I recently added a shot pressure gauge and two PID controllers to my already highly modified Bunn ES-1A espresso machine. My original modifications must have messed up the thermosyphon dynamics because the group was running too hot. I decided to add a pair of PID controllers to regulate the group temperature and shot temperature. This modification allows me to crank up the boiler pressure for better steaming performance without overheating the group.

The thermosyphon PID monitors the temperature of the group near the thermosyphon output port. It modulates the thermosyphon flow by switching a custom made valve mounted on top of the group. When not energized the valve blocks the thermosyphon inlet port and consequently limits the heating of the group. This control loop works quite well and can regulate the temperature within one degree. The thermosyphon valve is also interlocked with the group switch, causing the valve to close during a shot. This prevents the hot water at the top of the thermosyphon loop from entering the group during the shot.

A second PID measures the shot temperature using a thermocouple that is positioned right at the shower screen. If the shot is too hot it turns on a second solenoid valve that allows a small amount of cool water to bypass the heat exchanger and directly enter the group. I drilled a hole in the back of the group between the thermosyphon ports and attached a 1/8" line for the water injection. This control loop is a little harder to stabilize because of the transport delay from the injection port to the point where the temperature is measured. As long as the shot flow is around 100 ml/min the PID seems to do a pretty good job, settling out within a few seconds.

I know that with experience the shot temperature can be controlled by the proper flushing routine, but hey, what am I to do with this box of PID controllers?

wow! my dad used to build stuff for hospitals, is that what you do?

I am a retired electrical / mechanical engineer with a caffeine addiction and too much time on my hands.

It's awesome from both a technical and aesthetic perspective!

Holy crap. Is this real? That's so awesome.

Good grief! I wondered what they did with old space shuttles.

Now I know - but where's the boosters?

That's awesome!! Wish I had those mad skills to build such a thing.

Very cool to have a true shot temp PID. Would be interesting to see a video of it run with the new add ons -- it did look a bit bare before... but now reaching perfection with the new digital bling

benm5678 wrote:That's awesome!! Wish I had those mad skills to build such a thing.

Me too. I truly wish I had just a fraction of Eric's skills. I would love to build a mad scientist espresso machine...maybe something like this?

Er - sorry Eric, I really do think you are a genius and not mad at all.

The coolest-looking machine I've seen in a long time, great work! Now you really should get a better grinder.

I assume you keep the environmental temperature down on those PIDs so that they still read accurately?

What are the red and green LEDs in the top right? I assume they're not just xmas decorations?