PID.
Today’s session is mainly about the PID. I have a Gaggia Classic that had an Auber type PID in a very nice aluminium enclosure. I removed and replaced it with a Rex C100 PID, freeing up the Auber for this project. I had thought of fitting the Auber in a cutout in the front panel but have read that the PID doesn’t like heat and can go wonky when boiler is at steaming temperature, as I plan to only partially insulate the boiler I decided to mount the PID on the outside. The enclosure was too long to fit under the front panel so it had to be shortened to fit. It now fits but restricts movement of the steam arm, the arm will still ‘park’ over the drip tray and will swivel to the right for steaming so it’s all good.
I spent a long time with the wiring, working out and making the new connections. The Auber pinout connections to the SSRs are different to the Rex and that caused some confusion. Fired it up and found that the steam switch didn’t do anything, I discovered that I had connected both outlets from the steam SSR to neutral points, one quick reconnection to a switched live point and all working, no harm done. I still retained the overheat cutout as a safety measure, I made sure that the power from steam SSR goes through the overheat cutout too. Spent some time getting the temperature offset right, I used a digital thermometer with the probe clamped to the top of the boiler next to the PT100 probe as the datum. So the PID display now (hopefully ) reads the actual temperature at the top of the boiler. The PID settings were still as for the Classic so there was a large temperature overrun, the alarm was set for 137c and I saw the temp overshoot to 155c. Once I get the insulation installed and the top cover on I’ll do an autotune. All good fun but if you don’t have wiring instructions and have to work things out, it takes a lot of time, you don’t want to blow anything up. Some of the plastic shrouds on the connections over the boiler crumbled due to years of heat, replaced with spares
Pleased to see that the front gauge works without flutter. I realised that if I keep the steam knob closed, operating the hot water dispense switch pressurises the system and you can read the brew pressure on the gauge, can’t do that on a Classic. Gauge reads a steady 10 bar, so allowing about 1 bar difference between pump connection and group head the pressure is about right. No leaks from steam valve, so old O rings still holding.
On the home straight now, should finish in the next session.