PID-ing the Bezzera Strega

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BartG

#1: Post by BartG »

I've been a more or less happy owner of the Bezzera Strega for a few months now. I like the machine, its build quality and the espresso it makes.
Still I'm considering PID-ing the grouphead because I experienced that some beans really benefit from lower temperatures than standard. Lowering the temp can be achieved by flushing, but personally I find this a somewhat inaccurate method. Also the grouphead temp fluctuates a bit and a PID in place of the standard grouphead thermostat would counter this.
I am now using a temp probe on the outside of the grouphead to monitor its temperature, but I don't find this an easy way of making coffee at consistent temperatures.

I've read a few reactions of people on this forum who have done this change, but there isn't a step by step guide. With this thread I would try and record the modification I'm going to do.

Also I would like to hear opinions about changing the boiler thermostat with a PID. Since the brew water comes from an HX I wonder if a boiler PID is still useful for controlling the brew temperature. Maybe just the grouphead PID is enough for that on the Strega?

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BartG

#2: Post by BartG »

There's already some info and interesting discussion about a PID control for the Strega in this thread:

Bezzera Strega, how to cool it


Nonetheless I would like some feedback from Strega owners who did this modification. And foremost if they think it's useful to also PID the boiler.

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BartG

#3: Post by BartG »

I'm on the point of ordering this from Auber:

- 1/32 DIN PID
- PT100M4 temperature sensor or RTD probe
- 5A SSR
- 1/32 DIN Controller box (3x1.4x4.7")

I suppose that connecting cable is to be bought locally. Are there other components needed?



To summarize the install procedure (on paper, haven't opened the strega yet):


1. Remove the grouphead thermostat. Replace it with the RTD.

2. Connect the wires, previously hooked to the thermostat to the SSR. (This would be accomplished with male spade connectors and 16 gauge wire - polarity is of no concern. The wires get attached to the output side of the SSR. // Or by soldering if using the 5A SSR.)

3. Connect the SSR to the PID. (quote from manual: "Connect terminal 9 to the negative input and terminal 10 to the positive input of the SSR.")
I suppose also with 16 gauge wires.

4. Run the RTD wires to the PID. Keep in mind that some terminals on the PID need to be "jumpered" as per Auber's wiring diagram. (quote from manual: "For a two-wire RTD, the wires should be connected to terminals 7 and 8. Jump a wire between terminals 6 and 7.")

5. Connect a simple extension cord to the mains of the PID (polarity is of no concern).


Wiring of the PID from the Auber Instruments PID manual

Image

http://auberins.com/images/Manual/SYL-1 ... %201.0.pdf


5A SSR:

Image


EDIT: for the step-by-step guide please see page 5

Armand

#4: Post by Armand »

BartG wrote:Also I would like to hear opinions about changing the boiler thermostat with a PID. Since the brew water comes from an HX I wonder if a boiler PID is still useful for controlling the brew temperature. Maybe just the grouphead PID is enough for that on the Strega?
not really an answer but what I do when I think my shot are to bitter/hot: pull lever until coffee starts to drip, stop pump and let the coffee drip until it stops, then let the lever go but restrict it a bit to slow down the flow. For me this makes dark roasts much milder, it doesn't work very well for lighter roasts

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ravco

#5: Post by ravco »

I have just PIDed the grouphead of my Strega. I basically used the same components from Auber. I think 20 gauge wire is thick enough for the job. Did some rough calculations and Auber recommends 20 gauge in the manual for connecting the PID to mains. Wire needs to be heat resistant. I used silicon coated wire. You will need piggyback connectors to connect the PID to the mains switch of the machine, which is easily done. I wouldn't bother with an external extension cord. I had to extend the wires of the RTD. The 5A SSR only has pins. I soldered the wires onto it.
I had big problems with bitter/burned tasting espresso. I use dark espresso blends. As far as I can say at this stage of the testing, the PID has solved the problem (set at 90 C). I don't think PIDing the boiler is going to improve things. If I remember correctly this was also discussed somewhere in the owner thread.

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BartG

#6: Post by BartG »

Thanks for your input!
by ravco » 30 May 2016, 22:00
I had to extend the wires of the RTD.
What kind of wire did you need for the extension of the RTD cable?

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BartG

#7: Post by BartG »

Placed an order for the parts at Auber instruments. Also bought an 'Hi Temp RTD Extension Cable' just to be sure (costs +/- 1$).
I didn't go for the dual controller PID or two PIDs (so that the boiler could also be PID'ed) because costs would almost double and there aren't enough arguments to recommend this.
I am now at $123 shipping included.

Now just have to wait for it to arrive (international shipping).

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BartG

#8: Post by BartG »

Also got a reply from Auber Instruments. I asked them to give some general info about connecting the parts I ordered:

"Connecting cables are not included in the list. And we don't sell them. The electric current going to the controller is very small. It is less than 100 mA. So, 26 AWG wire is sufficient. The wire for the SSR output carries about 0.5 Amp. This is also very small. 22 to 26 AWG will be fine.We recommend you use fluropolymer insulated wire that has high temperature rating, high voltage rating and thinner jacket. You can get them from this source: http://www.ebay.com/itm/Teflon-wire-Alp ... SwqYBWoBdh

The connections on the SSR need to be soldered. "

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ravco

#9: Post by ravco »

BartG wrote:What kind of wire did you need for the extension of the RTD cable?
I extended the RTD wires with approx. 23 gauge wire. Soldered them together as well. I used this shrinking insulating tubing stuff to insulate them and other parts. All my wires are silicon coated and will take up to 180 C and a lot of volts. As far as I can judge, the wires in the Strega are silicon coated as well. Make sure the connectors fit the thickness of the wire.

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BartG

#10: Post by BartG »

Package arrived already, that was fast!

Quick question about the connecting wires, a lot was said about the minimum gauge, but is there such a thing as maximum gauge?
I ask because I have a lot of 1,5mm copper electrical wire (normally used for wiring the electricity in your house).