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Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
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Discussions > Espresso > Espresso Mods > Gaggia Classic...  
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,981
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Sat Aug 10, 2013, 8:12pm
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

jonr Said:

A couple of general comments.  PID doesn't do very well with rapidly changing conditions like water flow starting and stopping.  The result is typically undershoot and overshoot.  Always keep in mind that the temperature sensor may not be reading the actual temperature of the water.  For example, if you measure near the heating coils, you may see wide swings in temperature when the actual water temperature is pretty stable (or lagging the sensor).

My low mass PT1000 RTD arrived today so I can proceed with an Arduino controlled system (with PID during non brew, open loop control just prior to and during brew).

Posted August 2, 2013 link

My understanding of how PID controller works is that the PID algorithms are in control around the set temperature for idle, closed loop for stability.  The controller then is switched out of PID algorithms and functions as a 1*F, or my choice of temperature interval, on off switch to try to get and keep the temperature in the range set.  The only feedback in the loop is when alarm temperature is deviated from turning heaters on or off.  Not sure that the loop is really open since it is cycled on and off and has that temperature feedback.  A low alarm is used to turn on the heaters is the temperature is below a set and off is 1F over.  That gives full power from idle temperature until the alarm temperature is reached.  The controller is switched by the brew switch to alarm and then is full on until the alarm temperature.  No damping or modulation.  This approximates the use of the steam switch to raise the temperature.  Estimates were of about 60% power, and then T and E using a thermofilter allowed for on and off temperatures such that full power was applied enough of the time to add heat calories/joules to offset the water calories/joules.  One could leave the power on but modulate it such at the "ShortyJacobs PWM" method.  Other controllers with more sophistication and monitors are available such as Arduino.  I opted for simplicity and practicality; easy for me to choose the KISS route figuring that if I could do it and explain it then others could also do similar.

The big problem noted with calorie or energy matching is the lag, thus the 3 - 4 seconds of full power and rest for 3 - 4 seconds to get heat into the boiler wall to help blunt the intrashot fall with cold water directly into the boiler.  Easily understood watching AndyPanda surf the steam switch.  The PID controller did not easily allow for this function so it is done manually.  Ramp soak may be an option, but less simple and I could not confirm a ramp soak controller with 2 alarm functioning as I need for brew and steam.  I discussed this with Suyi at Auber early on.

A PID is an economical and simple approach for fairly simple and economical SBDU machines.

 
D4F also at
http://www.gaggiausersgroup.com/
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witoldb
Senior Member


Joined: 15 Aug 2013
Posts: 105
Location: Dubai UAE
Expertise: I like coffee

Espresso: Sanremo Treviso LX,...
Grinder: Vario,Elektra MXS,...
Roaster: DIY 250g drum roaster
Posted Thu Aug 15, 2013, 3:15pm
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

Using info from this excellent thread, I did simple test with a switch and diode and was able to get quite stable brewing temperature.
I've used thermofilter described in this HB thread:  http://www.home-barista.com/espresso-machines/nuova-simonelli-oscar-mods-t26716-10.html
I made additional 220V power connection to the heaters via switch and 8A/400V diode so it gives 50% of heat when energised.
50% power was on for 4 seconds before starting the pump.
The flow was adjusted with needle valve to 75 ml in 30 sec and pressure was stable 9 bar.
This resulted in meter reading 95 alternating with 96 deg C through entire 30 seconds (I still need to get a meter with decimals resolution).
It proves that with correct controls Gaggia Classic can match much more expensive machines.
I have Oscar and Sanremo Treviso LX machines but find Gaggia much easier to use at home environment due to short warm up time.
Also I don't make multiple shots nor steam the milk.
I'm planning to do some more mods like replacement of brew thermoswitch with 0.1 deg C hysteresis electronic thermostat driving SSR and adjustable delay circuit to switch on 50% power preheat before the pump.
If 50% of power through diode combined with preheat time adjustment doesn't maintain brewing temperature (some posters mentioned 60 % power requirement), I will have to increase the preheat/open loop power using dimmer or PWM/random type SSR.
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Thu Aug 15, 2013, 4:58pm
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

If you want complete control of brew temperature, you probably want to use a small computer.   In my opinion, something around a 3 degree drop throughout brew is ideal.

If you don't want to use a computer then temp surfing (boost boiler wall temp just before brew), what you are doing (50% power) or a PID can provide pretty good control of brew temp.  Doing none of the above tends to result in excessive temperature drops and bad taste.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,981
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Thu Aug 15, 2013, 7:49pm
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

Witoldb, welcome to CG.

I saw your work on Oscar on HB, does not look like you had much to gain from reading this thread, but thank you.  I have tried to use a simple approach to the Gaggia so that others can use similar, and so that the controls do not cost more than the machine. Looks like you are doing similar by using partial power.  There are a couple of other threads using more computerized controls. Jonr's note, and a thread using PWM. I think that many methods can gain fair intra-shot stability and rapid recovery of the boiler.  You can pick your "stability" by taste in the cup, flat profile of some degree of temperature variation. You can get fairly flat temperature and then add or subtract a bit of preheat and adjust for a small rise or fall, again taste driven.  Alternatively, same preheat and adjust the heat added with brew.  Flat temperature profile was illusive on the Gaggia Classic and now the trick is to adjust to taste.  With the thermofilter you can check what profile suits your taste. Nice thermofilter by the way.

You may want to adjust the flow to more like 30 - 40 gms in 25 sec before you refine the heat.  From what I read that may be a more common double size, and flow.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Sat Aug 17, 2013, 12:37pm
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

> If 50% of power through diode combined with preheat time adjustment doesn't maintain
> brewing temperature (some posters mentioned 60 % ...

I can come up with theoretical values up to 65% but I think that incoming water doesn't mix all that much with existing water in the boiler and that reduces it significantly.   4 seconds of 100% power preheat has been used to flatten the profile and spread over a 25 second shot, that suggests that as little as 16% power may be enough.   Maybe even less if you want a dropping profile.  Andy P tried 50% power and found that it caused a rise in temp.  I hope to have more data soon.

~6-8 seconds of flush appears to quickly drop a Classic boiler at steam temp to something close to brew temp.

Overall, I think that a Gaggia Classic + better initial temp control + something to reduce (not eliminate) brew temp drop is a very good combination.
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,981
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Tue Aug 20, 2013, 9:52am
Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
 

D4F Said:

If I understand the formulas correctly, then 1425 watts * 25 seconds for a pull is about 35kj.  If a double pull is about 70 ml, then to heat 70 ml from 25c to 100c is about 22kj.  If I could get the heater on for about 60% of the time then that would supply the approximate amount to heat the incoming water.  I am currently trying this.

Posted March 16, 2012 link

That was page 1 of the thread :)

Drop to 35 gm water throughput and that should be half of the above or about 30% on time.  The power requirement is volume dependent, and that on your ability shot to shot. Of course you can use a flow meter or output/throughput weight and a computer if it can adjust power quickly enough to titrate.  Also there is cost/benefit ratio and complexity of the Classic.  I simply used the thermofilter and measured output temperature and adjusted the alarm temperature cutoff to alter the “on” time and then titrate to taste.  In addition, if you want the machine to be able to quickly pull a second, you may need a different heat input than for a single pull with possible desired temperature fall, a bit of compromise.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Wed Aug 21, 2013, 11:58am
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

Some other factors (besides flow rate ~100%) that influence the power needed: incoming water temp (15%), voltage (10%) and individual machine (1250 watts in my Espresso, 1320 in my Classic, say 5+%)
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D4F
Senior Member


Joined: 15 Mar 2012
Posts: 1,981
Location: USA
Expertise: I like coffee

Espresso: Gaggia Classic PID
Grinder: Baratza Forte-AP
Posted Thu Aug 22, 2013, 7:53pm
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

jonr Said:

I can come up with theoretical values up to 65% but I think that incoming water doesn't mix all that much with existing water in the boiler and that reduces it significantly.   4 seconds of 100% power preheat has been used to flatten the profile and spread over a 25 second shot, that suggests that as little as 16% power may be enough.

Posted August 17, 2013 link

jonr Said:

Some other factors (besides flow rate ~100%) that influence the power needed: incoming water temp (15%), voltage (10%) and individual machine (1250 watts in my Espresso, 1320 in my Classic, say 5+%)

Posted August 21, 2013 link

As above, I initially calculated about 60% of "on" cycle for about 70 ml and now can probably halve that for half of the water.  The only reason for the initial calculation was to try to determine if enough heat could be added by the PID controller, not using the PID algorithms, to control the temperature.  That was the front end of the thread, and the old adage was that PID controller could not stop the intrashot drop.  I was trying to determine if there were enough heat joules, plus overage and "other factors" to counter the water cooling, not trying to determine an exact amount.  AndyP and I were a bit more T&E than precision.  While the heat was enough, the timing was off and the preheat was needed to get the boiler walls hot as it indirectly heats the water by transfer while the water cooling is very direct. It may take a few seconds for mixing, but the cooling is in the boiler.  I did not go back and correct the original figures as 60% was never precise.  A big correction would be something along the line of 15 seconds of "on" out of 25 seconds of brew but then minus 4 seconds of "on" from the preheat, so then 11 seconds of "on" from the 25 of brew.  Still, only a big approximation and mostly dwarfs the other factors.

The only reason I know for trying for a "stable" brew temperature is to gain and demonstrate control.  Once you realize that you can stabilize, then the trick is to control the hump/drop.  That comes back to taste in the cup, not precise computer or PID control on a graph.

 
D4F also at
http://www.gaggiausersgroup.com/
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jonr
Senior Member


Joined: 25 Jun 2013
Posts: 290
Location: Americas
Expertise: I like coffee
Posted Fri Aug 23, 2013, 10:14am
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

> That comes back to taste in the cup, not precise computer or PID control on a graph.

I agree, you first need to establish that you have precise and repeatable control.  Once you have that, then it makes sense to determine how you want to use that to get the best taste.  Trying to establish best taste on a inflexible, imprecise or inconsistent system will just be frustrating.
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bronc
Senior Member


Joined: 25 Aug 2013
Posts: 2
Location: Bulgaria, EU
Expertise: I live coffee

Espresso: Gaggia Classic
Grinder: Mazzer Super Jolly
Posted Sun Aug 25, 2013, 9:33am
Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
 

Guys, do you experience with Sestos PIDs? I installed one over the weekend but I'm finding it very hard to configure it. The settings for the P, I, and D are quite different from other controllers. The  range for all three settings is 0-9999 and I find this very confusing. I tried the autotune function but I can't stop the PID from overshooting. It mostly overshoots after brewing a shot/steaming but sometimes it goes 2-3*C above the set value even when it's sitting idle. For example, if I set it to 95*C it sometimes turns on the heating element even when the temperature is 95.6-7*C causing it to overshoot to 97-98*C. I tried increasing the differential - that only makes the reaction slower but still doesn't stop it from going past the SV. I've attached the TC to the lower lip of the front of the boiler hoping that this more accurately measures the water temperature. I guess on the other hand the PID might be having a hard time finding a correlation between turning on the heating element snd the chamge of temperature in the TC. Any ideas? The autotune seetings I get are P=1050/9999 I=450/9999 and D=110/9999. I tried playing the settings but the 0-9999 range is so wide that I can't really sense what's changing what..
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