24 Volt Temperature Sensor Wanted

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dogwood

Minister of Fire
Mar 22, 2009
825
Western VA
Is anyone aware of a 24 volt temperature sensor that would lend itself to being attached to the outside of a propane tank hot water storage vessel, and be readable from a remote location, say seventy feet away, mounted next to our thermostat.

I found one possibility in a thread about the AZEL - DS-60P Digital Temperature Gauge, Dual Source Display, http://www.azeltec.com/images/brochure.pdf, but was unsure if it's round looking probe could be successfully attached to the outside of the tank. Anybody have any experience with this model temp sensor who might know if this was possible? Or any other 24v model that might do the trick? Thanks.

Mike
 
Have you thought about the wireless 1 or 2-probe barbecue thermometers? They're not 24vac, but run on batteries, and if battery life is anything like my indoor/outdoor wireless thermometer in the house, the batteries last for a very long time. Do an ebay search "barbecue thermometer probe wireless" and you will find a good selection. If you are a bit handy, the indoor unit with some very simple parts can be converted to be powered by your 24vac line if battery life is short. I suggest the 2-probe if you go this route. You may find measuring two points on your tank, or one on the tank and one for outside air, or whatever, to be useful.
 
dogwood said:
Is anyone aware of a 24 volt temperature sensor that would lend itself to being attached to the outside of a propane tank hot water storage vessel, and be readable from a remote location, say seventy feet away, mounted next to our thermostat.

I found one possibility in a thread about the AZEL - DS-60P Digital Temperature Gauge, Dual Source Display, http://www.azeltec.com/images/brochure.pdf, but was unsure if it's round looking probe could be successfully attached to the outside of the tank. Anybody have any experience with this model temp sensor who might know if this was possible? Or any other 24v model that might do the trick? Thanks.

Mike


Mike,

The azels will work fine, they have a flat side on the thermister that you can put against a pipe or tank. They can run off 24v or the watch battery that they come with. I have 2 of these in my system right now.

Rob
 
ac or dc? If you just get a $2 rectifier you could use a typical 12v sensor.
 
Rob, do you have one of your Azel thermisters against the side of a tank? If so, how do you have it connected?

Btuser, I will be using 24v AC. I thought it would be simple to tie into the existing 24v AC line servicing the thermostat which will be immediately above the readout display. On the other hand the Azel is a little pricey since I might need two. Could you recommend a suitable, typical 12v temperature sensor so I could look it up and compare prices. I'm guessing from your reply they are DC and I could find a $2 rectifier that would convert 24 volt AC to 12volt DC. Is that what you meant? Thanks for both your help.



Mike
 
Is your current thermostat 2 wire or 4 wire? because depending on your thermostat/system you may find you can't use that. Your boiler control may interpit the coil in your sensor to be a short, and bypass your thermostat's funciton. No way to know untill you hook it up, but I've had bad luck trying to use the 24vac coming from my thermostat for anything else.

You can either get the rectifier at Radioshack, or be lucky like me and live down the street from a electronics surpluss store. I don't know if they'd be any cheaper, its just an idea if you get hung up on 24vac. Personally I like DC because its cheaper for power backup. I found once I started getting into fancy controls my cheapie little generator wouldn't cut it, so instead of $1000 generator I just hooked up a $40 DC power supply.
 
Btuser. my cheapo non-programmable Honeywell thermostat servicing my Lennox Pulse forced hot air furnace has four wires coming from it, G,R,Y,W. The thermostat only has two functions, "Auto" and "Fan (only)". I was going to tap into the Red wire coming from the low voltage terminal strip from the furnace's transformer which provides power to the thermostat. Do you think that might cause the problem you describe?

Mike
 
I have one of the Azels you mentioned and use that to visually monitor the tank temp. You can hook them up to 24vac easily if you have some already available. I did not and being cheap when I can, I took a 4.5vdc power supply that I had lying around, cut the end off and soldered it to the points where the battery attaches. Has worked great ever since!
 
I have my azels taped to pipes with metal hvac tape then insulated. I am putting small sensors on my tanks this week and plan to tape them on also with the same metal tape.

Rob
 
Thanks Rob. WoodNotOil, how did you connect your Azel's thermister to your tank.

Mike
 
dogwood said:
Thanks Rob. WoodNotOil, how did you connect your Azel's thermister to your tank.

Mike

I put wells in through the top of my tank because it is made of concrete. I wrapped the sensor in foil and pushed it down the well. The top well reads great, but the copper well I ran to the bottom tank was giving false readings because the length of copper was being heated by the top of the tank. Instead I put the bottom temp sensor outside of the tank on the pipe that runs to the bottom of the tank. When the pumps are running I get an accurate reading on what is going on in the bottom of the tank. At somepoint when I get time, I will make a new well that is CPVC most of the way down and then copper at the bottom.

The Azel units are nice even to just have on hand to check the delta T of various parts of your heating system. Mine was sold to me for setting up my radiant floor zone. They give you a 3 speed pump and basically tell you to try different speeds until you have a delta T of 10*.

taxidermist said:
Also I would not even waste your time with the 24v part as the battery last a long time

Rob

I really hate having to go out and find odd shaped batteries, but mine usually lasted more than a year. Now I don't have to worry about it...
 
Thanks y'all. How long are your batteries lasting, and are they easy to come by? Maybe I will just use the batteries. sounds a lot simpler. And squirt a little heat transfer paste on where I tape the Azel's thermistor to the tank for good measure.

Mike
 
dogwood said:
Thanks y'all. How long are your batteries lasting, and are they easy to come by? Maybe I will just use the batteries. sounds a lot simpler. And squirt a little heat transfer paste on where I tape the Azel's thermistor to the tank for good measure.

Mike

Mine is 1 year old and I left it on all summer and still running fine. It takes a flat round calculator type batt.


Rob
 
I have one and is within a few degrees of the temp on the boiler.
 
If you are attaching the sensor to the outside of a tank, I would recommend getting some thermal epoxy. This is pretty common for attaching heat-syncs to electronics. A common epoxy like JB weld which has a very high metal content might also work well. You want some heat sync compound or thermal epoxy between the sensor and the tank to get an accurate reading.
 
Scott, nice tip on the thermal epoxy. I do have some JB weld out in the garage, but I'll go pick up some of the real thing. Is thermal epoxy something I might find locally or do I need to order it off the internet? Where would you suggest I might go to find some locally, and is there any particular brand you like, or is readily available? Thanks.

Mike
 
dogwood said:
Scott, nice tip on the thermal epoxy. I do have some JB weld out in the garage, but I'll go pick up some of the real thing. Is thermal epoxy something I might find locally or do I need to order it off the internet? Where would you suggest I might go to find some locally, and is there any particular brand you like, or is readily available? Thanks.

Mike

The high performance computer-mod folks like Arctic Silver brand heat sink compounds - expensive "but a little dab'll do" They make both pastes and epoxies, and most of the overclocker types claim that the AS paste is the best performing stuff to put between a CPU and a heat-sink.

The Epoxy is also supposed to be almost as good when needing to attach heat sinks without having any external fastening points, but it is also supposed to be VERY permanent... Some articles I've seen suggested mixing the paste and the epoxy about 50-50 with the result being something that would hold stuff together reasonably well, but could be taken apart with moderate force...

Gooserider
 
Lots of listings on ebay.
 
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