Any HVAC experts here?

[Eugenereef]

I have been toying around with an idea of converting a home thermostat into a temperature controller. Finally I found one on the web in a brewing fourm. here is the link.

http://www.homebrewtalk.com/f51/diy-temp-controller-build-133364/

 

So, I set out to make one for myself and succeeded halfway. that is, I have a good working temperature sensor now. I wired the electrical outlet with mini relay (coil voltage 12V, contact voltage 120 AC) and the relay operates perfectly when I supply it with 12 V wall-wart! The problem is I am not able to operate the relay with the controller as described in above post. I do have a different relay that the guy using it in the post. Mine is this from radioshack:

http://www.radioshack.com/product/index.jsp?productId=2062482

Question I have to HVAC experts is what am I doing wrong here DOH! The entire wiring of the thermostat and relay is exactly like described in the post. Also, after reading a bit about thermostats, I do understand the circuit and priniciple on which these things work. So based on my reading, the system should just work fine(scratch)

 

Is it the relay that is having problem talking to the controller? (one guy here is controlling auto relay using theromstat!!!)

 

Thanks for your help.

[Emerald525]

I believe Topher is a HVAC person you might want to send him a pm.

[TidePool]

I'm not an HVAC tech, but I am a retired electrician.

 

1st step I'd take is to use a voltmeter to check for voltage at the relay coil terminals. Since you are using DC you need to make sure you have correct polarity at the relay coil.

If you have correct voltage and polarity at the coil, and the coil does not operate, then the coil is defective. If the polarity is incorrect, reverse the wires at the coil. If the voltage is not correct, at the relay coil, then you have a problem with the control circuit.

 

Make sure the stat contacts are rated for DC current (most are rated for 24 VAC). When I have done projects using these types of stats I always used relays with 24VAC coils. DC current is much harder on contacts than AC current.

 

Good Luck

[Drew]

Pretty cool idea for a heater controller. If you figure it out Eugenereef i might have to come over and check it out so i can build one. I don't like how my tank temp swings nearly 3 degrees between day/night.

[Eugenereef]

Ok, So after several long and very painful attempts, I am happy to say that the old thermostat in my home will now control the temperature in my Nano

 

here is a quick update.

 

Emerald525

I believe Topher is a HVAC person you might want to send him a pm.

 

Thanks for the info Emerald525. Never got around sending Topher an email but I'll keep him in mind if I run into any future issues with this project.

 

Pretty cool idea for a heater controller. If you figure it out Eugenereef i might have to come over and check it out so i can build one. I don't like how my tank temp swings nearly 3 degrees between day/night.

 

Thanks, Drew. Yeh! finally it worked so you are more than welcome to take a look at it. I am out until Sunday DOH! again, but after that we are good. If I do get back in town earlier, I'll let you know.

 

TidePool

I'm not an HVAC tech, but I am a retired electrician.

 

1st step I'd take is to use a voltmeter to check for voltage at the relay coil terminals. Since you are using DC you need to make sure you have correct polarity at the relay coil.

If you have correct voltage and polarity at the coil, and the coil does not operate, then the coil is defective. If the polarity is incorrect, reverse the wires at the coil. If the voltage is not correct, at the relay coil, then you have a problem with the control circuit.

 

Make sure the stat contacts are rated for DC current (most are rated for 24 VAC). When I have done projects using these types of stats I always used relays with 24VAC coils. DC current is much harder on contacts than AC current.

 

Good Luck

 

Thanks for your input Tidepool. You are right on the money with SSRs and I wish I had one of those. Instead, I was using the mini-relay.

 

Anyhow, After two days on continues effrot to figure out what was worng, I started to wonder if the thermostat was bad (scratch), sure eough, I removed my home thermostat and attached this new one, and nothing really happemed (flame). I wasted two day on this crapy thermostat trying to figure out what I was doing worng (flame)(flame). I was sooo.. frustrated that I event stoped recording pictures to share!DOH!

 

Anyhow, So I got a new thermostat from Jerrys and put it inon my home furnace ( the older one could only be programmed for 5 days, the new one is now 5-1-1).

 

So I located the thermister (the temperature sensor) on this thermostat (the yellow circle), removed it using soldering iron, attached a pair of thin wires and resoldered it back to the circuit board.

 

 

 

I used heatshrink tube to insulate the thermister and now I'll put silicon around it.

 

compared the temperature with the home thermostat! Not bad!

 

 

Finally wiried the relay, outlet and wall wart as done by the previous guy (post #1 on this thread) and I had my <$20 temperature contorller.

 

 

And connected the whole thing to the thermostat (or controller)

 

 

Here is the whole contraption

 

I tested it with a lamp and set the temperature to be 75 F( room temp was 69F). The lamp (Heater rep!) came on. I them stuck the sensor in the lamp shade, the temp started to go up. As soon as it was 76 F, the lamp went off. I then removed the probe off the shade and as soon as the temp hit 75, the lamp came back on again. Did this a few times to make sure it was doing what it was suppose to do.

 

I now have to seal the temperature probe with silicon or something just leaving the thermister exposed. Actually, thermal adhisive will be best but I don't have any at the moment! Then, it will be the real deal

 

So far, it worked in the test conditions, field test is coming soon. Stay tuned for the update (scary).

 

Let me know if you have any question!!

 

Thanks,

Upinder

[impur]

Very cool Upinder!! I'm going to do this for my fermentation enclosure i plan to build for brewing this summer, but it looks like it works great for our tanks too. Great job!

[Eugenereef]

Very cool Upinder!! I'm going to do this for my fermentation enclosure i plan to build for brewing this summer' date=' but it looks like it works great for our tanks too. Great job![/quote']

 

Thanks Miles!

 

Yeh! improvisation is the way to go in this hobby if one wants to keep it under check This will work very well for fermentation enclosure. I would recommend that if you use the controller in the post #1, then get SSR from ebay. "I think" those controllers are not able to handle the mini relays (also TidePool's point!).

 

I am looking for some thermal epoxy that I will use to seal off the thermistor. Also, let me know if you need any help. (but then, if I could do it, anyone can so this as I am not an expert in this area by any stretch of imagination )

[Eugenereef]

Cannot find thermal epoxy anywhere locally. Does anyone knows a place here in Eugene?

[Drew]

Any thought on using a thermostat that has hot and cold settings? Turn heater on or turn a fan on hehe

[Topher]

Any thought on using a thermostat that has hot and cold settings? Turn heater on or turn a fan on hehe

 

there are some thermostats the have an auto changeover from heating to cooling that could do this. they have adjustable dead band between heat cool that can be adjusted as close as 1 degree.

[Topher]

Thanks Miles!

 

Yeh! improvisation is the way to go in this hobby if one wants to keep it under check This will work very well for fermentation enclosure. I would recommend that if you use the controller in the post #1, then get SSR from ebay. "I think" those controllers are not able to handle the mini relays (also TidePool's point!).

 

I am looking for some thermal epoxy that I will use to seal off the thermistor. Also, let me know if you need any help. (but then, if I could do it, anyone can so this as I am not an expert in this area by any stretch of imagination )

 

i am wondering if the plastic dip would work. it is for tools and such and i beleive it is sold at home depot

[Topher]

Ok, So after several long and very painful attempts, I am happy to say that the old thermostat in my home will now control the temperature in my Nano

 

here is a quick update.

 

 

 

Thanks for the info Emerald525. Never got around sending Topher an email but I'll keep him in mind if I run into any future issues with this project.

 

 

 

Thanks, Drew. Yeh! finally it worked so you are more than welcome to take a look at it. I am out until Sunday DOH! again, but after that we are good. If I do get back in town earlier, I'll let you know.

 

 

 

Thanks for your input Tidepool. You are right on the money with SSRs and I wish I had one of those. Instead, I was using the mini-relay.

 

Anyhow, After two days on continues effrot to figure out what was worng, I started to wonder if the thermostat was bad (scratch), sure eough, I removed my home thermostat and attached this new one, and nothing really happemed (flame). I wasted two day on this crapy thermostat trying to figure out what I was doing worng (flame)(flame). I was sooo.. frustrated that I event stoped recording pictures to share!DOH!

 

Anyhow, So I got a new thermostat from Jerrys and put it inon my home furnace ( the older one could only be programmed for 5 days, the new one is now 5-1-1).

 

So I located the thermister (the temperature sensor) on this thermostat (the yellow circle), removed it using soldering iron, attached a pair of thin wires and resoldered it back to the circuit board.

 

 

 

I used heatshrink tube to insulate the thermister and now I'll put silicon around it.

 

compared the temperature with the home thermostat! Not bad!

 

 

Finally wiried the relay, outlet and wall wart as done by the previous guy (post #1 on this thread) and I had my <$20 temperature contorller.

 

 

And connected the whole thing to the thermostat (or controller)

 

 

Here is the whole contraption

 

I tested it with a lamp and set the temperature to be 75 F( room temp was 69F). The lamp (Heater rep!) came on. I them stuck the sensor in the lamp shade, the temp started to go up. As soon as it was 76 F, the lamp went off. I then removed the probe off the shade and as soon as the temp hit 75, the lamp came back on again. Did this a few times to make sure it was doing what it was suppose to do.

 

I now have to seal the temperature probe with silicon or something just leaving the thermister exposed. Actually, thermal adhisive will be best but I don't have any at the moment! Then, it will be the real deal

 

So far, it worked in the test conditions, field test is coming soon. Stay tuned for the update (scary).

 

Let me know if you have any question!!

 

Thanks,

Upinder

 

 

i am impressed that you have done the remote temp sensor on this thermostat. there are some stats that you can get the remote temp sensor without any mods

[Eugenereef]

i am impressed that you have done the remote temp sensor on this thermostat. there are some stats that you can get the remote temp sensor without any mods

 

Thanks for chiming in Topher. I am glad the thread caught your attention (I was too lazy to send a pm out to you after I found out the thermostat itself was bad!)

 

I have to look into this plastic dip. I did not know about it. Which area in HD should I look in for this plastic dip. From a recent LED project, I had some thermal epoxy left over and was thinking of using it. but then, it has aluminium and boron in it and I am afriad it might leach out in the tank. The plastic dip might be answer here!!

[impur]

I think he's talking about plastidip. I'm going to use it to blackout the badges on my truck

 

[Eugenereef]

An Update:

 

After about 2 months of controlling temperature on my nano, this controller is being put on my waterchange system.

 

The controller has worked flawlessly until a week or so ago when I noticed the temperature in the ank was off by 4 deg (the tank felt cold to the hand and second thermometer quantified the difference). I notice that the cualk from the thermister has come off a little and so the conductance had changed resulting in higher reading of the temperature! When the sensor is outside the water, temperature is accurate with in a degree to my home thermostat. I am going to follow-up on Topher's suggestion and look for this "plastic dip" in HD to resolve this sealing of the sensor issue.