I Believe a much larger temp problem on the BII is the swing in boiler temp because of that crappy controller. This is caused by overshoot. This can simply be estimated by timing your brew element cycle. My Brew element cycle is: on for 25sec then off for 9 minutes. This is because my machine overshoots boiler temp by about 6-8 degreees Celcius and then takes 9 minutes to come back down. Testing with a home made scace shows this difference to translate to 3.5degrees c at the puck (after a 60mm flush).
My machine has 2x2000 watt elements which I believe makes my overshoot worse than the US ones. I have learnt to "Surf" the machine by only letting the Brew element switch on for 5 seconds (I do this by switching the machine off for 20 sec when the element has been on for 5 sec). When I do this my brew element cycle dropsdown to 1-1.5 minutes. I have noticed a difference in cup consistancy. Expobar saw it enough of an issue to release their latest brewtus with a PID. I have ordered a new PID for my machine and will be fitting it shortly. Thanks David On Feb 9, 2:05 am, cgfan <[email protected]> wrote: > You're absolutely right - I realized too late that I had the memory of > the schematic all wrong when I looked it up in the files section, > hence my reaction in latter posts. My sincere apologies for the > confusion. > > On Feb 7, 8:06 pm, bobvilax2000 <[email protected]> wrote: > > > Most of that went over my head, but where you first lost me is this: > > > "The water that will brew your espresso is the very first volume of > > water which exits the pump. " > > > Unless I'm misunderstanding the water from the pump when the lever is > > pulled is not the water brewing the coffee. The pump is pushing water > > into the HX in the steam boiler and then into the brew boiler, > > meaning it's hot by the time it gets to the brew boiler. The water > > that you're brewing with has been simmering in the tank. > > > You also have to keep in mind the HX loop through the E61. Basically > > the hot water in the brew tank is rising and passes through the E61 in > > which it cools slightly causing it to pass down back into the bottom > > of the brew tank. The offset is to compensate for this loop. > > > Maybe I'm missing the point. > > > - -Barrett > > > On Feb 7, 10:47 pm, cgfan <[email protected]> wrote: > > > > A possible design flaw? I hope I'm wrong about this... > > > > In the course of trying to figure out the source of some recently sour > > > shots, in the past few days I've been through a tumult of long > > > sessions on the Brewtus running various experiments with brew temps, > > > offsets, thermocouples and thermometers, switching roasters and > > > espresso blends, posting to boards, formulating various hypotheses, > > > and even discussing with my fellow but non-java oriented engineering > > > colleagues. Through it all I've formulated a hypothesis that though > > > so far I've been able to confirm by experiment, I still hold out some > > > hope that I've overlooked something that invalidates my conclusion. > > > > Here's the conclusion that I've reached re. my Brewtus I, but should > > > also apply to the whole Brewtus series, and, in fact, most other > > > similarly designed dual boiler espresso machines. The conclusion that > > > I've reached: given a thermal drop of x deg C from the pump to the > > > portafilter (noting that x is negative), the maximum possible brewing > > > temperature at the portafilter is 100+x deg. C. > > > > So given an offset of, say, -6 deg C, this implies a maximum possible > > > brewing temperature at the portafilter of 100 + -6 = 94 deg. C. > > > > A corollary to this is that the thermal drop x, which is the offset > > > that we program into our temperature controller as C0, can easily be > > > mistaken/mismeasured to be greater than the "intrinsic" thermal drop > > > across the grouphead, given a key point in the hypothesis. According > > > to the hypothesis a meaningful thermal drop x can only be measured > > > under certain operating conditions. > > > > So here's the hypothesis: > > > > The water that will brew your espresso is the very first volume of > > > water which exits the pump. As we pump out the water for brewing our > > > espresso, it is first being pumped out into an empty (and therefore > > > non-pressurized) brew path whose volume I estimate to be around 1.135 > > > ounces. Thus barring any significant losses at this point the water > > > at the output of the pump will have a maximum temperature of 100 deg C > > > or Tbrew_boiler, wichever is less. This is because once the water > > > leaves the pressureized confines of the brew boiler it no longer can > > > reach temperatures above 100 deg C. Any water which was kept in the > > > boiler above 100 deg C will instantly lose its excess heat as steam > > > and drop to 100 deg C. > > > > Now this water, as it travels from the output of the pump to the > > > portafilter, will have dropped x degrees by the time it reaches the > > > puck of compressed coffee. > > > > Thus, noting that x is a negative quantity, the brew water is > > > determined by: > > > > Tpump_out = 100 deg C : for Tbrew_boiler > 100 deg C > > > = Tbrew_boiler : for Tbrew_boiler <= 100 deg C > > > > Tbrew_water = Tpump_out + x deg C > > > > Thus: > > > > Max(Tbrew_water) = Max(Tpump_out) + x deg C > > > = 100 + x deg C > > > > Ouch! Not a good situation when our desired brew temps are so close > > > to 100 deg C and our offsets, irrespective of any debate, is at least > > > (-) 5, the original factory default for the Brewtus I. > > > > So here's the corollary which follows the hypothesis: > > > > The "offset" that we program into our temperature controller x is only > > > a meaningful offset from the boiler temperature Tbrew_boiler when > > > > Tbrew_boiler <= 100 deg C > > > > This can be seen by the relation for Tpump_out above. Under any other > > > condition the offset x is only an offset off of a fixed 100 deg C. > > > > Thus if one tries to estimate their offset x via a measurement of the > > > brew boiler temperature, it is important to do so only when > > > Tbrew_boiler <= 100 deg C. > > > > (I suspect that the tendency for users to suggest offsets greater than > > > (-) 5 might be due to brew boiler and portafilter measurements taken > > > under conditions where the brew boiler exceeds 100 deg C. Under these > > > conditions every degree increase in brew boiler temperature will not > > > increase the brew water temperature at the portafilter and hence > > > result in a larger "apparent" offset.) > > > > I've verified the hypothesis via a simple experiment that's documented > > > here:http://groups.google.com/group/brewtus/msg/107c4e427e109637?hl=en > > > > Basically I take repeated measurements of the brew water under a fixed > > > target brew temperature but varying offsets. I found the brew water > > > temperature not to change for any condition where Ttarget_brew_temp - > > > x > 100 deg C (again noting that x is negative). As soon as > > > Ttarget_brew_temp - x <= 100 deg C, the output brew water temperature > > > started to change accordingly. > > > > Note that the hypothesis applies to only the initial volume of water > > > sufficient to fill the total volume of the brew path, which my > > > experiments estimate to be around 1.135 oz. As any water pumped > > > subsequent to this initial volume will be pressurized due to the > > > purging of any air in the brew path, subsequent flow can break the > > > temperature restrictions implied above. However the initial 1+ oz. > > > for even double espressos represents a sizeable portion of the total > > > brew volume, and in my case of super short ristrettos this initial > > > volume alone is enough to generate several shots worth of brew water > > > under these temperature-compromised conditions. > > > > Note that temperature flushes will not relieve us from these limits, > > > as the temperature flush still leaves the brew path empty of any brew > > > water. (However temperature flushes will help us get as high a > > > temperature of brew water possible while still being limited by these > > > constraints.) > > > > I wouldn't have gone as far as to post this if my experiments did not > > > support the hypothesis. Unfortunately so far they do just that. > > > Believe me this is a case in which I'd enjoy being wrong! > > > > Anyone else out there notice the same? Any findings or experiences > > > supportive or contradictory to these findings? Any alternate > > > hypotheses for the observed behavior? Any of you input or feedback > > > would be most welcome. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Brewtus" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/brewtus?hl=en -~----------~----~----~----~------~----~------~--~---
