Posted Tue Dec 17, 2013, 3:16pm Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
Brew temperature is probably best guided by using a Thermo filter. Another method that may help is use of boiler wall temperature. There is a central zone about two thirds up from the bottom of the boiler and up over the top of the boiler where the temperature is relatively stable. A thermistor, sensor, or thermocouple may be placed in this area. They may be adhered to the boiler. I have had reasonable readings by sliding a thermistor or thermocouple under the Thermo fuse clip. Since the Thermo fuse is in cylindrical silicone there is a little space between the silicone and the clip.
In the first pages of this thread Andy used a Polder thermometer with the bead cemented on the boiler. I happened to note his Polder temperature and the 235° F range, while adding heat during the brew. That temperature was approximated using PID controller alarms. Eventually 214° F was selected as SV on the PID controller and the temperature rise to about 235° F was controlled by selected alarm temperatures. It is interesting to note that there should be about a 20° F temperature rise of the upper boiler during the brew of a double to blunt intra-shot drop. Perhaps a couple of degrees to allow a minimal drop. As noted in other postings there still needs to be a 3 to 4 seconds steam switch blip of heat followed by rest so that the boiler shell is hot as the cold water enters. In the 7 to 8 seconds described above, the boiler shell temperature as measured on the upper central shell will not start to rise. My PID controller temperature will be rapidly rising but not the boiler wall temperature. Heat should be added to approximate about one third of the brew time or perhaps 8 to 9 seconds total of switch on time. The approximate 20° temperature rise of the boiler wall should be fairly smooth over the brew time. The heat on cycle will be weighted a bit toward the front of the 25 seconds. That approximate 20° rise may occur over a total time of 25 to 35 seconds depending on whether you time from brew switch on or from first drip. It will take the approximate 8 seconds of switch on time to offset the cold calories in the incoming water. Jonr noted a similar boiler wall temperature using his computer board controlled temperature, a few posts above. That suggests that a 20° F temperature rise during the brew will help stabilize the intra-shot drop whether using steam switch, PID, or computer based control.
If you stick to the approximate 20F rise, volume of brew will be accounted for. More volume through the boiler will take more heat, or on time to get the boiler wall temperature to rise 20F, and likewise a small volume will decrease heat requirement. I have tried 50 60 ml of brew water and 25 30 ml and had to adjust the amount of heat with brew accordingly to keep control of the intrashot drop. I also used a thermofilter, but could get close just using boiler wall temperature.
Posted Thu Mar 27, 2014, 12:07pm Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
A little update on Preheat and boiler temperature. Preheat with a copper coil can be done best if the OPV is plumbed to come before the coil so that it does not shunt heated water back to the tank. Most of the mods that I have seen use 1/4" copper tubing and get 6 - 7 rounds and about 35 ml of water. It does blunt a lot of the intrashot drop but the incoming water is still relatively cool. Pizzaman has even used an intraboiler tube and temperature sensor. Unfortunately the KitchenAid Pro probe is in place of the steam valve and steam is lost. Perhaps the steam valve could be drilled and a 1/8" tube soldered in as a down tube and give a probe port and still allow steam.
Posted Fri Mar 28, 2014, 1:33pm Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
This topic is still here? :)
I wandered in this topic by chance but figured that it'd see how things are going.
Last I heard you were pulling shorter shots, somewhere around 30mL, is this still the case? If so, how have you adjusted your brew switch alarm? I think my temperatures are mostly set at 214/235/285. the last being the steam. I don't really have any complaints. I also only turn on the steam switch 2 seconds and off 2 seconds before brewing. I adjust the 214 to 210 when its a dark roast and up a little to 215 for really light roasts. Although I have a thermocouple installed in a basket, I haven't actually documented too many temperatures in the portafilter. I get around 201 for my mostly set temperatures.
My latest adventure is into roasting. I am using an air popper now but will probably get a Behmor 1600 instead of trying to modify the popper (my sig other uses the popper for popcorn too, haha).
Posted Sat Mar 29, 2014, 1:54pm Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
Brinal, good to hear from you. Yep, now at about 30 gms output for a double. I am currently using Redbird Blue Jaguar and IIRC Jeff used to recommend 199F. At 214F SV, brew water was at about 200 - 201F. I am using 212F SV, then about 3.5 seconds steam an and then off. When at 214F and less steam blip, still too hot, but more of a drop. Intrashot heat at 224 - 225F and Alarm 294 and 295F. A boiler thermometer is interesting in that there is still about a 20F rise in boiler wall during the pull, very similar to using other values for grams output and then corresponding heat SV and inputs. See the post above from Dec 17.
Thermofilter was adjusted with hole size to approximate the 30 gm pull and that gave the starting points. The intrashot alarm sets were a little lower than I guesstimated. Higher gave more boiler temperature rise, and less to no intrashot drop.
Posted Tue Apr 1, 2014, 11:19am Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
So it's been about a year and a half since i adjusted the OPV on my classic. I wanted to run something by you before checking it again.
Do you preheat the device like you were about to pull a shot before checking? Do you leave in the filter basket or remove it? I am using a regular gauge on the end of the portafilter, which I believe is static pressure. this should be 10 BARs instead of the 9 BARs since the water isn't flowing (it's kind of trapped like I were backflushing)?
I have heard different things from different people but consider you the expert on all thing Gaggia classic ;).
Posted Tue Apr 1, 2014, 11:42am Subject: Re: Gaggia Classic SBDU Preheat PID Temperature Recovery and Stability, Steam
OPV adjustment with a gauge on the PF is without the basket. The basket has no seal to the PF and the pressure build up in the PF will leak at the basket-PF interface. Heat will not make a lot of difference though nothing wrong with simulating the pull. Static number that I have read are about 9.5 to 10.5 bar, and I don't think it matters all that much especially with the numbers noted on pressure profiling. Ending with dynamic of about 9, plus or minus 0.5, is probably fine. Of course you can loosen the gauge minimally and allow a thread leak, and quantify that to a reasonable amount to simulate a shot, and make it dynamic.
Not so sure about the expert part as the ex-has been, spert/spurt-drip under pressure definition comes to mind. Thanks, I think :)
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