Overkill temperature controller for terrarium

[ConKbot]

This isn't anything new, but I figured it would be appreciated around here.  No low level stuff, just industrial controls, but fun to build and put together.




Just a summary of what it does. 

The snake tank has 2 under tank heaters on one side (70W total), a CFL hood for lighting, and a LED strip for "evening" lighting which is dimmer, so I can see my snake when he's out and about. 
A 2 output digital timer controls the light and a PID temperature controller regulates the heater (both from omega engineering). The PID controller reads a K type thermocouple that's placed in the tank, and the auto-tune came up with a nice stable loop for the long lag/overshoot the system would have.     On the front panel for the lighting I have 3 position switches for Auto-Off-On, and for the heat I have a 2 position Auto-Off switch. 

For the top-down photo, on the DIN rail from left to right I have:
13A mains circuit breaker, (3) bussed terminal strips carrying breaker'd 120VAC, (3) bussed potential earth terminal strips that bond to the DIN rail also, (4) bussed AC neutral terminal strips,  10W (IIRC) 12VDC lambda TDK universal input DC power suppply,  (4) bussed +12vdc terminal strips, (4) bussed 0vdc terminal strips,  empty space, then 1 terminal strip for the DC input on each SSR (the signal goes to the front lamps  and switches also, hence the use of the terminal strips), and for the heart of all the overkill  (3) Crydom 20A 240VAC solid state relays. 

The relays would need spacing between them for the heatsink, if I was using them at their rated current, but for their current use they will do just fine tucked next to each other, stone cold, with each one supplying < 1A. 


The outlets along the back are decora face outlets wired up for , always on, daytime lights, evening lights, heater output.  They are the kind which tightening the screw clamps down the back-stabs so its fine using them for this, usually I'm leery on using the spring-loaded back stabs.

Looking back now, the only naughty things Ive done is fail to heatshrink the solder joints on the IEC inlet, and I didn't separate my mains and LV wiring, though the only low voltage which exits the box is the thermocouple wire.  I will probably slide some silicone aquarium airline over it to protect it now that I'm considering it, so it will be fine then once I do that.   

The enclosure is a 3U rackmount box from Hammond (minus the rackmounting hardware)   

Can I buy a nice controller to run the heater for as much as I paid for the enclosure? Yeah probably, but It cant pull double duty on a kiln when not needed by the snake ;p  Could I have ditched the timer/pid controller for a micro and some just sufficient SSR's? yeah probably, but I wouldn't trust my code writing to not hang in the worst possible way with the heater on, so I'll leave that to Omega. 


When space isn't an issue, ease of assembly and servicing is, DIN mount stuff is definitely awesome.  3 bolts holding in all the goodies, rather then 2 or 4 on each!

Hope you all enjoyed  a little DIY industrial control at home. 

[SeanB]

I put a PID controller on the fridge in place of the mechanical thermostat............ The aircon in my office uses another non PID controller to drive it. Not overkill, just nice use of quality industrial logic.

I tend to use relays myself, as they are a lot cheaper than the SSR modules, and are good enough for most uses. Just replaced one today, as either it or the H3BA-N timer driving it are sticky, and the relay is a lot cheaper than the timer. Hard to check, as the slightest vibration will unstick it, so it will only show up when the machine is not running, even opening the cover will release it.Smacked both onto the wall and they now work, but replacing the relay was a backup, as it drives a motor load that will lunch a SSR fast- AC split phase motor running in very short steps as a tensioner drive. It does tend to kill motor capacitors every year or so, so I keep some 2uF 450VAC motor run caps as spares for when they fail.

[ConKbot]

Thanks!
I agree that the PID definitely isnt the overkill here and its the SSRs.  The lighting circuits only cycle once per day, but with the SSR I can keep the heater set on a 1 hz cycle without listening to horrible noises all day.

My buddy is building a kegerator sometime soon, and that will most likely get an industrial temp controller to run it instead of hacking on the original thermostat. But probably an ebay cheapy instead of an omega one.

[gfc1968]

Do you have a wiring diagram for this.  It sounds just like something you would like to use on my snake enclosure.

[ConKbot]

Do you have a wiring diagram for this.  It sounds just like something you would like to use on my snake enclosure.

No wiring diagram, unfortunately as all of it was just hooking power to everything. The temp controller had a SSR output, so that just hooked directly to the SSR inputs. 

Of course, within a few weeks of finishing this, I found
http://ecozonevivarium.com/searchresult.aspx?CategoryID=  (or another similar one, cant remember)  Which looks like it would handle everything I'm doing and more.