RIMS PID help

[Cajun_McChicken]

I've got a single PID (budget Chinese type, MyPin TA4) powering a ULWD 5500W element running on 120v in my RIMS tube.

I recently replaced the HWD 1500W element I used to run in the RIMS tube with the one mentioned above. The problem I'll describe didn't pop up until I made this change, but I'm not sure why switching the element would have anything to do with it. Anyhow, here's my issue:

When I restrict the flow out of my chugger pump so as to recirculate without a stuck mash, the PID seems to lose it's ability to hold an exact temp. For example, it is set to 166 F right now with about 33% of max flow and the PID keeps bringing the temp up to 168 then down to 164, then back up again. I've tried using the auto tune feature a number of times but it doesn't seem to help. If I turn the pump back up to full output, the PID works perfectly.

Can anyone shed any light on this for me?

Thanks!

 

[rgauthier20420]

How was the pump flow when you ran auto tune? You should run auto tune with a similar flow rate so it's able to learn accurately.

 

[Bobby_M]

How do you have the temp sensor mounted?

 

[EODtony]

How do you have the temp sensor mounted?

+1 If your not getting a constant flow at the temp sensor the PID can't update properly.

Had similar problem trying to run one of my RTDs in my site glass T.


Sent from my iPhone using Home Brew

 

[Cajun_McChicken]

How was the pump flow when you ran auto tune? You should run auto tune with a similar flow rate so it's able to learn accurately.

I turned down the pump to the flow I wanted to recirc at before running auto tune.

My RTD sensor is mounted in one of your 18" RIMS tube kits Bobby. Though there isn't much space between the end if the heating element and the tip of the RTD... The RTD is a little less than 4" and the element is about 12" so only about 2" of clearance.

More info: element is a 5500w camco ULWD straight fold-back "lime life" (whatever that means), and the RTD I got from a link to auber inst. on another thread about bobby's RIMS tubes.

 

[Protto]

Did you autotune after installing the new element? It may have similar amount of power, but might have higher thermal mass. That could affect things. Any little change may need a following autotune.

 

[Cajun_McChicken]

I have auto-tuned since installing the new element, but that raises another interesting question: how often do most people auto-tune their PIDs? Every time you change the flow rate? Does it matter if you're running hot liquid or cold liquid when you auto-tune?

With regards to my issue yesterday, I eventually solved it by slightly upping the flow rate. The auto tune worked then (kind of; it held a constant temp 2 degrees higher than the set temp so I compensated by lowering the set temp).

Trial and error I suppose...

 

[Protto]

Autotuning works best when you have as real-life conditions as you can. Generally you have aprox the same flow from batch to batch. You may have a little more or less grains and total water, but that won't affect things to much, as long as you don't have your probe in the middle of the mash.

It is best to manually heat up the MLT to mash temp and run autotune when temp has stabilized. Preferably with grains and everything. You can use spent grains if you want to.

 

[augiedoggy]

I have auto-tuned since installing the new element, but that raises another interesting question: how often do most people auto-tune their PIDs? Every time you change the flow rate? Does it matter if you're running hot liquid or cold liquid when you auto-tune?

With regards to my issue yesterday, I eventually solved it by slightly upping the flow rate. The auto tune worked then (kind of; it held a constant temp 2 degrees higher than the set temp so I compensated by lowering the set temp).

Trial and error I suppose...

I also have this issue with both types of pids I use... sometimes they sort themselves out and learn quickly other times not so much...

I do believe it the way I have mine wired that messes up thier learning curve...

When I move my element power selector switch from HLT to BK the HLT pid is still on and trying to learn how to get to the temp setpoint even though the actual element power has been severed... so the logic gets all out of whack trying to make sense and adjust to reach the setpoint even though it cant...