Rancilio Silvia Mega-Mod part 5 Brew Timer
Avi's Silvia Mega-Mod
My way to a better coffee...
DISCLAIMER - Important!
This post presents the electric mod for the Brew timer.
The following drawings show the overall schematic layout of my Mega-Mod that combines all mods that deal with electric/electronics modifications, and a drawing focusing on the Brew timer control.
For specific details of each mod please see its relevant post.
For adding the brew timer I was looking for a dual set-point controller with built-in 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 a timer on its 2nd output. This Watlow 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.
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 an 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 a 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 recommended 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-100-ohm.
Tip: Please note the design of this mod may change according to the Watlow 935 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 other mods), use it to trigger 2x DC-AC SSRs, or 1x dual DC-AC SSR.
* protect each SSR by using a high rate Amperage and add a 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.
Video of extraction (using a double basket with a naked portafilter). Using fresh coffee.
Video of extraction (using a double basket with a naked portafilter) Using a 4 days roasted coffee.
As can be seen in the videos, this mod controls the preset time brewing with the Watlow 935 controller, to achieve the perfect Espresso, ~25-30 ml. in ~25-30 sec.
Comments, remarks and updates are welcome.
Some will be published, with hidden sender's details.
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