Results 1 to 14 of 14

Thread: Some Silvia temperature statistics

  1. #1
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,645

    Some Silvia temperature statistics

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    The Silvia has a reputation for producing good coffee. And thats due to its thermostability.

    Its when you start poking around with a thermocouple and digital multimeter you appreciate just how good it is for a very simple machine with no electronic control other than an on/off thermostat (which really could do with improving, Mr Rancilio).

    I hava a permanently attached K-type thermocouple on the roof of the boiler.

    Another is a roving one, and Ive tried different locations: in the basket, and on the exterior of the chunky group.

    Room temperature 16C.
    With the machine preheated for an hour, this is what happens when the boiler reads 108C, indicating conditions ideal for a pour.

    Top of boiler: 108C
    Basket fluctuated between 93C and 95C for the duration of a 25 second pour (without coffee). With coffee, this is most likely to fluctuate even less, to within first crack, as the grounds absorb and smooth out heat.

    Temperature on the group stayed steady at 66C.

    Group temperature is wonderfully static for a non-E61. It will go up as much as second crack through the entire heating 50-second cycle where boiler temperature can reach 120C, but by the time water comes back to a desirable 108, it will be 66C again and remain there.

    Robusto


  2. #2
    Senior Member
    Join Date
    May 2005
    Location
    Sydney Oz
    Posts
    503

    Re: Some Silvia temperature statistics

    Robusto,

    After warming mine up for 1/2 hour I do the old flush until the element light comes on trick and them wait roughly 30 secs until I pour a shot. Do you have any details on what the best time to pour a shot is after the element comes on. Ive seen times vary from 30 sec - 50 secs.

    Cheers,

    Matt

  3. #3
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,645

    Re: Some Silvia temperature statistics

    The times given vary with good reason -- because contrary to most advice, the temperature will NOT always be constant after a certain time has elapsed after the light comes on.

    Ive done a few experiments, and Ill do some more tonight which will hopefully give a ballpark figure within a narrowish band.

    Robusto

  4. #4
    Senior Member
    Join Date
    Apr 2005
    Posts
    1,176

    Re: Some Silvia temperature statistics

    I find that unless youre thermologging the date, spot measurements dont give you a real sense of how stable the brew cycle is. For example, the stability during a shot measured on a Silvia can exhibit variations of between 2 and 6 deg C, rarely less. The reason for this is also pretty simple; the cold feed water mixes with the hot boiler water. The proximity of the group feed pipe is such that this mixed water soon becomes part of the brew water (at least thats the 2 C instability). The 6 C instability results from the heating element generating large thermal gradients whilst on. It takes a while for these gradients to mix and average out in the boiler. Thats why I found the most stable region for brewing to be 130" - 2 after the element has switched off.

    This sort of stability for the Silvia is pretty well known. 1 deg C stability is the region of HX performance and none of the people that have studied this machine has claimed that Silvia can achieve that level of temperature stability. At least not without a few mods.

    A group temperature of 66 deg C is pretty cold. Ive logged Silvias group temperature in the 86-92 C range. Thats after its been running for over 24 hours and so should represent the final temperature. At 66 C, the cold group will have a dramatic effect on the shot temperature. You really want the group temperature to be as close to the shot temperature as possible. Maybe use a few warming flushes. Silvias offset group takes a while to fully heat up.

    Cheers,

    Mark.

  5. #5
    Senior Member
    Join Date
    Mar 2006
    Posts
    188

    Re: Some Silvia temperature statistics

    Hi, Mark -

    Didnt expect to hear that you prefer to pull shots while heating element is off. I always assumed (never verified) that having the heater energized during a shot would counteract the cooling effect of fresh water entering the boiler - hence a "good" thing.

    When everything goes right, the shot temps I have logged show a spike occuring a few seconds after hitting switch, followed by 3C-4C or so drop by the end of 25 seconds. I assumed this drop is due to cool water feeding in and that it would be worse if element was not on.

    Unfortunately, I dont have as much data as Id like because Ive gotten tired of blowing coffee all over everything. Still trying to come up with a good way to seal the hole in the filter basket that I feed the T/C wires through. Silicone caulking is definitely not the answer.

    -- JGG

  6. #6
    Senior Member
    Join Date
    Apr 2005
    Posts
    1,176

    Re: Some Silvia temperature statistics

    I think its really whatever works for you.

    I found that with the element on the temperature variation was up to 6C, but more like the 3-4C you mention. With the element off, the variation can be less than second crack (but of that order). The best interpretation of the data I took is that when the element is on, the hot element sets up strong convection currents. The problem with these currents is that they move a lot of water around with large thermal gradients. Water is a very poor heat conductor and needs efficient mixing to smooth out the temperature variations. No boiler Ive come across accomplishes this, especially with the element on. However if you wait long enough after the elemnet has switched off, the convection currents will slow down and enough mixing will have occurred to smooth out the temperature variations within th boiler. From my observations, this takes about 130" to 2.

    Ive found that the cold feed water doesnt mix too quickly with the brew water in the Silvia. This is an observation that was originally noted by Greg Scace on a.c when he first reported temperature measurements of his Silvia before he went the PID route. In contrast, my Faema Family had very pronounced mixing of cold feed water which caused very noticeable drops in brew temperature during thr course of the shot.

    Boiler instability issues are all moot with PID control. Cold water mixing issues arent. So a PIDed Silvia will be a pretty stable brewing platform (still in the second crack stability regime). At the end of the day, people only care about the quality in the cup. Silvia is able to deliver here, given a little care and understanding. However, she is still outclassed by HX machines for both ease of use and temperature stability.

    As for the TC, I run it over the lip of the basket. It can be sealed with the group seal, but it does end up destroying the TC after a while. I never liked the fliter basket epoxy approach as I thought it would make it more difficult to pack and tamp the coffee uniformly.

    Regards,

    Mark.

  7. #7
    Senior Member
    Join Date
    Mar 2006
    Posts
    188

    Re: Some Silvia temperature statistics

    Great info! Thanks.

    -- JGG

  8. #8
    Senior Member
    Join Date
    Mar 2006
    Posts
    703

    Re: Some Silvia temperature statistics

    I have also mounted a thermocouple on top of Silvias boiler, and found following;
    Ambient temp approx 20C
    Boiler heating cycles, element ON approx 93C and element OFF approx 105C, but top of boler continues to rise to maximum of approx 117C.
    For those who are trying to temperature surf, I found the boiler top temp at 80 seconds was approx 117C, and at 140 seconds was approx 115C, so yes it is stable, but still a bit higher than the suggested 108C. Boiler top temp of 108C took approx 280-300 seconds from the time the heating light turned OFF
    Then used my milk thermometer to try and measure temp of water coming out the shower screen into a foam cup, (maybe not best response, but I did warm it up first)
    with boiler top temp around 115-117C, I got water temp around 100C,
    with boiler top temp around 108C, I got water temp around 95C.

    I have not checked the calibration of my thermocouple, it might be out by 1 or 2 degrees, but my milk thermometer did show 100C in boiler water.

    Now having said all that, I am not yet convinced that my lattes taste better when the shot is brewed from boiler 108C compared to the slightly higher temp I must have had simply by timing approx 2 mins from the time the heating light turned OFF....

  9. #9
    Senior Member
    Join Date
    Mar 2006
    Posts
    703

    Re: Some Silvia temperature statistics

    Having just checked the other post on this subject,
    I see that my machine must be fitted with a 110C thermostat, whcih would explain some of the variations I found.

  10. #10
    Senior Member robusto's Avatar
    Join Date
    Feb 2005
    Posts
    2,645

    Re: Some Silvia temperature statistics

    Bullitt, your temperatures pretty much match mine. If the machine is farily recent it is the 100° C thermostat. But no thermostat is going to switch the heating element on and off dead on 100°. It would be switching on and off every second, burning itself out, so hysterisis is built in -- a wide band where nothing happens.

    The temperature keeps rising after the 105° switch off because the element is still hot, and because of convection currents in the water, and because of the lag in all the heat reaching the top of the boiler where your thermocouple is located.

    Your temperatures seem spot on.

    Robusto

  11. #11
    Senior Member
    Join Date
    Mar 2006
    Posts
    703

    Re: Some Silvia temperature statistics

    Thanks Robusto,

    I probably have missed the discussion about relative merits of 100C Vs 110C TStats, and yes I think Ive got a grip on the dead band controller principle, and subsequent effects, mostly thanks to your earlier posting above.

    Guess I got to spend a bit more time sorting out dosing and grind setting on Rocky.

  12. #12
    Senior Member
    Join Date
    Nov 2005
    Posts
    333

    Re: Some Silvia temperature statistics

    I havent got a clue whether my Silvia has a 100c or 110c boiler thermostat. BTW, what would temp would the steamer thermostat be? Theres a Rancilio spare parts place not far from me and last time I was there they pointed to a drawer of thermostats (with a range of temperatures) saying they only cost a couple of dollars each and would be quite cheap to change over.

  13. #13
    Senior Member
    Join Date
    Mar 2006
    Posts
    188

    Re: Some Silvia temperature statistics

    The wiring diagram I have for Silvia shows 140C and 165C for steam and overheat thermostats, respectively.

    -- JGG

  14. #14
    Senior Member
    Join Date
    Nov 2005
    Posts
    333

    Re: Some Silvia temperature statistics

    Behmor Brazen - $249 - Free Freight
    Thanks JGG



Similar Threads

  1. Consumption Statistics
    By Big_Steve in forum General Coffee Related...
    Replies: 0
    Last Post: 16th April 2012, 08:01 AM
  2. Silvia temperature control & PID
    By blend52 in forum Brewing Equipment - Midrange ($500-$1500)
    Replies: 5
    Last Post: 3rd April 2012, 11:08 AM
  3. Silvia Temperature Stability
    By KJM in forum Brewing Equipment - Midrange ($500-$1500)
    Replies: 7
    Last Post: 11th December 2008, 06:21 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •