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Old 12-09-2011, 03:38 AM   #1
kzimmer0817
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Default PID and PWM in same controller revisited

E-Brewers,

From my reading, it appears that a PWM connected to a SSR would be a simple and inexpensive way to control one's heating element manually. I'm thinking that accomplishes the same thing (perhaps not in the same manner) as the knob on the electric stove. This system would be totally manual. If I wanted to progress "gradually" into electric brewing, building/using a PWM might be a good entry point. All it does is electrify what I'm doing manually with my current burner's valve - although I would have much better control using electricity with a PWM than I do with my current propane cooker.

With the PID, I can set the temp I want, and it will power the heating element (thru a SSR) until the set point is reached. My understanding is that the element is fully on during the heating time.

When it's time to boil, it appears that folks shift their PID to manual mode and set it to a certain % of power (exact % found by experimentation). In this manner, it is functioning like a PWM - although I don't know if it accomplishes this by modifying the pulse width, but it shouldn't matter to me.

Someone mentioned that it was somewhat of a pain to set the PID to manual mode - that it took about 30 seconds to do this. If this is so, I was wondering if one might include a PID and a PWM in the same control box. I saw a thread where the idea of having both controls was mentioned, but it appeared that the PID and PWM were being connected in series. The concensus was that this was not a good idea.

My question is considering it from a slightly different angle. I'm suggesting that a DPDT switch be inserted into the circuit between the PID and the SSR where the operator chooses between PID control vs PWM control. The PID and PWM are totally separate.

I'll refer to the schematic for Johnodon's build for purpose of illustration (go to post #6 in the thread):

www.homebrewtalk.com/f170/my-official-e-biab-build-thread-269164/#post3263178

A double-pole A/B selector switch would be placed across the lavender and yellow wires that run from contact # 7 & # 8 to the SSR. I usually think of this kind of switch as a "Y" where power enters the bottom of the Y and one chooses which upper arm to send it out. In this scenario, the "Y" would be turned upside-down such that the 2 contacts from the PID would be connected to one "arm" of the Y and 2 contacts from the PWM could be connected to the other "arm". Two contacts would then go from the "base" of the Y to the SSR. This way, the PID and PWM are not interfering with one another. Of course, I would have to introduce a 9VDC circuit to power the PWM. This PID vs PWM selector switch would be "in addition to" the "Element ON/OFF" switch.

So, with BIAB, during the heating of the strike water, the above-mentioned switch would be set to "PID". During mash, adjustments will be made to the PID. Perhaps, the PID might be used to get just about to boil - perhaps even the alarm go off at 200*F. Then one might flip the switch to "PWM" and control the boil using the potentiometer on the PWM. At the end of the boil, the "Element" switch is turned OFF. With the PID still ON, the temp during cooling can be monitored.

NEVERTHELESS (emphasis), IF it's really quick and easy to get into "Manual Mode" on the PID and adjust the boil this way, then this entire message becomes irrelevant. I won't mind being told so.

Thanks,
Keith

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Old 12-09-2011, 04:01 AM   #2
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Quote:
Originally Posted by kzimmer0817 View Post
E-Brewers,

From my reading, it appears that a PWM connected to a SSR would be a simple and inexpensive way to control one's heating element manually. I'm thinking that accomplishes the same thing (perhaps not in the same manner) as the knob on the electric stove. This system would be totally manual. If I wanted to progress "gradually" into electric brewing, building/using a PWM might be a good entry point. All it does is electrify what I'm doing manually with my current burner's valve - although I would have much better control using electricity with a PWM than I do with my current propane cooker.

With the PID, I can set the temp I want, and it will power the heating element (thru a SSR) until the set point is reached. My understanding is that the element is fully on during the heating time.
PID, PWM, the knob on the stove (know as an Infinite Switch) all do the same thing. They turn the element 100% on or 100% off. PWM and Infinite Switch are a strictly manually controlled means of doing this. A PID is just smarter about turning it on and off so that it can maintain a specific temp.

Quote:
Originally Posted by kzimmer0817 View Post
When it's time to boil, it appears that folks shift their PID to manual mode and set it to a certain % of power (exact % found by experimentation). In this manner, it is functioning like a PWM - although I don't know if it accomplishes this by modifying the pulse width, but it shouldn't matter to me.
Yup. It generates a pulse, you specify an amount of time (2 seconds normally) and then what percentage of that 2 seconds you want to be ON. It's just like a PWM or Infinite Switch now.

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Originally Posted by kzimmer0817 View Post
Someone mentioned that it was somewhat of a pain to set the PID to manual mode - that it took about 30 seconds to do this.
That person might not have understood how to switch it. The Auber PIDS can be changed to manual through a menu system, or by pressing the handy [A/M] button on the front of it. Using the [A/M] button takes only a second or two.

Quote:
Originally Posted by kzimmer0817 View Post
If this is so, I was wondering if one might include a PID and a PWM in the same control box. I saw a thread where the idea of having both controls was mentioned, but it appeared that the PID and PWM were being connected in series. The concensus was that this was not a good idea.

My question is considering it from a slightly different angle. I'm suggesting that a DPDT switch be inserted into the circuit between the PID and the SSR where the operator chooses between PID control vs PWM control. The PID and PWM are totally separate.
This is exactly how my system is built. I did it simply because I wanted the ability to expand without over-purchasing control pieces. I bought a cheap PID (no manual mode) and built a PWM for like $3.

I currently do not have a dedicated HLT. I have one e-kettle that serves as a HLT and then later acts as my boil kettle. I select the PID or the PWM as the source for the SSR depending on what I am doing.

If I ever expand and add a second e-kettle, my controls are already there, I just need to dedicate the PID and PWM to the two separate kettles and get rid of the selector switch. No new control HW to buy and install.

Quote:
Originally Posted by kzimmer0817 View Post
NEVERTHELESS (emphasis), IF it's really quick and easy to get into "Manual Mode" on the PID and adjust the boil this way, then this entire message becomes irrelevant. I won't mind being told so.
It's quick and easy to flip between manual and auto mode on an Auber PID, so I guess this is irrelevant.

But at least you know that the stove knob is called an Infinite Switch now.
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Old 12-09-2011, 04:17 AM   #3
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It's quick and easy to flip between manual and auto mode on an Auber PID, so I guess this is irrelevant.

But at least you know that the stove knob is called an Infinite Switch now.
Walker,

Thanks. When something seems to make a lot of sense, but you don't see anyone else in the bunch doing it, there's probably a good reason why. I certainly don't need another switch, knob, plus circuitry if it's not necessary or helpful. So, now it's a matter of:

1. building an e-kettle
2. getting a definitive concept/design for my control box
3. get er done.

Thanks,
Keith
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Old 12-09-2011, 05:07 AM   #4
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I suggest you dont start a bunch of threads on the same subject. Yes they are a bit different i know but there all about your rig. It will be easier for people to follow along and help you if all your stuff is in one place. Then when you finish if you want to start a new one to show it off thatd be great.

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Old 12-09-2011, 12:46 PM   #5
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Originally Posted by TJTHEBEST View Post
I suggest you dont start a bunch of threads on the same subject. Yes they are a bit different i know but there all about your rig. It will be easier for people to follow along and help you if all your stuff is in one place. Then when you finish if you want to start a new one to show it off thatd be great.
i'll second that...

The switching between the two is a good idea for BIAB. If you are planning on switching to a more traditional 3 vessel system in the future you can just rewire and use the pid for HLT or MT control as it wont be needed on the kettle anymore
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Old 12-09-2011, 12:54 PM   #6
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Quote:
Originally Posted by TJTHEBEST View Post
I suggest you dont start a bunch of threads on the same subject. Yes they are a bit different i know but there all about your rig. It will be easier for people to follow along and help you if all your stuff is in one place. Then when you finish if you want to start a new one to show it off thatd be great.
Sorry, TJTHEBEST, I did start 2 threads late last night. I omitted one in which I was asking some questions about terminology. I figured that I could ask those questions along the way.

The 2 threads I started was "this" one to revisit the idea of having the PWM and PID in the same controller. I didn't want to muddy up a "build" thread with that. Later, someone else might have a similar question, and the single-topic thread might be easier to find on searching. It appears that my question was answered - just use PID, no need for PWM.

The 2nd thread is my "planning" thread where I hope to get my control box planned and receive advice. When I actually start building it - and the kettle, etc. - I'll probably change the title.

Thanks,
Keith
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Old 12-09-2011, 01:01 PM   #7
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i'll second that...
The switching between the two is a good idea for BIAB.
JTSIMS21,

Thanks. My main premise for asking about that was that someone had said that it was a pain to switch the PID to "manual" and dial in the desired % power. I figured that having a toggle to switch control of the element from the PID to the PWM would be simpler. During boil, I only need to adjust the rate of boil - nothing fancy.

Others have said that it's no problem to switch the PID to manual control. That appears to negate any advantage I might gain; therefore, it might not be worth the trouble to include it. Sure, it might be cool to have another switch and knob on the panel.

Thanks for the input,
Keith
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Old 12-10-2011, 01:49 AM   #8
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This is exactly how my system is built. I did it simply because I wanted the ability to expand without over-purchasing control pieces. I bought a cheap PID (no manual mode) and built a PWM for like $3.

<snip>

It's quick and easy to flip between manual and auto mode on an Auber PID, so I guess this is irrelevant.
Walker,

I started at the first page (earliest postings) on the Electric Brewing page and came across your thread from April 2010:

http://www.homebrewtalk.com/f51/my-h...ticism-173077/

It appears that the center portion of your diagram is exactly what I was looking for in my first post of this thread. With a switch, you are able to determine what will control your element: the PID or the PWM.

You mentioned that you had purchased a very inexpensive PID that didn't have a manual mode, so you must use the PWM to control the rate of your boil.

I'm guessing that the newer PIDs have "manual" mode and that it's easy to get into "manual" mode. Therefore, there is not much need for having both.

If you were to do it again, would you include both in your build? I'm assuming that, for 3-vessel brewing (not BIAB), you would use the PID to control your HLT. When it's time to boil, you would switch your control to the PWM and your element to the one in the BK and use the PWM to control the BK element.

I'm thinking that - if it's easy to get to manual mode on the PID - I should K.I.S.S. and omit the PWM and use the PID for both mashing and boiling.

Thanks,
Keith
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Old 12-10-2011, 04:00 AM   #9
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If I had to do it all over again I would not use separate controls. I am quite happy with the way my system works and do not see the need for a dedicated HLT.

I would just buy a PID that supported manual mode and be done with it.

Maybe someday I will add a dedicated HLT, but that would just be because I was bored and wanted something to work on.

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Old 12-11-2011, 03:51 PM   #10
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Please correct me if I'm wrong but would you want to continue controlling temperature while in PWM mode? Or am I missing something here?

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