That’s exactly how I do it makes life much simpler than building a separate dry room.
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I wish I had room for a grow tent! Until I do (have a bigger home), this is the best I can manage. Plus I enjoy building excessively complicated things 
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Hella Jelly small sample nug I pulled from the cabinet this morning, harvested 9/16. Still not quite ready to trim and jar the rest up but this little bud seems good enough to smoke test.
It’s filling up in there, half a dozen trays of harvest over the last few weekends, and going to be harvesting one of the big girls that’ll fill it in a few more days.
Been holding 64F and 64% (VPD is the same as 60/60 = 0.71), it’s working beatifully. The cooler temperatues outside have done exactly what I had planned and I’m getting a really stable temp inside. It’s a little below the average temp which is closer to 70 because of the TEC water cooler.
Overall I’m getting happier and happier with this thing, especially as it requires less maintence - no ice and other shit I had to do during the summer heat waves. I only open it every few days just to check on things. Seems like about ideal 14-day dry rate, so that VPD thing is working at controlling the pace of the dry.
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I’m just learning but it seems that a minimum airflow is required. Like you said 65% is not going to get it. I’m a little rough in my drying process part is my lack of knowledge. That’s why I’m listening in. I’ve been a 4-6 drying hacker. Just started to change, first step I just bought humidity control for my drying box. I no longer rely on manual. Now I need to learn the exhaust point. I’ll try 57 first unless you advise me differently. You obviously know something.
@SativaKid
Well, I’m not sure if I know what the right answer is with certainty yet, this summer has been an experiment so far. If you just want my answer to your question, it’s at the bottom of the post. The rest of this explains how I landed on that answer.
What’s generally recommended is a small amount of airflow over the buds, hold 60F at 60% RH and it should take 10-14 days for the bud to be dry enough to jar (somewhere around 10% moisture content in the actual plant material).
Because my box is in the shed, it’s subject to whatever the weather is. In my case, it’s been hot. WAY hotter than 60F. In any case, you don’t want to exceed 70-80F because some of the volatile monoterpenes just evaporate off immediately. So I designed a thing that basically averages out the day and night temperatures using a big water cooler full of water that pumps through to stabilize the temperature. Now that it’s cooler at night and daytime that’s working pretty well, and holding around 64F. Earlier in the summer I had to add ice to the water, and eventually a cooler setup to keep the water/air temperature below 70. But the temperature varied throughout the day, often running 60F exactly though the night, and sometimes as high as 80F during the days (it’d be 100+ outside the shed). Hindsight, I would have just built this thing in a fridge. But hindsight is hindsight because it’s too late to change now 
maybe next summer.
Anyway, at 60% RH, a temperature of 70F will cause the drying process to take much less time. I hypothesized that keeping the Vapor Pressure Defecit (VPD) constant, and adjusting the humidity to match, should equalize the drying rate so it takes a similar TIME regardless. So, my exhaust humidity level (again, this is experimental) changes based on the temperature to produce the same VPD. I don’t really care about the RH level, I’m trying to maintain VPD. That’s not typical, but I think scientifically it makes much more sense.
Here’s the same chart posted a few months ago when I concocted this scheme:
A higher number indicates water evaporates FASTER. Low numbers mean evaporation will occur slower. This is based on partial pressures, and the difference between the material and the air itself.
So, if you just look at that chart you can get an idea of the trend - between 50F and 80F the VPD stays around 0.7 if you match the RH to the temperature. The highlighted green box are the purportedly best zones to dry according to the internet and various books. So, I picked the VPD at 60%/60F which is the most popular recommendation, and said, regulate to a VPD of 0.71.
Of course, since I wrote my own code, I made it more complicated. There is another humidity sensor that measures the RH/T of the air by the intake filter, and I calculate how much water there is in the air. If that’s more than is inside the box (if the outside air has more water in it than the air I’m trying to dehumidify - exhausting would only make my problem worse), then I activate a small dehumidifier. If the air outside is drier than the air I’m trying to dry, then I simply pulse the exhaust fan on for a few seconds. Normally the dehumidifier has only run when it’s raining outside.
I have noticed the best results with a small air turnover in the cabinet. The circulation fans run all the time, regulating the temperature and ensuring my sensor in the box is measuring the air flowing over the buds. This runs really slow, but noticeably so. I’d say the air in the drying stack travels the height of the stack in a few seconds. I have a MERV-13 filter in this airstream before flowing over the buds, which should remove any mold spores and dust from outside, there’s also a dust filter on the air intake. The exhaust goes through a carbon filter to keep my shed from stinking.
In simplest possible words, my RH is approximately equal to my temperature. If you have a humidistat and want to follow my relatively unproven path, set the humidistat to be equal to the average temperature. In 2 weeks or so, your bud will be dry and I’m very encouraged by the results.
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Thanks for the detailed information. I knew I was wrong with starting at 55. Just needed to shorten my learning curve. I can try it next week as I have my own Mail Order Bride finishing in a week.
Interesting post. I would love to hit 60/60, but without supplemental a/c here, best I can do is 68F / 60. I didn’t adjust humidity to match a 60/60 VPD, and left it for 60. During the summer, its mostly dehumidifieing the tent, the humidifier is never on. I chart the RH, and you can watch the spikes when you put fresh flower in, dehu turns on, drops to 60, turns off, plants release moisture, rh rises, and repeat. You can watch those spikes get smaller and smaller over time. When they even out, and your RH fluctuates between 60 and 61 you can then leave it for a while. I’ve left buds 2 weeks, and as long as 5 weeks hanging before jarring, both felt the same at jar time, light snap to small branches, but no clean break. In the winter, the humidifier in the dehumidifieing tent runs, because ambient RH in the house drops to 30% or lower. But you still get those peaks and valleys, only difference is once it “evens out”, without the humidifier it would continue to drop due to ambient RH. If I left buds in there, they would be crispy in a few more days without supplemental humidity.
I have some buds jarred a year ago, that in the jar show 58% RH, with no boveda pack or similar, and while the jar smells a little, the buds REALLY come to life when you grind em.
NOTE on humidifiers / mini humidifiers. There are two types. ultrasonic mist, and evaporative. The ultrasonic mist ones are ok for growing plants, but I prefer not to use them to dry buds since they DO leave a film everywhere if you aren’t using distilled water. Calcium, etc. will form a powdery coating on everything. Evaporative humidifiers just have a filter/wick, a fan above, and reservoir below, with the fan pulling moist air thru the filter. Bonus? They are usually cheaper, I got mine for $5 at a church sale. Evaporative humidifiers will not leave the film that ultrasonic mist will… And you can use tap water with them, as they have replaceable filters.
I think one of the BIG keys is to not drop below 55% (preferably 58%) in the tent, and to extend the dry time as long as possible, while not drying too much, too quickly. And at the same time doing what you can to drop humidity to 60%.
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Excellent write-up FieldEffect…
Effective use of thermal mass!! A largely overlooked tool nowadays 
Cheers
G
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Chopped my Hella Jelly this morning, drying half and froze the smalls for hash.
Full house in there! Time to get trimming, there’s a few racks ready to go 
Here’s the overall view, you can see my TEC cooler ghetto-rig and the icebox full of water. Thermal mass indeed 
Here’s the inside, I space the fresh trays out by a slot so they don’t get folded over. The 4 trays of HJ are on the bottom. Once they’ve been in there a few days, the single-stacks go just fine.
Here’s what one of the trays looks like when almost dry, this Avenue of the Giants has been in there a week now, there are several more trays at the 2 week mark and almost perfect. I don’t have time to trim today, so I’ll get on that tomorrow morning.
Trim jail is looking increasingly menacing 
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Just figured I’d share some dryed/cured result images here too.
Hella Jelly: Sample nugs, harvested about 2 weeks before I chopped the plant - so a little less ripe than most of the harvest. Freshly trimmed/curing now.
Avenue of the Giants: Sample nugs, harvested about a week before I chopped. Freshly trimmed/curing now.
SAD Fast: Harvested: August 19, solid 4-week cure
Critical Kush Auto: Harvested August 12, 5-week cure. Stuffed into Grove bags because it didn’t fit great, little trichome damage.
Runtz XL Auto: Harvested July 22, 8-week cure. Some damage due to packing into Grove bags.
Super Lemon Haze Auto: Harvested July 22, 8-week cure. Same, damage due to stuffing Grove bags to their limit.
Some lessons here, buy bigger grove bags than you need - initially I tried to fill the bags up because I hadn’t bought enough…that’s fixed now and they’re comfy and have plenty of room. I hate to see the broken trichome heads on the autos. I chose to do this because the first few weeks of cure with the older harvest I didn’t burp the jars frequently enough. Then it became apparent that I’d need a dedicated closet with all the jars, and I ordered some Grove bags for 1) ease of curing, 2) volume reduction. Also, I’m overall very happy with the stash. Thanks to all of you guys for the advice and guidance that got me this great collection of weed so far. Harvesting is an art all on it’s own. PLUS, MORE TO COME!
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Boo! Sorry man, but this isn’t the right mojo in the Advanced Techniques section. May I escort you to the lounge?
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Wondering if one of these dry cabinets for cameras/electronics would work in a tent with a portable AC going…
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Looks interesting and had I not just bought mine I’d be tempted to give it a try.
I think it would work fine after the first few days. The sheer volume of water vapor to absorb is huge if you load that with wet herb. I’d bet my lunch money that for the first few days it would be way above target humidity as the dehumidifier does its best.
It’s basically 12" x 12" x 18" - I’m guessing you’d be targeting somewhere in the range of 4oz or so dry in something like that. So we’re talking about maybe 10-16oz wet, or 6-12oz of water removal. You’d probably be looking at about 20% per day, 1.2-2.4oz of water extracted per day to regulate humidity.
So, fundamentally, the dehumidifier is just a small TEC cooler. There’s one in the bottom of my cabinet to remove water when it was raining crazy last summer. It was just really slow - granted, often there was much more than a pound of wet weed - many trays with a pound EACH of wet weed. I recall the little thing not working particularly well, maybe pulling 30-60cc (1-2oz) of water per day. Not nearly enough to do the job start to finish, but fine as things get past the 5-7 day mark. That was a 12V 2-3A unit, so roughly 2-3x the power of that dry cabinet. https://www.amazon.com/VAVSEA-Electric-Dehumidifier-Capacity-Basements/dp/B087YTM19N
That would be my concern anyway, I’d start with a small amount of material to dry. Work upwards as you get familiar with it. There’s not much in terms of good documentation for most of these things. If you try it, please document your experience because there is a ton of interest in this community for these prebuilt cabinets.
Anyway, it seems the VPD control method I landed on is what the cannatrol system actually is. Which means you do want to regulate both temperature and RH. Just controlling humidity works fine, but results improve as the temperature goes lower. Unfortunately, there isn’t a plot of “Cannabis Terpene Retention” vs temperature or VPD. So, I’m mostly shooting in the dark guided by bits of scientific background and what I hypothesize is the best approach. The cannatrol solution likely uses two beefy TEC units, one for heat/cool and one for dehumidification. I believe they have a sponge-type humidifier.
I think the best possible results would be from a modified fridge with a 40-60F setpoint (hence the modified part), with a fairly large dehumidifier and small supplemental humidifier. You can get to a target VPD just by modifying one or the other variable. Dehumidifier turning on a 60RH is great, but for really great results there you want your temperature also being about 60F.
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Hello, I was wondering if you still had the boards. I’m pretty interested in building this and I really don’t want to order them through JLC because it looks very confusing.
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Yeah I still have a few 
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Whoa. Some pretty cool stuff you’re developing. I like it. 
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Thanks @FieldEffect for doing & documenting this.
Reading this half-baked after a nap is a little much but I’ll get there
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Really changing the game here, @FieldEffect
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I appreciate you guys taking a look. I’m making some modifications to the algorithms this season that will be posted over the next month or so
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