Gaggia Classic, Schematic diagrams, PID-ing

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Postby ben_edwards » Fri Jul 28, 2006 5:21 pm

Fantastic! Thanks for letting me know... I was just being lazy by searching for "SSR" :) I got the set you linked above. An excellent price! I'm sure the spare will come in useful sometime down the line!
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Postby ben_edwards » Fri Jul 28, 2006 6:24 pm

Just stumbled accross this which takes into account atmospheric pressure and altitude to give th eboiling point of water.

http://www.csgnetwork.com/h2oboilcalc.html

:D

So assuming your altitude is 0m and the pressure is 1014 mbar the boiling point should be 99.6deg C :) Note that even an altitude of 50m results in a 0.1 degree drop to 99.5degC. I think this may be ott however and what you have done already seems very logical. At the end of the day it will be calibrated 'to taste' so the exact temp will only be useful for comparison with other machines. I wonder why it was 2deg out though? Does the manual tell you to calibrate it?

.... off to download manual before it disappears!...

The almost 20degC range of temperatures for the boiler seems shcking! It does explain why sometimes the water is boiling (steam coming out of the group head) and sometimes relatively cool just on the normal (not steam) cycle! All the more reason to ditch the gaggia thermostat and use the pid though :) I'm regretting trying to negotiate a deal with the ebay seller now as I would have the pid if I had just paid up straight away!

What are your ideas on attaching the thermocouple Jon? Will you solder it onto the boiler? Is it easy to rempve the screw which comes on the thermocouple?
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Postby Captain_Crema » Fri Jul 28, 2006 6:54 pm

Steam from the grouphead? If it's not coming out under pressure I think it's likely to be water vapour (the two aren't quite the same). If the grouphead's over 100 degrees C the water will come out boiling.

Modifying the thermocouple is fairly straightforward if you're careful, but I need to take pictures to explain. Suffice to say that once done it's easy to attach to the boiler. You don't need to take the old thermostat off, either. All will be revealed presently, when I have taken some pictures. I'm proposing to have the PID in a separate case with its own mains lead and only low voltage wires going into the Classic. (thermocouple and SSR control). This is the safest way.

The SSR would therfore be mounted inside, using the stainless case as a heatsink. In order to avoid drilling holes I will mount it using the grille at the back although it might need to be relocated if the heater wires don't reach. It may be necessary to insulate the boiler (there is a thread about this) in order to keep the case cool so the SSR can lose excess heat, but right now I don't know about the heatsink requirements of the device.

The thermocouple can be attached to the boiler body by trapping it between the boiler and the earth tag, which is screwed in. This is how I measured the threshold temperatures. An alternative would be to unscrew the thermostat (it's the one on the left hand side of the boiler, not the top) and insert the thermocouple into the screwhole. It may be necessary to use some heat transfer compound here (there's some on the mating surface of the thermostat - it's like a white cream). Note that the thermostat body does not make contact with the water, it measures the boiler body temperature. In other words, the screw hole doesn't penetrate the boiler so there is no chance of leakage if you get it wrong.

The most important thing for me (apart from safety, of course) is to ensure that the operation is reversable if I find it doesn't work well enough or I want to sell the machine. I think if I can get one of those Gaggia plinths (with a drawer for a knock box) I could butcher it and fit the PID in there. It would look neat and be electrically safe, but it's a way off for me. I need to test it out first.

More soon.

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Postby ben_edwards » Fri Jul 28, 2006 8:45 pm

Captain_Crema wrote:Steam from the grouphead? If it's not coming out under pressure I think it's likely to be water vapour (the two aren't quite the same). If the grouphead's over 100 degrees C the water will come out boiling.


Yes I agree... if the boiler is above 100 deg C steam / water vapour will be produced. I have never seen any differentiation between these two terms: As far as I was aware the vapour (definition: gaseous state of a substance) of water is steam. Could you clarify/provide a source if I'm mistaken.
Captain_Crema wrote:Modifying the thermocouple is fairly straightforward if you're careful, but I need to take pictures to explain.

That would be great :).

Captain_Crema wrote:Suffice to say that once done it's easy to attach to the boiler. You don't need to take the old thermostat off, either. All will be revealed presently, when I have taken some pictures. I'm proposing to have the PID in a separate case with its own mains lead and only low voltage wires going into the Classic. (thermocouple and SSR control). This is the safest way.


good thinking.

Captain_Crema wrote:The SSR would therfore be mounted inside, using the stainless case as a heatsink. In order to avoid drilling holes I will mount it using the grille at the back although it might need to be relocated if the heater wires don't reach. It may be necessary to insulate the boiler (there is a thread about this) in order to keep the case cool so the SSR can lose excess heat, but right now I don't know about the heatsink requirements of the device.


I think this will be fine. The SSR you pointed me to was 30A. I think this will be fine as it is way over - rated for this purpose :).

Captain_Crema wrote:
The thermocouple can be attached to the boiler body by trapping it between the boiler and the earth tag, which is screwed in. This is how I measured the threshold temperatures. An alternative would be to unscrew the thermostat (it's the one on the left hand side of the boiler, not the top) and insert the thermocouple into the screwhole. It may be necessary to use some heat transfer compound here (there's some on the mating surface of the thermostat - it's like a white cream).


|I think this is like cpu heatsink compound? I'm sure I can dig some out.
Captain_Crema wrote:
Note that the thermostat body does not make contact with the water, it measures the boiler body temperature. In other words, the screw hole doesn't penetrate the boiler so there is no chance of leakage if you get it wrong.


Yes, obviously this would be ideal but impractical! The pid needs calibrating with measurements from the grouphead maybe?

Captain_Crema wrote:The most important thing for me (apart from safety, of course) is to ensure that the operation is reversable if I find it doesn't work well enough or I want to sell the machine. I think if I can get one of those Gaggia plinths (with a drawer for a knock box) I could butcher it and fit the PID in there. It would look neat and be electrically safe, but it's a way off for me. I need to test it out first.

Thats another great idea. John Lewis were recently sellin them for £15 so maybe worth checking.

Keep the updates coming!

Cheers,

Ben.
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Postby ben_edwards » Sat Jul 29, 2006 8:25 am

Ah... Just realised that by water vapour you mean not the product of boiling. My mistake :) I think that there is definately steam coming out of the grouphead on the cooling flush though (when its been on ages). There is also a faint hissing sound when its not in use! Best keep on topic though so I'll leave this for now.
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Postby Captain_Crema » Sat Jul 29, 2006 3:44 pm

Yeah Ben, mine hisses sometimes too.

Right, back to it. It looks like the SSR has too high a threshold voltage (it says it's 20V DC but the PID outputs 12V DC), because I've connected it all up and nothing happens. I know the SSR is switching the output on because the relay's clicking. I have the Outy setting to 2 (SSR + Relay J1 as alarm). So, the SSR is busted, or not triggering, or the PID's SSR output is dead. I won't know until I get my multimeter out. Dammit.
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Postby lukas » Sat Jul 29, 2006 3:55 pm

Now thats bad luck. You did read the specs prior to purchasing, did you? :P

The temperature cycle is between 94 at its coldest and 113 at the hottest (and I can see it is overshooting quite a bit, as the heater turns off way before the temperature stops rising).


I just did the same with my thermometer and got nearly the same values. Heater switching off at about 100°C, temperature overshoots up to 114°C, slowly goes down to 88°C and the heater goes on again. Measured on the top of the boiler, but I don't know how accuratly these measurements are. I mean, I just hold a small metal ball kind of thing onto the top of the boiler ...
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Postby Captain_Crema » Sat Jul 29, 2006 6:00 pm

ben_edwards wrote:Yes I agree... if the boiler is above 100 deg C steam / water vapour will be produced. I have never seen any differentiation between these two terms: As far as I was aware the vapour (definition: gaseous state of a substance) of water is steam. Could you clarify/provide a source if I'm mistaken.


Try this : "In physical chemistry, and in engineering, steam refers to vaporized water. It is a pure, completely invisible gas.."

Comes from Wikipedia entry : http://en.wikipedia.org/wiki/Steam

What you can actually see is the partially condensed water vapour, although most people commonly refer to it as steam.

Now thats bad luck. You did read the specs prior to purchasing, did you?


No I didn't, and that's why I'm in this fix. D'oh.
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Postby ben_edwards » Sat Jul 29, 2006 8:48 pm

...PID outputs 12V DC...

its 10V DC according to the manual. Have you measured with a multimeter or was this a mistake? I have found http://www.qis-uk.co.uk/ which seem to sell them for around a tenner. I'm not sure if they do individual items though as prices are only for bulk. Will enquire...
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Postby ben_edwards » Sat Jul 29, 2006 8:55 pm

Just had this reply from the seller of the SSR so are you sure the pid is correctly set up. Have you tried both of the SSRs?...

I was asked before about the control voltage range on these, and as I have no data on them I had to conduct an experiment.
My test rig used a 30V dc 3A current-limit supply as the load, using the relay to short out the supply.
I then tried a variety of control voltages and found that 5V dc was no good, but 9V derived from a rechargeable PP3 battery (!) worked every time.
This is of course a bit empirical, but hopefully indicates that not all is lost.
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Postby Captain_Crema » Sun Jul 30, 2006 8:31 am

ben_edwards wrote:
...PID outputs 12V DC...

its 10V DC according to the manual. Have you measured with a multimeter or was this a mistake?


No mistake, Ben - section 2 says 10v but section 4 (note 1) says 12. My multimeter measures 8v. I tried both SSRs and neither are triggering. I've tried a 9v battery and it doesn't trigger. Then I clipped two 9v batteries together for 18v and it triggers fine. Maybe your SSR will have a slightly higher output. My batteries measured 8 and 8.5v repectively.

The eBay advert doesn't specify the trigger voltage. The only mistake I've made so far (ha!) was to grab these SSRs without checking with the seller first. What a Dibley.... :roll:
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Postby ben_edwards » Mon Aug 07, 2006 7:41 pm

Jon, did you get the SSRs sorted? I have some on the way from the US which I'm hoping will do the job this time!

I would be interested to know how other classic owners have mounted the PID... there doesn't seem to be much internal space and I'm guessing it may get too hot inside the machine for the PID anyway. Maplin have some project boxes which could be mounted somehow but they cost a lot for what they are and the one that fits is quite a bit bigger than the PID. Any suggestions?
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Postby mocha » Mon Aug 07, 2006 10:52 pm

After extensive modifications with my Gaggia, I would recommend to fit the pid separately (http://i96.photobucket.com/albums/l166/ ... cn0980.jpg), to place the temp sensor at the front side of the boiler right above the group and set the pid for 86-87 C. That will provide about 90 C at the cup. A H/D pressure gauge sensing between pump and boiler is very helpful. Boiler should be always on during the steaming of milk. Cheers
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Postby Captain_Crema » Tue Aug 08, 2006 8:58 am

Ah-ha! Right on, mocha.

I've set the thing up temporarily with a couple of batteries connected to the PID relay output and the SSR (after badly injuring my hand in the process - see my other post). The thermocouple is on the top of the boiler and the setpoint is 97 degrees, which it is maintaining very well. I came to the same conclusion as you as regards the PID location. There is no space for it to be mounted inside the Classic, unless you want the display facing to the side or the top and in any case it is very difficult to get a good result when cutting stainless steel. However, the SSR is inside the machine which means there are no high voltage cables coming in / out of it, just the SSR trigger and thermocouple leads, and these pass throught the existing grille at the back.

I have just acquired (from another eBay seller) a pair of SSRs with a much lower trigger voltage (something like 3-25v) and I will plumb one of these in permanently when I get them. Once I've done that, I'll post the pictures here.

Can you tell me how the thermocouple is attached to the side of the boiler? I might try soldering it but access is very tight down there. The other thing I was going to attempt was resusing the threaded hole that the existing thermostat is screwed into, but it is not in the same location as you suggest. I think there is some sort of tape that can be used, but I've no idea where to get it from.

Finally let me say FOR GOD'S SAKE UNPLUG THE MACHINE FROM THE WALL SOCKET BEFORE FIDDLING WITH THE INSIDES!!!!!

Cheers


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Postby lukas » Tue Aug 08, 2006 1:14 pm

Ouch!
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