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Old 10-01-2012, 01:42 PM   #11
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Originally Posted by Ragtop232 View Post
Keith, the PWM/control knob on this device does not cycle the element. The element will be on 100% of the time, but the PWM will vary the wattage to the element. Think of it like a dimmer switch on a light bulb.

This is incorrect. A PWM controls the percentage of the frequency the control circuit is off/on. The off or on is 100%. At 50% the control circuit is on 100% for half the time and off 100% for the other half of the time. Most PWM's use very short frequencies so it appears the device is running on lower power.
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Old 10-01-2012, 02:19 PM   #12
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Actually, now that I think about it, the PWM is actually going to be detrimental. The PID has an auto-tune mode wherein it actually cycles several times and learns how fast your system heats up and cools off in order to anticipate how fast/how much/how long to apply power to keep the temp constant. This is how we set up our PID parameters.

Now......that happens if you set your system up and the PID "learns" it's setting with the PWM cranked to 100% cycle BUT then on brew day you decide to turn the PWM down to 50% cycle? Now the algorithm that the PID uses is not going to be correct because even though it is cycling the element as it did when the PWM was at 100%, only half of that power cycle is going to be applied to the liquid and the temp will not increase as fast as the PID expects it to. The results are going to be that the PID won't be able to maintain temp properly unless you run the whole "auto-tune" process again with the PWM set at 50% cycle.

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Old 10-01-2012, 02:50 PM   #13
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Post How it works

Hi Guys,

This is Dave, the guy in the video.

We take a different approach than most people when we build brewery controllers. This is because we started several years back with manual control, and developed our own analog power modulation circuit. We like it so much, that we have continued to include it in all of the next generation controllers. We do not use an SSR at all. We use two mechanical relays, and switch both hot wires so that when it's off, it's off. The PID is operating in the simple thermostat mode, and the power level is modulated with the TRIAC based circuit. We modulate the pulse width of each half-cycle of the line power.

While some might say, Why use a PID in simple thermostat mode, when you can pulse an SSR and let it Autotune?" We say, "Why would you want to control a boiling kettle with up/down buttons?

Cheers,
Dave Knott

High Gravity
7142 S Memorial Dr
Tulsa, OK 74133
(918) 461-2605

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Old 10-01-2012, 02:59 PM   #14
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Todd and I were just discussing this. I'm glad he posted his concern to the forum. I had wondered if the PID might start cycling/pulsating the current to the element as it reached the set temp.

Having a PID and a PWM wired in series (or in-line) is analagous to a pair of 3-way switches connected to a light bulb. If you have 2 kids operating these 3-way switches such that 1 switch stays on and the other is flipping on/off - e.g. 1 sec on 1 sec off for 50% of a 2 sec frequency - then the light will be on 50% of the time. If they are both flipping their switches at exactly the same frequency and for the same portion of each cycle, the light will either be ON all the time or OFF all the time depending on where they start their flipping. Really confusing is if they're flipping their respective switches at completely different frequencies and at different pulse-widths. There will be a stuttering ON signal sent to the SSR. I'm thinking that the control signal going to the SSR would resemble a Morse code message - only very rapid. Might this cause undue stress on the SSR and premature failure of the SSR?

So, I reiterate, that the only logical way for this to function appropriately - unless I'm not understanding the logic - is (1) for the PWM to be at 100% (if it's possible) during ramp up and mash and (2) for the PID to be in Manual Mode at 100% if you want to control the temps with the PWM.

Ragtop, I wonder, since you and Dave are communicating, if they might be willing to add a DPDT selector switch to this controller (PID/PWM) in order to make it more functional? One can select PID during the heating of the strike water and during the mash. Then, you flip the switch to PWM to get to and maintain the boil.

Respectfully,
Keith

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Old 10-01-2012, 03:15 PM   #15
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Quote:
Originally Posted by DaveKnott View Post
Hi Guys,

This is Dave, the guy in the video.
Dave,
Thanks for weighing in on this. I'm sure that there will be other question, so please stay tuned. You might find a great market here for the EBC-SV.

One quick question: my understanding of why folks use SSRs instead of mechanical relays is that the mechanical ones would wear out at the pulse frequencies used by PIDs and PWMs. I don't guess this has been a problem in your controllers since you've been doing this for a good while.

I'm sure that I could build a controller, but I'm not sure I want to put myself thru the challenge with everything else I have on my plate right now. I'm trying to build up a comfort level with this controller (your product) using information I've gleaned from studying various e-build postings on this Forum.

Thanks,
Keith
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Old 10-01-2012, 03:20 PM   #16
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OK, I was completely wrong in how this works. I was thinking the PWM or varying the wattage via the analog knob is what was being referred to as the PWM. I'm sorry for the mis-information and wrong answers. I think Dave has answered the questions in his above reply.

I will delete my posts so as not to confuse anyone looking at this thread for answers as to how it works.

Jim

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Old 10-01-2012, 03:59 PM   #17
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Dave,

Thanks for the answers! I'm not aware of a simple thermostat mode for a PID. It looks like you use Auber PID's and so do I, but I've been through the manuals and can't find a simple thermostat mode for it. How is this accomplished?

And honestly, you push 1 button to get into manual mode then push another to set the percentage. It's almost exactly the same as changing the temp for mash out, but I understand your logic now.

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Old 10-01-2012, 04:11 PM   #18
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Appreciate the explanation too Dave, I guess the only question that I have is why install that nice multi-functional SYL-23xx PID when you're simply going to use it as a "dumb" t-stat? Why not use a base model PID like the SYL-1512A so that all the additional features (PID, manual mode, alarms, etc) aren't going to waste?

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Old 10-02-2012, 03:46 PM   #19
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We like the SYL-23XX series controller because it displays the set point and the measured value simultaneously.

Setting the parameter At=0 puts the controller in thermostat mode.

Since the thermal mass of a hot liquor tank is fairly large, once the temp has reached the set point, the heating element spends most of the time in the off state. There is really no need to use any fuzzy logic here. Simple thermostat mode will maintain the temperature very well. But people can still play with the Autotune parameters here if they want to. You would just want to have your cycle time (t) set to 20.

There are many ways to put together a brewing system that does the job very well. Since we are designing controllers for people that didn't build their own, we wanted the operation to be simple and straightforward for everybody. Twisting a power knob is something that everyone understands.

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Old 10-02-2012, 03:55 PM   #20
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Understood, thanks for the reply.

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