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Using a PID to control solonoids in a herms build

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chefg1124

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Hi. So I am my current MLT is a cooler. I would like to start playing around with stepped mash Temps. I was looking into a rims system but I like the qualities of a herms better. My hlt is also a cooler. So my plan was to place my mlt cooler next to my burner and have a pot of boiling water with a coil in it. I would like to create 2 loops. The would both start at the bottom of the mlt and go to a pump. Then they would hit 2 solonoid valves. If the pid temp is satisfied the loop would just recirculate the wort back up to the top of the mlt. If there is a need for heat 1 solonoid would close and 1 would open to the coil and the wort would circulate through the hlt and back to the top of the mlt. I was going to have 2 solonoids at a T on the return to the mlt also but I dont know if thats overkill. My question is how do I wire up the solonoids to the pid. Is this an easy task? I have 0 experience with pid controllers but I have knowledge of electrical circuits. My extent of experience with solonoid valves is my sprinkler system. I need a simple closed open function. Thanks for any input!
 

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Brumateur

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It's not hard to wire valves to PID and it will work mostly as you expect. However this design has 2 big problems.

- Boiling water in HLT. To maintain an MLT temperature PID will switch circulation path back and force and while "short" loop is engaged portion of your mash in HLT coil will quickly get heated close to boiling temp. As a result all enzymes at that portion will be destroyed. Then when MLT get slightly cooled PID swict loop back to HLT and that portion with "dead enzymes" goes back to ML . Yes it a small portion and one of it doesn't change to much. But it will be repeated again and again.

- What is a resource of your valves? PID will engage them every few seconds . Check your valves datasheet and calculate how many hours they will last .
 
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chefg1124

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This is a very valid point. I really don't want to damage any of the wort and doing so an oz at a time could add up over the course of an hour. I would need to clear the coil of wort or not keep it at boiling. Not keeping it hot enough will take too much time if I do a stepped mash. Thanks for the input!! Its greatly appreciated.
 

Brumateur

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Install a 120v heating element it to your HLT and use PID to control it. Use burner to preheat water close to mashing temp then switch to electric heating to maintain desired temp. 120V will be enough since you need only 200-500Watt to keep a temp.
 
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chefg1124

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I know thats technically how its done in herms system. How about stepping the mash. Its not a nessesity right now but the boiling water (which I now think is not such a good idea) would allow me to step. If I put in a bigger element i asume I could raise the temp faster. How big and do I need a 220v line (which I was trying to avoid)

Also do I need some kind of motion in my hlt so the water is being circulated around the heating element so the whole body of water stays constant?
 

Brumateur

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How big is your HLT? And How fast you want heat it up?
You don't need to do anything special about water circulation at HLT. A natural convection will do it for you.
 
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chefg1124

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I have a 5 gallon pot i dont need it completely full but let's say 5 gallons just for the fun of it. I haven't dove into stepping yet. But figure if if I want to raise the temp 30 to 40 degrees that should cover me. Again I am not savy with stepping yet so how long should I shoot for to raise mash temp. I just want the capabilities of doing it but want to make sure I have enough juice.
 

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120V 1500Watt is OK for stepping 4 gallons of mash. Though initial heat up and boiling will be slow. So if you can use burner as an aux for preheating and boiling you are fine with 120V . Without a burner it will work as well but will add a couple hours to your brew day.
 
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chefg1124

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Ok cool. I will look into that. I planned to heat the water on a burner. The element will be to maintain and then at some point step the mash. Thank you all for your help!! I will begin to gather my supplies now.
 
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Just FYI, I run my gas fired HLT with coils and HERMS this way too. I keep the HLT at ~165'F and then have ASCO solenoids that bypass or circulate into the HLT coil. You could also just stop running pump, but I like to continue circulating in Mash to keep temp more even. Just a couple notes here.

1) You show needing four switches (SV). You only really need two or a single "3-way" valve (one in the upper leg of the coil path and one in the bypass path wired opposite control polarity or one in the lower leg...but not both). More over, I have a "manual" one in the bypass leg, just so it is easy to tell which leg it is running. Also, and I made this mistake myself...NEVER EVER put a valve on the INLET and OUTLET of your HERMS coil. Even in the BEST intentions or normal operation with correct wiring, IF you ever in a fault case or manually leave one closed and the automated switching is bad, you can create a case where the coil is closed.

IF YOU EVER HAVE BOTH inlet and outlet valves closed, and do even 5'F temp change (like say you have them closed and start heating your HLT from 165'F to 175'F to mash out), you will EXPLODE your coil system. there is an INSANE amount of pressure that builds from thermal expansion of liquids (or contraction if cooling). Mine, blew apart the copper soldered fittings on the inner coil due to heating 50-foot of coil only 10'F. I've seen coils collapsed from cooling while closed and copper pipes split open. Fortunately I was not injured, and I just had to remove one valve and repair the system. Don't EVER allow a completely closed loop to exist where temp will be changing!!!

2) While many have commented to just run HLT near your mash temps, and that works, I like being able to start stepping the HLT higher and still recirc but not expose to the HLT temps...so just like you draw (with caveat in #1) I bypass on a temp controller in MT.

3) Lastly, I made my solenoids be "NO" so that when de-energized, they actually drain so it is easy to clean (and just flip the manual valve in the bypass leg to force the clean up through the coil, etc.) This also makes it so a solenoid failure should fail OPEN not closed.
 
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