Posted Fri Nov 9, 2012, 12:17pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability, Steam
I have seen several Gaggia posts recently involving various Gaggia SBDU machines, especially the Gaggia Classic and Baby Class. Temperature control has been one of the issues affecting taste in some of the threads. While this thread is a bit long, it covers temperature control both with temperature surfing and with a PID.
It was shown by AndyPanda that the heaters can essentially put out a continuous shot making the Gaggia act almost like a thermoblock. That is the heat input can match the caloric cooling of the incoming cold water at about 2 oz/25 seconds on a continual basis. With proper timing of heat input using the steam switch you can stop the intrashot drop, and be ready for the next shot. No preheat is necessary.
Similar can be done with a PID and proper wiring using an Auber SYL-2362 with two alarms and the PID function. The PID function controls brew water/idle temperature, one alarm controls steam temperature, and the second alarm turns on the heater, and cycles it, when the brew switch is turned on, doing essentially what was done manually. It will hold the intrashot temperature from dropping and in fact if not adjusted properly, will raise it. Again, no preheat coil needed.
Posted Sun Nov 18, 2012, 4:42pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability, Steam
I found another interesting resource link, of steam pressure vs temperature. This helps explain why a PID, or proper surfing to keep the steam temperature up, helps with pressure. There is a fair fluctuation of pressure within the bimetallic tstat range.
Posted Fri Jan 11, 2013, 7:21pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability, Steam
I was asked to comment, from the Youtube video, on the wiring of the brew switch to turn on heat, and about using a 1/32 din PID with alarm for doing this. I orignally had a 1/32 PID, Auber SYL 1512, and used the PID algorithm side for idle or brew temperature and the alarm for turning on brew heater, leaving steam control OEM. I like the steam control on the PID alarm function also, so the 1/16 din with PID algorithm and 2 alarms.
The "heater with brew function" is accomplished with a cell phone charger that is turned on with the brew switch AC and then it then sends DC signal to the SSR via the PID alarm side with alarm temperatures set to switch the SSR on and off. A diode was used at the SSR similar the Skene method of using alarm for steam control. That diagram is pages earlier. The OEM wires are spade connectors and I used a piggyback spade to leave the brew system and 3 way intact and piggyback off a switched AC line.
AndyPanda used the steam switch to add heat before and during the brew to help intrashot temperature stability and recovery of temperature for the next brew. This is most easily done in a machine without a 3 way, as the Gaggia steam switch activation keeps the 3 way from letting water out the brew head. Andy also bypassed the function by adding a jump and switch off of the steam switch to activate the steam function without the 3 way. That use is described earlier and videos demonstrated the effectiveness.
The PID controller with one of the alarm functions can also add heat during the brew by activating an alarm circuit and the SSR to run the heaters when the pump runs. Alarm temperatures are set to cause the SSR to run and cycle. The temperature limits will affect the on and off time of the heaters and when selected correctly, will balance the heat calories with the cold water calories. PID algorithms continue to control idle/brew set temperature, and a second alarm can control steaming, all through the SSR, using diodes and the Skene method also described previously.
Now the above newer method uses a pulse width modulation to control power to add the correct number of calories of heat to balance the cold water calories. Idle temperature is by the PID function and alarm for steam.
An interesting similarity for all of these methods is the attempt to add a correct number of heat calories to balance the expected cold calories. All of these methods work best if the shot flow and volume are very consistent brew to brew. If you are surfing or adding heat during the shot manually, and if you are good at the technique and see that the flow is up of down from usual, then you can vary the amount of on time to compensate. If using an electronic method as above, then you can dial the heat up or down but eventually, it is nice to find a set point and let the electronics add the heat. It actually works well once you the operator are consistent with flow/volume. I set an alarm temperature that compensates for the cold calories of a 45 - 50 ml brew and it works great. Attempt to reach and stabilize at that temperature causes the heat to cycle on and off. Raising that temperature causes more heater time. A 60 ml brew adds too much cold and the system is slightly out of balance, not enough heat. In practice, it would still help and be very close, but best if the volume is the same. I suspect the same for PWM heat, as the heat need is anticipated and the PWM controller set. Again, it can be varied, but that somewhat defeats the concept of it happening repetitively and "blind" to the operator. I do not mind setting it up, but I want it to work on a day to day basis as easily as the Gaggia works. I use the brew switch and the steam switch normally and the PID controller does the rest. If not done electronically, then back to flipping the switches.
Another interesting note is the timing of the heat addition. Watching the manual method along and looking at the construction of the Gaggia seems to suggest that heat added before cold water is best. Cold water is introduced into the boiler internally while the heat is added to the boiler case and needs time to affect the internal temperature. I watched the manual method and Andys description in the thread and see that adding heat prior to the brew helps greatly. In fact, if none of the methods are used but about 4 seconds of heat, via steam switch, and 4 seconds of rest are added just prior to the brew, then the intrashot is blunted a bit. I use that method when I start a single/first brew even though heat is added during the brew. The preheat made the system work well.
Finally, it seems that an Arduino with a flow function could help all of this. Additional parameters of flow and perhaps group temperature or water outflow temperature could be added. I do not speak "Adruinoese," so I will have to wait for someone else to try some of that.
Posted Mon Jan 21, 2013, 8:21pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability, Steam
Another thought on combining the systems, PID function with 2 additional alarms, and PWM. Perhaps PMW could be used to run the pump, not the heater. The heater could be switched on with the pump, to a DV voltage source then alarm function as described in this thread, but the PWM could be turned to preinfuse at low pump pressure and then to 9 bar. Since the pump would pre-infuse at very low flow, the heat would be starting ahead of any significant cold flow, similar to starting with a blip of heat from the steam switch.
Posted Tue Feb 19, 2013, 9:59am Subject: Re: PID Controller supplies and directions for Gaggia and SBDU
In response to a couple of threads asking about supplies and directions for DIY PID controller.
The first supplies are the PID controller and I like Auber for quality, service and understandable instructions. I have used the SYL 1512A and like it for PID function and 1 alarm. It is small and works well and has a nice fitting install box if you are inclined. The box is unfortunately $20-$25, so you may skip that for DIY. I prefer the SYL 2362A, the AC version, not the 2362B 12V DC. We already have AC switched voltage to power the system. I prefer the 2362A, over 1512A, because of the ability to have 2 alarms both setable to low alarm limit. That is how I control steam and add brew heat.
For DIY, you will need the PID controller and sensor. I do not know of a prefitted sensor other that the Auber Gaggia RTD screw in. It has the proper threads and works well. Most inexpensive K thermocouples, or T, will have to be attached by the user. I do not know of a proper threaded screw in thermocouple for the Gaggia.
25 amp SSR from your source. Auber is not cheapest, but you can get the big supplies at one place that way. Ebay is so cheap for some, I probably would get 2 and have a spare if I went that route. There is a recent SSR failure thread on Silvia.
You will need a small amount of thermal paste, so that is fine. I found similar in an electronics store so already had some. I would get the RTD sensor as noted unless you have a solution, a cheap thremocouple and attachment.
You can look at the boxes available. There are some commercial project boxes of approximate size for cheap, but you will have to cut to fit. I am not using a box, but remember that at the back of the controller you have 120V into the controller. You can tape over or insulate so that you, or others in your household, do not grab the back by mistake. I am happy without a box, just making sure that you know.
Wiring and connectors are earlier in this thread, but I will cover it again following. In addition power for the alarm functions. I am using cell phone chargers that I already had, no expense. I just saw some in a surplus store about $2.50 each and have seen similar in second hand type stores.
High temperature 26 – 22 awg stranded wire for non-load connections. I like the 26 or 24 as the wire get bundled in to the back of the PID. Larger is more difficult to work with in the bundle. NTE stranded 105C wire, or surplus PTFE mil_spec wire like here
Note 2 heavy leads, and the rest all about 26 awg. You will need connectors and diodes, to follow if there is interest. Connections needed are more than shown. There will be the PID controller power cables, sensor and cables, PID controller to SSR, Heavy load cables on SSR power side and then cables for steam and brew if you elect that, as well as the DC power sources noted.
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