Adding a PID to a Gaggia Coffee espresso machine.
Adding a PID to an Espresso machine
It can be hard to achieve consistent shots with a domestic espresso machines because of the temperature instability. One of the most popular ways to overcome this problem is to fit a PID temperature controller the the machine to give a fine level of control over the brewing temperature. Here's a tutorial if you want to give it a try. The Gaggia Coffee really is an ideal machine for this as the small boiler means that any advantage you can gain in stability will help consistency considerably.
Warning - you will void the warranty on your espresso machine by doing this. Additionally you are working with high voltages that can cause harm or death. Do this at your own risk, take appropriate precautions and please check your wiring carefully
SSR stands for "Solid State Relay". If you're considering modding an Espresso machine I guess you have some experience of electronics and if you haven't come across an SSR suffice to say that it's like an old reed-relay but solid state so silent when switching. The thing to check is that your SSR can be switched on and off by the DC voltage supplied by your PID and that it will take suffucient current. I wanted an 10 amp unit but picked up a 40 amp unit from ebay for £5 inc P & P!
The Other Bits.
Your local hardware store can supply everything else you need. My complete parts list is as follows:
- SSR (10A +)
- 1 meter of 3-core cable with a rating above 10 amps
- Zip Ties
- 2 Sticky pads
- Project box for SSR
- Low-voltage cabling for DC control (I used speaker wire)
- Steel 0.7x4 nut
- 10 x male and female disconnects
- 2 x 10A+ connector blocks
Wiring the thing.
The wiring on the Gaggia Coffee is broadly similar to the wiring on the Gaggia Espresso and the boiler is identical (See image here). There are two thermostats - the coffee thermostat and the steam thermostat. The steam thermostat is the brass unit you see screwed into the top of the boiler, the coffee thermostat is the visually identical unit you can see screwed into the bottom of the boiler on the side facing you in the picture. It is the coffee unit that we have to replace. Here's the left side of the boiler with the thermostat removed.
Never having done this before I wanted to be able to return the Gaggia to it's original state easily and so decided to do all the wiring with disconnects and patches so that I didn't have cut any of the existing cables. In order to connect the PID to the AC supply I made this adapter to patch into the power connector..
The female connectors on the right go to the power connector, the males on the left connect to the existing internals of the machine and the shorter male connectors on the left supply the PID.
A moment with a multimeter, iced water and a kettle confirmed that the solder on the thermocouple was good and it screwed nicely into the threaded hole in the boiler. I'm really happy with this method for mounting the thermocouple and it gives good results - although it's worrying seeing how fast the temperature in the boiler drops when pulling a shot!
With the thermocouple taking the thermostats place we need wire the old thermostat connectors into the SSR to take current to the heating element. Again I made two short patch wires so that I could use the existing disconnects. Just remove the wiring from the coffee thermostat and connect it to the AC side of the SSR; Then connect the DC control side the the PID. I then connected the AC supply for the PID with disconnects and turned the thing on - worked first time. Here is a picture of the internals before cleaning-up and reassembly.
The Final Result
And here's the unit with everything in place - the SSR is secured with a sticky pad. NOTE: If you are in a country that uses 110v mains power, or you have purchased a low amp-rated SSR you will probably need to install the SSR with a heat-sink. A 40A rated SSR on 240v should be OK to attach with the method shown, but using a heat-sink is preferable and an important safety consideration.
Finally the upgraded Gaggia back in it's place.
If anyone is interested the cost breakdown for this project was £27 for the PID and thermocouple (inc P&P), £5 for the SSR and around £4 for the additional cable, ties and disconnects. The grand total therefore runs to £36, or $66. Not too bad at all.