Gaggia Classic, Schematic diagrams, PID-ing

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Gaggia Classic, Schematic diagrams, PID-ing

Postby Captain_Crema » Thu Jul 27, 2006 8:57 am


Does anyone know where I can get a schematic for my Classic? There must be a picture somewhere on the Internet, but I've not found it yet.

I am going to fit a PID and SSR soon, and want to be sure I have the right connections.

This PID is the one on eBay from seller "palmelectronics". It cost about £18.00 (with postage!) and it arrived a couple of days ago (with a free K type thermocouple, no less).

Here's a link to the item :

There's a link on the eBay listing to his own web site and you can download a manual there. It does seem to have "fuzzy logic" self-learning / auto setup mode, which is amazing given the price.

Anyway, I'm going to try it out on the Gaggia and use this thread to report on how it goes, and ask questions (of course).

The thermocouple is a screw in type, so I may need to find an adapter to screw it into the boiler where the existing thermostat is.

In the meantime, I need a parts diagram and schematic. Anyone got one?
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Postby bainesy » Thu Jul 27, 2006 10:26 am

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Postby Captain_Crema » Thu Jul 27, 2006 12:09 pm

Thanks. I will now get hold of an SSR! I presume at least 10A rating zero switching (whatever that means).
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Postby knewmans » Thu Jul 27, 2006 7:04 pm

Be careful of the rating. The capacity generally varies with temperature. As its going inside the Classic it will get quite warm. You need to check the specs.
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Postby Captain_Crema » Thu Jul 27, 2006 7:53 pm

I've had a look at the thermostat. It is a screw in surface mounted device, and the thermocouple that the PID came with won't fit (it's too big). However, by taking the metal outer of the thermocouple, I've got this tiny pair of wires welded together with a blob (this is the actual thermocouple). I can't see an insulated shroud in the inside of the casing - does it need one or is it OK to just connect the thing to the boiler (which is earthed)?
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Postby Captain_Crema » Thu Jul 27, 2006 8:54 pm

Right, some experimentation with the PID and an exposed thermocouple.

It doesn't seem to matter if it's in the shroud or just touching earth, it still works. Without the shroud it reacts much quicker, so this seems to be the way to go. Oddly enough, I discovered that it is polarised, so if you connect it the wrong way round to the pid, it shows decreasing temperatures as the real temperature increases.

First I calibrated the PID by dunking the thermocouple into a kettle full of water. Turned it on, let it boil and it's reading 102 degrees C. Have calibrated the PID back to 100 degrees C and reboiled. It goes no further than 100, and since I'm in a coastal town I reckon I'm as close to sea level as makes no odds.

Next, I attached the thermocouple to the surface of the boiler in the Classic and turned it on. The results are rather surprising.

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).

This is a good reason for me to have varying quality shots - any comments?

The PID seems to work fine, although until I can get it controlling the heating elements directly (need an SSR now) I can't tell how effective it will be. But it would be hard to imagine it being worse than the Gaggia's built in thermostat. For now, I'm very impressed. Remember it only cost £18.

I've now ordered a couple of 240v 30A SSRs from an ebay seller. We'll soon see!)


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Postby lukas » Thu Jul 27, 2006 9:34 pm

Please keep us updated, Jon. This is very interesting! I'd like to do this to my old gaggia, too (whenever that is ...) and would be very happy about pictures from how you fit everything together and stuff. Thanks!

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Postby Kevman » Fri Jul 28, 2006 7:39 am

I would also be very intested to hear how you get on.

Off topic a bit - has anyone with a Classic ever ovened up the boiler - mine is three years old and although i have descaled fairly regularly, i am thinking that i would like to open her up to see how bad / much cleaning is required.
Also would you need to replace the seal ?
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Postby Captain_Crema » Fri Jul 28, 2006 9:18 am

Kev, could you start a new topic for your boiler question please? I want this thread to stay on topic as it's the sort of thing that will be very interesting to lots of people.



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Postby clovissangrail » Fri Jul 28, 2006 9:47 am

Depending on the impurities in the water isn't it possible that the water may boil at a different temperature? Just a thought - but suppose if you are using the same water in your classic then it may make no odds...

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Postby kingseven » Fri Jul 28, 2006 10:05 am

Wouldn't you need a great deal of impurities in the water though? Even huge amounts of salt have barely any effect on boiling point, certainly compared to altitude.

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Postby Captain_Crema » Fri Jul 28, 2006 12:24 pm

Cor! It's getting technical.... :D

OK, we use a built in ceramic water filter to fill the kettle (and the Gaggia) so I doubt very much that there are many impurities.

As regards the temperature thresholds, are these typical for an espresso machine with a thermostat? It seems to me that the high point is way too high. Obviously the water temperature in the group is the most important factor, but it's not likely to be much less if everything is warmed up properly (portafilter included). I've seen water come out boiling when doing a cooling flush without coffee in the basket and I reckon this would result in some pretty nasty coffee. Although what I'm measiring is the boiler surface temperature; the water inside might be a little cooler, but I reckon it's still over boiling point.
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Postby ben_edwards » Fri Jul 28, 2006 1:00 pm

Captain_Crema wrote:

I've now ordered a couple of 240v 30A SSRs from an ebay seller. We'll soon see!

Are there more of the same available on ebay? I couldn't see any when I looked. How much did they cost? I still haven't recieved my pid but I paid later than you so I guess I have to wait maybe another week :( I look forward to hearing how you get on... it'll make my life a lot easier when the bits arrive!
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Postby Captain_Crema » Fri Jul 28, 2006 1:44 pm

Ben, they were about £6 with the postage. There are two of them, but they're old new stock (apparently there are no scratches on the spade terminals so the seller is saying they are unused...). Well, I don't care as long as at least one of them works properly!

Incidentally, I found loads of them on eBay. Search for "Solid State Relay", not "SSR". Here are the items I bought :
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Postby Captain_Crema » Fri Jul 28, 2006 1:47 pm

Ben, he has another set up for £5 + postage. Get your order in!!

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