where the wire enters the vessel. You’d need a good seal between the outside of the heatshrink and the hole. I am hoping that the silicone is compressible enough to form a seal in a slightly undersized hole.

My silicone tube arrived from China today. It cost $7.66 for 5m, with free shipping. I only need about 30cm, but that’s ok. It is food-grade for coffee machines (it links the tank to the heater and the outlet). Inner diameter is 6mm, outer diameter is 8mm. I will drill a 7mm hole in the lid of the brewing vessel and push the tube through from the inside (I only need to push a couple of centimetres through).

I need a connector on the end of the flying lead that is less than 7mm diameter as that will be pushed through first. Maybe I’ll use a 3.5mm stereo plug and just remove the housing. I can protect the wires with some heatshrink instead.

Dunno if I’m too late with this, but perhaps this item would work for you?

Stainless Steel Waterproof Gland For 5-10mm Cables
Someone on another thread suggested a similar product. (Found it!)

I think I will just try to pick up a rubber grommet or failing that use some aquarium silicone.

Put up a pic when you’re done, would like to see how you get on.

I wouldn’t trust putting a probe with shrinkwrap in beer - you probably will never get it 100% sanitary. A thermowell avoids these issues since they are completely smooth and can be sanitized easily.

I think @MmmBrewPi was suggesting putting only the stainless probe part through the cable gland. At least I hope that was what he meant.
I agree that any temperature sensor with shrink wrap cannot be trusted.

Hey guys! @mdma & @Elco Thanks for the response. Well what if I said I’d intended to just heat shrink the temp sensor up and have it dangling in the beer?.. :blush: Is it really that bad an idea? Not really gone on the thermowells for 2 reasons, laziness and being awkward.

The thermowells sound great, but how sensitive/resposive are the temp sensors through a layer of steel, air medium, more steel, epoxy, temp sensor. Re-reading that is making me feel pedantic. But… food for thought?

In a dream world I’d prefer to have the bare sensor (no steel sleeve) in the thermowell with a pool of thermal paste/fluid in the base.

Is the reason for concern with the heat shrink in beer the opening seal? I was kind of going to check out how tight I could get the seal when the temp sensors arrive and make a decision based on that maybe add some aquarium silicone if needed.

Oh wall of text, sorry about that…

Thermowells are metal in contact with the metal of your sensor (no need for expoxy) so the response is fast. Orders of magnitude faster than the response time of the beer to temperature changes.

Does anyone have any experience/opinions of immersing a DS18B20 directly in the beer? A DS18B20 is encased in epoxy which is quite inert. It could be pushed into the end of some 4mm I/D silicone tubing, with a couple of mm of teh package sticking out, then the tube and sensor can be dropped into the beer from above.

Beer is slow to change temperature, the slow response of the sensor doesn’t matter at all in this application.
Here are some photos of a prototype sensor we’re developing. This will be good for mounting directly in a kettle or fermenter wall.

The flange on this prototype is 24mm, we’ll increase it to 35mm so it is the same diameter as the sealing locknut. Then it will press the wall flat and there won’t be a gap between locknut and wall.