Brewzilla Gen 4 PID

[tondy79]

First of all, I'm not sure that this is interesting. It seemed interesting to me, but I am perhaps a dull person.

I was running a test for PID settings the other day, and up to now with my Brewzilla I have always set the heating power to ~30% for mashing as this seems to be the common wisdom for avoiding overshoots.

In test however (with 26l water and no grain), having heating elements at 100% and relying on the PID resulted in a nicely ramped approach to mash temp and then held stable for 15 mins or so before I pressed on to boiling point.

Incidentally, the couple of "blips" on the way to the boil seem to be my wife turning on the food mixer, and then the plateau is her boiling the kettle. She didn't even make me a cup of tea.

Anyway, does anyone know whether the heating power really does need to be dropped when PID is on?

Cheers!

 

[The-Engineer-That-Brews]

I was running a test for PID settings the other day, and up to now with my Brewzilla I have always set the heating power to ~30% for mashing as this seems to be the common wisdom for avoiding overshoots.
In test however (with 26l water and no grain), having heating elements at 100% and relying on the PID resulted in a nicely ramped approach to mash temp and then held stable for 15 mins or so before I pressed on to boiling point.
Anyway, does anyone know whether the heating power really does need to be dropped when PID is on?

Very good idea to do a test, you can't beat having a bit of real data to work with

I don't have any experience with all-in-one's, but you might find the results are a bit different when you've got grain in because the wort takes quite a while to flow down through the grain. Time delay is a menace when it comes to control systems and can easily result in more overshoot. [edit: thinking about it, time delay probably won't have much of an effect for you because your PID is controlling the temperature of the wort in the sump]

Also in many cases a constant temperature ramp (of the recirculating wort) might not be what you're looking for: typically the aim is rather to get the majority of the grain from temp 'a' to temp 'b' reasonably quickly in order to get the most out of the enzymes. Usually a bit of overshoot (of the recirculating wort temperature) doesn't really matter, because the temperature of the grain bed only changes pretty slowly. Also it's surprising how much the temperature of the grain can differ from the temperature of the recycling wort: with thicker mashes I often find it can be a good 1-2 degrees lower for the first 15 mins, which is a country mile in terms of enzyme activity. When aiming for a specific mash rest it might be worth sticking a probe into the grain...

FWIW with my setup, at a reasonable mash thickness the wort travels down through the grain at about 5-10cm per minute - so while recirculating it ends up spending about 80% of its time in the grain-bed compared to the time in the 'sump' and the heat exchanger

PS: I very much doubt that the heating rate dropped because of other appliances being used in the house: that could only happen if the mains voltage was considerably reduced (and if that's happening you seriously need to get your wiring checked)

 

[The-Engineer-That-Brews]

In case it's of interest, I did some measurements a while back of the temperature at different depths of the grain bed versus the temperature of the recycling wort, during a mash step (https://www.thehomebrewforum.co.uk/threads/monitoring-mash-temps-results.94598/)

 

[tondy79]

FWIW with my setup, at a reasonable mash thickness the wort travels down through the grain at about 5-10cm per minute - so while recirculating it ends up spending about 80% of its time in the grain-bed

Interesting! Thanks for all the info, and intrigued to know how you measured this flow rate?

Also worried that I need to get the wiring checked now! It's an oldish house I'm in here

 

[Twostage]

What PID settings did you use ? And do you have the RAPT probe ?

Obviously the heater should be 100% when you are ramping up to temperature as you want to get there fast and the PID algorithm should get the water to the target temp quickly without overshooting.

I'm not 100% convinced that a water only test replicates a mash as when its just water the heater is heating the water and that's it. With a mash the heater is heating the water and the water is heating the grain.

If I remember started off with keeping the heater at 100% during the mash but I was getting temperature fluctuations and now I reduce it to around 40% and it seems to work well for the mash at that level. Might need to test that again.

 

[tondy79]

I was using 26l water with setting p0.58 and i0.15

I do have the RAPT probe.

Definitely agree that water only doesn't replicate the mash experience, I was just surprised that it hit temp and maintained it so smoothly, even with water.

I've done ten or so brews and having researched fairly heavily before purchasing I have always set to around 30% power when approaching mash temp and have had good results, but it does irk me that I have to do this, and that I cant program it to happen!

 

[gavp1979]

You might have already seen it but here is David Heath giving his suggested starting points for the PID settings in a G4

 

[Twostage]

I was using 26l water with setting p0.58 and i0.15

I do have the RAPT probe.

Definitely agree that water only doesn't replicate the mash experience, I was just surprised that it hit temp and maintained it so smoothly, even with water.

I've done ten or so brews and having researched fairly heavily before purchasing I have always set to around 30% power when approaching mash temp and have had good results, but it does irk me that I have to do this, and that I cant program it to happen!

There is a fairly busy GitLab site for RAPT and a backlog of feature requests for the BZ including being able to control PID settings, heating %age etc. in profiles.

It does make sense - step 1 (strike), PID on, P=X, I=Y, Heater 100%, target 67c, alarm when target reached, next step on button press. Step 2 (mash), Heater 30%, target 65c, time=60 mins, alarm when time reached, next step on button press. etc. etc.

 

[tondy79]

You might have already seen it but here is David Heath giving his suggested starting points for the PID settings in a G4

Thanks, yes I've seen this and it seems that he keeps the heating power at 100% when using the PID...

 

[Twostage]

I was using 26l water with setting p0.58 and i0.15

The 'I' seems high, the numbers I've seen (including on the video above) is 100 times less than that.

 

[tondy79]

The 'I' seems high, the numbers I've seen (including on the video above) is 100 times less than that.

Yes, just missing a couple of important zeros here!

P=0.58
I=0.0015

 

[The-Engineer-That-Brews]

Interesting! Thanks for all the info, and intrigued to know how you measured this flow rate?

Also worried that I need to get the wiring checked now! It's an oldish house I'm in here

To measure the flow rate I ran the pump into a measuring jug, with the same pipework and speed I use for recirculating; to get the litres per minute.

Once you've got that, you can divide by the volume of different parts of the system (sump, tubing, heat exchanger, etc) to get the time the wort spends in each one (obviously multiply by 60 to get it in seconds).

Note that the amount of liquid in the sump will depend on how well the mash is draining versus the speed you're running the pump - but at the end of the day you're only after an approximate figure.

If you want to know the speed at which the wort penetrates down through the grain, first work out the amount of wort around the grain (eg. by subtracting the volume of the sump etc, from the total amount of water you added to the mash). Then use your pump rate to work out how long it takes the pump to completely recirculate that amount of liquid. Finally, divide the depth of the grain bed (in cm) by the recirculation time (in sec), to get the speed in cm/sec.

I think I've got that right!

 

[The-Engineer-That-Brews]

By the way, I wouldn't worry too much about your wiring: if the voltage drop caused by putting on the kettle was enough to change the boil rate by that much, your wiring would probably evaporate!! You definitely want to plug your kit directly into a wall socket though: do NOT use an extension reel or multi-plug.

 

[tondy79]

If you want to know the speed at which the wort penetrates down through the grain, first work out the amount of wort around the grain (eg. by subtracting the volume of the sump etc, from the total amount of water you added to the mash). Then use your pump rate to work out how long it takes the pump to completely recirculate that amount of liquid. Finally, divide the depth of the grain bed (in cm) by the recirculation time (in sec), to get the speed in cm/sec.

I think I've got that right!

Thanks TETB, I'm going to take a couple of paracetamol and think that over