DIY Cool Bot Builders

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CidahMastah

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I have been looking into building a cold storage room for some time and finally want to start the process.

I am interested in building a cool bot clone. Have any of you guys been able to build a controller that is similar to the cool bot? I have searched and haven't seen a build yet. However at $300 I am interested in taking my time to see if it can be done cheaply.

For my use I will likely keep a storage temp around 45F or so (I might be able to simply get away with a Johnson controller and not have to worry about freezing).

Thanks for any recommendations, or possible build attempts you may have to offer.


Key aspects to the cool bot:

1. Some kind of therm. resistor that tricks the A/C unit temp probe into thinking the room is warmer than it is so it will not shut off.

2. Freeze over protection by placing a probe into the A/C units fins that I assume kills the power when the temp goes below a certain set value near 32F

That last part could simply be controlled by a 1 stage Ranco in the cooling mode.

I don't have any experience with electronics that would help with aspects 1 and 2. The ranco part is of course the easiest.
 

rekoob

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just out of curiosity, what size room are you talking about? The only reason I ask is that I have been thinking about adding to the side of my garage (about 6 feet or so) and doing this same thing. Won't be anytime soon but I think it's on my list of items to do. Maybe I do 8 feet and use the front section for my brew storage... hmmmm...
I think the ranco/johnson controllers either a two stage or a couple single stage would do the trick for you. I beleve you may be able to modify the AC by removing the temp prob, if I remember correctlly, if not I am sure I someone knows and will comment.
Good luck, can't wait to see how this turns out.
 
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CidahMastah

CidahMastah

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I am looking at a space that after 4'' insulation will be about 9'x9'x6' in my basement. Which rates me just below the recc cu ft for 12,000 btus A/C unit on cool bots site.

The only major concern I have is the A/C unit compressor cooking if it were to freeze up. Right now that seems to be the main obstacle in safe proofing the unit.

Like you said, remove the A/C probe/ trick it, and use a ranco. However where I live gets humid as hell. So I have a real concern that all that extra moisture could condense and freeze then bang. $300 A/C unit is toast.

I was going of estimates listed here:
http://www.storeitcold.com/sizebrand.html
 

BeardedIdiot

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As far as humidity goes, really good airflow around the AC fins and a dehumidifier sitting right below them?
 
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CidahMastah

CidahMastah

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A fan is a good idea. The humidity will always be a challenge since it will be in a basement that has plenty of moisture with two dehumidifiers running.
 

Junkster

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Walk-in coolers run the evaporator fans continuously. Some window A/C units have separate motors - one for the evaporator fan & one for the condenser fan. Others have a single motor with a shaft extending front & rear for both fans. This may be something to consider when selecting your unit......
 
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CidahMastah

CidahMastah

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Walk-in coolers run the evaporator fans continuously. Some window A/C units have separate motors - one for the evaporator fan & one for the condenser fan. Others have a single motor with a shaft extending front & rear for both fans. This may be something to consider when selecting your unit......
is there any easy way to tell this? or just trying to break the display unit open? :D
 

Junkster

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Hmmm...... I don't know if you can see through the louvers how it's configured or not - you may have to pull the cover. You may be able to find out on the 'net via the model number.
 

H22W

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Mimicking the bot is easier than you think. You put two stc-1000 units in series.

The first stc measures your desired temperature of your chamber. When the chamber is aboved desired temp it powers the cool outlet where you connect your second stc unit.

Now have your second stc unit's temp sensor attached to the coils of your AC. Set this second stc to a temp that avoids the coils from freezing and power your AC from this second sensor. So long as stc is demanding cooling then the second stc will keep cooling as much as it can without freezing.

Depending on airflow and humidity you can temporarily allow the coils to below 32F. When ices starts to cover them that restricts the cooling airflow and the internal temp of the coils drops fast.


Tip 1: find your AC temp sensor and either hotwire it or relocate it outside the cooled chamber, so the AC thinks it is warm and needs to cool.

Tip 2: many AC units have a sensor on the coils to shut down the compressor when the coils drop below 32F, so detached this sensor if you have it.
 

toadhall

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I realize this is an old thread but I found it and expect others may also find this. I will also post as a new thred in the Equipment category.

I got involved with some agriculture folks who were going to use a Coldbot to chill produce and when I looked into it and saw the simplicity of this concept I built a controller for them based on an Arduino (I used the Arduino Pro Mini 328P, but it could be done with any of the Arduino family). This is a very simple control concept; I worked out how to make inexpensive probes of very good quality and a "heater" using a simple 3W power resistor ($1.50), so I have a $15 mimic of Coolbot - without display or buttons - fits in a small mint tin - you just program it for a temperature you like (I set the prototype for 42F) and that's it - easy to reprogram as needed, and easy to add more features (settable temperature, display, etc) if you need that. It should control an air conditioner in the same way as the Coolbot. I wanted a very stripped down controller for this prototype for simplicity and reliability, and have done the testing to show it is working as planned and the prototype is off to the growers for actual testing to start in June 2015; the control program may require some revision since I don't have an AC unit for testing and will have to see how it works in actual practice.

I am referring to this project as the "Coldsnap". Nothing is for sale - this is information for DIY people. It is implemented with an Arduino, but could be easily ported to a different microcontroller that you are more familiar with; the control algorithm is just very simple. I'm just putting the info out there to save people some development time. I am going to get the code and images onto my website in a few days at: http://people.umass.edu/~dac/projects/ColdSnap/ColdSnap.html
 

LavaAle

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I'm currently testing a makeshift coolbot I put together. It involves two STC-1000 units in series, as stated in a previous post, but instead of connecting the a/c unit, the STCs trigger a small 5v light bulb.
I used two STC-1000 units, a 5v light bulb and a 5v power supply (old cell phone charger).
First, I connected the +wire from the power supply to the light bulb. Then ran the -wire to the first STC COOL relay; from there it goes to the second STC's COOL relay in series, and finally to the other pole in the light bulb. Cover the light bulb with foil, attach the A/C unit's temp probe to this fixture and cover with foil again.
Place the temp probe of either STC inside the A/C's evaporator fins, set the STC to 32. This will prevent the evap from freezing out. Use the other unit's probe as your room temp sensor, set it to whatever your target temp is.
Set your A/C to the coldest setting.
The idea is, just like with the coolbot, to trick the A/C into thinking the room is warmer than it really is, by heating the A/C's probe with the light bulb or whatever heater you want to use, while the STCs monitor both room and evaporator temperature and relay or cut power only to the light bulb. This way there's no need to mess with the A/C unit in any way, and you can use whatever A/C you want.
 

banjanti

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I see it's been a while, so sorry for resurrecting old thread


I'm about to use that approach to to build a coldbot clone, from the video on youtube it looks like exactly it, you heat the probe to fool the thermostat to control that with external thermostat just like STC-1000

I was just wondering about the wiring in LavaAle setup: why break the - instead of a +? Also is this wiring a dc connected directly to STC-1000? I don't have the device yet, but from spec on ebay it looks like the relay controls are 250 VAC, so you'll need to break the AC power before the bulb or resistor DC transformer. Then you should definitely break the live (+) wire.
From what I understand LavaAle wiring is rather DC after the wall transformer. If author is still here and could elaborate it would be great!
If not I'm going the safe route and breaking live on AC

EDIT: Quit search on ebay and I see STC-1000 with DC relays, they seem to 12v dc though, not 5v dc
I would rather buy the AC one anyway as it have more applications if we're using the old cellphone charges like lava suggested
You break the live before the charger in a socket, then polarity won't matter I guess
 

LavaAle

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I don't think polarity matters much with this setup, I just wanted it to switch the circuit on and off. Hell, I'm not even sure if its the + or - the one running through the relay! It works though, and it's been running flawlessly for some time now. Feel free to modify it so it suits your needs, the basics here is to run both STCs COOL relays in series.
 

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I'm interested in duplicating this project. It seems the information on the website is incomplete. Also, is there a video that goes along with the information?
 

Tegra

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Toadhall:


You wrote...

.."I'm just putting the info out there to save people some development time. ".....
(And in the code it mentions this is in the public domain)

Does this mean you are open sourcing this?
 

toadhall

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Toadhall:

You wrote...

.."I'm just putting the info out there to save people some development time. ".....
(And in the code it mentions this is in the public domain)

Does this mean you are open sourcing this?
---------------------------------------------------------
I guess I have to say that I don't know the fine nuances of open source and public domain. I developed the project myself and made the schematics and code available for people to use in any way they see fit. My intention is that people can build it for themselves. Realizing that not everyone wishes to take on building, I hoped that some company or person might see that they could build a "Generic 2-input sensor/controller board " that could be sold unprogrammed without getting into the patent rights issues around the Coolbot - the purchasers of such a controller could personally download my code, or some derivative or other code, to perform the ColdSnap (Air Conditioner Override) functionality.

If you have any advice about the correct way to make sure that this project should remain free to people to use as they wish, I could do something like that. I figured that if I put the information is out there with my intentions stated, then people have it and who can stop them?

I just find it really objectionable that someone should try to patent such a simple and obvious concept, and then advertise how they are helping developing countries and such, when the technology and basic functionality is so simple and cheap and should be available to small farmers and in developing countries, and where ever and however it can be used at a much lower cost without the bells and whistles and displays and keypads.... I don't know the status of the Coolbot patent application, but since I have no commercial interests, I figured that releasing my project for people to build themselves is an effective end-run around the patent issues. And if someone finds a way to commercialize it, the fact that the info is out there will keep them from being able to charge too much, else they will find company in the marketplace.

Best Wishes to all!
 

Tegra

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I agree with you completely!

I know very little about patent law, but I would find it hard to believe that they could patent this item. It is just a fancy thermostat. The only unique thing is the "trick the internal thermostat" with a little heater. That was the same trick used in the retrofit setback gadgets that came out before programable home thermostats. (They were just a timer that turned in a resistor heat source below the wall thermostat). Also each mechanical thermostat had an "anticipator" heater built in that would push the sensor along a bit. Couple this with the concept of infrared repeaters and there is really nothing new. (I am not sure if you can get a copy of a pending patent to look up what they are claiming).

As you say the price they charge is $100 to expensive and the layout with all those plugs seems to scream reliability problems.

I think I will try out your code. My first problem is the ac I have for testing has a mechanical thermostat that would require a long string of resistors over the length of the capillary tube to keep it all warm. (This slows down the reaction time to 3-5 minutes)

Will keep in touch.

Tom
 

banjanti

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Hey Lava!
Do is the ac your breaking or dc? It wouldn't matter much in 5v, but in 110/220 it does matter as you leave in circuit energized, once I had that issue with a light in the oven, not only it kept burning down the lightbulb but also I got a nice jolt when I was changing it! That's how I figured that stupid thing was polarized without proper polarized plug! Very bad design. From that time I understand that in a.c. It really does matter
In that case you won't be shocked as it's 5v on the output, but the phone charger can prematurely wear out or burn

Thanks for the idea of using the controllers though! Cheap and out of the box solution
Both goes for $20 on eBay, so it makes coolbot not $100 but $300 overpriced!
It shouldn't really cost anything more than $50 taking into account parts involved
 

banjanti

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Tegra - if resistor trick is not reliable enough there is always an option to wire STC directly instead of internal thermostat
They are only $10 on eBay
 

toadhall

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........... My first problem is the ac I have for testing has a mechanical thermostat that would require a long string of resistors over the length of the capillary tube to keep it all warm. (This slows down the reaction time to 3-5 minutes)

Tom
I don't think you need to heat the whole capillary tube. I think only the bulb needs to be heated; the capillary tube is relatively low volume and rigid so most of the expansion of the internal liquid is happening in the larger volume of the bulb at the end. I think it would work about the same as described for modern thermistor AC probes - but maybe insulate the first few inches of the capillary tube closest to the bulb (it is not a sensor) to slow heat lost through conductivity away from the heated bulb. It still may be a bit slow to respond, but you would just use less, or zero, "dead time" - would tend to cycle more slowly naturally. The mechanical switch probably has some built-in hysteresis, but you want a little to minimize cycling. I think that something the volume of only a glass of water will dampen the temperature swings to a couple of degrees. By leaving the air/room temperature tiny thermistor free in air, or with small thermal mass (attach to a small plate of aluminum, etc), it will detect the air temp rise and start the heating (and thus cooling to follow) before larger masses in the room change in temperature significantly. It is also possible to mimic the "anticipating action" in software since you can do that with open source :) - you can control the resistor heating and it's power (with PWM) so that after it turns off (heater drive) you could implement a delay and then set the heater to ramp up in increments, or set a "pre-warm" power level to hold it a bit below the switching point

Not sure about any of that, just my thoughts from a distance....

Good luck!
 

Tegra

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.... I think only the bulb needs to be heated....
On this unit there is no bulb just an 18 inch tube, all the same diameter. I am guessing that since they wanted to measure the ambient they figured if they got the majority of the length in front of the coil it would all average out. I guess the unit I choose to test is the worst possible example.

(I messed around with it far too long for anyones good!)

I guess the cold snap could have a relay option that replaces the thermostat?

Tom
 

toadhall

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Sure, you could use a relay. I'm attaching a design that would replace the resistor on D10 of the Arduino (but could be any digital logic output. Note that this drives a small relay (available from Digikey or Newark) that requires only about 17mA to operate and can drive 3A/120VAC. This will not be enough to drive an AC (I'm not sure how the mechanical thermostats switch the power) but a larger capacity relay would be connected the same, just paying attention to provide sufficient drive, or using the scheme in this schematic where the small relay drives a "control transformer" which drives a power relay/contactor.

Note that the resistor/LED in parallel with the relay is just for local indication that the relay is being driven, and note the diode in reverse polarity across the relay to clamp the inductive surge when the relay turns off.

Or you could use a more extended heating element (with appropriate lower voltage!) to cover the whole sensor - like this 13W(@120V...) element 15.5" long -
http://www.ebay.com/itm/252150266940?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT
I have used these to warm my fermentation cabinet (my cellar is too cold!) If you used one of these at a lower voltage, remember that the power output will scale with the square root of the voltage - 13W @120V,, etc... You could parallel 2 elements driven by 15v to get more total heating.

BackupHeater-pg2.png
 
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Case

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Hey guys, this is very interesting as I have been looking at the Coolbot to turn my van into a cooler to deliver produce. I am a rookie when it comes to putting together electronic components such as this, although it kind of reminds me of the boards that Radio Shack use to sell that you could make your own radio and other things when I was a kid.

Are there any videos on Youtube that will help me in constructing a Coldsnap? Also, it would be nice if I could hook up a digital thermometer so I could see how cold the temp in the back of the van is.

Thanks,

Casey
 

toadhall

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Sorry, there is no easy kit - yet. I am working on a PCB that will eliminate the tedious hand wiring and so one only has to solder a few components and the Arduino Pro Mini board to the PCB, add the sensors and AC probe heater, download the code to the Arduino. The PCB is in an early stage and I just finished it and need to look it over carefully. I've got this first version done in Eagle (Light, free version) and hope to get it into KiCAD eventually. It is sized to less than 5x5cm so it meets the criteria for dirtypcbs.com to make PCBs - 10 for $14 including postage. Supposedly we can send the Eagle ".brd" file and that is all they need. I'll be updating my web page on this soon, and it may end up on a different home site before long. But I'm posting an image of the PCB layout - if you compare to the tinycad schematic I have posted, note that the component labels are different, but the sensors, power, heater resistor will attach to the solder pads around the edge and the layout is similar to my prototype point2point wiring.

ColdSnap_01_a2.png
 

wieldling

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This is really awesome. I am planning to build a couple of these for a friend. Is there any potential to use off-the-shelf temperature sensors? I am new-to-arduino but I am assuming this would change the code? The PCB sketch will be very helpful for putting this together.
 

toadhall

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You can use off the shelf thermistors but you will need to calibrate them and find the A/D counts for the important temperatures and then enter them in the code - the code as I published it sends the A/D counts for the 2 probes to the serial port so you can use the ColdSnap to do the calibration. I've seen some 10k thermistors on ebay for very cheap. I think the tube size of some of them is 4mm which is a bit larger than the 1/8" brass I used, but it will probably fit - be gentle.

Here is what the ColdSnap sends:
-----------------
PWM = 128
FinsTemp = 819
RoomTemp = 568
Variable (Potentiometer) reading = 502
Using Default programmed SetPoint
SetPoint = 559
State = ON
-----------------
PWM = 128
FinsTemp = 819
RoomTemp = 568
Variable (Potentiometer) reading = 502
Using Default programmed SetPoint
SetPoint = 559
State = ON
-----------------
It just continuously sends this, so you would just wire it with your sensors and place them at freezing (with another thermometer), etc and write down the values for the different temps as it slowly warms up, then enter those values in the code in the constants section defining the counts/temperatures.

I will get the Eagle files onto my website with the other stuff in the next day or 2.

For what it is worth, I'm attaching front and back images of the hand-wired prototypes - these could be useful - the hand wiring isn't too bad for experienced people.

FYI, I have found that you can use the inexpensive PL2303HX cable to both monitor the serial data AND for programming the Arduino Pro Mini. For programming you have to press the reset button on the ProMini just before you click on the Upload button in the Arduino IDE; when it comes out of reset it looks for programming briefly before going on to the executing the program on the chip so if you hit it right it will accept the programming; this is cheaper than the FTDI Basic unit. You can find the PL2303HX on ebay for less than $2 delivered (slow, china).

Cheers!

ColdSnap_01_bottom-1.jpg


ColdSnap_01_top-1.jpg


ProMini+FTDI-Basic-1.jpg
 

wieldling

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You rock! Thanks for sharing all this. I just got boards in the mail so I'll be trying to hand wire.

I am going to try to order some of those thermistors and figure out how to code for them. I suspect that soldering the SMD thermistor will be quite challenging. Going to give it a shot, though!

I am surprised that the epoxy is a good enough conductor of heat. Would using a different type or amount change the sensitivity?
 

toadhall

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You rock! Thanks for sharing all this. I just got boards in the mail so I'll be trying to hand wire.

I am going to try to order some of those thermistors and figure out how to code for them. I suspect that soldering the SMD thermistor will be quite challenging. Going to give it a shot, though!

I am surprised that the epoxy is a good enough conductor of heat. Would using a different type or amount change the sensitivity?
If you have any questions contact me directly - my email addr is at the bottom of the parts list on my web site:
http://people.umass.edu/~dac/projects/ColdSnap/ReferenceDocs/ColdSnap parts list.pdf

I don't think the epoxy should be an issue. The temperatures are changing slowly enough that I think it will not have much of a lag in response - they are amazingly quick to respond - you'll see when you get them assembled and touch one.

I've ordered a few of the 10k thermistors from ebay to check out. I just don't know how they will fit into people's AC coil fins. I got ones that are 4mm dia (some of the ones offered are 5mm). I'll update the web page if these seem good (or not) since they would make it much easier for people to get their probes.

Cheers!
 

zazbnf

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Just saw this thread for the first time. I have been running a controller using 2 stc-1000's, a 12v wall wort, using a 1W 100 Ohm resister and a pulse width modulator for the heat source. It has maintained 55 degrees in a small walk in cooler for the past couple years. About $30 for everything. You don't need to do any modification to the A/C, just wire the 2 stc-1000 so that if either hits the set temp it cuts power to the heater(resistor). 1st stc-1000 probe hangs into the cooler and has a set temp of 55 degrees, when temp is hit contact opens and kills power to resistor. Second stc-1000 probe is placed into the cooling fins where the air conditioners temp probe was(you simply unsnap the air conditioner temp probe and let it hang down)I currently have it set to 40 degrees on the before it cuts out. Trial and error showed that it takes a a minute or so for the air conditioner to respond after power is cut off to the heat source and the fin temp can drop very fast during this time. The 1 W 100 Ohm resistor is heat shrinked to the air conditioner probe that was left hanging down earlier and connected to the 12v Power supply with the pulse width modulator set to a level to warm it up but not get so hot it might burn itself out or cook the air conditioner temp probe. The air conditioner runs when the "heater" is on and turns off when either stc has an open relay.
 

4Doose

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I went to your site for the great info and it cant be found. Did you take it down?

I would love to view it if its still available.

Thank you.
 

Case

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Hi Terry, I am converting part of the back of my van into a refrigerated unit as I deliver meats and produce to some of the local restaurants in my area. I need to keep the temp below 40* for food safety reasons. I plan on using either a window unit or an RV roof top unit to cool the compartment. Can I use the 2 stc 1000's for this purpose and if so how hard will it be to hook them up to the air conditioner? I am somewhat mechanically inclined but have never tried anything with electronics like this. Any info you could give me would be greatly appreciated.

Thanks,

Casey
 

zazbnf

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Hi Terry, I am converting part of the back of my van into a refrigerated unit as I deliver meats and produce to some of the local restaurants in my area. I need to keep the temp below 40* for food safety reasons. I plan on using either a window unit or an RV roof top unit to cool the compartment. Can I use the 2 stc 1000's for this purpose and if so how hard will it be to hook them up to the air conditioner? I am somewhat mechanically inclined but have never tried anything with electronics like this. Any info you could give me would be greatly appreciated.

Thanks,

Casey

Might not be the best use for an air conditioner. While they work well for a cooler that is opened infrequently, I would assume delivering produce would mean the area was opened frequently over a short time period as deliveries are made to different restaurants.

A controller and an air conditioner have a hard time maintaining temp in this situation. It takes a while for the air conditioner to bring the box back into temp if the door is open very long or frequently. This is because it works by lowering the temp a few degrees then the compressor shuts off for a while to prevent the coils from icing over, then it will start up again and lower the temp a few more degrees before the compressor stops again repeating until the desired temp is reached.
 

Tegra

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Guess it all depends on the size of the AC.

T
 

bembel

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I'm currently testing a makeshift coolbot I put together. It involves two STC-1000 units in series, as stated in a previous post, but instead of connecting the a/c unit, the STCs trigger a small 5v light bulb.
I used two STC-1000 units, a 5v light bulb and a 5v power supply (old cell phone charger).
First, I connected the +wire from the power supply to the light bulb. Then ran the -wire to the first STC COOL relay; from there it goes to the second STC's COOL relay in series, and finally to the other pole in the light bulb. Cover the light bulb with foil, attach the A/C unit's temp probe to this fixture and cover with foil again.
Place the temp probe of either STC inside the A/C's evaporator fins, set the STC to 32. This will prevent the evap from freezing out. Use the other unit's probe as your room temp sensor, set it to whatever your target temp is.
Set your A/C to the coldest setting.
The idea is, just like with the coolbot, to trick the A/C into thinking the room is warmer than it really is, by heating the A/C's probe with the light bulb or whatever heater you want to use, while the STCs monitor both room and evaporator temperature and relay or cut power only to the light bulb. This way there's no need to mess with the A/C unit in any way, and you can use whatever A/C you want.
I have a small analog GE window unit, 5000 BTUs, the copper temp sensor wire for the AC was connected to the inside facing cooling fins with little plastic snaps and was easily removable, and could be simply moved backwards to the outside portion of the unit, ie, the hot section, wouldn't this trick the sensor into remaining on without the need for a separate 5v lightbulb build or similar heating measure?

I just want the room down to 50-55F, so I'm hoping that a single INKBIRD will be fine without the need for a second to keep the fins from icing up?

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LavaAle

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It will do, but you won't have control over the room temp, only over the fins/evaporator temp. Which may be enough though, definitely give it a try!
 

bembel

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It will do, but you won't have control over the room temp, only over the fins/evaporator temp. Which may be enough though, definitely give it a try!
Sorry I was not clearer, I meant using the single temp controller to turn the AC on/off based on room temp, and that by pushing the copper bulb of the current temp sensor outside where its warm, the AC won't stop cooling when it hits 62F. I just wonder if pushing it beyond 62F to say, 55F, will cause the fins to freeze up.

Not a big deal to add the second controller for the fins, just might not need it.
 

LavaAle

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Sorry I was not clearer, I meant using the single temp controller to turn the AC on/off based on room temp, and that by pushing the copper bulb of the current temp sensor outside where its warm, the AC won't stop cooling when it hits 62F. I just wonder if pushing it beyond 62F to say, 55F, will cause the fins to freeze up.

Not a big deal to add the second controller for the fins, just might not need it.
My bad. AC evaporators get cold really fast. The beauty of using two controllers (or the coolbot) is that you don't have to worry about the fins freezing, which will happen eventually if you just let it cool beyond the factory minimum, especially the first time.
 

bembel

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My bad. AC evaporators get cold really fast. The beauty of using two controllers (or the coolbot) is that you don't have to worry about the fins freezing, which will happen eventually if you just let it cool beyond the factory minimum, especially the first time.
Hi I appreciate the advice, time to wire up another Inkbird or wait for my tech buddy to make me an arduino version, if using an arduino set up with smaller thermistors, is it best to attach the thermistor to the coils going into the fins, or attach to the fins themself, or does it not matter?
 
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