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Thread: Coffee machine experiments
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13th Aug 2019, 12:52 AM #31
I know Bob, use some translucent tube and put some coloured LEDs in the bottom, a few strips of reflective tape on the spindle and you have a light show. Should look good in a dark cupboard...
Best Regards:
Baron J.
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14th Aug 2019, 08:03 PM #32Member: Blue and white apron brigade
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As suggested by BJ.
from a piece of olycarbonate 1mm thick scrap sheet.
Pumpscreen2.JPG
I also found some beaut 10mm ID, 1mm wall, SS tube and turned the bits all to the same length and used it as a more accurate way of aligning the pump and motor and this helped reduced the vibe a bit more.
Pumpscreen1.JPG
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14th Aug 2019, 10:46 PM #33
Hi Bob,
I like that clear 1 mm sheet tube that you have made ! Much better than leaving it open and exposed, dropping a cloth or something on that rotating shaft could cause problems. Those tubular spacers are a much better way of lining the two surfaces up as well. You now can guarantee that the plates are parallel to each other.
Nice to know that the vibration has reduced. What little is left could be the coupler itself.
PS. You know that my suggestion about the LED's was not a serious oneBest Regards:
Baron J.
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19th Aug 2019, 07:31 PM #34Member: Blue and white apron brigade
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I finally got back to this project and was for a few days stuck on why nothing was working.
I hooked up the VFD and a water supply to the motor/pump and the first obvious thing is that water flows straight through this pump but of course it's a pressure addition pump.
Then, changing the speed of the motor didn't change the pressure much, and hardly changed the flow rate at all.
Varying the VFD from 30 to 70 Hz only changed the pump pressure by ~15% and the flow rate changed by <5%
After wondering what was going on, it struck me that of course, this is EXACTLY how these pumps are supposed to work so that if someone flushes the loo or turns on a HWS etc which can change the incoming water pressure which will throw the pump pressure out as it's a P-adder pump. But I don't need this as I already have a highly regulated water supply - what I want to be able to do is control P&F with the VFD.
Opening up the press regulation mechanism I could see how it worked.
Plunger P sits in a passage connecting the pump outlet back to inlet.
Spring Sp supplies a back pressure to seal P inside the passage at the outlet end with the tension of the spring determined by screw S position.
As the pump pressure builds up, once the pressure starts to overcome the spring tension this opens up the passage from the outlet water back to the inlet.
Final flow is limited by any pump outlet restriction but if that is fixed it will maintain a fixed flow at a fixed pressure.
springrep.JPG
To get around this I replaced the 7mm diameter x 19 mm long spring with turned brass cylinder C, the length of C is adjustable by a short brassscrew on the end.
Then here is the testing setup
I = incoming water
WR - water pressure regulator set at 4bar
IWP = gauge shows input water pressure
P = pump
OWP = gauge showing putt water pressure
NV = Needle valve to supply a back pressure
V = VFD
All I did was set the motor speed and record the OWP and measured the amount of water delivered by the pump by catching the water stream into a container for a set time period.
Setup.JPG
Replacing the the spring with the brass cylinder effectively removes/decouples automatic pump pressure/flow control enabling these now to be controlled by the VFD.
Below you can see with the VFD ranging from 30 to 70 Hz the pump output pressure more than doubles (+122%) while flow increases by ~70%
This means a barista can now control P & F even during a shot/extraction depending on their specific requirements.
P&Flow.jpg
Some more testing to do to determine the optimum position of the length screw on the brass cylinder.
I have spoken to SWMBO about giving up some valuable kitchen cupboard space to accomodate said pump and she was surprisingly positive about it!Last edited by BobL; 17th Sep 2019 at 06:38 AM.
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23rd Aug 2019, 01:48 PM #35Member: Blue and white apron brigade
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Started prepping the machine and under cupboard plumbing for the new pump.
One major issue while doing all this is to keep coffee machine in action - ie coffee has to be available at all times
I moved the solenoid and filtered water pressure regulator from under the sink to the cupboard immediately under the machine. The benefit of this so I can see what happens at the machine while adjusting the filtered water pressure. Otherwise I'm going back and forth all the time.
Thought I had everything done up tight ie could see no leaks, so went down shed for a bit and came back up later (for a coffee) and found the inside of the cupboard full of water!
DANG - had to completely empty the cupboard and then mop up and let it dry out - ie crockery everywhere.
Then I needed to par-strip down the machine to see what additional internal plumbing and electrical fittings would be needed to attach the new pump. Turns out its not going to be too hard.
I will have to bypass the old pump over pressure valve which is separate from the old pump but that should not be too hard.
To see where the pump was going to be connected required 4 panels on the machine be removed but while I was doing this I looked for a placed to attach a thermocouple so ended up stripping it down this far - Even this far stripped down, apart from the milk steaming wand, the machine still works
GUTTEDMACHINE.JPG
To attach a thermocouple I needed a flat bit of machine close to the water chamber just before the water goes onto the coffee and that I could easily drill and tap to attach a bolt or screw through which thermocouple wires could be run. I fully envisaged removing the "group head" (Big fat brass chamber that forces the hot water onto the ground coffee) and putting it on the mill but I quickly spied a screw that didn't seem to be doing anything.
I checked the screw on the machine schematic in the manual and it turns out to be a test point that goes all the way into the inside of the group head. ie perfect
SCREWPOSN.JPG
Running a couple of fine wires though the middle of that screw was not going to work and using a standard hex bolt head was not going to be any better because with all the panels back on I would not be able to get a spanner in there to tighten it and there is no room for a socket either.
So this is what I did using an M6 capscrew. Where the wires come out they sit just below the bottom of the key.
The long hole down the middle was done in the lathe and the side hole on a drill press.
The 2 mm bit snapped just as it broke though from the side hole into the long hole but I was able to get the broken bit out, resharpened the bit and carried on.
Now the holes get filled with epoxy for a 10+ bar pressure seal.
CapSCREW.JPG
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23rd Aug 2019, 02:32 PM #36Diamond Member
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The PID conversion kit for my Silvia came with a screw-in RTD temp sensor that screwed into a spare hole in the top of the boiler. The setpoint of the unit is 107 degrees, which corresponds to some lower temp at the face of the group head - when I first got it, I put a thermocouple on top of the packed coffee before locking it into the head, so I could see the temperature of the water as it met the coffee grounds, and adjusted the setpoint to suit. Your sensing point looks pretty much ideal - much closer than mine to the actual coffee grounds.
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23rd Aug 2019, 05:15 PM #37Member: Blue and white apron brigade
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23rd Aug 2019, 07:47 PM #38Diamond Member
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It may well not be needed - I think your machine probably has a greater boiler volume and overall thermal mass which means it's able to maintain a more stable temperature, whereas the Silvia suffered the hysteresis and overshoot you get from a simple thermostat, relatively large heating element and relatively low thermal mass. I guess being able to monitor the temp during the shot will give you some idea of how stable it really is.
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23rd Aug 2019, 08:22 PM #39Member: Blue and white apron brigade
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Yeah we'll see soon enough.
The Cimbali Junior has a 2.5L boiler and even with a 2000W element it still takes ~ 8 minutes to warm up before the ready light comes on, but the brew head is still not hot so the first shot or two are underdone. Things improve markedly If I flush the head for 30s before pulling the first shot.
For comparison purposes I looked up the Silvia and it said it had a 300ml Boiler, 1100W heating element and a machine weights of 14 kg, versus 33 kg for the Jnr.
I'm now going to do a basic hook up of the pump to the machine so that the pump is turned on/off by the existing electrics. The pump speed will be done manually by simple analog pot, and pressure/temp monitoring done via an Arduino. That way I can get a feel for what it's doing before attempting a more automated setup.
Also while all this is happening I have to keep the machine functional.
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23rd Aug 2019, 09:17 PM #40Diamond Member
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Gosh - the difference in volume and element size was considerably greater than I assumed.
I have a bit of a routine - I turn on my machine at least 1/2 an hour or more before I get up in the morning, then once up, turn on the steam stetting and give it another 10-15 minutes to build up the heat. Then steam the milk, run the head into the cups to drop the boiler temp and heat the cups, then pull a double shot.
My lunchtime routine is to just let the machine come up to temp for at least 15 minutes, then pull a double shot. The temp is probably more stable for the lunchtime coffee, but there's no milk, so a bit more critical, although if it's looking a little over extracted, I add a dash of milk.
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23rd Aug 2019, 09:58 PM #41Member: Blue and white apron brigade
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We use the larger boiler quite a bit to make tea or soups or for cooking etc.
Your routine sounds like my routine when I was employed and we had the machine on a timer to come on 1/2 an hour before we got up.
My first coffee was always a double espresso and I wanted it just so and then usually followed it with another.
I used to drink 90% espresso (at work we had a Jura), with the odd iced milky coffee in summer, but have now substituted cream for milk - doesn't work with ice unfortunately.
Still make a lot of steamed milk coffees for SWMBO and guests etc.
These days I get up anywhere between 5 and 7 am so the timer has be decommissioned and my first coffee is a double shot with a slug of with cream, topped up with hot water.
I have another one of these after walking the dogs and another one after dinner
The rest of the day I have a variety of coffees; usually espresso, but also long blacks and machiattos using cream.
And as far a cream and body weight are concerned, even though I have been going through a lot of cream, my weight since April has gone down by 7 kg.Last edited by BobL; 17th Sep 2019 at 06:42 AM.
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2nd Sep 2019, 10:12 AM #42Member: Blue and white apron brigade
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Still waiting for the pressure sensor to turn up.
In the meantime I started on the micro controller- a $10 Arduino Uno clone.
Initially its just going to monitor a few machine parameters an I will control the pump speed manually via the VFD.
Here is the prototype MC/monitor hanging off the side of the machine.
The two pots on the RHS of the MC box are the pots fro controlling the VFD
Arduino1.JPG
The power for the MC/monitor and the VFD come from a double GPO wired via the coffee machine mains switch so that the MC and VFD are switched on/off when the machine is switched on/off.
The MC draws about 35mA while the VFD/Motor draws about 1/2A so it should not over tax the coffee machine electrics.
Also the 3P motor only runs for no more than 30s at a time while the coffee is being extracted.
The only sensor currently connected is the Brewhead temperature (BT) thermocouple - see below.
The LHS number is the instantaneous temp, the other is an average of 20 readings over one second.
PP: will be pump pressure in bars
ET is elapsed time or extraction time (the shot clock) from when the pump is turned on to off.
MF is the VFD/motor frequency
Both ET and MF are working on the test bench with dummy inputs but as I don't yet have the new pump connected they are not working on the machine
arduino2.JPG
Wasted a lot of time getting the thermocouple to work properly.
It was working fine on the bench, even when using boiling water, but when connected to the coffee machine the TC output temp was all over the shop (25 - 140ºC).
At first I thought it was a noisy PS (I'm using an old Telstra 9V AC/DC adapter to power the MC) because the MC ran fine on the coffee machine a 9V battery.
What eventually tipped me off was I saw a tiny spark between the TC tip and the coffee machine, just when I was for the umpteenth time removing the TC from the coffee machine.
It turned out the voltage between the coffee machine and the MC grounds was 105V AC !!.
As soon as I connected the MC signal ground to mains earth the problem virtually disappeared.
There’s still something small and funny going on - might need to put a filter on the TC input.
Now I have to recalibrate the TC and it should be good to go.
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2nd Sep 2019, 01:23 PM #43Golden Member
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A fantastic amount of intellect being applied to this. Looking forward to seeing the finished result.
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2nd Sep 2019, 02:19 PM #44Member: Blue and white apron brigade
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12th Sep 2019, 08:37 PM #45Member: Blue and white apron brigade
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Finally got my pressure sensors so I could finish up this project.
Lucky I bought two because in between calibration and the prototyping I buggered one - that will teach me for buying cheapies.
Once this all gets sorted I will buy a decent one for long term use.
Decided to do the prototyping outside - just as well as I had two leaks - water pissing out everywhere. That's also why I had everything sort of spaced apart.
The prototyping set up is shown below.
PR is the mains water coming in via a garden hose and a pressure regulator (drops the mains pressure to about 3 bar) - on the coffee machine a solenoid completely shuts this down to zero in case there's leaking in the system - especially when no one is around. The solenoid only opens when water is needed.
PS is the new 20 bar pressure sensor.
The typical pressures used will be between about 7.5 and 12.5 bar.
There are auto pressure relief valves on the motor and another on the machine that will open at ~14 and ~15 bar respectively.
V is the VFD, A is Arduino box.
N is a needle valve that was used to simulate the back pressure generated by a coffee puck.
Prototyping2.JPG
The aim of this prototyping was to make sure the Arduino was measuring the pump pressure and reading the VFD frequency.
And here it is - The temp reading (BT) is meaning less as the temp sensor has been disconnected for this testing - it's screwed in back at the machine.
PRESSDISPLAY.JPG
The pots on the side of the ARDUINO box control the motor speed so the operator will be able to force more or less water though the coffee.
The values shown are averages of 10 readings per second. The number of readings per second being limited by the time needed for the pressure sensor and associated analog port to settle between changes (~70ms).
Maybe - tomorrow I will try it all on the machine.
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