PID ON REFLUX STILL NOT CHASING TEMPERATURE

[Slow42]

This is more of a human interest story but it also provides some we interesting information and inspiration. This is a video by George of Barley and Hops. This is about his efforts and others in helping the blind or handicapped community. The individual running this still is blind and his very inspiring! Regardless of your opinion of George this is an interesting video worth watching. Enjoy!

[GCB3]

Slow42, thank you for posting this. I’ve been 80 to 90% blind the last year and a half which makes this hobby even more challenging! I want to listen to this video but I cannot get the volume to play. Is it just me or are others having this problem? Thanks again for posting this.

[GCB3]

Opps, it was me!

[6 Row Joe]

Thanks for posting. I have been following George's progress on this project. Cool stuff. He just released a 4 part 240 volt pid controller. I have built his 120 v. pid and pulse width modulator. Both work very well for me.

[Slow42]

GCB3 I tried the volume and it is low. I’m using an IPad so you can just raise the volume on the IPad it’s self and you then can hear and just the video. Not use if you can do that with a PC but I can’t see why not.

George shows how to build the unit in a separate video all the parts and pieces. It’s easy to build but the code needed to make it work can be challenging. He is more than will to help though. Glad you enjoyed the video. The operator of the still is amazing in how he runs it.

[Slow42]

6 row joe he makes making a PID, SSVR, PWM controller enjoyable. Everything in detail down to wiring it on the board where you can follow what he’s doing vs just listening.

[Tennessee_Spirits]

After dozens of runs using George's PID design with SSR I could not stop the temperature swings at the still head in pot or reflux mode. I did find that putting the 3 gallon boiler on a stove top and letting it provide 1/2 the heat reduced the swings considerably. It was not just temperature swings. The still out put would go from a pencil stream to stopping every 2-3 minutes.

It was easy to see that this was a thermal feedback loop or relaxation oscillator. The temperature would rise and the PID shut down and then the column would cool and output slow then the PID would increase activity and output would rise rapidly and the process would repeat itself.

So I asked George what was going on and he wrote back (he is good about that) that surface tension was causing the oscillation.

So I added a PWM control to my PID controller. After all, the PID is great for heating water without a boil over or heating to a set temperature such as strike water or sparge water.

It looks like this

The way it works is that there are two SSRs and heat sinks. The SSR provides isolation with the power circuit which can be 120 or 240 volts AC. The meter is actually a square wave generator (Amazon) that displays its percentage on time.

In operation either system can be used as desired. It still provides full PID functionality when the PWM is turned down and PWM control that is very precise when the PID is set low.

[LWTCS]

So I asked George what was going on and he wrote back (he is good about that) that surface tension was causing the oscillation. 

Really?
It's good if you've been able to get more compliant behavior to be sure.
The production slow down comes from the target temps being achieved and the PID killing power to the element.
Any practical interruption (cycling) in power input will drop vapor out of suspension.
Dropping vapor out of suspension is not at all optimal for isolating constituents.

[StillerBoy]

After dozens of runs using George's PID design with SSR I could not stop the temperature swings at the still head in pot or reflux mode. I did find that putting the 3 gallon boiler on a stove top and letting it provide 1/2 the heat reduced the swings considerably. It was not just temperature swings. The still out put would go from a pencil stream to stopping every 2-3 minutes.

You have now experience using a PID, but haven't learn from the experience.. adding more items is not improving an item that was not design for the application in distilling..

As it seem you have funds to waste, try a simple SSR with a potentiometer, and see the different in performance and behavior..

Mars

[jonnys_spirit]

What's surface tension?

Cheers,
jonny

[Berserk]

As it seem you have funds to waste, try a simple SSR with a potentiometer, and see the different in performance and behavior..

Mars

I think the PWM generator works more or less the same way. He turns a knob to set a percentage and it switches on the element that percentage of time (e.g. 75% is 75ms on, 25ms off, 75ms on, 25ms off and so on), effectively outputting that percentage of it's power. Same as the potentiometer and the SSR, but a slightly different implementation.

[LWTCS]

What's surface tension?

Cheers,
jonny

Well,,err,,not what George thinks it is.

[NZChris]

Now try disabling the PID control and only using it as a thermometer.

[seabass]

Pids are great for heating up strike water. All you need to do now is add a proper controller for the still.

[Yummyrum]

What's surface tension?

Cheers,
jonny

Its what causes a drop of water to stay in a neat little ball while a drop of Alcohol falls into a flat pool .

It’s also why a sight glass is fogged up when its got mostly water vapour in it while its clear as when there is lots of Alcohol vapour in there .

I like Larry’s answer better .

Pids are great for heating up strike water. All you need to do now is add a proper controller for the still.

[Saltbush Bill]

What's surface tension?
Cheers,
jonny

Its the cause of all evil according to George
Fortunately most people here know better.

[Tennessee_Spirits]

What I like about this forum is the diverse perspectives. There is a lot of collective experience here. Yes, George has a few things wrong and many things right. The square wave generator produces the necessary control over on and off times and it displays that percentage. But it is functioning like the potentiometer but of course there is additional circuitry to trigger the triac hidden in those boxes.

Cost of any of these DIY control projects is a fraction of what an electrician charges to just bring power to where you need it.

It is possible to change a menu setting on the PID and have it do PWM control of the still. But I would rather have more complexity in the controller and more simple operation. It cost about $30 to add this feature to the PID and the PID is great in control of heating. The PID takes the still head to where it just starts to produce and usually avoids puking, but not always and it frees me during warm up to set up the cooling water and collection. Then I found as most of you that PWM control of distillation is better, at least at this hobby scale, regardless of what George says.

I think George has been very busy building and selling those PID controllers. At last report he was at about 500 sold.

[NZChris]

I think George has been very busy building and selling those PID controllers. At last report he was at about 500 sold.

Having that on your record and getting income from it, it would take some big kohones to own up when you realised you had it wrong

I won't be holding my breath.

[Saltbush Bill]

I think George has been very busy building and selling those PID controllers. At last report he was at about 500 sold.

Thats just great , we can look forward to about another hundred or more unhappy newbies turning up here wanting to know why their stills don't work properly.

[jonnys_spirit]

500 units sold? How’d you come up with that # Tennessee?

Cheers,
Jonny

[Sulaiman]

Just to state the obvious that is implied in some of the responses above...
The temperature at the top of a column is determined ONLY by %ABV and (atmospheric) pressure,
a PID controller is worse than useless in this situation as it would cause significant swings in heating power, causing changes in vapour velocity, upsetting the equilibrium in the column.
He/we would be much better off using constant heating power.

If really want some kind of automatic control then I suggest that it should be controlling the heating power to maintain a constant pressure difference between the top and bottom of the column,
which gives a near constant vapour velocity.
I suspect that a practical implementation may not be worth the effort.

[NineInchNails]

Tennessee_Spirits, if you get two cheap PC fan guards/covers it would allow you to cut out large openings to get significantly better air flow in comparison to the flow you get with drilled holes.

[cob]

What's surface tension?

Cheers,
jonny

surface tension is what makes a rain drop try to be round.

it is also what allows you to pour water into a glass above

the rim without spilling. or float a paperclip on water.

[still_stirrin]

What's surface tension?

Cheers,
jonny

Here's the explanation from Wikipedia: (look it up to learn more)

Surface tension is the tendency of liquid surfaces to shrink into the minimum surface area possible. Surface tension allows insects (e.g. water striders), usually denser than water, to float and slide on a water surface.

At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). The net effect is an inward force at its surface that causes the liquid to behave as if its surface were covered with a stretched elastic membrane. Thus, the surface comes under tension from the imbalanced forces, which is probably where the term "surface tension" came from.[1] Because of the relatively high attraction of water molecules to each other through a web of hydrogen bonds, water has a higher surface tension (72.8 millinewtons per meter at 20 °C) than most other liquids. Surface tension is an important factor in the phenomenon of capillarity.

Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the term surface energy, which is a more general term in the sense that it applies also to solids.

In materials science, surface tension is used for either surface stress or surface energy.

[acfixer69]

It appears that some folks will take pids off topic to continue the wars that have been settled.