HLT PID controlled from MLT temp probe?

lasersnake · Joined: 23 Jan 2018 Posts: 10

Hi Everyone,

Has anyone tried controlling the HLT temp (therefore the MLT temp) by plugging the MLT temp probe in to the HLT PID?

I am very new to all of this and just trying to think logically that controlling the mash temp is the end game here so why not just use that temp probe? In the end I am planning on automating the whole brewery and will have a micro-controller with a cascading PID using both temp probes but for now I have Auber PIDs.

This topic has probably been thrash.. appologies if I couldnt find an old thread covering the same topic!

sillbeer · Joined: 15 Sep 2016 Posts: 44 Location: West Point, UT

When I first started brewing with an electric controller a couple years ago I started off by doing this. I would get some wild swings by 10 degrees or more and couldn't understand why. After I started controlling the HLT and monitoring that temp my swings went away. The controller I had could only handle one element and monitor one temp so I had to monitor the gauge in the MLT for comparison. I was usually about a degree off and would consistently maintain that. It was a world of difference and my frustration went away.

**kal** · Posted: Sun Jun 10, 2018 1:27 pm Post subject:

Welcome the forum!

This question comes up from time to time.

Further decoupling this like isn't something I'd recommend. You do control the MLT temp through the HLT temp - they're directly connected but I feel it's better/safer to control the heat source (HLT) directly as the flow there never stops if you follow my design (the water is constantly recirculated).

Decoupling too far (controlling HLT heat by MLT temp) can lead to serious issues if you ever have problems with flow in the MLT where the HLT tries to compensate. While you shouldn't have flow issues if you use my recommended parts and process, not everyone does, so having a stuck flow in the MLT could lead to dangerous temp conditions in the HLT if you decouple like this.

Decoupling like this also does not offer any advantages as far as I can see, but I've seen some people do it probably because they think it's better to control the mash more "directly". But it doesn't work that way: You're heating the HLT to whatever you want the mash to be and the mash simply follows. In effect it's a more direct control. Decoupling will always lead to larger deltas and less rigid control of temperature.

That said, people will often built their setups differently/have a different brewing process. Feel free to use whatever works best for you! Good luck!

EDIT: Another thread on this subject another forum I found when Googling: https://forum.embeddedcc.com/viewtopic.php?t=2845

Kal

perogi · Posted: Sun Jun 10, 2018 1:29 pm Post subject:

I'm wondering if the lag in temperature changes would cause the swings described by sillbeer. Remember how much mass the mash has compared to the water in the HLT - the HLT will continue to rise in temperature (way overshooting the desired temp) while the mash is trying to catch up.

imo - go with the tried and true.

**kal** · Posted: Sun Jun 10, 2018 1:38 pm Post subject:

A PID is an intelligent device and should in theory be able to adjust for that if the behaviour of the system is steady and repeatable. The problem is that it isn't... it's too far decoupled and brewers may do things like turn off or slow down their mash pump sometimes for whatever reason. Or flow may be restricted slightly in the mash at the start until the grain bed adjusts and settles properly... this confuses the PID.

Kal

Ozarks Mountain Brew · Posted: Sun Jun 10, 2018 5:44 pm Post subject:

I have a slightly different set up, and have had it hooked this way for a year with no issues, I have a bottom drain for my mashtun and I put a temp probe there and have a pid displaying that temperature but I also have a temp probe right where the wort is going on top of the grain and that is hooked to an EZboil, so on my panel I have a mash in and a mash out and I can see the difference and there usually is for the first 30 minutes, it will eventually catch up but, I don’t really care what temp the hlt is the EZboil will turn off the power if the wort gets to the set point, I have it set where it will never overshoot, it took a few brews to get it dialed in but I’m liking it

perogi · Posted: Sun Jun 10, 2018 7:49 pm Post subject:

Ozarks - so if I understand you correctly, the temp probe is only for the wort coming into the grain and *that* controls the HLT element.

Ozarks Mountain Brew · Posted: Sun Jun 10, 2018 7:55 pm Post subject:

correct these arrows show where the temp probe's are hooked, bad angle but the wort is coming out of the coil on the bottom and goes into the grain, I have a 3 way there to divert either up to the mash or out to the fermenter because I chill with the HLT coils