Announcement

Collapse
No announcement yet.

temperature for roasting in corretto

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #31
    Re: temperature for roasting in corretto

    Hi Peter,

    Im glad Belinda and I were able to help.

    The heat gun adjustments required around and after FC are very fine... and I doubt you will be able to make them with a standard heatgun - well not without a lot of pain.

    Part of the problem is the thermal lag... the effect of any change isnt visible on the probes for 20-30 seconds (in my corretto) so you firstly need to get a feel for what is required that far in advance or you will overshoot or undershoot the correction.

    Ive modified my heatgun for finer control - if you have a friend who is an electrician you could do the same.

    Firstly I opened the heatgun (voids the warranty) and identified the heating circuit. I then built a 16 amp triac "light dimmer" with 12 switched stages of output between full and about 60 deg C output.... (using 11 equal resistors to set the output of the triac) and connected it externally to the heating circuit.

    That improved the control of output a lot - but I still found it a bit coarse.

    I then installed a potentiometer (variable resistor) of the same value as each resistor.... so one complete turn of the potentiometer gave 1/12 of the heat range...

    Now I control the temperature from first into second crack with the variable control (temperature up to just before first crack with the switched control). I find the variation required to be about half a turn of the knob on the potentiometer - or about 4%...... and you wont get that with any standard heatgun.

    I can even maintain the temp at a constant setting by fine adjustment of the potentiometer - and providing I allow for the thermal lag of the roaster.

    Total cost of the mod was about $20 .... and I think it will also extend the like of the heatgun heaps - it is hardly ever "flat out" and at the end of the roast I can turn it right down to cool down the gun.

    I even used the lowest setting (60C) to cool the beans in the corretto once. It worked well - took a little time to cool them down- but is possible. You just have to start the cooling a little earlier as the beans will continue to roast a bit.

    So if you have a mate who is an electrician ..........

    Comment


    • #32
      Re: temperature for roasting in corretto

      I think JavaB is the Heat gun mod god after that bit of work.

      Comment


      • #33
        Re: temperature for roasting in corretto

        Originally posted by JavaB link=1167177851/30#30 date=1167788268
        Hi Peter,

        The heat gun adjustments required around and after FC are very fine... and I doubt you will be able to make them with a standard heatgun - well not without a lot of pain.
        Hi JavaB,

        hhmm, you maybe right, I already had the sneaking suspicion when looking at the heat output vs dial settings of my HG as posted above, ie 60 deg change for just changing dial from 6->7, how to hit your 4% heat output change with that ...   ;D

        But in addition to your solution there may be some other options:

        1) getting the Ueber-HG from control point of view http://www.steinel.de/en/thermo_fuer...se/hg_2310_lcd, but then again temp changes may in steps of 10 deg only (at least for their similar models) and fan-step changes are not clear form this. Also risk is how such HG would adjust internally the temp settings when you change the fan speed (otherwise temp rises), so there may be some iffy transients depending on their logic, how should one know this beforehand ? And this thing is spendy (~100 EUR). In principle I like the idea though of fan speed changes in this very convection oriented setup of mine (faster reaction times?)

        2) I could split the heat supply between HG and the gas burner and then do the finer adjustments on the gas burner in/after FC. But I havent tested this yet properly, ie how much extra heat is still required from HG when the burner is in low-moderate settings. Dont know if the burner adjustments are any faster as the bowl has some thermal inertia. Anyway the burner setting needs some headroom for up/down changes, so I may end up running the thing in drum-style roaasting only with little convection.

        I think your mod may not be all that tricky, a quick search showed there are ready-made TRIAC controller modules around for some EUR 20, you only need to add 1 .. 2  potentiometer for course/fine control and thats it.

        Need to ponder all this further.

        JavaB, looks you are already pretty much down the road to upgrading the "Coretto" into a precision profile roaster , you got all the sensors with data computer uploading, you got 100% electronically controlled  super fine heat adjustements , you got possibility for electronic activation of the cooling cycle ... hey, wait, makes me wonder if you are already working on a PID controller and hooking the whole thing up to your laptop, from which you only need to mouseclick on a predefined roasting profile from your favourite sofa or why not via cellphone during the drive home 

        All the best,
        Peter

        Comment


        • #34
          Re: temperature for roasting in corretto

          Originally posted by arcticroaster link=1167177851/30#32 date=1167849881
          JavaB, looks you are already pretty much down the road to upgrading the "Coretto" into a precision profile roaster , you got all the sensors with data computer uploading, you got 100% electronically controlled super fine heat adjustements , you got possibility for electronic activation of the cooling cycle ... hey, wait, makes me wonder if you are already working on a PID controller and hooking the whole thing up to your laptop, from which you only need to mouseclick on a predefined roasting profile from your favourite sofa or why not via cellphone during the drive home

          All the best,
          Peter
          HeHe.... very true- I had thought of automating the setup - but that would remove half the fun! Its one thing to have good tools to do the job - its totally different if you have someone (or something) do it for you!

          Im not sure how fine the adjustment of even the best heatguns is..... after all they werent designed with this sort of precision in mind. Air flow variation is a possibility but I would imagine reduced airflow would increase the temp of the air out of the gun..... but transfer less to the beans.... hard to work out what would happen!

          The other method which doesnt require a mod or an expensive gun is to change the distance - and this doesnt have to be by a lot to change the amount of heat transferred. So maybe a combination of coarse steps on the gun and fine adjustment by distance changes and you would get the same effect.

          By the way, distance changes dont suffer the same amount of lag that changing the heatgun power does...... another possibility.

          Comment


          • #35
            Re: temperature for roasting in corretto

            Originally posted by JavaB link=1167177851/30#30 date=1167788268
            Hi Peter,
            The heat gun adjustments required around and after FC are very fine... and I doubt you will be able to make them with a standard heatgun - well not without a lot of pain.
            Hi JavaB,

            I did a bit more fiddeling with my HG to understand the control better. Temp is controlled with a large dial with has many "teeth" (can be seen on the the pics I posted earlier).
            Couple of observations from measurements (TC in front of nozzle, outside the bowl) in the 60 .. 75% power range:

            1) when stepweise increasing power by advancing by one tooth, temp rises quite consistenly by 10 deg after some time lag

            2) its impossible to map these dial position to **absolute** temps. Eg when running the HG for some 15 min temps were 10 .. 20 deg higher (gun heats up, maybe the control Triac circuit is is temp sensitive, resistance of TRIAC may chnage, 1000 effetcs etc)

            3) when changing control direction from eg up to down , there seems to be some hysteresis before the HG responds  with appr. 10 deg down steps. You have to dial back 2 .. 3 teeth for that. I also read somewhere that certain Triac "dimmer" circuits have such hysteris behaviour

            4) when giving over some time up and down commnads , the temps come always out a bit different. However, smaller **relative** temp up/down changes are consistently possible with these caveats

            I tend to believe that in my case building external TRIAC dimmer circuit makes not much sense. The HG appears to already have a basic dimmer circuit  type of control, although with only one potentiomenter moved by the dial. So I already get roughly 10 deg steps control, just like at above mentioned Steinel HG and incidently like your external circuit (power change with 10 deg at 250 deg operating temp = 10/250 = 4%). And different control circuit doesnt help against the thermal lag and need to "plan ahead" with the temp settings, which, in this case I suppose means that when during the exotherm phase of 1st crack the beans produce heat and increase temp you should probably *increase* the temp by one notch in anticipation of the heat absorbing phase coming in 30 sec later or so , etc.

            Now being better aware of these issues you mentioned my last roast went roughly like this (sorry no nice log file yet):
            start of 1st crack  around 7 min @ 199 deg,
            8 min:  209 C
            9 min: 216 C
            10 min 220 C
            11 min 224 C sencond crack starts
            12 min 228 C, roast off  

            So between 1st & 2ncd crack I have initially a slope around 10 deg/min, then down to 4 deg/min until the end. Does this look reasonable ?

            I used some peruvian beans, is endothermic behaviour very bean specific, ie are some beans more prone to stall than others after 1st due to high heat absorption ?

            Anyway, I am almost exclusivley using these beans, its a workmate who runs a specialty coffee as 2nd business in his "free time", so its very convenient for me to get the beans from him (and they are good for espresso roasts). So maybe with some more roasts I will learn to manage the temp behaviour of these beans together with all the thermal lag in the control loop. Well, thats the main fun of this whole home roasting, cranking the HG controls around like mad and yet having in the end a decent cup and being able to do roast profiles which even a professional Probat roaster owner cant do (with larger charges) and all this with a heap of kannibalized home tools for a few bucks ...  

            Sorry for putting you all asleep with these tedious ramblings, every Coretto-roaster wonders probably since hours why the heck arcticroaster is not backing off his HG, there you got your nice continous control of flow an heat without any fancy TRIACs or whatever, but the sad truth is in my setup backing off the HG is not an option: the lid is in the way of the nozzle and I would loose all temp readings as I would be pulling out also all TCs as well ... :

            Cheers, Peter

            Comment

            Working...
            X