Added 1/11/14: As you'll soon see this is also a thread about how to PID a simple espresso machine like the Prestina. If the idea of this intimidates you, I've listed some basic principles after the appropriate warning about trying this yourself. That list is in my next post.

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Although this small commercial lever functions well when dialed in to a coffee, as a home barista I like to brew different coffees in a single session. The stock position of the PSTAT gives access just behind the drip tray and I now have an OEM PSTAT in place (the Jaeger brand is the old SOPAC). However that PSTAT adjusts somewhat coarsely and I don't like flexing the pipe each time I adjust it.

Recently a more compelling reason arose to add a PID (Proportional Integral Derivative) controller to this machine. The steam pipe clogged with deposits that hadn't been fully cleared in restoration. Pressure maxxed out and was intensely venting from the OPV (Over Pressure Valve) when I shut it down. I had to reset the needle in the manometer and do a more thorough vinegar descale of the pipe but fortunately there was no permanent damage. I had a primitive heat fuse on one of the leads to the heating element but it didn't melt, so it offered no protection. I'd considered installing a simple heat safety switch but was challenged with where to mount it on the boiler.

Another reason to install a PID is finer tuning of shot temperature, and with one of these machines the critical place for doing that is boiler temperature. So I contacted Auber Instruments, specced out what I would need and decided to learn how to PID my machine. This thread shows how I did that. It's working really well now and I'm happy I undertook the project. My next posts will detail how I installed the PID, including some of the challenges for a first timer and methods used. I now feel capable of adding a PID to other machines and will probably do this for my Caravel where I obtained an extra lid during the Orphan Espresso summer close-out sale.

Very cool! Is there a way to tuck it under the drip tray?

*Updated: Now that I look at the pic again, I can see there isn't enough room. A slimmer PID box might fit though.

@ arcus: One of the goals I haven't yet stated is that of modifying this collectible machine in a way that's totally reversible. I considered putting the machine on taller feet to place the PID underneath but then realized I ergonomically prefer the controller where it is now set up. I also prefer the lowest possible center of gravity because when I help the lever I already hold down the drip tray to keep the machine from tipping backwards.

Circuit Modifications

These were pretty straightforward when I look back, but I had to do some head scratching to figure this out the first time.

And first, of course, there's a necessary caution. I am not an electrician nor a trained appliance repairman. Any modifications you make in the circuitry of your appliance is done at your own risk. Take care, and it's your responsibility to have a knowledgeable person check your work before plugging it in to a live outlet. Electricity can kill or cause serious injury.

I'll summarize what I've done with the guidance of other people and online references.

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Added 1/11/14: First, some basics on how to PID a simple espresso machine like the Prestina.

• 1. The PID provides fine temperature tuning at the boiler.
  
  2. The PID provides another switch, like a PSTAT.
  
  3. You put the PID and other switches on the hot side of the circuit. The neutral goes from the heating element out to the power cord.
  
  4. The PID fits before the PSTAT to control temperature. The PSTAT is set at its upper limit and becomes another safety device to keep the machine from overheating.
  
  5. There are many ways to position a temperature sensor. You don't have to always drill into the boiler, although water immersion is best.
  
  6. The PID components are the controller, the sensor and the solid state relay (SSR). The controller and solid state relay need to be kept cool. This is not too great a challenge.
  
  7. The controller tunes itself. Setting up the controller for your type of sensor is easy. Then you just put in the temperature you want.

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Added 1/17/14: If you run a machine like this on an appliance timer and you haven't equipped it with a vacuum breaker, the heating element may be always on in equilibrium with boiler contents of air and water. No damage has been done but I'll stop using the timer until I reinstall a vacuum breaker.

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When I was initially wiring the Conti Prestina Ray Johns provided a circuit diagram that I followed with success.



My modification replaces the thermal fuse with a PID and places the PID before the pressure switch (PSTAT) in the hot side of the circuit. The PID now becomes a safety device.

I've added a terminal block near the start of the circuit but wire the hot lead directly to the On/Off switch so if it's not on it's not live. The PID components consist of the controller you see at the top of my first photo, a thermocouple (temperature sensor) threaded into the boiler, and a solid state relay (SSR) that acts as an On/Off switch to the hot lead that's toggled by the controller.

Just curious about the physical placement of the thermocouple / RTD, since I consider this to be the hardest part when PIDing any machine?

Since one of my goals is reversible modification I threaded a thin wire K type thermocouple under the group to boiler gasket. It's so thin that the group can seal tight without damaging the thermocouple lead. I also fashioned gaskets to attach the thermocouple tip to the dipper tube. It works perfectly. Before coming up with this solution I specced an RTD sensor that could have been immersed in the boiler or tucked under the boiler insulation for a non-invasive install. Here's the actual installation. I used leather punches to create fastening rings out of gasket material.



The second photo shows the TC lead tucked under the group to boiler gasket. Although it looks that way it isn't crimped.

Speccing Components

Rather than learn all of this from the ground up, I like to save time by getting expert help to specify components. It may cost slightly more to buy the components this way but it's saved me lots of valuable time. I contacted Suyi at Auber Instruments since he was very helpful in the past and they are experienced in offering PID kits for espresso machines. My component purchase cost about $100 delivered and included the following parts:

PID controller: Model SYL-1512A: $37.56



Miniature Aluminum Project Box: Model SBOXS: $25.00



25 Amp Solid State Relay (SSR): Model MGR-1D4825: $15.00



RTD sensor: Model PT100S: $15.65 (I didn't use this but instead installed the following thermocouple).



Thin Wire K type Thermocouple, Teflon coated: Model 5SCTT36 from Omega. These cost $72 for a pack of 5. They were shipped to me accidentally when I ordered glass braided insulation TC's so Omega comped me on the 5 pack.



The spool cap was difficult to fit into the project box and I had to snip off part of the plastic cap to fit it in. There was enough room it was do-able.

Connecting the PID

The controller came with fairly clear instructions. I read them through to get the basic concepts and noted some abbreviations that weren't defined on first use. Programming instructions were understandable. The controller itself is marked to help users properly attach components. Ray Johns used the same controller to PID his La Pavoni, so his circuit diagram for that (below) was a useful reference, although my installation doesn't require separate switching for steam. This is because the Prestina has a large enough single boiler that there's ample steam power without powering up the heater. My thermocouple also attaches a little differently, I believe only to terminals 6 and 7. If you have one of these controllers it's clearly labeled for attaching the sensor correctly. Pay attention to the hot (positive) and neutral/common (negative) leads for correct operation of the controller.



If you look at Ray's diagram you'll see that the PID controller is powered through the current in the machine, it sends a weak signal to the SSR that switches the hot lead on and off. The SSR is very straightforward and is clearly marked for its input from the PID. Here's another image from Ray's project to show this.



The output leads can be connected to either terminal as it simply opens or closes a connection.

Installation Planning with Heat Shielding

My installation is much more easily accomplished than Ray's* was because I'm working with a larger machine and face less need for fitting things into tight spaces and protecting components from heat. Suyi at Auber advised me to place insulation under my controller box if I planned on seating it on the cup warming tray. He also told me the SSR needs to be protected from temperatures exceeding 170F. This led me to position the SSR on the back, bottom frame, under the boiler, with boiler insulation already shielding much heat and with air circulation from under the machine.


* Ray's La Pavoni PID project was done with consummate skill as he created many of his fittings by hand and fit the whole thing into the base of that small home lever. It's really worth a look. Here's that link:

La Pavoni + PID = better temperature control?

Color Coding Wires

I decided that with this installation I wanted to achieve consistent color coding for later troubleshooting or mods. I obtained wire from Home Depot and Radio Shack. The power cord and my larger wires are white for hot, black for neutral, green for ground. My smaller wires are red for hot, black for neutral, green for ground. The indicator lights are pre-wired with red for hot and yellow for neutral. I also obtained heat shrink tubing from Radio Shack for color coding, where I'd also obtained my 6 lead terminal block, which I cut in two thinking I was connecting only 3 leads. Thinking back on this project the installation would have been more elegant using the full terminal block, as I'll explain below but it works as is.

Physically Positioning Components

I've removed the front cowl to show off the group. This leaves a gap behind the group with an opening to the interior. I decided the wires would poke out from behind the group.



To insulate the PID in the project box I installed gasket material underneath. Those gasket sheets are held in place by a tough, 3m plastic hook and loop sticky back fastener. The controller box is held onto the other side of the gasket with Velcro (TM) hook and loop sticky back fastener. I left a channel under the middle of the project box to lead the wires underneath, starting from the back of the box. When connecting the thermocouple lead I didn't think about the need to thread it through the exit port of the project box so I improvised by cutting a small slot at the edge of the project box back plate. The installation looks clean enough for me and is mostly obscured when cups are on the warming tray. I used hook and loop fasteners so I can easily remove the project box from the cup warming tray if I need to remove the case of the machine. The PID remains attached through the opening above the faceplate.



Here's how that was assembled. This is the 3M hook and loop fastener obtained at Radio Shack.



Here it's attached to the gasket sheet strips with the Velcro fastened to the bottom of the project box.



I improvised high heat silicone tubing as a cable lead on the top of the frame and the side. The tubing is held in place by cable ties fastened onto the top frame with the 3M hook and loop fastener. This photo shows the insulation from the boiler removed. It slides on and off like a cap and was reinstalled later.



The power cord is fitted with a cable tie to the frame to provide strain relief. Its hot lead goes directly to the On/Off switch. The neutral and ground attach to the terminal block whose other side connects power to the PID, the indicator lights and the hot lead that connects to the SSR, which in turn connects with the PSTAT and the heating element.

Here you can see the terminal block in place.



And this is the SSR mounted to the back of the frame. It has a plastic protective cover. You can see in the photo that the hot lead between the PID and the SSR doesn't have adequate strain relief. It came apart later and I took off the strain and covered it more thoroughly with heat shrink tubing to keep it from easily bending.



Making the wire connections was a bit complex and improvised. I'll cover that next along with soldering technique.