Max temp setting

[skinny]

I brewed my first batch with the BCS this weekend and all went well except for one thing. I am using a HERMS system with the BCS controlling an element in the HLT based on the outlet of the HEX temp. At the end of the mash, I would like to raise the temp to 168 for mash out, but I don't want the HLT temp to get too high in the process since I am going to turn right around and use the water for my sparge. During the brew session the temp got up to 188 before I realized it, and I had to add water to cool it back down to start the sparge. Is there a way to set a max temp of say 175 in the HLT and stop the PID controller from exceeding it during the ramp up? I am sure there is a fairly easy way to accomplish this, but I have been drawing a blank for two days.

[Broph]

You could use the State Exit Conditions portion of a process...

[skinny]

I can get it to exit the state, but it exits before the mash gets to 168. I am trying to figure out how to get it to keep going without the HLT exceeding the setpoint.

[Baron Ken]

If you are using an exit condition of the Mash temp being 168, then just set the PID on the HLT to be what you want (175F in your example). It will stay at 175 and then when the mash temp gets to 168, it exits the state.

EDIT: NM, I see now that you are using the mash temp (i.e. HEX output) to control the HLT temp. Missed that, sorry.

[ECC]

I think I understand the problem.. Your PID controls the HLT heat and is associated with the HEX outlet temp. Basically there is a lag in your system due to HEX inefficiency? Or in other words, by the time that the HEX outlet registers 168, the HLT has already overshot significantly, upto 20 degrees or more.

You have quite a few options depending on how you want it to work. What do you want to happen when the mash hits 168, assuming the HLT is somewhat hotter? If you leave the setup as is, and just kill the HLT heat, the MLT will keep rising over 168 while the pump is recirculating. Is that acceptable?

Here's a few options that come to mind.

• Instead of controlling HLT with HEX temp in this state, hold HLT heat with HLT temp to 175. Create an exit condition when HEX temp >= 168 to either kill the heat or maybe even turn off the pump. You can use the Alt Pid feature to swap the temperature association of HLT heat output PID for this state.
• Heat the HLT with HTL temp to 175, and use a PID on the pump output with the MLT temp associated, held to 168. This will keep the HLT constant, and only turn on the pump when you need mash heat. The HEX temp probe probably won't be accurate when the pump is off, so this assumes that you have a probe in the MLT.
• Add a few more coils to your heat exchanger, or stir/recirc the HLT. This will increase the efficiency of the HEX such that the HEX temp and HLT temp track more closely. This will not only help this problem, but also help with holding temp during rests efficiently.
• Turn down the flow rate of the recirc. Slower flow will give better HEX tracking, although this comes at the expense of overall system heating efficiency.
• Tune the PID. Slow down the PID Sample Rate. I'm sure that PID settings/coefficients exist that won't overshoot the HLT temp as much in your system, but finding them may take some trial and error.

I'm sure any one of those solutions will work for you, just a matter of picking the 'easiest' one. I think some variation on the first option is the easiest, depending on how you want it to work. Let us know how it turns out.

[wilconrad]

I know this is an old thread, but I thought I'd post a reply as I faced the same issue. I used a PNP transistor ($1.99 at radioshack) to add a "Max Temp" feature; I associated an unused output on the BCS with the HLT temp, put it in "Cool" mode and set it to the max temp I wanted to observe (175, let's say). Therefore, when the HLT temp reaches this temp, the new output will kick on.

I put the transistor in line between the relay (which drives my gas valve) and ground, and since it's normally closed it has no impact on the ground connection during normal operation. I hooked the new "cooling" output to the base of the transistor, though, so when the output kicks on it opens the transistor and disconnects the relay from ground, turning off the heat. Once the HLT cools below 175, the output turns back off allowing the relay to connect to ground again and turn the heat back on.

Hope this helps anyone who might find themselves in this same situation.