# PID on a Gaggia Classic



## rgoodcoffee (May 25, 2016)

Hi all,

I'm thinking about possibly putting on a PID onto my classic at some point. I was just wondering If people think they are really worth it?

Does brewing at exactly a specific temperature make a difference?

Also could anyone tell me what temperature a classic (if left on for around 30 mins) would run at out of the box?

Thanks!


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## timmyjj21 (May 10, 2015)

Yes.

Yes.

All over the place!

To elaborate further...

The Classic has a small boiler and simple bimetallic thermostats that are slow to respond. As soon as you start brewing, cold water enters the base of the boiler, altering brew temperature. The thermostat swing also makes getting a set temperature difficult hence the concept of 'temperature surfing'.

Installing a PID was the best mod I ever did on my classic, to the point that I didn't make any more sink shots.


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## GCGlasgow (Jul 27, 2014)

As timmy say's, a PID was the best mod I did to my classic and well worth it. It takes the whole variable of guessing the temp out.


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## zoglet (Jun 1, 2010)

What they said. Possibly a bit late for this reply but if you're still on the fence, I just PID'd my oldGaggia and it's completely tranformed my machine. I had already done a fair few mods (see signature) and noticed a big difference in quality after installing. After a couple of weeks usage, I can now be absolutely sure that the PID has made the shots significantly more consistent and higher in quality. Best thing I did to the little fella!


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## broon71 (Aug 15, 2017)

Not sure if I'm missing something, I've read through all of the relevant threads first, I think!

Is the PID mod 'simply' replacing the thermostatic function of the boiler from bi-metallic (mechanical) to an electronic thermostatic control w/relay?


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## DaveP (Jul 14, 2017)

broon71 said:


> Not sure if I'm missing something, I've read through all of the relevant threads first, I think!
> 
> Is the PID mod 'simply' replacing the thermostatic function of the boiler from bi-metallic (mechanical) to an electronic thermostatic control w/relay?


Yes... in short (and in long as well)


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## MrShades (Jul 29, 2009)

broon71 said:


> Not sure if I'm missing something, I've read through all of the relevant threads first, I think!
> 
> Is the PID mod 'simply' replacing the thermostatic function of the boiler from bi-metallic (mechanical) to an electronic thermostatic control w/relay?


Take a quick look here: http://www.eurotherm.com/principles-of-pid-control-and-tuning

On that page you'll see an initial graph - showing how temperature fluctuates when using an "on/off" control, such as a mechanical thermostat.

Beneath it you'll also see a very similar graph - showing how temperature control is stabilised when using a "PID" control.

Hopefully this helps explain the difference.


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## broon71 (Aug 15, 2017)

So a PID controller isn't just an electronic thermostat, but pulses the output signal based on response? Wouldn't a standard electronic thermostat or controller with a 1' differential perform the same function in this case?

(please don't take offence MrShades, am just trying to get my head around this)

Also, why are SSR's used? The boiler probably doesn't pull more than about 6amps does it?


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## MrShades (Jul 29, 2009)

broon71 said:


> So a PID controller isn't just an electronic thermostat, but pulses the output signal based on response? Wouldn't a standard electronic thermostat or controller with a 1' differential perform the same function in this case?
> 
> (please don't take offence MrShades, am just trying to get my head around this)
> 
> Also, why are SSR's used? The boiler probably doesn't pull more than about 6amps does it?


Answer to your first question - no... Google and read much more about PIDs and how the PID aglorithm and config variables work. It's much much more than a thermostat! That said, some thermostats can use PID algorithms - but it very much depends on what they're controlling, etc. The ability to adjust the PID config to suit the applicance / application is key.

Second question - it needs to be a relay or a solid-state relay, and having a relay in your machine clicking away merrily will soon get VERY annoying.


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## broon71 (Aug 15, 2017)

Thanks MrShades! I think I'm starting to get it, thanks for your help.

Suspect I've used up all of my work 'googling' time today....


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