dry cure cabinet ideas

[mjdeez]

Anyone know what is in the walls of the non frost-free freezers? Blog post says "In non-self-defrost fridges the air in the fridge is cooled by direct contact with a plate that has coolant running through it."   How much of the wall space is taken up by these cooling plates?  I want to make sure I can drill through the walls like Expat did for the intake and exhaust fans.

http://curedmeats.blogspot.com/2007/07/key-equipment-piece-3-curing-chamber.html

I believe that would depend on the year, make and manufacturer of that particular freezer as to where the wires and coils are located.

Thanks. Turns out the coils for this particular model are routed all through the inside of the fridge, so that each shelf is actually just a coolant line. I had to pass this one up unfortunately. 

I think all the manual de-frost models have the lines in the shelves. At least any I've seen have.

Mike

Good to know. I had a bunch of open tabs in my browser for freezers I've been eyeing and looking at them closer some of these also have the coolant shelves.  In any case I'm glad I only had to drive across town to figure it out. Better than an hour drive each way.  I'm not really in a rush to do this so I'll just keep waiting for the right deal to show up. In the mean time I'm lining up the parts I need and writing the code for the temp / humidity controller (microcontroller).

I had a link to plans for a PID that could heat and cool, and incorporated a humidity controller. I wish I had the skills in that area to understand it and build one.

Building / tuning a PID is not easy. I'd be concerned that if I tuned it under one set of conditions that it may not be stable under all conditions. My garage can be as cold as 0F to 100F so I'm not really sure I'd be able to tune the PID so it would respond well under all conditions. 

My plan is to start simple, with a two-stage ON/OFF design, and forget the PID at first.  The two stage refers to controlling heating AND cooling.  I'm going to experiment with something like: temperature set point is T_Set, fridge would turn on T_set + 3deg, turn off at T_Set.  Heater would turn on at T_Set-3deg, turn off at T_Set. Clearly there's a wide band of error here, but I'm willing to start with this. BigJohn's post in Non Bradley Equipment highlights my plans for temp sensing materials. Similar deal with humidity.  Here is the sensor I'm planning to use. Cheap, available at digikey for $7 and easy to use (a linear output that can be fed into a ucontroller and digitized / measured).  The danger of this ON/OFF design is oscillation. If fridge turns on at T_Set+3, turns off at T_Set but continues to undershoot to the point where the heater turns on, I'll need to tweak it a bit but at the expense of total accuracy.  A Fridge has a pretty large thermal mass so I'm counting on this all happening slowly (fingers crossed) so hopefully there won't be too much over / undershoot in temp.  Not so sure about humidity.

If this controller turns out to be terrible, I may change it to a PI controller. Since this will all be coded into a microcontroller, my original ON/OFF controller can be just reprogrammed to be a PI with no hardware changes. But I'm hesitant to start with this approach as I'm not sure how well a two-stage PI controller would work, or how well I could get it to work. I don't want heat / cool interfering with each other, and same with hum / de-hum.  I'd need to think about it before I dove into this one.  The reason I say I'd be doing a PI and not a PID is I'm standing by my claim that the thermal mass of the fridge is so large that the "D" term would have minimal impact and only complicate the design and tuning of the controller.

If this ever gets off the ground I will write a tutorial of it.  If you find those plans, let me know and I can help you. I should tell you that while I've read up on control theory, I'm not an expert.

[mikeradio]

Heres a link to the 2 stage heating/cooling controller I am using in my cheese cave / dry cure cabinet


http://www.etcsupply.com/ranco-etc211000000-stage-p-105.html?osCsid=07d21f50f699da2d83daa9f1d4152a94

[Habanero Smoker]

I forgot to post this. I found the link to the PID Humidity Controller, but it only regulates the humidity. When I initially found it I thought it controlled both the temperature and humidity.

PID Humidity Controller

[mjdeez]

Thanks for the links guys. The out-of-the-box controller is nice (tempting) but I'll use that or similar as a backup plan if mine falls flat. I plan to size my humidity SSRs according to what they'll be driving (humidifier / extraction fan) so that will be relatively cheap, $10 max for both relays. If I used 2 15A relays it would cost me around $50 for both. Its tough to find an out of the box solution that is not overkill for what we need in a curing chamber.

I'll check out the DIY that Habs posted later.

I was thinking more about PI / PID on my drive to work this morning. I think I will try to do this even if my ON/OFF controller is working, at least as an experiment.