Digital Thermostat Controller Schematic Review

[jmferris]

Was hoping I might get a review of my schematic. Looks simple and straightforward to me, but it has been at least fifteen years since I have done any sort of electronics projects. I have a non-programmable digital thermostat already laying around that needs a use, so with warmer temperatures hopefully soon to come, a temperature controller for my upcoming fermentation chamber seemed to be in order.



Basically, this will hook up to a non-programmable digital thermostat. Two outlets, the one on the left always live and the one on the right is split. All the Out / Return pairs are wired to phono jacks, for quick connection points. H-Out goes to the heating relay lead on the thermostat, C-Out goes to the cooling relay lead on the thermostat. Since only one of the relays is active at one time, the only leg that should be live would be the relay position that is closed.

Because of the fact that only one of the heating or cooling relays would be active at once, if at all, the SSRs should be only be powered when that leg is closed. So, both H-Return and C-Return are wired to the common ground of the thermostat. F-Out and F-Return are to the fan that will be attached, as well. The fan should only be powered when either the heating or cooling leg is closed.

Not pictured, there is a small enclosure that the H pair and C pair run through that will provide a red and blue LED en route to the thermostat. This enclosure would be optional, and haven't decided if I care to have it yet. Figured since the main enclosure will mount on the back of my fermentation chamber, I would need a way to put indicators on the front, if I end up wanting them.

Any feedback / critiques would be appreciated. Was hoping to begin the build tomorrow, as I have everything already laying around the house, apart from a couple of 15 amp outlets.

Cheers!

 

[shildebr]

Looks good to me, this is the same way I wired mine (minus the heat side). I also hard wired a transformer to the 110V AC, I assume you're doing the same.

Which thermostat did you go with?

 

[jmferris]

Thanks! I likely am doing the same. Have an extra Blackberry adapter laying around (a few of them, actually) and was just going to bust it open and wire it in. If I am impatient, I can always just plug it in to one the auxiliary outlets until I get back around to hard-wiring it.

I have a Honeywell RTH111B that I picked up at Home Depot when I was going to change out the coil thermometer in the living room. Since that was one more project I didn't do this last winter, I've quietly moved the package over to my brewing shelves. Which model thermostat do you have? Haven't seen anyone using one of the Honeywells, mostly just Hunter or the generic brands that I can't seem to recall the names of at the moment.

 

[shildebr]

I have a ritetemp, it was cheapo home depot model, but the only one I could find that would go down to 35 for lagering.

 

[jmferris]

Also, this is the indicator panel. Really simple, as it would act as a passthrough between the junction box and the thermostat. Only thing that I might change on this would be to add a DPST between the inputs and the resistors, to enable me to kill the feed to the thermostat (and keep the split outlets off).



This whole thing fits into a 3"x2"x1" enclosure. I would probably orient it flat so that there is a 3"x1" profile in the front of my fermentation chamber. Figured I could mount 90-degree angle braces to it from behind, and flush-mount it in the cabinetry, when I get around to that phase of the project.

 

[jmferris]

I have a ritetemp, it was cheapo home depot model, but the only one I could find that would go down to 35 for lagering.

I was thinking about seeing if they had one of those when I was over there for the outlets. The attractive part of going down that low for me is to cold crash in the chamber. I am an ale person, myself, but it would also give me that option in the future.