EcoRenovator - View Single Post - my temp sensor idea for inside of collector panels

strider3700 · 10-17-14, 12:47 AM

I started on the road to building my own solar DHW heating system almost 5 years ago. Life got in the way but I've got back at it lately. It's going to be a copper/aluminum fin hizer design. Somewhere on the board there is a thread or two about an arduino based differential controller I was building. I've been using it for awhile to measure temperatures around the house and I wanted to use it to measure things for the solar setup. The sensors for that are DS18b20. I ordered a bunch off of ebay and they work great but are not water proof/resistant at all.

The lack of water resistance worries me so I've been mulling over ideas for a year or two. In the panel I want to measure income water temp outgoing water temp and panel temp in probably a couple of places. I wasn't content with just attaching the sensor to the outside of the pipe. I wanted as close to direct water readings as possible.

I knew that I didn't want to solder anything with a sensor in it directly to the copper so when i build the hizer I added 1/2" pex to copper adapters with the intention of crimping on a small chunk of pex with the sensor inside it "somehow" and getting the wiring back out. all without causing a leak.

Tonight I think I came up with something that will work. I took a standard end cap for the pex.

Then I filled the inside with melted leadfree solder. this was just a standard roll left over from soldering the hizer together.

next I flipped it over and driledl a hole in the top making sure I didn't go all the way through.

here's one of the sensors

and here's how it fits inside

I can't find the cat3 I've been using to build these so I can't complete tonight but the next step is to solder the 3 wires on to the sensor and wrap in heat shrink. Insert it into the plug. Carefully add a couple of drops of oil to transfer the heat to the sensor better. then use a few drops of silicone to seal the oil and sensor in. That will be the hardest part as any oil on the wire or cap will prevent a seal but the good news is a leak isn't the end of the world like a water leak would be. it just means a slightly less accurate reading. Really the oil should make such a little difference just filling the entire opening with silicone should work.

Anyways when I get some more wire I'll take a few more pictures but I think this will work well. My only concern is about air getting trapped in the system next to the sensors as they're both in high points. that may require some minor changes to the collector or maybe adding an air valve or release of some sort makes sense. At my current pace I'll have the answer before the end of the decade

I think for in the tank I'll do a similar idea but with the sensors inside of some 1/2" copper with a cap on one end and massive silicone plug on the other. That's what I've used outside for temp monitoring for 4+ years and they still work fine although that's a much easier environment then submerged in the tank.

10-17-14, 12:47 AM	#1
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	my temp sensor idea for inside of collector panels I started on the road to building my own solar DHW heating system almost 5 years ago. Life got in the way but I've got back at it lately. It's going to be a copper/aluminum fin hizer design. Somewhere on the board there is a thread or two about an arduino based differential controller I was building. I've been using it for awhile to measure temperatures around the house and I wanted to use it to measure things for the solar setup. The sensors for that are DS18b20. I ordered a bunch off of ebay and they work great but are not water proof/resistant at all. The lack of water resistance worries me so I've been mulling over ideas for a year or two. In the panel I want to measure income water temp outgoing water temp and panel temp in probably a couple of places. I wasn't content with just attaching the sensor to the outside of the pipe. I wanted as close to direct water readings as possible. I knew that I didn't want to solder anything with a sensor in it directly to the copper so when i build the hizer I added 1/2" pex to copper adapters with the intention of crimping on a small chunk of pex with the sensor inside it "somehow" and getting the wiring back out. all without causing a leak. Tonight I think I came up with something that will work. I took a standard end cap for the pex. Then I filled the inside with melted leadfree solder. this was just a standard roll left over from soldering the hizer together. next I flipped it over and driledl a hole in the top making sure I didn't go all the way through. here's one of the sensors and here's how it fits inside I can't find the cat3 I've been using to build these so I can't complete tonight but the next step is to solder the 3 wires on to the sensor and wrap in heat shrink. Insert it into the plug. Carefully add a couple of drops of oil to transfer the heat to the sensor better. then use a few drops of silicone to seal the oil and sensor in. That will be the hardest part as any oil on the wire or cap will prevent a seal but the good news is a leak isn't the end of the world like a water leak would be. it just means a slightly less accurate reading. Really the oil should make such a little difference just filling the entire opening with silicone should work. Anyways when I get some more wire I'll take a few more pictures but I think this will work well. My only concern is about air getting trapped in the system next to the sensors as they're both in high points. that may require some minor changes to the collector or maybe adding an air valve or release of some sort makes sense. At my current pace I'll have the answer before the end of the decade I think for in the tank I'll do a similar idea but with the sensors inside of some 1/2" copper with a cap on one end and massive silicone plug on the other. That's what I've used outside for temp monitoring for 4+ years and they still work fine although that's a much easier environment then submerged in the tank.