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Old 02-16-2009, 04:10 PM   #1
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Default PID, Love, Ranco arggghhhh...

Hi everyone, frequent lurker, infrequent poster, basic noob here!

I have been reading about setting up an electric brewery, especially Pol's threads listed here:

http://www.homebrewtalk.com/f51/pols...6/#post1038184

I have a question about controllers since I do not know that much about them, specifically, why would you use one over the other? What are the benefits of a PID over a love controller or a ranco and why do you need an SSR with the PID?

If I am installing a hot water heater in my HLT to heat strike water and for a HERMS coil, and installing one in my BK to boil the wort, wouldn't a simple love controller work for both. What would I need the fuzzy logic of a PID for?

Sorry for all the questions, but I would certainly appreciate any help.

Dave

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Old 02-16-2009, 06:09 PM   #2
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Can only answer some of the questions, since I've been toying with the idea of an electric build but haven't actually done it yet.

Quote:
why do you need an SSR with the PID?
The PID outputs a low amp/low volt signal when it decides the element/pump/whatever should be turned on. The PID itself is not capable of switching the 120/240v high amperage connection needed by a heating element. The SSR is basically just a switch that can handle the volts and amps. The PID monitors the temp and says WHEN to switch, and the SSR is on your power feed and does the actual switching.

Sort of like you holding a thermo in your HLT, and telling your buddy holding the extension cord when to plug/unplug the heating element.

*note* - I think some PIDs are available with a built in relay, but I'd imagine it'd be better to get them separately because it's A:cheaper to buy, and B: cheaper to fix/replace

Quote:
What are the benefits of a PID over a love controller or a ranco
Depending on the model you get, a PID can also offer more options such as setting a timer so your strike water is ready when you wake up or get home from work.

I'll let other folks with more experience chime in though.
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Old 02-17-2009, 11:23 AM   #3
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Thanks caspio, that helps clear a few things up. I really appreciate the reply!

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Old 02-17-2009, 11:52 AM   #4
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Yes...

The Ranco/Johnson controllers are basic ON/OFF controllers and do not have any "learning" capability. The PID can be programmed and learns from your system, it learns the lag time and things of that nature when heating so that it can anticipate temps and stop a temp overshoot before it happens (within reason)

The Johnson/Ranco controllers are only capable of switching 15A... which when you are dealing with anything over 1650W, will, simply not work. They are nice, they are simple, but they are not very capable.

The PID is a "smart" controller as stated.... some PID have a 10A relay in them which makes them great for a fridge controller, but not for an electric heating element controller. If you couple the PID output (on/off signal) to an SSR though... those things are capable of switching huge loads. I use a 40A SSR on my rig to switch my 25A load from my boil kettle element. Dont forget the heat sink as well... the SSR gets hot while switching those large loads, so a decent heat sink is required as well to extend the life of the SSR.

The nice thing is that in most cases you can get a PID, SSR and heat sink for less than a Ranco anyway, and it is a much more capable setup.

Pol

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Old 02-17-2009, 02:12 PM   #5
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Another option for a temperature controller is the BCS-460. Its programmable, so you can control a heat source differentially (like a Ranco), or with a PID algorithm. One 460 can control upto 6 outputs (SSRs required), and 4 temperature probe inputs, and more.

You could even use both types. You can control one stage of your process with differential control, like heating your Strike water, and then switch over to PID control to maintain the Mash temps on the same element. Its extremely flexible, if you don't mind a little learning. Plus you get data logging and graphs to monitor and learn from your brewdays.

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Old 02-17-2009, 02:52 PM   #6
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Thanks Pol, I didn't want to high jack any of your build threads so I was hoping you might find this.

I am beginning to understand the choices you made now. What threw me off was where you said that you run the BK PID on manual and only have the thermowell attached because the PID needs it to run and the byproduct was being able to watch your wort cool.

It seemed that if you were running it on manual, then you didn't need functionality that it offered so why not use a love or ranco. Now I see that you need it because of the load.

Thanks!

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Old 02-17-2009, 02:58 PM   #7
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A nutshell description:
No controller will absolutely hold a precise set point. It is always dancing on either side. Whether it be a motion control, temperature control, pressure control, or flow control loop.

It all boils down to how much over/under shoot one can live with in the design parameters.

An on & off controller is simply that. If the live situation, on one side of the set point the output will turn on to correct. This typically ends up in an overshoot situation, which cause the output to turn off. This typically ends up in an undershoot situation that turns the input on. Hence the dancing around set point.

PID stands for Proportional, Integral, & Derivative. We naturally perform this each time we drive a car. Picture trying to merge with traffic on the highway. The proportional is the window of position you want to obtain. In this example, maybe 60-70 MPH. One has to press the gas pedal. This is the integral. The amount of throttle one puts into the situation to obtain set point. Once one is close to 60-70 MPH one will ease off the throttle. This is derivative. The amount one eases off the throttle. Eventually by performing this sequence repeatedly, we end up dancing around our set point of 65 MPH.

As one can see a simple on & off controller would not perform very well in our example.

Essentially, a PID controller has the capability to control the amount of throttle to get towards set point and begin to throttle itself back before it actually gets to set point. Thus minimizing over & under shoot situations.

Is this as clear as mud?
I hope it helps.

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Old 02-17-2009, 03:24 PM   #8
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You are right, I use the PID in manual (% output) for the BK.

The JC A419 works really well in the HLT for the HERMS portion since it is not really controlling a process. It is only controlling the HLT temp. My mash temp is monitored with a through the wall digital thermometer, and it varies by +/- .25F according to the thermomter.

The PID % output is great for maintaining a boil. I can keep a NICE viforous boil going at 65% with my 5500W element in 40F weather.

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Old 05-30-2011, 02:14 PM   #9
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Thanks so much for the tip towards the BCS controllers!

I've been researching my own e-brew system design and have recently been mulling over PID/controller options. Having studied computer science (and a bit of electrical-computer engineering), I had been considering trying to write some controller logic to have embedded in a chip since the various options fall short of full control and very little useful logging available (at least without lots of custom parsing once downloaded). The BCS controllers (for those who don't know of them yet, the BCS stands for BREWERY CONTROL SYSTEM!!! ....why the heck people are jerry-rigging with Rancos and such I have no idea).

My design thoughts just received a serious "gotta rethink this now" jolt!

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