Turning a small chest freezer into a low & slow bud dryer

[cbdhemp808]

I live off-grid in tropical Hawaii and have a perpetual outdoor greenhouse grow. The climate is warm, wet, and humid. We live in the jungle and there's a crazy amount of fungus and mold. I've had no way to dry my buds at home. I was planning on making a closet-size drying room with AC and dehum, but I figured my solar power system is too small to support it.

About 3 weeks ago I came up with a new idea...

 

[cbdhemp808]

[written Feb. 11]

I have a small chest freezer that I can run using an Inkbird ITC-608T (temp/RH). Essentially, it will run as a not-very-cold fridge. I also have a mini dehum that I'll place inside it. The buds will be wet trimmed and placed on racks/screens. (Or should I hang them?) Temp. will be set to 68°F for the first three days, and then 64°F after that. RH will be set to 55%. (as per Rosenthal)

I gotta laugh... it took the experiment with the buds in the little jar, and the drawback of silica gel causing a vacuum, to get me to consider the chest freezer running as a fridge. And then tonight I realized the little dehum could easily fit in there. The volume of the fridge is only 5 cu. ft., which should be very energy efficient to run at 64-68°F, especially with some thermal mass in there (1 gal glass bottles filled with water). Likewise, also energy efficient to run the dehum.

The only unknown here is the performance of the dehum. I've actually never used the one I have (Pohl Schmitt) – I was saving it for the day I could build a small drying room. This particular unit has gotten some bad reviews on Amazon, saying they die fairly quickly. But there are many other options on Amazon, and this one gets a high rating. So I'll try out the Pohl Schmitt and see how it goes.

It seems like the power requirement to keep 5 cu. ft. of air at 55% RH would be very low. I don't plan on opening up the fridge for 10-14 days, so that means once the RH is brought down to 55%, it should take very little power to keep it there, as the buds are drying out. According to Rosenthal, the buds will lose 60-70% of their moisture in the first 3 days.

Another dynamic is that the dehum produces some heat while operating, which will cause the fridge to turn on. During the first 3 days, this will probably happen a lot. After that, the rate of moisture emitted by the buds will decrease.

One thing I could do to conserve power, if necessary, is put the power to the dehum on a timer, so that it doesn't run during the night, and only comes back on once the sun hits the solar panels. Humidity would rise above 55% during the night, but it shouldn't be a problem.

 

[cbdhemp808]

[written Feb. 11]

But you'll still have to open the fridge to empty the dehumidifier, no?

I think the dehum reservoir will be big enough to hold all water from the buds and initial air humidity in the fridge, which will be closed for 10-14 days. I also think the evaporation of water from the reservoir, into the air, would be negligible.

Here's a calculation... Let's say my harvest will turn out to be 8 oz of dried bud. Let's say dried bud is 25% the weight of wet bud. So that means 0.25X = 8. X=32oz of wet bud (2 lb). That means 32oz - 8oz = 24 oz, is the weight of the water extracted. How much volume is 24 oz of water? 23 fl oz ... slightly less that 3 cups.

So, that's the calculation for 8 oz of dried bud, which is typically a lot more than I get from harvesting one plant. I usually fill about 1.5 quart jars with dried bud from one plant. That's more like 3oz dried bud. That would be about 8.6 fl oz of water in the reservoir. My current dehum has a capacity of 17 fl oz.

An upgrade would be a better-rated mini dehum with larger capacity (35 or 41 fl oz) and/or drain tube. I can also retrofit a drain tube. I can route the drain tube to the drain in the bottom of the fridge.

And you probably should have a humidity sensor (preferably one you can view remotely) to make sure the night levels don't get too high. Probably will be fine as it's a mostly closed system, but for the first pass or two you'll probably want to be more attentive.

That's what the Inkbird ITC-608T provides... two probes, one temperature, the other humidity, and display. I will probably run the wires through the fridge door gasket – i.e. drill holes and use silicon. If I want to control the time of day that the temp. and humidity control is powered – i.e. off during night hours – then I will need to use separate temp. and humidity controllers (Inkbird), because the ITC-608T doesn't support that. At this point, I'm guessing I'd want the temp control always on (24 hrs). If it turns out I need to conserve power by turning off the humidity control at night, then I'll put the humidity controller on a digital timer outlet.

I'll might also use a VIVOSUN THB1S to monitor the high and low temps and RH. But at ±5% RH accuracy... not very accurate. This one looks better: Amazon.com

 

[cbdhemp808]

[written Feb. 23]

I just ordered the equipment for this!

* Inkbird temp/humidity controllers, pair (saved $5 buying as a pair) Amazon
* Temp/humidity monitor and data logger with probes Amazon
* Lamp pipe, to build DIY cable glands Amazon
* Sturdy stainless steel screen for building a bud drying rack insert for the fridge Amazon

The reason I'm buying separate temp/humidity controllers, and not Inkbird's dual contoller, is so I can run the humidity controller on a digital timer outlet, so that I can regulate dehum off-time at night, to conserve power with my limited solar power system. I'm guessing the temperature controller won't need that, since it will be very lower power consumption to maintain 64-68° F.

I'm especially stoked that I found the monitor/data logger, because it will give a complete readout on the temp and humidity over the entire drying period, with high granularity. It also easily shows me the daily min and max values of both temp and humidity. The unit will also provide an accuracy check against the Inkbirds. This monitor/logger will be key for testing and tuning the system.

The "lamp pipe" is for making "cable glands" – i.e. tubes that the temp/humidity probe cords will go through, and also the dehum AC/DC power adapter cord. I'm planning to drill holes in the lid of the chest freezer, toward the back. The cable glands will fit in these holes, and will be locked in place with the nuts. I'll route the cords through the glands, and seal with a small amount of silicone, top and bottom. There's 5 cords to accommodate, so I'm thinking 2 or 3 glands.

I'm planning to mount the equipment on the wall behind the fridge, just above where the lid will be when fully open.

For the drying racks, I plan to make a custom wooden-frame insert. The whole insert will easily lift in and out of the fridge w/ a handle at the top. Drying racks will slide in and out of the frame. The dimensions of the insert will be 15" x 12" x 24". The depth of 24" should give me seven 12"x15" racks, allowing for a top w/ handle and a 3" space at the bottom for feet. Total drying space, 1,260 sq in. (8.75 sq ft). I have been using about 784 sq. in. drying space, in the food dehydrator, for a 1-plant harvest, so this would be a 60% increase in drying space (1.6x). (If I change the rack dimension to 13x15", which will also work, and reduce rack spacing by 3/8 inch, I can double the drying space over the dehydrator.)

A can put the whole system on one outlet power strip, and plug the power strip into my power meter to monitor power consumption.

 

[cbdhemp808]

WillCall wrote:

You might consider adding a small low-cfm fan. It helps mix the air, speeds eqilibration. Your dehumidifier will stir the air when it is ON, but things go still when it is off. Doesn't need to be much. I use an 80mm Enermax fan in a 16cu ft space and it is very nice and gentle. This one is about 28cfm (gentle) and 15 dBA sound (very quiet); 0.15A on a 12V supply.

I went for super quiet and ridiculously low power consumption. 21 CFM. 9 dBA. 12V, 0.45 watt (0.0375A).
$13 free delivery.

Amazon.com

 

[cbdhemp808]

Equipment arrived today!

The Inkbirds and monitor/logger will be mounted outside the fridge, with probe wires routed into the fridge via holes drilled in the door and improvised cable glands. The 12v fan will be mounted inside and will always be on once the drying process starts.

Setting on top of the Magic Chef 5 cu ft freezer... Clockwise starting with the roll of wire mesh: stainless steel #5 mesh 15.7" x 10 ft, "lamp pipe" to make DIY cable glands, Inkbird humidity controller IHC200, Inkbird temperature controller ITC308, Elitech temperature and humidity monitor and data logger, Noctua NF-R8 12v fan.

The humidity controller. I'll need to get creative because the probe won't fit through the cable glands.

Taking the back off the Inkbird humidity controller. I disconnected the probe from the circuit board.

I'm planning to cut these down to size to make "cable glands" – i.e. tubes that the probe wires and power cord for the dehum will go through, after drilling holes in the door. I ordered this "lamp pipe" from Amazon, but they shorted me on the nuts. I may exchange for already cut pipe. Once the wires are in place in the cable glands, I'll seal them with a small amount of silicone.

The fan and the temp/humidity monitor and data logger.

Stainless steel #5 mesh for the drying racks.

Mini dehumidifier and power adapter cord. Adapter plug will easily fit through the cable gland.

Inside the fridge box... dehum sits on the equipment side. The wooden drying rack will fill the other side and will have a handle on top for easy insert and removal.

 

[bluter]

nice little project.

is there any reason you just didn't use a normal refrigerator? it wouldn't need anything special, that's the advantage of the ziggy method. it works everywhere on earth you can plug in a regular fridge.

 

[cbdhemp808]

nice little project.

is there any reason you just didn't use a normal refrigerator? it wouldn't need anything special, that's the advantage of the ziggy method. it works everywhere on earth you can plug in a regular fridge.

We are off-grid with limited solar power. We are already running one mini fridge for food, because we can't power a normal size fridge. So, there's no room in that one, and it wouldn't be good for humidity control anyway.

I considered buying a 2nd mini fridge, with upper (open) freezer section, but we wouldn't have enough power to run it at low enough temps to keep the freezer section frozen and serving as a dehumidifier.

The breakthrough for me came when I realized I only needed to cool to 64°F, and that a mini dehum could fit in the chest freezer. Suddenly I could see that this system would use very little power.

We already had the chest freezer and weren't using it. With this solution, we are only running it at 68°F for 3 days, and then 64°F for the rest of the drying time, so that will take very little power. Since the space is only 5 cu ft, power required for the dehum should be minimal, and if necessary I'll put the dehum controller on a timer so it doesn't run during some nighttime hours. The fan uses only 0.45 watt.

This solution also allows control over both temp and humidity, and provides more drying space than a mini fridge.

 

[bluter]

We are off-grid with limited solar power. We are already running one mini fridge for food, because we can't power a normal size fridge. So, there's no room in that one, and it wouldn't be good for humidity control anyway.

I considered buying a 2nd mini fridge, with upper (open) freezer section, but we wouldn't have enough power to run it at low enough temps to keep the freezer section frozen and serving as a dehumidifier.

The breakthrough for me came when I realized I only needed to cool to 64°F, and that a mini dehum could fit in the chest freezer. Suddenly I could see that this system would use very little power.

We already had the chest freezer and weren't using it. With this solution, we are only running it at 68°F for 3 days, and then 64°F for the rest of the drying time, so that will take very little power. Since the space is only 5 cu ft, power required for the dehum should be minimal, and if necessary I'll put the dehum controller on a timer so it doesn't run during some nighttime hours. The fan uses only 0.45 watt.

This solution also allows control over both temp and humidity, and provides more drying space than a mini fridge.

is there a lot of off grid there or was it a personal lifestyle decision ?

 

[cbdhemp808]

is there a lot of off grid there or was it a personal lifestyle decision ?

yes and yes.

 

[bluter]

yes and yes.

nice choices. not sure i could do it without ac lol

 

[cbdhemp808]

nice choices. not sure i could do it without ac lol

Air conditioning? It doesn't get very hot here. Usually not over 85°F. Typically 75-80°F.

 

[bluter]

Air conditioning? It doesn't get very hot here. Usually not over 85°F. Typically 75-80°F.

for comparison it's -2f here right now. the rh is like 20% lol

we just had a huge storm with 15 inches of snow. most of the highways are still closed. the temp is supposed to plummet to -20f in a few hours.

 

[cbdhemp808]

for comparison it's -2f here right now. the rh is like 20% lol

we just had a huge storm with 15 inches of snow. most of the highways are still closed. the temp is supposed to plummet to -20f in a few hours.

Oh wow! Funny, because today I was thinking, once I get this bud dryer built, I could say "throw the buds in the oven", and then I thought, in a climate like Alaska in the winter time, that would be pretty much true, cuz this oven will run at 64°F and 55% RH.

In Hawaii, 64° is quite cold. I used to live in the Pacific Northwest, and was adapted to cold and rainy weather, and sometimes freezing. Now I consider 70° to be cold! So, below 70° is like below zero to me.

 

[gwhunran]

Would it be possible to put up more solar panels to generate more power? I have no idea of the cost associated with solar? I have too much shade on my property for solar. Love my trees, big hardwood, full of squirrels and birds.

But my electric bill was over $400 one month during the last grow.

 

[cbdhemp808]

Would it be possible to put up more solar panels to generate more power? I have no idea of the cost associated with solar? I have too much shade on my property for solar. Love my trees, big hardwood, full of squirrels and birds.

But my electric bill was over $400 one month during the last grow.

Yes, I could get more panels, but I can't really afford that right now. Also I would need more rack space to mount them, which is a hassle. Actually the next big thing I need to spend money on, for solar power, is new batteries which will probably cost around $800-$1,000. That will definitely help with available power at night.

 

[cbdhemp808]

Update...

I ordered more parts for the DIY cable glands that will allow the placement of the probe cables into the fridge through the lid. When those parts arrive (2 weeks or less), the first thing I'll do is a temperature controller test. I'll run it for a day to check power usage and to get a feel for the settings of the controller. After that I'll do a humidity controller test w/ the dehum installed and both humidity probe cable and dehum power cable going through the one cable gland.

If that all checks out, I will then go ahead with the full build, except for the drying racks. I'll test with both the temperature controller and humidity controller active for a day or two. Finally I'll build the drying rack insert. If all goes well, I'll be ready to dry buds from the next harvest, probably around the end of April.

 

[cbdhemp808]

Parts arrive tomorrow!

 

[cbdhemp808]

Got the parts... here's some new pics...

New parts here: power monitor, cable glands of the right length w/ nuts, pluggable union for the humidity controller's problem cable. The temp/humidity monitor & logger, and Inkbird temperature controller are shown w/ probe wire going through the cable glands. The DIY cable glands are 3" segments of M12 "lamp pipe" w/ hex nuts.

This cable gland is a bit tricky... both the humidity probe and the dehum power cable need to go through it. The humidity probe itself is fixed to its cable (can't go thru gland), so I'll need to cut the cable and install the 4-wire union. The dehum power cable plug is just slightly too big to fit through the gland, so the plug will need to be sanded or ground down a bit. Also there's a slight burr on the inside of the tube openings, so these need to be filed down.

Inkbird temperature controller, ready to go for the first part of the project. First step is drilling a hole in the lid of the fridge to accommodate the cable gland. The top side of the gland will then be sealed with a little silicone. Then I'll plug the Inkbird into AC power and set for 64°F, and plug the fridge into the Inkbird. I'll probably also use the power monitor, to see how much power is used in a 24-hour period, and possibly also the temp/humidity monitor to see the min and max values over the period.

EDIT: Shoots! I forgot about the fan... a thin 12v 3-wire DC cable will need to go through one of the glands for this fan, terminate inside the fridge box with a 3-wire pin connector. Not a problem.

 

[Azimuth]

Do they make slightly bigger cable glands?