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Brainiac
Join Date:July 27, 2007
Location:New Zealand
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2kg drum roaster - help me design one! ;)
stuartgrant

Quote

Koffee Kosmo wrote:
Its probably best for even heat distribution to use 2 or 3 elements to achieve your total wattage needed


Hey KK,

That's the plan. I've emailed a few places and they recommended those ceramic infrared elements as being appropriate for the environment. They tend to come in 500-600W half-size and 1000-1200W full-size. I'm far from working out the final element configuration, but there's plenty of flexibility there.

Cheers
Stu.
stuartgrant
Brainiac,

I remember from grade 12 physics that P = I.V... doesn't that mean that 25W running off 12 volts is actually pulling 2 Amps?? Or is my understanding wrong?


Boom,

Yeah, I'm a little worried about that. If I have the heaters on when I start the motor, voila, un probleme. But I'd love to have a setup which didn't have any of those potential issues every time I roasted...

Similar to if I ran 2400W-worth of elements when I only had ~2000W available; it would be a blown-fuse waiting to happen. Any thoughts on solutions to that one?

Thanks for the replies!
Cheers
Stuart.
boom
Get a bigger fuse! :)

The answer is....GAS!
A good espresso should give you hair on your chest!

Nuova Simonelli Mac Cup S, Mazzer Super Jolly, 1962 Faema President 2-group Lever, 1960 Faema Urania Grinder, 2kg profile controlled roaster
seedlings
Yes, stuart, but that's 2 amps at 12 volts. 25 Watts will only draw 0.11A at 220V, so if you put your current meter on the 220V leg going to your stepdown transformer, you'll see 0.11 amps. If you put the current meter on the leg from the transformer to the motor, you'll see the 2 amps.

Brainiac won't lead you astray.

And, gas is not a bad idea - although I share your desire for the instant control that electricity allows. You're on the right track, and remember even the best laid plans require some post-engineering. Build it, test it, adjust it.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
stuartgrant
Duh!

Haha - I get it now! Thanks Chad. And Brainiac - I knew I could trust you! :P

In that case, as for boom's warning about the starting current for a WW motor spiking to 4 Amps, that will means that the PC power supply will have to be up to providing ~4A - albeit momentarily. Correct? Would most PC power supplies be able to handle that?

Neil - of course gas would provide a simple solution to lack of power! But I'm fairly determined to stick to electric for now - it's almost a key design parameter... Give the above advice, I'll actually have more like 2300W available to the heaters, so that's a lot more likely to handle 1.5kg (3.3# ... 45.78 shekels) which would be ideal.

Bigger fuse, tho? If our circuits are (nominally) 10A... I can't exactly exceed that, can I?

Thanks again, everyone!
Cheers,
Stuart.
stuartgrant
Ok - time to be greedy and ask another question!

Airflow! I'm looking for a ballpark figure to aim for. It will at the very least help me to know what fans to look for. My major assumption here is that airflow needs to be proportional to bean load (ie. larger roasters will have a higher airflow rating). Pretty sure that's right.

Looking at boom's design, he opted to go for about the same as the Diedrich IR-3 which (as listed on their website) is 132 CFM (3,700 L/min). Scaled to my bean load (1.5kg), that would be 66 CFM (1900 L/min).

[This figure on the Diedrich website is for "exhaust air flow at 1" static pressure" does this refer to what I think it refers to?? I'd guess that it's the maximum airflow - which I've heard to be highly adjustable.]

Jim reckon's his drum roaster has an airflow of around 1 CFM for 2lb. Scaled to my bean load, that would be 1.7 CFM (50 L/min).

As you can see, they differ by a factor of 40! I realise different roasters will aim for different rates of airflow but can anyone point me in a useful direction here?

Cheers
Stuart.
seedlings
I'm no genius, haven't built a drum roaster, and I'm generally a simpleton... Since hot air rises... Why not just put a "vent" on the top rear, and an opening on the bottom front. This would draw air in from the lower front and out the top back. It would be a fairly gentle airflow, but, isn't that what you want?

Regarding the fuse rating... You're right, that you don't want to exceed the 10 amps. However, remember your AC fuse passes only 0.11A for the motor running, so it may peak at 0.22A, or 4 amps at 12V. You're still OK. If it will make you feel better, just have independent switches for the motor and the heat. Switch the elements on to preheat, then switch them off while you load and power on the motor, and once it's at full speed (in a few moments) switch the heat back on.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
Brainiac
Stuart

I'm pretty sure that the Diedrich figure includes airflow for the bean cooler: i.e. this is the sum airflow for drum air AND cooling air.

Many traditional-style commercial roasters provide fine adjustment of the through-drum airflow with a damper-type control; newer electronic controllers allow for variable-speed fans, so that the only real consideration is maximum airflow required (factoring in exhaust duct and chaff cyclone parameters and so on)

Brian

... and the afterburner!!!
stuartgrant
Thanks Brian - I hadn't thought about the cooler as well. I can imagine wanting that high an airflow for cooling, but not roasting!

I had figured that the Diedrich figure was the max airflow... but your observation brings the roasting airflow down significantly, I'd say.


Chad's right, I do want a gentle airflow. I think having a perforated drum with solid vanes (inside), this will actually act as a fan and produce a reasonable current of air inside the drum. So really, just a gentle fan drawing the air/smoke out should do it. Perhaps I'll aim for a max airflow of, say, 200L/min (7 cu.ft/min) - probably "use" 25-50% of that at a guess.

Cheers
Stuart.

ps. Thanks a lot for all the suggestions, guys! I'm getting closer to being able to "re-pitch" my whole design with much more clarity. Thanks to youse I'm about 2/3s of the way there.
seedlings
Braniac (halogen) and Farmroast (turbo-oven based) have roasters that are sealed, without intentional fresh air flow, and neither of them have trouble with smoke or smokiness in the roasts. Turns out that once the available oxygen is used up, there's not much smoke. But you couldn't do that with gas.

CHAD
Edited by seedlings on 10/06/2009 6:59 AM
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
stuartgrant

Quote

seedlings wrote:
Braniac (halogen) and Farmroast (turbo-oven based) have roasters that are sealed, without intentional fresh air flow, and neither of them have trouble with smoke or smokiness in the roasts. Turns out that once the available oxygen is used up, there's not much smoke. But you couldn't do that with gas.


That's good info. Thanks Chad - I remember reading it in their respective threads, but I'd forgotten the details.

(Almost) total exclusion of oxygen would do more than reduce smoke; surely it would alter the flavours produced? I mean, most of coffee's flavours come from the breakdown of starches/carbs in the presence of amino acids and whatnot... but surely the makeup of the atmosphere in which that happens is relevant? Side issue, obviously - though a very interesting one.

Brian and/or Ed - since you both have experience with other roasters (just a hunch!), have you noticed any differences in the flavours you get with these roasters?

Cheers
Stuart.
stuartgrant
Oh I forgot the reason I started that reply was to say that, while I like the idea of reducing smoke etc., I want a moderate (and controllable) airflow through my roaster.

Why? Well, it's just theory, but what I decided after the brains trust assisted me in this thread on nutting out some of the science of convection/radiation/conduction and all that.

The conclusions (for me) were that convection will always be the predominant form of heating, but that aiming to have a reasonable proportion (say, 10%) of total heat transfer from some other source (radiant, in my case) is a good idea and will give you a more even roast. Main reason for that is that high percentage convection roasters tend to dry the beans out too much when you're aiming for a 15-18min roast to SC. Not all of that is hard facts... some of it has been interpreted by me and that's what I decided on!

So yeah, I want airflow. :)

More importantly, I want it to be adjustable. More design required!

Cheers
Stuart.
Brainiac

Quote

stuartgrant wrote:

Brian and/or Ed - since you both have experience with other roasters (just a hunch!), have you noticed any differences in the flavours you get with these roasters?



Hi Stuart

My other favourite roaster (picture attached) is almost all convection (a sort of tangential roaster using a heat gun but mechanically agitating a half-pound of beans in a stainless mesh drum).
The halogen radiant roaster tends to produce deep flavours of caramel and chocolate; the tangential air roaster tends to accentuate the citrus and fruity character of the beans (this of course is REALLY over-simplifying things; bean origin, roasting profile, and final degree of roast have much more influence on the eventual flavours).

Brian
Brainiac attached the following image:
tangent.jpg
seedlings
I've admired that heatgun roaster before, and would like to see the operation of loading and unloading of beans.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
stuartgrant
Hi everyone!

Digging up this thread because I'm about to return to Australia and get started on the roaster! If you remember back to the opening post, I said that this thread was my "drawing board" while I was overseas and unable to do anything but dream! Well, my wait is almost over - we leave Bulgaria to return home in a weeks' time.

I'm very keen to re-kindle this project. The other thing that's happened in the mean time is that I was offered (and have accepted) a job at a new roastery in my home town! Amazingly lucky and very happy to get into it. As such, this drum roaster project will give us a sample roaster for the roastery, as well as providing me with endless entertainment and roasting fun.

New plan - probably going to limit the roaster to 1/2 kg because a) it'll be easier, and b) it's a better size for using as a sample roaster. Also, I'll probably use gas, not electric. May or may not design it to match our Diedrich IR-12 roaster, currently being manufactured over on your side of the pond. ;)

In the next week or two, I'll probably start a new thread to document THAT particular roaster-building journey.

Thanks to everyone who helped me in this thread - it was very instructive!
Cheers
Stuart.
Edited by stuartgrant on 03/29/2010 10:17 AM
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