Wort-O-Matic: Remote Sensing DIY Controller for Less Than $25

Remote Sensing DIY Controller for Less Than $25

Thursday, March 27th, 2008 by J Thornton

After building a Son of a Fermentation Chiller and using it for a while.

I found the following problems:
· It would only hold one carboy
· The analog thermostat sucked
· It is a PIA to deal with the ice in deep narrow ice chambers

So I redesigned the controller first to use a digital remote sensing thermostat for under $25.

The Controller

The RiteTemp Model 8029B digital thermostat can usually be found for less than $25 at your local home improvement warehouse.

It is run by two AA batteries and has a thermistor on the circuit board. It is easy to modify the thermistor to remote sensing. It will go as low as 35°F (1.6C).

Disassembly

The first thing you do is to remove the battery compartment.

Then remove the SIX screws that hold the upper circuit board on.

Do Not Remove the two screws on the left of the circuit board.

It will not blow up you just don’t need to remove them.

Remove the upper circuit board.

Remove the screws holding the lower circuit board on.

Carefully remove the lower circuit board.

Do Not tip the front case over lots of stuff will fall out!

If you tip it over all the little goodies will fall out. This is how they looked before you dumped them out.

Locate the thermistor on the upper corner of the lower circuit board.

Carefully heat the solder and pull out the thermistor wires one at a time.

If you have a solder sucker you can clean out the holes but it’s not necessary.

Solder two wires in place of the thermistor.
You can heat the solder up and push the wire through.

I used solid core 24awg wire I had from another project.

I got the wire from Radio Shack it was 4 conductor and I just stripped two off.

Make sure you have a good solder joint.

I use a low wattage soldering iron with a pencil point.

No Solder Guns Please.

Clip off the extra wire with a wire cutter or nail clipper.

Reinstall the lower board.

Reinstall the upper board.

Route wires as shown or your favorite way.

Reinstall the battery compartment.

Route the wires as shown or your favorite way.

Solder the thermistor to the ends of the wire.

Put heat shrink tubing on the wires before you solder.

Tin the ends of the wire and solder each one on.

Slide the heat shrink over the joint and shrink.

Complete the project by putting a larger heat shrink tube over the entire thermistor and the solder joints.

After installing on your fermentation chiller tape the thermistor to the side of the carboy.

Put a couple of paper towels folded up as shown or a square of bubble wrap over the thermistor for insulation from the ambient air.

Connections

If you need to switch over 24 volts use a relay.

The capacitor across the switched legs can’t take 120vac. How do I know, well I tried so you don’t have to smell the smoke when it comes out.

This is a general diagram on the hookup for the controller using a 12 – 24 volt fan and power supply.

This is the general hook up if you use a relay to control a 120 volt AC device like a fan or a pump.

Make sure the relay contacts are rated for at least 120 volts AC and are rated to handle the load amps.

This is a wiring diagram if you're using a DC fan and pump for the glycol chilling system. (Thanks Joe)

Installed

Here it is installed on the front of my fermentation chiller.

If you need any more information just let me know.

John

Posted in Temperature Control | 58 comments »

John on 03/27/08 06:40 pm writes

Nice!

John

John Thornton on 03/30/08 05:17 pm writes

Thanks
John

B-Town Brewer on 05/01/08 02:04 pm writes

Clever. This is a great idea as you can get these cheap almost anywhere. Now where is my soldering iron...

Vine on 05/06/08 09:30 pm writes

could you use this on a chest freezer for a kegerator? How do you wire this if you wanted to do that?

John Thornton on 05/07/08 06:49 am writes

Vine, It will work for anything inside of the temperature range of the control. You just use the relay wiring diagram to control the freezer. Just make sure you pick a relay that will handle the current load of your freezer.

John

Surfbrewer on 05/24/08 01:22 am writes

In the original chiller plans he says "Do NOT use "programmable" or "digital" thermostats, as they require the "normal" 24 VAC power supply to operate, rather than the 12 VDC we're using. Stick to the simple, mechanical units described here."

I'm feeling a little dense because I'm sure you have it explained above in your instructions, but I am having trouble grasping how to hook up the 12 vdc to the digital thermostat without problems. Would you mind breaking it down for an electronic idiot.

I've got a 12 vdc fan, a 12 vac-dc adapter, and I am trying to figure out what thermostat to buy, any help would be great.

Thanks for the great details, I am looking forward to getting this sucker in operation.

Evan on 05/28/08 01:39 pm writes

Thanks for including that second wiring diagram. I should have figured out on my own that I could just get a DC power supply to switch a relay for my 120 volt devices. Looks like I'll be shopping for some thermostats.

John Thornton on 05/29/08 07:45 am writes

Surfbrewer, Well the original plans are not correct. While some thermostats require 24vac to operate you will notice the first description states that the ritetemp runs off of 2 AA batteries.

The first wiring diagram shows the complete connections for what you are doing and there is only 2! Basicly you are "switching" one wire on and off between the fan and the wall wort with the ritetemp's built in relay.

John

Surfbrewer on 05/29/08 04:07 pm writes

Thank you John,

When I was looking for thermostats I was unable to find the same model that you used but I ended up with a similar Ritetemp model. Just yesterday I finished making the connection for the temp. probe. It all went smoothly and I am planning on hooking up the fan this weekend. Thanks for the help.

Cheers

DAlter on 05/30/08 12:08 pm writes

John,

What is the original "lowest temp" this thermostat can be set to? I've found other makes that are similar; all can only be set to 45F at the lowest. Is the ritetemp also rated to 45 at the low end, or will it hit 35F "out of the box"? Thanks for any input.

DAlter on 05/31/08 08:55 am writes

All,

Found the answer to my own question (see post above).

Also, for those that can't find the 8029B model, Home Depot carries the RiteTemp 6020. Pretty much the same layout as the 8029B, and the same price.

Thunder Chicken on 06/01/08 07:15 pm writes

John,

When it comes to modifying anything thats deals with electricity Im a complete idiot.

Ive wired this up exactly how it is said but it will not kick on. Is there a delay or did i just mess up the wiring? Ive reconnected everything to stock and it works fine, i just have to keep it inside the box.

DAlter on 06/03/08 11:44 am writes

Thunder,

I had the same issue. Turned out it was a bad thermostat. Took it back to HD, the new one worked perfectly. Try wiring this way:

1) Jumper wire between the RH and RC terminals
2) Positive lead from DC converter connected to the RH terminal
3) Positive lead from fan connected to G terminal
4) Negative leads from converter and fan connected to each other

There may be a small lag time before the fan starts, and will be one approx. 2 minutes after adjusting temp if fan is already running. Hope this helps

Townie Aler on 06/08/08 10:58 pm writes

DAlter -

thanks for that jumper issue... i had the same sort of problem with the fan needing to be 'on' and not on 'auto'...

Jay on 06/29/08 11:10 pm writes

Mine reads 28* F and Fro some reason will not power up in the above posted configuration... i used a different config but only the fan powers on but does not shut off...

RPHeld on 07/04/08 01:47 am writes

What type of resistor is needed for a 12/24v thermostat to a 120v fridge? I've looked at them online, but all those numbers... it's all greek to me. So do you need a 12v or a 24v relay? or Do you need a 120v relay? And should the amp rating of the relay match the requirements of the fridge?

waterkc on 07/31/08 12:17 am writes

John, This is great, Project like this is what I live for. This is next on the DYO list.

Thanks

Northern Ike on 08/11/08 10:28 pm writes

I'm going to put this together next weekend. Any fan suggestions? What are you all using?

Thanks!

Bluelou6 on 09/06/08 06:37 pm writes

Electrical noob here. If I understand the first diagram above correctly, the wall wort is the power for the fan and the thermostat runs on batteries?

Bluelou6 on 09/12/08 02:59 pm writes

Could this controller be used to control the temp of a chest freezer if the 120v relay was used?

Push Eject on 09/12/08 03:20 pm writes

Ike, a 100mm 12v computer fan from All Electronics would work as an example.

Blue, yes to both questions.

Joe on 11/04/08 10:05 am writes

John-

I already have the thermostat and I am looking to add a dorm size refrigerator(summer) or a heater (winter).

I need guidance as to which relay and which power source to use...A shoppin list if you will...

-Joe

ChrisW on 01/02/09 02:43 am writes

Does anyone have a clue what amps these controllers can handle at 12VDC and/or 24VDC?

I have an application for a larger fan and would rather not overload the circuit!

Thanks for the easy demonstration and instructions!

BTW- most HVAC guys have a bunch of used ones they will give away if you just ask- when they upgrade peoples systems they usually install some of the big fancy ones and either just toss these old ones in the back of their van or in the trash. *most* of the similar models work about the same (I've got a LUX and a generic one that both work great!) Also, many of these are cheaper at a local HVAC supply shop.Sometimes if you tell them what your doing with it (or bring a couple beers) they will give it to you at the contractor price or even free if they have a few returns sitting around.

Thanks again to everyone submitting on this awesome DIY site!

ChrisW on 01/02/09 12:03 pm writes

Per Lux (one of the manufacturers of many of these inexpensive units) "The maximum amperage for the TX500 is 1.5 amps per terminal."

I'm guessing that this would probably be about the same for the rite-temp and others.

Bravo11 on 04/16/09 05:36 pm writes

Tried, before reading comments, to use a Carrier digi thermostat then I learned that it runs on 24 VAC and my power supply and relay is DC. Looking for a DC thermostat now, hopefully free as is everything else in my setup. A note on using an old PC power supply. After testing different voltages of the different wires of the power supply I found that the blue and yellow wires yield 24 vdc. I don't know if that is a standard but it might save some time as other combinations only output 5, 12, 16 vdc--Thx for all the tech help!

Schaeffer on 05/24/09 08:15 am writes

I have a three pin fan, the third pin is a tach. Can i still use this fan, should i just cap off that third wire?

Skinny on 07/22/09 05:59 pm writes

Anyone know if the thermistor in these has a positive or negative temperature coefficient?

Travis on 10/08/09 10:18 pm writes

Quote:
"Solder the thermistor to the ends of the wire.
Put heat shrink tubing on the wires before you solder.
Tin the ends of the wire and solder each one on.
Slide the heat shrink over the joint and shrink."

How do you solder the wires together if there is heat shrink covering the connection? Doesn't the heat shrink tube have a metal connector in the middle that you squeeze onto the connected wires? Please explain this step to me. Thanks. :)

Matt on 10/11/09 05:06 pm writes

You need the heat shrink on the wire before you solder just not right where you're soldering or you'll never get it on later.

SteveWeizen on 11/25/09 07:37 am writes

So the RiteTemp thermostat will switch 12 VDC OK? My switched circuit is 12 VDC and the fan is 180 milliamp. Thanks in advance for the help.

James on 11/26/09 08:51 pm writes

What are my jumper settings, or placement if I have a heat pump. It is not giving heat, but AC works great
Please help

WindwardS on 12/17/09 07:45 pm writes

What a great post! I'm developing this right now (as it's December) toward a heating application, to run a relay that switches some source of heat off/on. I don't really understand electronics, but I had to apply the positive side of the DC power supply to the W post, instead of G.

I've attached it to a drugstore heating pad, and I've gotten the relay to make the connection, however there must be something about the heating pad, b/c I haven't gotten it to warm up yet. Still working on that one.

fartingdog on 12/31/09 06:04 pm writes

Does anyone have a quick recco on best place to grab a decent 120VAC relay? (and part #?) I plan to rig this up for a ferm-wrap for the fermenters.

fartingdog on 12/31/09 06:13 pm writes

Dang, wish I could edit my post. FWIW- I'd like to get away as cheap as possible- can you use a 120V relay with the Rite temp and batteries? or do you need another power supply for that (as shown in the diagram). I have have several 5 and 6V adapters here.

Push Eject on 01/01/10 12:05 pm writes

I've always used separate power supplies, fartingdog. Try All Electronics or Electronic City for transformers and relays or your local surplus joint.

Travis on 01/27/10 06:07 am writes

I used this design on my SOF chiller, and it works great! Thanks Thornton! Peace.

rje45 on 05/07/10 11:12 pm writes

So...I'm completely new to homebrewing. I am trying to get everything together before I jump innd over again. For anyone who has wired a digital thermostat to control the temperature of a freezer or refrigerator, can you please post a wiring diagram for this setup? I've looked at the diagram above, but I don't know what kind of relay is used. Please elaborate if possible!

Thanks!!!!

Rob

Brad on 05/19/10 06:16 am writes

I need this dumbed down for me guys. Could someone give me a list of the supplies so I can buy them. I am not worried about getting something from a buddy and piecing it together. I need a list of the stuff that makes this the easiest way even if it costs a little more to go that route. I have a hardware store, Walmart and a Radio Shack. I know nothing about electricity so easy instructions would be appreciated.
Thank you for the help....

Matt on 05/21/10 03:33 pm writes

Is the relay in photo 111 or 112 rated for 30VDC?

Matt

c c on 06/09/10 08:59 pm writes

thanks for the directions, finished this up today and everything worked perfectly!

Brian on 06/14/10 12:50 pm writes

Since this thermostat is battery-powered, can the fan be powered by a battery too? I would like to convert my kitchen cupboard to a cooled one, but there is no access to an electrical outlet. What type of battery would be suggested?

Thanks.

Brent on 06/29/10 04:33 am writes

I bought the ritetemp 6025, I have no clue where to find the thermosistor. Can you help?

Brent on 06/29/10 04:44 am writes

I think I found it, right next to the temp adjuster, little resistor TH1

Brent on 07/08/10 09:54 am writes

I have the cold side hooked up, 12vdc positive to thermostat G in RH out. what if I wanted to do another for heat. which letters would i go through?

AJ on 07/26/10 10:42 am writes

Great website! I have used the fermentation chamber and thermostat they are great! I am plannin on keeping my chiller in the garage and I am going to have to heat it in the winter. How would I add a heat lamp to it?

Yeastmaster on 08/26/10 04:41 pm writes

Does anyone know how cold this system will get down to?

Dave C on 08/29/10 09:52 pm writes

Great write up! I used a new model ritetemp and it's working great in my version of a 'mother of a fermentation chamber'. I think I will eventually use the heat relay on the thermostat, to feed another relay which turns on a light bulb in one of the ice chambers on the bottom.
Do you have any advice on what relay to use? I'm not familiar with wiring relays, but I do understand the concept at least.

Eric on 10/08/10 08:43 am writes

Hey, Thanks for this!!! I am using it for a different application though. For my hot tub, the motor compartment in the heat of the day with the sun on it, the water temp rises above tolerable levels. So I use the fan as a exhaust inside the motor compartment to remove the excess heat. Just have it on air condition setting and set it to the top temp 37 degrees C on my model, might look for thermostat with a slightly higher temp range (41 would be great) Thank you for your wiring diagram.

Ken on 11/22/10 05:57 am writes

I have built a few temp controllers from scratch. For anyone wanting to use this to control anything with a compressor, you shouldn't, not quite. The issue is that you really need to ensure that you avoid cycling the compressor...it needs 10 seconds or so between cycles for the system pressure to equalize so it does not start up pushing against pressure, which it hates. You can use this device but be aware of the cycling issue shortening the lifetime of your compressor. Adding a time delay relay will alleviate the issue with little change in circuit... an example: ST7P-2A13T-ADC for about $30. They come in different coil voltages so pick one that works with your setup. I would use this relay to turn on your existing high current relay. If you cannot find a 12V coil time delay relay (on-time delay), there is no reason not to use a cheap 12V reed relay to turn on the timer relay that turns on the high current relay...ugly as hell? Sure. Functional? Absolutely.
I'm not SAYING, I'm just saying...

qicaluseo on 02/20/11 06:56 am writes

thanks for this nice post 111213

Dave on 03/29/11 01:37 pm writes

In response to Ken's post above:

There shouldn't be any need for a time delay relay using this thermostat. In the documentation for the one I purchased it states that there is a 4 minute minimum cycle time, which should be more than enough for a compressor. Makes sense, since you wouldn't want to short-cycle a furnace or A/C unit either, which is of course what a thermostat like this is really designed to control.

jp on 08/22/11 01:24 pm writes

Do I need additional wire or can i strip the wires attached to the AC adapter and fan and attach those to the thermostat directly? If these are not long enough, what wire should I get. Have a radioshack/Ace and Home Depot nearby.

Doug on 09/25/11 04:39 pm writes

I just made one of these and it is working great. I used
a Honeywell RTH111 Thermo from Home Depot and
from Radio Shack an Enercell AC to DC power adapter
273-357 and a Ernercell Adaptaplug tinned lead
adapter 273-349. Used terminals G and RC on the
thermostat and removed the factory jumper from
R to RC.

Doug on 09/25/11 04:39 pm writes

David in FL on 10/10/11 05:59 am writes

Doug - agreed RTH111 easy model to use for this project, in fact the thermistor is already on (short) "extension leads" on this model. It is run into the corner inside the unit covered by a blob of glue.
Also you can disable compressor protection, which is not necessary with a little dc fan, in the menu of the unit.

David in FL on 10/11/11 01:10 pm writes

Note the RTH111 uses a tiny bead type thermistor that is not like the rite temp thermistor.

Philip on 12/02/11 12:31 pm writes

I bought the RTH111 today and I'm trying to find the thermistor, but I have no clue what I'm looking for. What does it look like?

tom on 01/22/12 12:17 am writes

do u need a fan i have a refridgerator i want to install this thermostat on it any help please break it down barney style

Remote Sensing DIY Controller for Less Than $25

The Controller

Disassembly

Connections

Installed

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