Gaggia Classic, Schematic diagrams, PID-ing

Equipment, technique, or just drinking the stuff

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Postby GeorgeW » Sun Sep 10, 2006 5:26 pm

Don't know if it helps but I eventually followed Cakey's example and fixed the t/c halfway down the boiler using a large jubilee clip which I modified by threading it through a thin metal plate. This gave me a larger surface to press the t/c against the boiler. I used paste as well and the temp would seem to be accurate.
That said I still can't get the pid to switch on the heater and I seem to remember that some of your settings on your pid were reversed. I'm now wondering if mine is the same.
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Postby Captain_Crema » Sun Sep 10, 2006 7:17 pm

George

Check trigger temperature and output mode settings. Also, check the input voltage on the SSR; the PID output is a bit on the low side (a very weak 9v despite the manual tating 12v). Maybe your SSR isn't triggering. If you're trying to use the relay output direct to switch the element it's probably burned out (well, the contacts at least) . IIRC it's only rated 3A, or at least, not enough for a coffee machine element.
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Postby ben_edwards » Mon Sep 11, 2006 8:32 am

GeorgeW wrote:That said I still can't get the pid to switch on the heater and I seem to remember that some of your settings on your pid were reversed. I'm now wondering if mine is the same.


George, I would say there are a few possible problems:

1) the pid is not switching. the PID I am using has a cooling option, which would not switch the heater, as it always sees a temperature below the setpoint. On my PID it is just a 1/0 option on the setting menu. The default was heating, but the instructions to set it up wrongly stated to switch it to cooling.

2) the pid is switching but the ssr is not. The first ssr i tried would not swich at the voltage output of the PID.

You really need to set the thing up and have a multimeter chech the dc current across the SSR ouput of the PID (or the input of the SSR). If you see a voltage of around 7-12V when you require heatng then the PID is doing its job. The SSR would then be prime target. Carefully check the AC 240V across the SSR's output terminals. If there is no voltage across the SSR output when the DC input is on then the SSR is not switching. Be careful with that multimeter mind, I heard that Captain_Crema now has a wooden arm, which is not great for drinking espresso. Definately do not check the current across the SSR output unless you like fireworks ( I did by accidently having the multimeter on current mode -oops)
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Postby Captain_Crema » Mon Sep 11, 2006 12:17 pm

Wooden leg is more like it, Ben!

You can test the SSR with a PP9 battery (if it's input trigger voltage is low enough).
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Postby GeorgeW » Mon Sep 11, 2006 12:53 pm

Thanks guys, I've already checked out the ssr with a battery and it is switching. Again I have had a multimeter across the pid o/p terminals to the ssr and there is nothing there. Target temp is ok and the temp read by the t/c seems about spot on. I've checked the polarity of the i/p to the ssr and that right and the polarity of the t/c seems right also. So it seems that it may be the o/put mode settings that are wrong so I'll have to check these AGAIN. It could be the pid itself not working, I'm on my second one (not the same fault though).
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Postby ben_edwards » Mon Sep 11, 2006 1:48 pm

The manual with mine stated the default setpoint temp was 80C.. it turns out it was 800C :/ What about testing it in relay mode so you can listen for the click. If that works the SSR [edit] output of the pid [/edit] must be duff, if not I guess its another setting...
Last edited by ben_edwards on Tue Sep 12, 2006 2:22 pm, edited 1 time in total.
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Postby Captain_Crema » Mon Sep 11, 2006 8:37 pm

Nah wait a minute Ben he says the SSR's OK. I bet it's in (as you suggest) the wrong mode.

I have mine in relay mode as I'm using the relay to supply 18V from a pair of PP9s to the SSR as it's trigger voltage is too high. Got a nive 3v SSR just itching to get in there but.. err... I'm scared ....

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Postby lukas » Mon Nov 06, 2006 11:04 pm

I'm hooked. Yesterday, I installed the PID, and I'm totally hooked. The thermocouple is clamped between the boiler and an old brew-thermostat (with a whole lot of head conducting paste between), and it just works wonderfully. When the setpoint is at 107°C (the same as the thermostat's "setpoint"), the double ristretto just gets veeeeery tasty, and no single shot went down the drain (except the ones I needet to find out that 105-110°C was about the right setting :) ). when set to 107°C, the temperature goes down to about 102°C during the shot. But still, no signs of too hot water (not much bitterness), and also no signs of too cold water (not sour at all!). I'm really impressed. I really didn't expect that the shots improve that much!
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Postby ben_edwards » Tue Nov 07, 2006 9:58 am

Yay! Glad you finally got the PID sorted Lukas! How's yours going George ;) I was meaning to post about this before but your post has prompted me to now so... I got a fancy (cheap) multimeter from HK via ebay which tests the temperature using a thermocouple. So I bunged the thermocouple up one of the portafilter spouts and ran water through after warming it up. I was fairly surprised to see that there was a 10(ish)C drop from PID (boiler wall) temperature to output water. I thought as the boiler was directly above the group on the classic that the drop would not be as much, but hey... never mind. So now my PID is on 105C which equates to a 95C starting temperature which drops a few C after a few oz of water has passed through. I think the beans I was on when I first set the PID up liked the cooler temperature, but recently I've had a lot of sour/green flavours. I'm too lazy to react quickly to these things but now I know why and this was occurring. My current beans like the hotter temperatures. Incidentally this also solves a previous problem I had with consecutive shots. The second shot runs much hotter as the group is hotter, as kindly pointed out by Davec. The solution to this seems to be a lower PID setpoint but use a warming flush prior to the first shot. I will continue playing with the new toy and see if the temperature of the espresso under pressure is differing to water under no pressure. I am guessing less temperature fluctuation and more influence from the group temperature.
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Postby GeorgeW » Tue Nov 07, 2006 10:50 am

I haven't got back to mine as yet Ben, bit I'm going to try to fix the thing before selling the Sylvia on. Mind you, it could be handy as a back-up machine. I think the temp drop between boiler temp and pf temp sounds about normal. I'm sure someone mentioned a 20 degree drop before but they were talking in F. It may have been Simonp I think.
Well done with the PID.
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Postby Gouezeri » Tue Nov 07, 2006 11:05 am

GeorgeW wrote:I haven't got back to mine as yet Ben

Hmm, did I buy one of these things... hmm maybe I did... now where where did I put it!!! :roll: :lol:
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Postby lukas » Tue Nov 07, 2006 12:10 pm

The temperatur-drop makes total sense, if you take into account that the normal thermostat is a 107°C one. The point where the temperature is measured is on the lower outside of the boiler. the water gets into it in the other side, and travels all the way to the upside, where it enters the long tube to the grouphead. So, you effectively measure the temperature on the lower outside of the boiler, not the temperature of the water inside.

I usually do long heating flushes anyway, so that should not be a problem here. And yep, if you just flush water w/o a loaded portafilter, the temperature drops indeed much faster than with a loaded pf. I get about 10-20°C drop in say 30 seconds w/o pf, and about 5-7°C drop with a loaded pf. This reminds me that I need to check how the temperature of the water coming out of the gh matches the PID measured one...
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Postby knewmans » Tue Nov 07, 2006 8:15 pm

I've considered PIDing my Classic and probably will but I wonder if a second mod would help as well.

The PID essentially gives you a consistent starting point for each shot. The size of the Classic boiler means that there is necessarily a temperature drop because of the amount of cold feed water entering relative to the size of the carefully temperature controlled boiler water.

Would it help stability if when the brew button was pressed:

1) the heaters came on for a few seconds to provide a reservoir of heat in the boiler walls to offset the cooling and

2) the pump startup was delayed for a few seconds to allow this heat to start reaching the water.

You effectively go from a steady state at the beginning through what should be a consistent cycle drawing the shot with compensation for the cooling water. Anyone have any thoughts if this might work?

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Postby Seb85 » Tue Nov 07, 2006 8:44 pm

I thought about this myself but the electronics required for the delay would be rather more complicated than just a pid controller. Probably the best way to do it woudl be to use some kind of programmable controller.

On the other hand i thought that perhaps a good way to achieve some kind of the same benefit woudl be to fit a pre heater to the water inlet that could come on as the pump is turned on. This would probably lessen the temperature drop a little.
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Postby lukas » Wed Nov 08, 2006 9:20 am

I had a similar idea before, but I think it won't work this way. With this, you are trying to simulate the heating behaviour of HX machines, so if you heat the boiler up before the pump starts, you heat the water up too - and the first ml on top of the puck will be way too hot I think.

It would be great to just preheat the water from the tank .... that would solve it quite ok :)
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