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Koffee Kosmo
OfflineAdmin
· 08/12/2020 5:37 PM
And I thought it was just me that couldn't access the site All good now - coffee kept me company

JackH
OfflineAdmin
· 08/10/2020 8:46 PM
Had to make myself another cup of coffee to get through it.

snwcmpr
Offline
· 08/10/2020 7:33 PM
I went into withdrawal for a bit. Now .. all is good. roar

mtbizzle
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· 08/10/2020 7:26 PM
Yeah Jack I think so, I couldn't access for a bit

JackH
OfflineAdmin
· 08/10/2020 6:51 PM
Did we lose the site for a while?

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Cyclops - my 1kg drum build
allenb
The chart doesn't convey what I'm looking for. What is the temperature leaving the elements at a fan power level you expect to use to allow removal of chaff and smoke and at 90% or somewhere around there power level to the element. The chart is showing a maximum of 161C (321F) discharge temperature which will not get you where you want to go. Or, am I missing something?
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
pjvdl

Quote

allenb wrote:

The chart doesn't convey what I'm looking for. What is the temperature leaving the elements at a fan power level you expect to use to allow removal of chaff and smoke and at 90% or somewhere around there power level to the element. The chart is showing a maximum of 161C (321F) discharge temperature which will not get you where you want to go. Or, am I missing something?


No. You are not missing anything. I agree that it doesn't show what I would expect either.

The temperatures at the exit are definitely lower than what I would expect. It is unclear why this is the case. As an aside, this is why the table is incomplete, as I realised that I was not getting the results that I would expect (and I blew an element at 100%/100%).

I have a couple of theories as to why this may be. Either there is an issue with the responsiveness of the K-type thermocouple that I am using to take the measurements. Or, the airflow is too high at high fan %, causing significant variations in the temperature. I did notice if II moved location of the probe, the temerature reading did vary significantly, supporting this theory. I am not an expert in fluid dynamics, but I think the data also supports this, as you will notice the measured temperature at 80%/80% and 90%/90% is lower than 60%/60%, even though the colour indicates it should be hotter. I would be interested in other's thoughts on this.

Because I didn't trust the absolute temperature readings, I was guided more by the temperatures relative to each other, building up a picture of how the temperature curves develop as a factor of heat and fan.

I was also guided by the colour of the elements at their hottest point, which I did also record, although I neglected to include these in the table that I attached. I have now updated the table with the colour, so this might give a better indication (attached below). You will see that the colour at 100% fan / 100% heat is yellow. This is when I blew an element, ending my test :( On this basis, I am assuming that my "Orange/Yellow" is as high as I can go.

I did also run a couple of tests the next day with the tip of the thermocouple inserted into the end of the pipe as close as I could get to the live element without actually touching it - probably 5mm from the end of the live element coil. At this point I was measuring around 540C at 90% when the element was orange/yellow, which is more in line with what I would expect.

Chaff and smoke are removed when the fan is at least 50%, so I have some room to move in this regard.

As I mentioned, this settup is heating my roasting chamber to 250C in around 6 minutes, so clearly the temperature readings that I have recorded are incorrect for some reason.
pjvdl attached the following image:
screenshot_from_2020-07-30_09-07-06resized.png

Edited by pjvdl on 07/29/2020 6:58 PM
-- Paul

ECM Rocket espresso
Eureka Mignon grinder
500g BBQ rotisserie roaster
1kg drum roaster (under construction)
 
pjvdl

Quote

renatoa wrote:

You should use 1 Hz PWM for at least 2% (1.67% on 60Hz) control resolution... 8Hz will degrade significantly your control precision.


I think I understand why you would get a 1.67% control resolution at 60Hz, but are you sure you would get a 2% resolution at 1Hz? To be fair, I struggle to get my head around the ATMega bit control theory of PWM, but from my testing, 1Hz PWM on a Arduino/TC4 setup switches the power on/off at a maximum frequency of 1Hz. To achieve a 2% control resolution you would need to include 50 cycles in your control cycle, which at 1Hz is 50 seconds for one cycle through. Or am I missing something here?

From user.h file in the aArtisanQ_PID arduino shield (you will see that I have 8Hz uncommented):

////////////////////
// Time Base for slow PWM on OT1, OT2
// When NOT using PHASE_ANGLE_CONTROL option
// choose one of the following for the PWM time base for heater output on OT1 or OT2
//#define TIME_BASE pwmN4sec // recommended for Hottop D which has mechanical relay
//#define TIME_BASE pwmN2sec
//#define TIME_BASE pwmN1Hz // recommended for most electric heaters controlled by standard SSR
//#define TIME_BASE pwmN2Hz
// #define TIME_BASE pwmN4Hz
#define TIME_BASE pwmN8Hz
// The faster frequencies below are for advanced users only, and will require changes to the PWM16 Library
//#define TIME_BASE 15 // approx. 977 Hz
//#define TIME_BASE 7 // approx. 1.95kHz
//#define TIME_BASE 6 // approx. 2.2kHz
//#define TIME_BASE 3 // approx. 3.9kHz


Quote

renatoa wrote:
Are you using TC4 ? why not going with ICC ?


TBH, I started using PWM because I was initially learning how to work with an Arduino/TC4 and that is the default. I have been meaning to look at the alternative control mechanism, but haven't had the time. I think ICC is also dependent on the presence of a zero cross detector, which I have had a quick look for, but have not managed to source yet. This is definitely something that I want to try.
Edited by pjvdl on 07/29/2020 7:28 PM
-- Paul

ECM Rocket espresso
Eureka Mignon grinder
500g BBQ rotisserie roaster
1kg drum roaster (under construction)
 
renatoa
When using PWM, the SSR command that comes from TC4 could be of an infinite degree of precision, but this not matter because is not sync'ed with the mains frequency, so you can chop (or miss) a random part of the sine.
As a result, when you dial for example 50% heater, and using 1 Hz cycle, the output could be anywhere in the 49-51 sine waves passed through the SSR.
From here, the 2% precision (for 50 Hz), and 1.67% = 1/60, for US mains.

I found this fact following this intriguing statement that you can read in any PID leaflet "...set the control period for SSR outputs to 2 seconds...".
After some digging, the explanation was been clear: this cycle time is required if you want 1% precision of control... elementary... if you see on screen 1...100%, then you want to feel on heater the difference down to 1% step.

For 8Hz PWM, for each PWM pulse you have practically only 50/8 = 6 sines available to control. So you have only 7 levels of power control:
0, 1/6 = 16.7%, 33%, 50%, 67%, 83% and 100%
This is dramatic decimation of control choices, that could led unusable my roaster for example... where 80% of roast time I play with figures between 72 and 77%, sometimes 1% in a minute change making a difference in final roast !
1% of power is 3 C degrees in hot air temperature, how much this matters depend on your specific machine inertia, quite critical for FB, acceptable for heavy drums.

With ICC the power modulation is done by passing or blocking the entire half-sine, (thus the need for a zero cross detection, as you well guessed)
So if you you have 100 half pulses for 50 Hz mains, then you can have 1% resolution/precision, and this is true instantly, in any moment.

Another advantages of using ICC:
- don't exhibits transients, because the switching is always near zero of the sine, so less or no perturbations in the sensible house equipment.
- the heater is less stressed with temperature swing, as for on-off
- for halogen heaters, less annoying pulsing light
 
danst
I see no problem with precision degree of 1 Hz with SSR and it is well suited for resistance heaters and their longevity. For heating control of electric drum roaster is 5% or even 10% scale of power enough.

The nichrome heater is usable (for classic drum roaster) only when it holds all the power without airflow. It must be so designed, not as these airflow-heatings from heatguns etc. (this means several power units in series and parallel or one with thick wire, but long for reducing power- amperage and load, all this results in bigger space requirments)
In a classic roaster, it must be possible to go on max even without forced airflow, above all in drying phase.
With common kind of nichrome (what you are using) is the airflow too high for good power usage.
The idea with inductive heating is for me a bit risky. Not easy for DIY.
Proved solution are tubular elements. It must be space for it, just like for gas heating.
I believe, it is a good idea to copy professional roasters.
1000g Ugly roaster, QM Alexia EVO, Bezzera BZ09, Niche Zero, Fiorenzato Doge 63, Mazzer Jolly(Mestre), Handground, T. Moccamaster, Aeropress.
 
allenb
Something to consider with resistive wire forced air convection heaters as you are using. If engineered correctly and established heater watt density is not exceeded, you will be able to increase cfm to a point where the element will show little to no visible glow in a normally lit room at design full power. If you are not exceeding the design voltage then you're air flow is insufficient at full power. I can take any 1500 watt nichrome forced air convection heater and flow slightly more than optimum designed cfm and end up with no visible color.

Danst brings up a good point about being able to operate during the drying phase with little to no non-recirculating air flow which allows a humid environment during the drying phase. Studies have been done, but don't ask me by whom, that show a more even and beneficial heat transfer during the first few minutes when steam is allowed to surround the beans while being driven from them. This obviously only applies to mechanically agitated roasters and recirculating fluidbeds.
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
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