Posted Mon Mar 19, 2012, 4:49pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I just did a quick little test on the flow rate that the heater can keep up with ... I put a large container under the steam wand and cracked the steam valve slightly and found a good starting temp. I picked 205F because much hotter than that I was getting spurts of steam instead of water - it was just an easier temp to work with but a more accurate test might be using a PF with a needle valve so you can adjust the flow through the group rather than the steam wand so you aren't getting steam from the top of the boiler.
But for now, I feel like this gave a ballpark reading. I adjusted the steam knob until I was holding a steady 205F on the thermometer with the pump running then I put my cup under the wand and captured 10 seconds of the flow.
I weighed 49g (I believe 49g of water is 49ml - right?) so in 10 seconds the boiler was able to hold a steady temp with 49ml of cool water coming in.
That would explain a few things ... in the past, most people I've read posting about trying the steam switch have complained that the temp dropped at first and then rose way too high by the end of the shot (they were simply turning on the steam as they started the shot and leaving it on through the shot). And the test I just ran would indicate that unless you were pulling a 122ml shot in 25 seconds the heat would be rising higher and higher all through the shot (after the first temp dip if you don't anticipate by starting the heat first).
My method is to start the steam switch 4-5 seconds before I hit the brew button and then cycle the power off-on-off-on about 40% of the time during the shot for a 30ml double in 25 seconds.
D4F Senior Member Joined: 15 Mar 2012 Posts: 1,193 Location: USA Expertise: I like coffee
Espresso: Gaggia Classic PID Grinder: Preciso
Posted Mon Mar 19, 2012, 6:16pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
AndyPanda Said:
I think most of the people interested in Gaggia are at the Yahoo Gaggia group. I think a lot of people here have had experience with the Gaggia and have since graduated to higher end equipment.
I guess it depends on which forum appeals to you. I joined this one because I liked the tone of the group. I know that you are not saying to go to the Yahoo Gaggia group, but just stating a fact. Many times I see people referred there from this forum. It seems like to keep a group/forum active that having beginners is a good thing. I see people loose interest in posting as they settle in on a machine, so noobies needed.
D4F Senior Member Joined: 15 Mar 2012 Posts: 1,193 Location: USA Expertise: I like coffee
Espresso: Gaggia Classic PID Grinder: Preciso
Posted Mon Mar 19, 2012, 6:39pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
AndyPanda Said:
I weighed 49g (I believe 49g of water is 49ml - right?) so in 10 seconds the boiler was able to hold a steady temp with 49ml of cool water coming in.
That would explain a few things ... in the past, most people I've read posting about trying the steam switch have complained that the temp dropped at first and then rose way too high by the end of the shot (they were simply turning on the steam as they started the shot and leaving it on through the shot). And the test I just ran would indicate that unless you were pulling a 122ml shot in 25 seconds the heat would be rising higher and higher all through the shot (after the first temp dip if you don't anticipate by starting the heat first).
My method is to start the steam switch 4-5 seconds before I hit the brew button and then cycle the power off-on-off-on about 40% of the time during the shot for a 30ml double in 25 seconds.
That seems to agree with the prior post on matching calories. At flow rates for reasonable espresso, the heater can over heat. The on duty cycle is about 1/3 to 2/3 of the time. You can't do it with the PID portion of a PID because that is little/short blips of power to stabilize a set temperature. The alarm function of a PID, commonly used for steam, can cycle the heater full on and off through an SSR. This can be done with second SSR as commonly done for steam, or with a dc voltage source and diodes as described. I have a set temperature of 218-220 measured at the brew stat. I set the alarm temps to cycle on and off a couple of degrees higher. The difficult part is to see the sensor temperature bounce up and down with water coming in and heat going on and off. The water is much more buffered, which is why you don't overtemp in the first few seconds of heater on manually. If you had a sensor at the brew stat it could look unstable even with your fine touch, as the sensor is almost sitting on the heater. I am still not sure of the working of my system at various flow rates or pull sizes, but I think that it will work as you do manually.
Using the heater, on with the pump, may effectively help the machine be able to make multiple pulls without long delays, similar to a larger boiler.
D4F Senior Member Joined: 15 Mar 2012 Posts: 1,193 Location: USA Expertise: I like coffee
Espresso: Gaggia Classic PID Grinder: Preciso
Posted Tue Mar 20, 2012, 1:38pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I finally got a chance to realy look at this. Using a fantastic site, Wolfram Alpha Computational, a scientific search/database/calculation site I found that 1425 watts for 60 seconds is 85.5Kj of energy and will heat 273 ml of water from 25c to 100c. You got 49*6 or 294 ml from around 25c to about 98.5c. Interesting that math and experiment seem to agree, of course they should. Once again, you have a good touch and accuracy.
Important to have the whole machine at stable temperature so that all energy is heating water, and not still heating the machine. There is still heat lost to the surrounding environment, sides and top of the machine are warm.
If you could titrate energy in at just the correct rate you hold the water temperature, but fluctuate the tank temperature with heater on and off, which you seem able to do, at least when concentrating on that and not your espresso. This should still work well enough for brewing even if a little off.
Now figure how to get all of the steam we need, that would require some incoming water as the supply is used and 25c water into 140c tank does not cound good for the equipment on an ongoing basis.
Very cool! Thanks for supplying the math and I'm glad to hear it agrees closely with what I observed.
D4F Said:
Important to have the whole machine at stable temperature so that all energy is heating water, and not still heating the machine. There is still heat lost to the surrounding environment, sides and top of the machine are warm.
Although most of my posts are about the classic, I happened to have the plastic cased baby (same boiler, pump etc.) on the counter that day - it doesn't seem to require much warmup and the cabinet doesn't really radiate much heat (and the boiler is mounted with those insulating shims - that is what gave me the idea to put a spacer between my classic boiler and the stainless case). I'll have to test again with the classic and we may find it isn't able to keep up with quite as much flow with all that metal in the cabinet radiating the heat away.
bigeric Senior Member Joined: 30 Dec 2011 Posts: 4 Location: Northern VA Expertise: I like coffee
Posted Tue Mar 20, 2012, 5:33pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
I just got an old Gaggia Coffee for $15 and rebuilt it (painted, descaled, new o-rings & gaskets, new steam valve, new boiler valve) with 15' of 1/4 copper for preheat, an OPV near the pump, and an Auber pid (not the kit). I'm using a Type T thermocouple mounted where the original brew thermostat was. I use the alarm with a 9v battery to drive the PID with the steam button. The schematic is posted in multiple places around the web.
I played with the PID parameters to balance post-shot recovery and settled on: P - 3.1% (33 degrees) I - 30 seconds D - 6 seconds damping - 0.4
I get recovery back to the set temp in 45-60 seconds depending on how hot the preheat water is. The PID parameters are a balance between quick recovery and time for the temp to overshoot and settle down. These recover a bit slower than some others I tried (P - 3, I - 16, D - *, damping 0.3) but the lack of overshoot results in a shorter recovery time.
Before the preheat coil, the temp during a shot would drop between 5 and 10 degrees. With the preheat, there's significant improvement and I only get 3-5 degrees drop. These are drops in the PID readout. I haven't measured the brew temp stability during a shot yet.
All in all, I'm extremely happy with the performance of this little machine. Thanks to all that figured out all these things and made the plan easy to follow!
Posted Tue Mar 20, 2012, 6:12pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
What color did you paint it? What color was it before? Got pictures? I'm always tempted to have my old Coffee painted/powder coated some day ... it's got some rust.
D4F Senior Member Joined: 15 Mar 2012 Posts: 1,193 Location: USA Expertise: I like coffee
Espresso: Gaggia Classic PID Grinder: Preciso
Posted Tue Mar 20, 2012, 6:43pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
bigeric Said:
I just got an old Gaggia Coffee for $15 and rebuilt it (painted, descaled, new o-rings & gaskets, new steam valve, new boiler valve) with 15' of 1/4 copper for preheat, an OPV near the pump, and an Auber pid (not the kit). I'm using a Type T thermocouple mounted where the original brew thermostat was. I use the alarm with a 9v battery to drive the PID with the steam button.
The battery obviously replaces a dc power supply like I used. Easier and cleaner to install, but will need eventual replacement. Diodes into the original SSR, or second SSR? Did you get 15' in one layer, or second layer? Do you know how warm the preheat water is? Obviously it works, so heating is sufficient. IIRC, about 9-10 ml/ft of tubing, so you have a large reserve. Also, you solved the OPV placement.
Good info, nice to see what others are doing. What brew temperature and what is your usual pull volume?
bigeric Senior Member Joined: 30 Dec 2011 Posts: 4 Location: Northern VA Expertise: I like coffee
Posted Wed Mar 21, 2012, 6:14pm Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
It was white with a black front panel. I scuff sanded the metal and sprayed it with metallic gray hand-hammered spray paint. I sprayed the front panel with black textured spray paint to cover some scuffs. It looks pretty good in my kitchen that has stainless appliances.
I use only one SSR with both the alarm and SSR outputs of the PID wired through diodes. Kudos to whoever though of that simple design.
15' ended up covering two layers of tubing around the boiler. Initially, the preheat coils heated up very slowly. Air doesn't transfer the heat very well from the boiler to the coils. I filled the gaps between the tubing and the boiler with crumpled up aluminum foil and it transfers the heat much faster.
One thing that's not great is the transition from the copper tube to the teflon tube into the boiler inlet fitting. That's out of contact with the boiler so it doesn't really preheat. That means the first bit of water into the boiler when you start the pump starts isn't as hot as the water in the main part of the preheat coils. I counter that by pulling 1/2 ounce and letting the boiler recover prior to my first shot. I haven't measured the temp of the preheat water or tubes.
I typically pull between 1 1/2 and 2 ounce doubles. I have been getting good results setting the PID at 215 degrees. I don't have the ability yet to measure the actual brew temperature in the filter basket.
D4F Senior Member Joined: 15 Mar 2012 Posts: 1,193 Location: USA Expertise: I like coffee
Espresso: Gaggia Classic PID Grinder: Preciso
Posted Thu Mar 22, 2012, 10:20am Subject: Re: Gaggia SBDU Preheat PID Temperature Recovery and Stability
bigeric Said:
I just got an old Gaggia Coffee for $15 and rebuilt it (painted, descaled, new o-rings & gaskets, new steam valve, new boiler valve) with 15' of 1/4 copper for preheat, an OPV near the pump, and an Auber pid (not the kit). I'm using a Type T thermocouple mounted where the original brew thermostat was. I use the alarm with a 9v battery to drive the PID with the steam button. The schematic is posted in multiple places around the web.
How about a link to the 9v schematics when you get a chance.
The Jerry Skene diagram was with a dc power supply noted earlier in this thread, and the FRCN modification to dual SSR is found in CG here. That shows a Silvia, but focus on the PID and SSR for Gaggia use. Use our Brew switch to activate it with the pump, instead of the steam switch noted on the diagrams.
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