Tips for overshooting temp control?

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petrolSpice

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I have a 5 cuft chest freezer that I use as a fermenter. Heating is provided by 2 fermwraps. Control is achieved with an STC-1000. The temp probe is in a thermowell that it in the center of the wort. I am using a Speidel 7.9 gallon fermenter and usually have around 7.5 gallons in it.

The issue is that when fermentation is not active and the wort is still, the fermenter is overshooting the target temp. This leads to it cycling between cold and hot with swings of 1-1.5 degC even with the offset set to 0.3 degC in the STC-1000. Eventually it will level out, but sometimes it will go back and forth for 10+ hours.

I believe this is happening because the probe is in the middle of the wort where it takes longer for the heat or cold to reach it. By the time it reaches the probe, the rest of wort is already past the target temp.

When I was doing 5 gallon batches in carboys this seemed to be far less of an issue.

I could move the probe to the side of the fermenter but I like the accuracy of the thermowell especially during active fermentation.
 
You pays your money and you takes your chances.

I pin probes to the sides of fermentors (and kegs) under ~ 4x4" chunks of 1" closed cell foam using a 2" wide velcro strap.
The plot below shows a fermentor in the throes of peak fermentation and the resulting recovery from 1°F rises (that's the controller differential setting).
Barely any undershoot to be seen...

temp_tracking.jpg

That said, I imagine this would be a practical problem when there are heat wraps around the fermentor.
Don't have any experience in such configurations so I'm not sure what you could do...

Cheers!
 
I think you're pretty accurate in your assessment of what's going on. The thermowell is going to get you the most accurate temperature reading but I don't think it's going to give you the most accurate temperature control because you're going to have carry over (you're problem in this case). Since you're using an STC-1000 I think the best thing would be to increase your on off threshold a little bit until the temperature stabilizes. Maybe up to 0.7 or 1.0C. Give the wort in the middle of the speidel a chance to heat up. It will cut off early but probably carry the temperature up a degree. Kind of a jerry rigged fix but without a proper PID to mess with its what I would do. once fermentation kicks off i'd lower the threshold back down to the 0.3C min.
 
I have a 5 cuft chest freezer that I use as a fermenter. Heating is provided by 2 fermwraps. Control is achieved with an STC-1000. The temp probe is in a thermowell that it in the center of the wort. I am using a Speidel 7.9 gallon fermenter and usually have around 7.5 gallons in it.

The issue is that when fermentation is not active and the wort is still, the fermenter is overshooting the target temp. This leads to it cycling between cold and hot with swings of 1-1.5 degC even with the offset set to 0.3 degC in the STC-1000. Eventually it will level out, but sometimes it will go back and forth for 10+ hours.

I believe this is happening because the probe is in the middle of the wort where it takes longer for the heat or cold to reach it. By the time it reaches the probe, the rest of wort is already past the target temp.

When I was doing 5 gallon batches in carboys this seemed to be far less of an issue.

I could move the probe to the side of the fermenter but I like the accuracy of the thermowell especially during active fermentation.

I was pleased to see petrolspice post as I was about to raise the same question regarding using a temperature probe located directly in wort near 1/2 radius of fermenter. Like you, I wanted to control the wort with direct measurement.

Trying to control my first brew using ITC 308 with fridge and 100W heater (reptile bulb) is not going as planned. Since these Inkbird thermostat controllers don't use PID control and are simply on-off devices (as it must be for controlling a refrigerator compressor), wort temps are creeping well past my set points and differential. In my case I am seeing as much as an added 1F on top of the 1F heating & cooling differential. Additionally, I resorted to unplugging heater when in cooling mode and visa versa when in heating mode to keep cycling between heating and cooling.

At this point I am concerned with what the yeast must be enduring.

Thoughts and suggestions?
 
You pays your money and you takes your chances.

I pin probes to the sides of fermentors (and kegs) under ~ 4x4" chunks of 1" closed cell foam using a 2" wide velcro strap.
The plot below shows a fermentor in the throes of peak fermentation and the resulting recovery from 1°F rises (that's the controller differential setting).
Barely any undershoot to be seen...

View attachment 374771

That said, I imagine this would be a practical problem when there are heat wraps around the fermentor.
Don't have any experience in such configurations so I'm not sure what you could do...

Cheers!

day_tripper. Nice chart. Are you using Inkbird thermostat with the only difference (vs petrolspice and I) being sensor location? Looks like you have good control. It would be interesting to see another overlay graph of what the "core" wort temp is doing.
 
day_tripper. Nice chart. Are you using Inkbird thermostat with the only difference (vs petrolspice and I) being sensor location? Looks like you have good control. It would be interesting to see another overlay graph of what the "core" wort temp is doing.

His chart is during active fermentation. When mine is actively fermenting I have very good temp control also because the wort is mixing itself, so the heat/cold at the outside of the fermenter reaches the probe at the center much faster. With the differential set to 0.3 degC it the temp will stay within 0.3 degC of target.

My issue is that when it's not fermenting, the probe at the center of the wort does react quickly enough to the change in temp because the wort is not mixing well. I could move the probe nearer to the outside of the fermenter (but still in the wort), but there is little to no room for adjustment unfortunately.
 
His chart is during active fermentation. When mine is actively fermenting I have very good temp control also because the wort is mixing itself, so the heat/cold at the outside of the fermenter reaches the probe at the center much faster. With the differential set to 0.3 degC it the temp will stay within 0.3 degC of target.

Same here. I'm using a DIY Brewpi setup with a thermowell in the wort and the chamber probe dangling in the air.

My issue is that when it's not fermenting, the probe at the center of the wort does react quickly enough to the change in temp because the wort is not mixing well. I could move the probe nearer to the outside of the fermenter (but still in the wort), but there is little to no room for adjustment unfortunately.

I was seeing the same thing and agree that the lack of mixing late in the fermentation will introduce some lag time to the thermowell probe response. My heater is also too strong but I digress.

What I've started doing is that when the chart indicates that things are slowing down with respect to fermentation, I'll switch to Fridge constant mode with the temp set to whatever I had as the target during active fermentation. I stay in Fridge mode as I raise the temp a couple degrees for a couple of days. Doing this has avoided the wild swings in chamber temp as well as smoothed out the beer temp later in the process.

Todd
 
...My issue is that when it's not fermenting, the probe at the center of the wort does react quickly enough to the change in temp because the wort is not mixing well. I could move the probe nearer to the outside of the fermenter (but still in the wort), but there is little to no room for adjustment unfortunately.

If you had a controller that used PID, then it would be able to account for the difference from when the wort is being mixed and when it is not. The PID values are constantly updated for the changes in over/under shoot.

With a simple on/off controller I don't think there is much you can do to fix your situation.
 
...I was seeing the same thing and agree that the lack of mixing late in the fermentation will introduce some lag time to the thermowell probe response. My heater is also too strong but I digress...

I think the root cause is your heater being too strong. I have a 200W heater in my chamber and it is too strong also. With BrewPi, IIRC, it has a minimum on time of the heater set to 180 seconds. The only way to change it is to change it in the code and recompile. The PID can't properly deal with overshoot if the call to stop heating is over ridden by the 180 second minimum on time.
 
His chart is during active fermentation. When mine is actively fermenting I have very good temp control also because the wort is mixing itself, so the heat/cold at the outside of the fermenter reaches the probe at the center much faster. With the differential set to 0.3 degC it the temp will stay within 0.3 degC of target.

My issue is that when it's not fermenting, the probe at the center of the wort does react quickly enough to the change in temp because the wort is not mixing well. I could move the probe nearer to the outside of the fermenter (but still in the wort), but there is little to no room for adjustment unfortunately.

Good point. The fermentation is not only moving but also generating heat. With that said, maybe locating sensor on surface of of fermenter is better. It will be accurate during activity due to movement and will respond faster when there is no movement or heat being generated?

I'm in the same boat with an internal, yet close to the wall, position. I have a 12" long NTC probe mounted into a Big Bubbler top flange with a plastic compression fitting.
 
I could move the probe to the side of the fermenter but I like the accuracy of the thermowell especially during active fermentation.

I have a batch fermenting right now. It's amazing the level of churning going on in that fermenter. There are eddy currents as the yeast rises and falls.

I don't think it's convection, just yeast rising and falling w/ CO2--but it seems to be similar to convection. I'm uncertain that there is very much difference in temperature throughout that fermenter given all that activity.

Have you ever tried comparing the two as to temperatures? I doubt there's as much difference as people might expect, and there might be almost none at all.

That wouldn't account for the overshooting, but perhaps it's something else that's going on. And if the above is not correct, then ask yourself this: would you rather err on the cool side or the warm side? I'd think cool--so put the temp probe where it reads the highest.

My 2 cents.
 
The STC-1000 uses 10K NTC Thermistors. Perhaps I could get two 20K thermistors and wire them in parallel? One goes in the beer and the other on the side of the fermenter.
 
I have a bunch of spare temp probes for the STC-1000 which uses NTC Thermistors. Can two probes be wires in series or parallel to provide an "average" reading between the two of them? I could place one in the beer and the other on side of the fermenter.

I don't know the answer to your question.

But--what I know about fermentation temps is that you don't want to exceed a particular temperature (unless you're looking at one of those hi-temp ales). It's better to be lower than your limit than to exceed it, in other words. So choose what results in the lower overall temp in the fermenter.

Since you have spare temp probes, find two that read the same or as close as you can. Put one in the thermowell, the other attach to the side w/ a block of foam. Then you can switch between them to see what kind of temperature variance you actually get. Then choose the location that gives you the highest temp, as you want that location to define the upper limit of temp.
 
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