Greetings peeps, this will be my description of my cannatrol alternative project. Short version is that you can build one yourself with much larger capacity for a lot less money than buying a Cannatrol. 
Background:
I have processed my weed most ways, eventually settling on drying in paper bags and curing in Groves. but all methods were more hassle than I liked, and many had risk of overdrying because control of the process was not easy. One of the ways I processed was to hang separated and wet trimmed branches in a good sized cardboard box, and last year I tried increasing control of that method by adding an Inkbird controller to ventilate the box only when humidity got too high. That failed because after the first day or so, the RH got too low, and I was not able to keep it up in the large cardboard box.
So this year, after reading all the glowing reports from Cannatrol owners, I did some more head scratching, and launched this project. My DIY addiction just will not give up.
Principles:
Beyond the hype, as well as the claims by Cannatrol that their machine cures a special way by using vapor pressure to decide process, the bottom line is this: Cannabis with a water activity of less than .6 is too dry to support bacterial growth, and very likely too dry to support mold. This is just standard food processing tech that has been used for decades in the food industry. The Cannatrol recommendations will result in a water activity of about .57 (this is displayed along with dewpoint of 53F on the Cannatrol display at recommended settings), which by definition will always happen when bud is stable in a RH of 57%). I assume that using .57 rather than .6 is just to ensure that minor variations in equipment accuracy or other conditions might result in an actual water activity over .6 which would risk mold. In any case, the only thing the Cannatrol does is quickly dry bud to, but never past that level of dryness. Once fully equilibrated at an RH of 57%, cannabis in the Cannatrol is shelf stable, and never overdried. More to the point, any setup that can dry quickly to ~.57 without ever allowing RH to go below about 57% will achieve close to if not identical results to the Cannatrol. That was what I tried last year with the cardboard box setup, but the box arrangement did not seal sufficiently to support RH control.
The Project:
With the above background, my objective was a dry box better sealed than the cardboard attempt, with the same Inkbird controller that I used last year, and enough capacity to handle my entire 4x4 crop. I ran a test run in a tote to see whether temperature and RH control in a better sealed container worked ok, and it did. I then chose to construct my new full sized box out of 1" butt joint Styrofoam SM house insulation board because it is relatively cheap, reasonably strong for the loads involved, and easy to glue together. And I wanted a lot higher capacity than my tote test permitted, so the tote was not going to work for me.
Further discussion of design will follow pictures.
Here is the box all sealed up during an early calibration run to see how temperature and RH behaved.
I tried the tape to check how hinges would work, but have found it easier to just completely remove the front cover when needed.
And here it is open to show the tray shelves:
The computer fan in the ceiling sucks air out of the top of the tray chamber and pushes it down sides and out the holes over the trays. The RH sensor is the black thing with the wire next to the fan. The trays are 3/4x3/8 wood frames with aluminum screen epoxied onto them, each is ~18"x20". Once the last one is tidied up, there will be 11 trays. I expect capacity to be roughly twice what a Cannatrol can handle, maybe more given the ability to remove more moisture quicker during the initial part of drying a big load. Still theory at this point though.
This is the air inlet which permits taking low RH air into the box to lower RH. Air enters through this when the squirrel cage extraction fan is turned on by the inkbird controller. It is mostly covered with tape in order to slow down the RH drop when the fan turns on. Keeping the rate of change slow reduces overshoot of the target RH. The squirrel cage fan is likely overkill at least once bud dries out a bit, but it should keep the RH under control even with a large load of fresh bud in the dryer.
This is the air valve on the air outlet to the extraction fan:
The valve is just a ping pong ball which seats nicely in the taper of a 1.5" abs plumbing fitting. The intake valve is similar. Both valves close to prevent any air exchange when the fan is not activated by the controller. Unless the extraction fan is going, the box is tightly sealed, and the air in there is circulated vigorously. It is possible that another computer fan could be adapted to achieve needed extraction, but I had the squirrel cage fan aready, so that is what I used. It will be important to have adequate fan power to keep RH from staying too high during the intial dry of a large load of bud.
And here is the whole setup for extraction:
And here is the extraction fan, one I salvaged from a hot water heater. I also use it for other purposes which is why it is mounted on a plywood board. In this setup, it exhausts into the grow drobe to reduce smell in the house.
This shows the upper air chamber:
The circulation fan is on the left. The blackened LED bulb provides ~11 watts of heat when energized by the temperature controller, and the tray with water and sponge add humidity. The intake valve can be seen in the back on the right. The circulation fan is a salvaged computer fan, and runs continuously to suck air out the top of the tray chamber and push it down the side channels and out the holes feeding each tray. The fan is a strong one (1.6 amps@12v), and it produces an easily detectable flow of air over every tray in the box. The holes in the foreground are air passages from the upper air chamber into the large passages on either side of the box that lead air to all the holes directing it over the bud trays. Putting the heat source and dry air source in the upper chamber means that air is well mixed before going to the bud.
Initial testing of the box demonstrate that with the box empty the temperature ranges from about 66.8 to 68.2, which is not bad since the differential can only be set to 1 degree. RH is controlled between ~52% and 54%, so plenty tight enough for intended purposes and will be lifted to 57% when I get bud into the box.
That is about it for now peeps, I will update with performance results once I get some weed into processing. Any questions, add them to the blog entrythread.
Background:
I have processed my weed most ways, eventually settling on drying in paper bags and curing in Groves. but all methods were more hassle than I liked, and many had risk of overdrying because control of the process was not easy. One of the ways I processed was to hang separated and wet trimmed branches in a good sized cardboard box, and last year I tried increasing control of that method by adding an Inkbird controller to ventilate the box only when humidity got too high. That failed because after the first day or so, the RH got too low, and I was not able to keep it up in the large cardboard box.
So this year, after reading all the glowing reports from Cannatrol owners, I did some more head scratching, and launched this project. My DIY addiction just will not give up.
Principles:
Beyond the hype, as well as the claims by Cannatrol that their machine cures a special way by using vapor pressure to decide process, the bottom line is this: Cannabis with a water activity of less than .6 is too dry to support bacterial growth, and very likely too dry to support mold. This is just standard food processing tech that has been used for decades in the food industry. The Cannatrol recommendations will result in a water activity of about .57 (this is displayed along with dewpoint of 53F on the Cannatrol display at recommended settings), which by definition will always happen when bud is stable in a RH of 57%). I assume that using .57 rather than .6 is just to ensure that minor variations in equipment accuracy or other conditions might result in an actual water activity over .6 which would risk mold. In any case, the only thing the Cannatrol does is quickly dry bud to, but never past that level of dryness. Once fully equilibrated at an RH of 57%, cannabis in the Cannatrol is shelf stable, and never overdried. More to the point, any setup that can dry quickly to ~.57 without ever allowing RH to go below about 57% will achieve close to if not identical results to the Cannatrol. That was what I tried last year with the cardboard box setup, but the box arrangement did not seal sufficiently to support RH control.
The Project:
With the above background, my objective was a dry box better sealed than the cardboard attempt, with the same Inkbird controller that I used last year, and enough capacity to handle my entire 4x4 crop. I ran a test run in a tote to see whether temperature and RH control in a better sealed container worked ok, and it did. I then chose to construct my new full sized box out of 1" butt joint Styrofoam SM house insulation board because it is relatively cheap, reasonably strong for the loads involved, and easy to glue together. And I wanted a lot higher capacity than my tote test permitted, so the tote was not going to work for me.
Further discussion of design will follow pictures.
Here is the box all sealed up during an early calibration run to see how temperature and RH behaved.
I tried the tape to check how hinges would work, but have found it easier to just completely remove the front cover when needed.
And here it is open to show the tray shelves:
This is the air inlet which permits taking low RH air into the box to lower RH. Air enters through this when the squirrel cage extraction fan is turned on by the inkbird controller. It is mostly covered with tape in order to slow down the RH drop when the fan turns on. Keeping the rate of change slow reduces overshoot of the target RH. The squirrel cage fan is likely overkill at least once bud dries out a bit, but it should keep the RH under control even with a large load of fresh bud in the dryer.
This is the air valve on the air outlet to the extraction fan:
The valve is just a ping pong ball which seats nicely in the taper of a 1.5" abs plumbing fitting. The intake valve is similar. Both valves close to prevent any air exchange when the fan is not activated by the controller. Unless the extraction fan is going, the box is tightly sealed, and the air in there is circulated vigorously. It is possible that another computer fan could be adapted to achieve needed extraction, but I had the squirrel cage fan aready, so that is what I used. It will be important to have adequate fan power to keep RH from staying too high during the intial dry of a large load of bud.
And here is the whole setup for extraction:
And here is the extraction fan, one I salvaged from a hot water heater. I also use it for other purposes which is why it is mounted on a plywood board. In this setup, it exhausts into the grow drobe to reduce smell in the house.
This shows the upper air chamber:
Initial testing of the box demonstrate that with the box empty the temperature ranges from about 66.8 to 68.2, which is not bad since the differential can only be set to 1 degree. RH is controlled between ~52% and 54%, so plenty tight enough for intended purposes and will be lifted to 57% when I get bud into the box.
That is about it for now peeps, I will update with performance results once I get some weed into processing. Any questions, add them to the blog entrythread.
