For adding the brew timer I was looking for a dual set-point controller with build it timer, but couldn't locate one, so I was forced to use a timer only for the brew timer mod.
While hunting for a Watlow controller, I found they have a nice small 1/32 size obsolete controller that has timer on its 2nd output. This model 935 can be used as a timer only.
Yes, I know it has a PID in it that I don't use but since I already have a PID, I don't mind using it just for its timer. Its cost is similar to other poor quality timer only units, so why not use a product from a reliable manufacturer ?
In my search, I have seen a timer that was programmed to control both timer and pre-infusion. Since my experience with manual pre-infusion on Silvia showed little difference, if at all for the coffee taste, I skipped this expensive controller and made a simple pre-infusion mod instead (see 5.)
Tip: Please note this Watlow 935 controller requires the presence of a sensor in its input. Connecting a 100 oHm resistor across its input terminals and setting it to rt.d simulates 0.1 RDT sensor and will allow it to work as timer only.
The controller 2nd output can be C, K, or D type.
Mine is 935A-1CD0-000R (which is common of finding) its 2nd output is type-D, a mechanical relay (2A@250V) that can trigger the pump easily with SSRs or with additional relay.
To trigger two SSRs that activate the 2 separate AC lines in the brew switch, one for the pump and the other for the 3-way valve, I could have used either AC or DC.
Since I already have a 12V power source available, I decided to use it for this purpose. I used the Watlow 935 internal relay to drive a dual DC-AC SSR which saved space as well.
Yes, I know this output is a mechanical relay with limited lifetime but this is the controller that I got. Since brew timer function is used once for each brew cycle and only few times per day with a simple ON-Off operation, I believe it will hold for the next few years.
This dual SSR operates the pump (48W@220V) and the Solenoid (7W@220V).
Though it seems it can be with low amperage rate it is not. Due to surge/peak currents, it is strongly recommend to use 40A or above SSR’s that has better protection. Adding a Snubber/Arc arrestor across the SSR contacts is also advisable.
I have used Crydom D2440D dual SSR with 2x ITW Quencharc p/n: 104m06qc100, 0.1uF-100oHm.
Tip: If you can’t find a Quencharc, built one yourself, this is easy to do and will be much cheaper.
Use in series 0.1uF 10% metallized polyester film capacitor and a 100 oHm 0.5W carbon film resistor.
This is a Quencharc, a capacitor and a resistor in series. (see images below).
Tip: Please note the design of this mod may change according to the controller model you get:
for type K 2nd output, use 2x AC-AC SSRs to trigger the brew switch.
for type C 2nd output, use 2x DC-AC SSRs to trigger the brew switch or 1x dual DC-AC SSR.
for type D 2nd output, which is a mechanical relay, you can trigger 2x AC-AC SSRs with mains voltage, or, in case a 12V power is available, (see next mod), use it to trigger 2x DC-AC SSRs, or 1x dual DC-AC SSR.
* protect each SSR by using a high A rate and add Snubber/Arc arrestor across its contacts.
Tip: Though I wrote that a relay is the worst option to use, if you don't have a choice, you can trigger another relay that will connect the brew switch contacts. If you do so, don't forget to add Quencharc to each contact of the relay.
Note that the relay will need a coil voltage according to your mains. If mains is 220VAC, you need a relay with coil voltage of 220VAC.
Tip: If you don't have space inside Silvia for 2x SSRs, you can use a dual SSR instead.
(=2x separate SSRs in one body). Crydom for example has dual-SSR family for DC-AC SSRs.