Posted Fri Mar 16, 2012, 12:38pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
Temps would drop without heat input, PID does not change that. That is why you blip heat. Depending on my alarm temperature choices, I can end up higher or lower than set starting temperature. I am still playing with this.
I did not mean to imply that the Delonghi was similar to Gaggia, only that I had a little "manual PID" experience before getting a Gaggia and PID. As noted you do not need a PID, it just does your functions electronically. I am glad to see that you are not anti PID.
Posted Sun Mar 18, 2012, 1:45pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I know the heater is capable of holding the shot steady (because I can do it manually with lots of practice and trial and error). So if the PID could remember a routine or let you manually program a routine - once you figure out how the heat cycles needed for a standard double (and for a ristretto and a few others) you could pull up the temp profile you want ... hmmmm.
When I use a Gaggia without a 3-way valve, I can simply use the steam switch ... but with a 3-way valve I add a switch that lets me kick the heat on without activating the solenoid valve. My routine for a double is to get the boiler temp idling steady at my target (and make sure the boiler is full) - then I hit the heater for 4 seconds then off and start the shot - then throughout the shot it is on-off-on-off at a rate of about on for 2 seconds off for 2 seconds. When I get it right, the temp doesn't vary at all (or maybe one degree) through the entire shot. Or I can let it drop a little if I want that profile. Anyway .. that's about my routine if you know a way to get your PID to emulate it. (but my idea of a double is 30 ml ristretto or maybe 40-50 occasionally - never 75 but it's all personal taste - if you were pulling 75ml shots you would need a lot more energy than I use to keep the temp steady).
How are you measuring shot stability, how accurately? What do you do on a Classic with 3 way? How long to recover between shot and how stable? When I started doing using blips of heater, or steam switch, I was surprised how quickly the temperature can rise and how much overshoot.
Posted Sun Mar 18, 2012, 5:28pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I've tried it many ways .... this is a pain to do (can be messy and wastes coffee) but with a fast reading TC, you fish the wire up over the edge of the PF (it will get pinched and after enough times you may break the wire) --- someday I will sacrifice a PF to make one with the TC permanently mounted inside with a puck simulator.
So I've done it that way (wire over the edge) on top of a tamped puck and watched the temps while pulling an actual shot. I've also tried using something to restrict the flow and a some styrofoam packed in there to fill up the space the coffee puck would fill up.
With the classic (because of the 3-way) I put a toggle in the back (through the vent holes so I wouldn't have to drill a hole in the nice, stainless cabinet). I wired it so when I hit the toggle it bypasses the brew thermoswitch - the same way the steam switch does but without the second leg of the steam switch to trip the 3-way.
It doesn't take any time, really, to recover because my boiler is still at my starting temp at the end of the shot.
You will get overshoot unless you learn the technique - you don't wait to see the temp change because the temp change comes a good 5-10 seconds AFTER the electricity hits the heater.
So if my target temp is 216F but my boiler thermometer is reading 212F, I will hit the steam switch for 2-3 seconds and then off (no change at all on the thermometer yet) and after another 5-10 seconds I will start to see the temp rise and with some practice I can settle in at my target. If the temp is far away from your target, you have to do this a few times to get it settled.
Now if I've got my basket dosed and tamped and my boiler is reading 216F, I hit the steam switch while I load the basket and lock the PF (PF is hot) - steam switch is on for a count of 4 seconds then off and hit the brew switch.
I think I told you my timing in an earlier post - but I'm pulling 30-40ml shots and you are pulling 70ml shots so you would need a completely different timing than I use.
At the end of the shot, my boiler is still reading 216F and if I had another basket prepped I could load it up and hit the steam for 4 seconds and pull another shot. I could do this until the water tank was empty without any recovery time.... but maybe not with 70ml shots (I'd have to practice).
Posted Sun Mar 18, 2012, 9:41pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I am still adjusting shot size. 70 ml was to find a set point for energy calculation. Changing double shot size changes some numbers, not the concept. Neither my PID nor its operator are clever enough to have multiple curves and switches. Not available on the inexpensive PIDs to my knowledge. Interestingly, I think that we are doing similar, I am just doing it electronically, and you are being the advanced PID, no offense intended, more respect.
How are you measuring boiler temperature, thermocouple type and placement. I am trying to understand what you see and do. Even without repeating puck temperatures that you have already done, I wonder if I can almost infer that if the ending boiler temperature is about the same as beginning, then the brew water temp has been fairly stable??? The boiler temperature with an RTD sensor in the brew stat position will bounce up and down with power cycles, but the water does not change that quickly, and the water pickup is more central, away from aluminum jacket fluctuations as I understand. You know that the temperture spikes are coming and use shorter cycles than the PID which depends on the sensor. The more slowly changing water temperature may buffer this. I would try to confirm, but do not have the extra thermocouples, digital rapid thermometer, and PF's to set up.
Temperature is rapidly stable and back to starting as soon as the pump and heater go off.
Thinking out loud here, and I will have to consider it further. Good discussion for me, and may give others with SBDU's some ideas.
Posted Sun Mar 18, 2012, 10:00pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I'm sure there is a limit (and 70ml in 25 seconds may be beyond it) to how much the boiler can keep up with. One way to determine this might be to hit the steam switch for 4-6 seconds then start the pump and crack the steam knob a bit and try to adjust the steam knob to the point where the heater is able to keep up with the water flow. I do know for sure that if you just let it pump as fast as it can - the temps plummet, the heater can't keep up.
I'm curious enough to give this a try - I'll let you know how much volume it can pump through without the boiler temp dropping while the heater is on full.
I keep wondering where the very best place is to put the thermometer. I've tried putting it on top (this is the easiest because there is the thermofuse clip you can simply put your TC bead under). But I always read much hotter temps there and it doesn't seem as consistent a readout. I also didn't want to mount too close to the heaters because I don't want to know how hot the heaters are, I want to get some idea of the average temp of the boiler. My guess is that cool water coming in at the bottom and hottest water going out at the top -- so I mount my TC bead right in the middle of the flat side of the boiler (between the two heaters and between the cooler bottom and the hotter top) with the hope that this is about the average temp. And so far that has been working well for me.
Posted Mon Mar 19, 2012, 9:41am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
The calculation that I used earlier showed that about 60% of heater on time would supply the calories to heat the water, 70 ml. About 15 of 25 seconds. 35 ml should only need about 7.5 second of heater in 25 seconds. Of course there some system losses to keep up with also. In practice, I think that this is working. I have the RTD unit in the boiler stat hole, so it is reactive to say the least. I see the temps rise with heater on and fall when off, but back to starting very quickly when the pump is off. I think that based on your system and measurements, that if I end up at the starting temp shortly after the pump, and heater, go off, then I have probably calorie matched and held the brew temperature fairly close. The aluminum and sensor at the heater fluctuate the most. The water and all of the brass components serve as a buffer.
I think the water exits the tank from a central place tube. I surmised that looking at a parts diagram, so not sure. That also help buffer off temperature fluctuations.
I think that I understand your "test" and will be very interested. I agree that at some volume, you will begin to overwhelm the systems ability to smoothely recover, especially on multiple puills.
How about a little more information on your toggle. What are the hook up points. Hard to imagine that some others are not interested in being able to rapidly brew a second pull. I understand that the steam switch keeps the 3-way selenoid closed to the brew head, so, you are activating the steam, not the selenoid.
After some thought, you are proactively activating the heating, but should still need about 8+ seconds of "on" in 25 seconds. My PID/alarm method is reactive using a sensor, but still puts the heat on somewhat distributed over the 25 seconds and comes out a wash at the end. You can adjust by feel and experience to different volumes and lengths pulls. I will need to play for a while with different volumes and lengths of pulls to see if the reactive system adjusts for this, or if different settings are needed. I think that the bottom line is that the calories of heat need be supplied, distributed somewhat evenly over the 25 seconds and you will get about the same result. I guess that is my working theory.
Posted Mon Mar 19, 2012, 9:48am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
The calculation that I used earlier showed that about 60% of heater on time would supply the calories to heat the water, 70 ml. About 15 of 25 seconds. 35 ml should only need about 7.5 second of heater in 25 seconds. Of course there some system losses to keep up with also.
I find that on a plastic case Gaggia (like New Baby or Carezza) the boiler isn't transferring much heat to the case (nor the case to the room) ... I also noticed in some of the newer models that there is a plastic or silicone shim between the boiler and the case which I assume is to insulate the boiler a little from the case. My old Classic had the boiler mounted metal to metal and the case sucked a lot of the heat away from the boiler --- so I put a large o-ring around the bottom of the boiler and bolted it back to the case (the screws that hold the boiler to the case are still metal to metal but it is less surface area - I will have to try o-rings on the screw heads too). Since putting the o-ring under the boiler, the case doesn't get as warm and the boiler heats up faster and doesn't cool down as fast.
I'll have to open up the case and look or take a photo - but I remember that I spliced into one of the two wires on the steam t-stat up top and the other wire to the steam switch (but you'd have to know which, it was easy to do but I have a multimeter and electronics background - this is as dirt simple a circuit as you will ever come across). Or you could do the same thing by having your toggle to the brew t-stat - but that is in a location that is harder to reach so I did it up top instead.
The reason the steam switch triggers the 3-way is because it is a double pole switch with one pole working the 3-way and the other switching from brew t-stat to steam t-stat. So you want your new toggle to do one but not the other - pretty simple to see just by looking at the two sets of wires on the steam switch and seeing which relates to the t-stats and which relates to the 3-way.
Posted Mon Mar 19, 2012, 2:31pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I'm interested in trying some of these tricks.
One thing I will mention now is that I improvised a temperature measure using a K type bead thermocouple fed through a portafilter spout with the rubber "perfect crema" device that came with the machine (with a small additional hole) in place and an old basket with a hole drilled in it. It's not perfect, but it's not that far from the right level of flow (adding some coffee would help adjust the flow). This avoids the leak from feeding the thermocouple over edge of PF, but does lead to water running down the thermocouple wire (a couple of judicious kinks helps here).
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