STC 1000 Calibration Question

[banks412]

Hey Guys,

I've recently purchased a STC 1000 and wired it up based on several folk's recommendations on this forum (thanks! couldn't have done it without y'all).

Having said that, I'm wondering about something with it. I am planning to use it in conjunction with my Holiday 7 cubic foot deep freezer. It seems to be working as designed but I'm wondering a bit about calibration. I set the desired temp to 20 Celsius and inserted the probe into a water bottle half filled with vodka. My difference temp is set to 1 degree Celsius and my compressor delay is set to two minutes. When it kicked on, the compressor turned on as it should and the temp readout chilled down to 20 Celsius and then promptly turned off. Eureka! I wired it properly!

But, the temp kept falling. 19, 18, 17, 16, and now it seems relatively stable around 15 Celsius. What the heck? Is this just due to the great cooling/insulating ability of the freezer? I verified that the freezer outlet was indeed off and the heating outlet was on (I used a nightlight). If I'm going to use this set up as a fermenter to maintain consistent fermentation temps, should I wire up some sort of heating element as well to not let the temp continue to drop that much? I'm leaning towards the paint can/light bulb idea at the moment...

Thoughts? Did I do something wrong? The controller/outlet I made seems to be working as designed - I just don't know what to do when the freezer kicks off as it should and temps continue to fall...

As always - thanks in advance. Can't wait to post my step by step DIY on the controller box (I know there are tons, but one more won't hurt!)

Thanks,
tim

 

[DanH]

Do you have a carboy in there? You could tape the probe to the outside and cover with a little bit of bubble wrap. I think the larger volume of liquid would hold a more steady temp.

And you're d@mn right one more DIY thread won't hurt. DIY threads are always awesome.

 

[Chrisl77]

That's how chest freezers are. Especially the first time cooling down your liquid the probe is in. It might fluctuate less now that the liquid is in the temp range.

 

[banks412]

No carboy in there, but I'll gladly fill one with water and let it settle down in there and see how it does. I also cut a piece of 1" EPS foam to fit the bottom of the freezer as I didn't want to be setting carboys directly on the bottom of the freezer, exposing them to the super-cold metal floor, possibly creating a cold spot in the beer when I do get some ready to go in there....

I'm excited to write the DIY - I finally remembered to stop and take pics throughout the process, hopefully this upcoming week I'll have time to get it done...

 

[banks412]

Well, I checked it again last night before going to bed, and sure enough, without putting a carboy in there it was right around 20.2 Celsius. I checked it again this morning and it was 18.5, so I'm guessing the freezer had just cycled again. Wonderful! I think it's working....

Now it's time to brew the beer!

 

[The_Mad_Scientist]

Also remember when you get a few full kegs/carboys in there you will have a larger thermal mass. Which will help maintain a constant temp.

 

[Ramitt]

Mine flucuated in temp much more when empty, now with 3 kegs and a full fermenter it is much more steady.

 

[banks412]

Sounds great, and thanks for confirming guys. Many have mentioned insulating the probe and taping it to the side of a fermenter while in there. How do you guys 'insulate' the probe after taping it to the primary/secondary?

 

[DanH]

I had a little bit of bubble wrap that I used. I wrapped an elastic hair band thing (stolen from my wife, oops) around the carboy then put a wad of bubble wrap under it with the probe between the wrap and the carboy.

 

[DanH]

...I've used a small foam block too in the same manner.

 

[IslandLizard]

Really good suggestions here.

You may want to set that compressor delay to 10 minutes, the maximum on the STC-1000. You don't want it to flip-flop on and off too much.

 

[uatuba]

You need to use the heat side as well in order to get a truly stable temperature. When I cold crashed with it, I got wild temperature swings. Using a 75w shop light cuts down on those dramatically.

 

[banks412]

Well I did go back and buy the materials to fabricate the "paint can" heater. Super easy and I threw in a 60w bulb just to check my work. It seems fine, but you suggest a 75w bulb? Seems a bit like overkill? That paint can got warm darn quick when I plugged it in and I was thinking of even stepping down to a 40w...

 

[FuzzeWuzze]

Well I did go back and buy the materials to fabricate the "paint can" heater. Super easy and I threw in a 60w bulb just to check my work. It seems fine, but you suggest a 75w bulb? Seems a bit like overkill? That paint can got warm darn quick when I plugged it in and I was thinking of even stepping down to a 40w...

I'd be hesitant to be fighting heat and cold using a paint can heater.

Your just going to have fluctuations the other way. Something like a fermwrap that heats the beer and not the air would help.

That said, its not going to really affect you much if at all if your beer gets 1-2F colder than your set point. On the other hand if that paint can heater gets going it with the additional heat from fermentation you could easily find yourself a few degree's hot, which is never good.

The paint can heaters IMO are really only useful if your ONLY heating your chamber, like if its winter you just unplug the freezer and use the paint can heater to keep it at 65 or whatever inside. Fighting them will just end up costing you more electricity and not really gain you any more accuracy.

 

[banks412]

Point taken - I'll try it without the paint can and see how it does. Thankfully it wasn't terribly expensive to fabricate... Once it 'leveled out' it seemed to stay relatively stable, varying only a degree or two.

 

[uatuba]

There is a lot of different between a paint can heater and a single shop light. The paint can heater will overshoot because the metal will remain hot when your bulb kicks off. With a plastic shop light, only the bulb remains hot and will quickly cool to the cooler ambient air temperature. With my compressor delay set at 10 minutes, I keep my fermenting beer within .4 of the target temperature (.2 either way). Before the shop light it was 1.2.

 

[banks412]

Can you give me an idea of what kind of shop light you're referring to? Those are variations I can live with! Considering, I'm only used to fermenting in my 77F closet, either of these options are LIGHT YEARS better than what I used to do...

 

[uatuba]

The cheapest plastic piece of crap you can find. Just turn the shield so that it blocks direct light from hitting the fermenter.

 

[Stealthcruiser]

Attaching the probe to the fermenter: Lots of folks use several wraps of an Ace bandage, which insulates it as well.

 

[Lumpyyyyy]

I use insulated tape from Home Depot to tape my probe to the carboy. It is rated for insulating on Ducts, figured it'd be good for this application. I haven't had any problems with it yet.

 

[Soldevi]

I place the probe on the fermenter as well. Temps don't swing nearly as bad. In the summer I only use the cooling side, and winter the heating side. The air in the chamber overshoots a little but it takes a while to make a difference on 5 gallons of liquid.