BCS 460 mash temp. control

[HollisBrewCo]

Had my first brewday with the BCS last Sunday and loved using the controller. I was having a little bit of trouble holding my mash temperature. I use an uninsulated 30 gallon blichmann mash tun with a false bottom. It's directly fired and I recirculate throughout the entire mash process. I have my only temperature probe placed in the return tube for the wort and I seemed to overshoot or undershoot my mash temperature by about 2 deg. I'm wondering what people with similar systems do in terms of mash temp. Probe placement. I was thinking a 6 inch probe placed in the mash itself could be a better option while leaving the probe in the return tube to make sure the wort temp. Does not exceed say 165ish deg. Another issue i had on this brewday was I was never able to hit my strike water temp exactly it kept fluctuating. My mash burner never stopped cycling but continued short bursts for the better part of an hour. I decided the temperature was good based upon the analog thermometer in the tun, I managed to come close and hit one degree over my mash temp. I am currently using pid control with a .5 deg swing.
In short am I chasing temps due to my probe placment, my pid needing to be tuned or both ?

 

[Walker]

no real experience with direct fired MLT, but I would think that you would need to put the probe at the output of the MLT rather than at the return point.

With HERMS and RIMS, the temp probe is usually put at the point closest to, but AFTER the heat, which is the return to MLT. Since you are heating the bottom of the MLT, maybe the probe should go right at the output of the thing since that is the point closest to, but after the heat in your system.

 

[RiverCityBrewer]

I use 2 probes in my mash tun - a 12" in the lid to try and get center of mass and a probe on the kettle outlet before it gets recirculated back to the top. The BCS fires the burner based on the temp of the internal probe and I recirculate as fast as I can with as low a flame as I can to keep from overheating. I was going to put a shutoff point if the circulating liquid got above a certain point, but using the method above I was able to return wort to only be about 2-3F higher than my internal temp, which makes changing temperatures slower, but much easier to control. Also once I get to temp I move to differential control as PID hammers the burner too much.

 

[HollisBrewCo]

River, does your program switch to differential control or do you run in manual mode ?

 

[RiverCityBrewer]

I use PID to get to my strike temp, then dough in, then the next state is a hold temp and that state uses differential control.

 

[Bonch]

You need to take your temperatures at the exit of your MLT. Otherwise you are getting some cooling from the tubing though the pump and back into the tun. You will likely notice even more problems in the winter with control.

You really want to take your temperatures as close to the actual heating zone as possible. Even if taking them in the middle of the tun, the temperatures can be different at the bottom of the tun if you are not getting good circulation.

 

[HollisBrewCo]

Okay so i will change the placement of my probe to the outlet of the mash tun and change my program to have the mash state held by differential control. Anybody have opinions on what my swing should be ? I'm thinking that .5 deg would give me tight control of the mash.

 

[RiverCityBrewer]

I use a differential swing of 2 which comes out to +1/-1 degree F... using .5 would be +.25/-.25 which might be a bit unrealistic, but I have never tried it. The lowest I would probably go with my system would be 1.5 to 1 but depending on how your system works you might be able to go lower.