I recently added an Auber PID temperature control for the heating elements in the water cylinder. At the same time, I used a solid state voltage regulater (SSVR) and a potentiometer (rheostat) to comtrol pump speed (pre-infusion pressure). The whole project fit inside a medium sized projuct enclosure. I'm posting the photos here, because the thread describing PID'ing Strega is closed.

Anyone interested in the PID instructions can find the parts list and instructional description and photos in Bart G's excellent post (PID-ing the Bezzera Strega).

Parts that I used for the digital pump pressure control are:

• Auber 25A Solid State Voltage Regulator, High power SCR, SSVR.

• • - I used the rheostat tor 120VAC 60Hz.

• PTFE wire, 22 ga, silver plated

Final assembly with control enclosure on the right.


View of enclosure


Top view of enclosure with pump pressure rheostat


Open project enclosure

PID = Digital Temperature Controller
SSR = Solid State Relay (5 Amp)
SSVR = Solid State Voltage Regulator (25 Amp)
Rheostat (Potentiometer): 0 - 160 kohm (resistance matched to V & Hz)


Rear view of SSVR placement


Top view of SSVR (thermal paste placed underneath SSVR for heat dissipation)

The tempeature control of the piston cylinder is excellent (boiler pressure set to 1.05 - 1.2 bar). The digital pump control is similer to using a dimmer switch, but fits in a much smaller enclosure, and the high voltage SSVR is located in the back of the Strega frame.

You'll also notice that I built simple detachable bracket system to enable removing the PID enclosure from the Strega frame. That way it's easy slide the enclosure box away from the frame in order to remove the Strega stainless steel body panels whenever needed.

Wow, what a mod Rick. That little box looks good and practical.

I see that you use the SSVR, but the kit has 2 pieces of modules: potentiometer and SSVR and they take up space if I may say and also I don't think you need the 480v max voltage. Well, its good to have For others who think of modding and want to save some space (and cost too), you can use something more compact like this PWM controller. I have built a voltage router dimmer using this type of PWM controller, together with voltage LCD indicator, AC input and AC output which has the same function as this type of factory built controller.

As my strega still under warranty, I did not have the courage to open up the machine and make the mod, but eventually I definitely will. I have not added PID but I did use the above DIY router controller to manipulate pump pressure by lowering the voltage I figure it will slow the pump down and I guess it does. The drawback is that the boiler takes longer time to heat up under lower voltage, but the heating element still works.

I have been trying to replicate a Slayer shot (fat chance, Ha!) and recently pulled shots using a NPF, 14gr HQ basket and this external voltage regulator, setting about 170v (here the voltage is 220v by the way), to get to 1-3BAR pre-infusion. It would take about 20-25 secs for the beads to form under the basket, then I would just turn the potentiometer to 220v (full power) till I get about 2grams in the cup (about 5 secs?), then I will release the handle. The shots (depending on the grind size and type of beans) would take from 30 - 40 secs. Total time is in the 50s to 1min+. One thing I notice is that no matter how I pack my puck, with a firm tamp, whether using WDT or not, the stream will not make a mess, even though no a mouse tail, but no squirting all over the place. I guess that's what a pre-infusion is meant for

Hey Triton -

The PWM Controller, looks like a great alternative to the SSVR I used, and should be able to be placed in the same project enclosure that I used (or a slightly larger one). Great idea! Seems to me that if you use a DYI controller to control the pump, you only need to turn the voltage down during the preinfusion phase, otherwise it should run at full-voltage and the effect on the boiler should be pretty short lived... Once you decide to open Strega up it's a very easy machine to work on! Good luck!

- Rick

Yes Rick, you are right, just the pump, no group head temp control. I think I might mod it at the end of the year after the warranty runs out. Your mod pretty neat, having the box by the side with all the controllers. Thumbs up!

If you go back a few years in this thread you'll see that I used a basic lighting rheostat to control the pump voltage only which allowed me to dial in a group fill pressure from 2 bar up to 11 bar without affecting the heating element or anything else.

I think I read your writeup John, but it takes opening up the case and mod the cable connecting the pump. I refrain from doing that till the end of the warranty. So I use external router controller

No, it didn't require modding any cables. Do you void the warranty by opening the case? I would think playing with the voltage to the heating element, control box, ect. would be a definite warranty killer.

I agree...

John, as a matter of fact, after you posted a few years back, I followed your lead and used a lighting rheostat to control my pump too. That mod. served me well and I used it for several years. The reason that I changed that out for the SSVR now, was only because I wanted to put both controllers (heating elements & pump) in the same, small project enclosure box.

The SSVR and rheostat work just like the lighting rheostat, the range is non-linear and skewed a bit clockwise.

JohnB. wrote:No, it didn't require modding any cables. Do you void the warranty by opening the case? I would think playing with the voltage to the heating element, control box, ect. would be a definite warranty killer.

Really? Could void it eh? Will check it out your post soon then. I read Tom's post on mod P/I instruction of rewiring the pump wire, I guess that's the same case with your post (havent been able to find it here yet). I am actually trying to avoid the electricity work on the machine. Not sure will void the warranty. I think there is no cutting of wires just adding more, will check it out when I open up the case, when I do, I will have more insight of how to do it. As for use of router controller, might get away with the excuse that my house's electricity line is not stable at times

Rick,

That is a seriously clean PID and reostat mod! Thank you very much for posting such great pics. I do have a question for you, and other owners of Stregas. Rick, your boiler looks very tarnished in the areas directly below the pressure valve - is this normal, and has it promoted rust anywhere in the base?
Now that the original machines are a few years old, looking at a second hand item, are there any weak points or tel-tails that a second hand machine would have and should be avoided?