Gaggia Classic, Schematic diagrams, PID-ing

Equipment, technique, or just drinking the stuff

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Postby GeorgeW » Thu Aug 10, 2006 3:29 pm

ben_edwards wrote:Just tried bumping it up to 208F (99C) from my previous 200F (93C) and the comparison is akin to wine and dishwater! The 208F brew is weak, thin and sour/bitter, crema is thin settling at a few mm. The 200F brew was thick, and well balanced with a thick crema. These settings will obviously be applicable to my thermocouple location only.


Right but with my t/c halfway down the boiler my sweet spot was at 202f.
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Postby CakeBoy » Thu Aug 10, 2006 3:59 pm

C_C you may well be right. I have the same one as George and Dom. Will try to find a link, but couldn't see anything about fuzzy logic and assumed it was without being so cheap. I'm such a muppet.

Nice enclosure Ben. Which size did you buy? I will follow your lead :D
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Postby GeorgeW » Thu Aug 10, 2006 4:09 pm

No, ours were from someone called "tibetwalk" Cakey. Mind you they could be the same company I suppose.
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Postby ben_edwards » Thu Aug 10, 2006 4:50 pm

Nice enclosure Ben. Which size did you buy?


AB9 102 (4in.) 70 (23/4in) 38 (11/2in.)

was a tight fit though, looks pretty neat even though without the pid in it looked like i swung randomly with a jagged blade. If I were to do it again I may have gone for a plastic one as I don't have a workbench it proved difficult to hold the enclosure whilst operating power tools :) Still got all me fingers though... dangerous game this pid lark. Oh and I must get round to earthing the box as its metal (it just needs a wire connecting PID earth terminal to the inside of the enclosure)... don't want any C_C esque fireworks ;)
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Postby CakeBoy » Thu Aug 10, 2006 5:11 pm

That's the one, thanks George. I couldn't recall the name in my current state of flux :D

Sounds like you were lucky to keep your digits all intact Ben .... crikey :D
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Postby Captain_Crema » Thu Aug 10, 2006 7:01 pm

C_C esque fireworks... you cheeky monkey. The only fireworks were the loud swearwords I shouted as I shaked blood all over the kitchen floor. What a mess. Now you can see why my avatar is Mr Bump... :D

My PID settings after auto calibration are:

P = 02.4
I = 0099
d = 024
SF = 001
Bb = 038
ot = 002
FILt = 0

..but bear in mind my thermocouple is on top of the boiler as stated previously, not at the side where the thermostat is. I think the thermostat is positioned too close to the element anyway. I mean, the heat is going right to the thermocouple on yours through the boiler body, so you've much less chance of getting a decent measurement of the water temperature. I would suggest siting it at the front near the bottom of the boiler and re-doing the auto-calibrate.

Ally enclosures are fine. The best way to cut them prettily is to use a sheet cutting device called a nibbler, but you have to drill holes at the corners. It is earthed, right?

Following your comments about temperature, I've altered my set point to 92 degrees C. The HasBean Cup of Excellence is waiting for the machine to warm up even as I type. But the temperature is all over the place, so I think it might be necessary to recalibrate it. The coffee's not very good either. :(

Never mind, time for some more experimentation.

Edit : Just found out I had a loose connection to the SSR's low voltage supply (a couple of PP9s in series)... sorted now - let's have another go...
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Postby Captain_Crema » Thu Aug 10, 2006 7:36 pm

Yep, the fix has worked and I am now brewing at a more or less constant 92 degrees. I think it's too cold as the coffee's coming out with an odd bitter taste like you get at the bottom of a shot if it goes a bit cold. I have to experiment more, but if I carry on I'll be on caffeine overdose, so enough for tonight...
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Postby ben_edwards » Thu Aug 10, 2006 7:54 pm

Glad you took my humour in good heart ;) If its any concilation I blew up one SSR by letting 240V jump across the load contacts whilst checking the voltage :|

Well a little reading about control theory - woosh! - and the little I did absorb tells me something was wrong - the constant offset I reported is only correct if the integral part of the PID is not working. So I guessed that it was working and there is some roundoff error involved - although bizzare this seems due to the calculations being done in C and then converted to F:

setpoint 200F = 93.3C -> the PID then uses some sort of integer conversion and uses 93C...
93C = 199F which I was getting.

So I am now working in C as there seems no point in using F if it just introduces error. The PID now sits at the correct value so I geuss I'm right, at least in some way?!

And urm... the case is earthed mutually through sitting on the metal caseing of the classic :) could have gone to that trouble of cuttng but it really doesn't matter it looks fine after everythng (PID, tape...) s in place :D. Anyhoo now just have to play with different temps. I think there are going to be tradeoffs wth all locations for the thermostat - I measure the heating element while you measure the steam! It really needs to be in the water, but of course with the small boiler and huge heating elements the gradient of temperature in the water volume will be large enough tomake internal positioning an issue ;)
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Postby CakeBoy » Thu Aug 10, 2006 11:45 pm

C_C, that is the flavour I am discerning from the Audrey described perfectly. Very odd as the temp is clearly right and it was checked with a Fluke just in case. Will be interested to see what you find as you continue to experiment.
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Postby Captain_Crema » Fri Aug 11, 2006 8:11 am

What's the setpoint on your PID, Cakeboy? Where is the thermocople located? I'm wondering if we haven't all got the temperature too low.

My problem is I'm still trying to master tamp & grind, so I have a lot of variables to deal with.
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Postby CakeBoy » Fri Aug 11, 2006 4:09 pm

Setpoint is currently 101C Cap'n, because the water exiting the grouphead is then 95-97C which is the same as the L'Anna. The t/c is halfway down the vertical boiler on the side.
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Postby Captain_Crema » Fri Aug 11, 2006 6:15 pm

Hmmm. What about the Audrey - that's got a PID too hasn't it?
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Postby CakeBoy » Fri Aug 11, 2006 6:30 pm

It is the Audrey with the PID. She is set at 101C because the output water is then the same as Anna's at 95-97C. Anna has no PID. She is a big girl and doesn't need one. She laughs in the face of 10oz flushes and just stays stable :D
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Postby ben_edwards » Fri Aug 11, 2006 6:38 pm

I just tried 100C on my setup and got a thin crema which was really dark at the edges...is this the burnt crema I've read somewhere? Anyhow it was with a different bean (Ethiopian) and tasted nice, maybe it was a burnt taste but it was good.

Pre-PID the classic would produce a really strong flavour (not sure how to describe it really) at the bottom of the cup (last sip) I think C_C and someone eles on a recent thread also found this with the gaggias. I thought it might be a result of hot temperature but the 100C I just had wasn't like it. Maybe I need to go way higher, maybe lower! Any ideas?

What was the temp reange with the thermostat you measured C_C... I might try min and max and see whats more similar.
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Postby GeorgeW » Fri Aug 11, 2006 7:54 pm

Ben, try surfing while checking boiler temp on the PID at which you get a good cup. This then will be your ref. temp to set the PID. My Sylvia is at 34 secs. after the heater has switched off which corresponds to 201F.
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