Hello:

Bodka Coffee wrote:Sounds good! Keep us posted on your roaster.

Thanks, I've been at it for the longest while.
It's a gas fired Burns type design, open end, no trap door, tilt to empty and running on 12VDC.

The main design directive I set myself on was that it had to be simple, as much DIY as possible, using recycled and binned parts from whatever source was suitable to build it and with little external intervention.
The inevitable welding, rolling and lathe work had to be kept at a minimum.

I don't have any proper photos yet and when I do I'll start another thread but for now I can tell you what I have used:

- crankshaft pulley from a 1994 R18
- burners from a gas fired water heater
- gas valve and safety device from an IR heater
- igniter parts from a gas fired room heater
- freon charge valve from a split AC unit
- old set of bearings from my Cimbali Max Jr.
- auto-centering bearing from a lab machine
- wiper motor from a 1990 Suzuki Swift
- 12v battery from a server room UPS
- assorted rotary cam switch parts to make 'one'
- adjustable leg ends from discarded office chairs
- off the shelf heavy duty weld-on hinge
- screws, bolts, washers, cabling from my various bins.

And now a question regarding the firepower needed to roast coffee ...

I recall having read somewhere (probably here) that the new Huky 500 model will roast 500 grams much better on a 20,000 BTU burner instead of the one that the manufacturer offers.

But then I have also seen values way below that for that and other roasters, so it would seem to me that the BTU values are all over the place, so to speak.

Is there a formula for that? Is 5,000 BTU / pound (~ 10,000 BTU / kg.) an adequate value?

Thanks in advance,

CIV

EDIT:
Found this a while ago, lot of difference.

BTU to roast 1lbs?

another_jim wrote: ... IIRC, the burners on Probat sample roasters are 8000 btuh per drum; and those are designed for 250 gram samples.

germantown rob wrote:My Diedrich IR-1kg is 8000btu an hour at max.

.

I would guess a 1/4lb..
I had a BBQ mesh drum and it was about the same size as the coffee can your using..

I think I can help you here also. Send a pm to JohnnyLSU. Or maybe he will answer here. He has a Huky with a larger burner and can roast a full pound.

But then I have also seen values way below that for that and other roasters, so it would seem to me that the BTU values are all over the place, so to speak.

Smaller, less insulated, and designed to be fast roasters need more energy per unit weight. If you're running an insulated, air recirculating one bagger all day, and can wait an hour for it to heat up, you don't need that much heat per pound. An exposed, fast roaster like a Probat sample roaster or a Huky is not going to be very efficient, and will run a lot higher.

Obviously, small powerful roasters are more profilable than large insulated ones, just as race cars are more maneuverable than trucks.

Bodka Coffee wrote:I think I can help you here also. Send a pm to JohnnyLSU. Or maybe he will answer here. He has a Huky with a larger burner and can roast a full pound.

Even HUKY owners using the IR burner supplied by Mr. Li can and do roast a full pound.

Thanks for the clarification, Susan. That's nice too know. Still haven't bought one, still want one.

Hello:

Bodka Coffee wrote:I think I can help you here also.

Thanks. =-)

Some background on the burners:

The burners I am using come from (a set of 12) installed inside an on-demand water heater with a max output of 21,000kcal using the standard OEM size jets (0.55 mm) for use with bottled gas. The jets for mains pipe gas are of a larger diameter.



This works out to 1750 kcal for each burner and a total of 7000 kcal for the four burners I initially intend to test.
At first sight, 7000 kcal seemed an outrageously high number to me (a whooping 27760 BTUs), so I reduced the jet size to the minimum they would suitably work at (0.45 mm) but as a result I don't know what the heat output is now.

What I have been told is that the reduction of heat output is not proportional to the reduction in jet size as other factors such (eg: pressure) enter into the equation. But I have no idea as to how to figure out the new number.

That being the case, I think I can safely assume (?) that I've been able to reduce the four burner's combined heat output it by ~ 1/3 and (if this is correct) they now put out ~ 18507 BTUs which is a number that falls in line with posts I have read.

I always have the choice of using only two burners instead of four which would give me an estimated ~ 9252 BTUs and if that number is low, I can always go back to the larger (0.55 mm) jets for a heat output of 3500kcal / 13880 BTUs.

Bodka Coffee wrote:I think I can help you here also. Send a pm to JohnnyLSU. Or maybe he will answer here. He has a Huky with a larger burner and can roast a full pound.

The Huky seems to be close in size to my contraption, let me check.

EDIT:
Added burner photo.
From what info I have been able to find on the Huky (which is not a Probat type design), it apparently has a 130 mm x 170 mm drum, which makes for a volume of ~ 2257 cc / ~ 137 cu in. with a (formula calculated) load of 13,80 oz / 391 grams.

So ...
20000 BTU for 1.0 lb. / 500 gr. roasts?

Thanks in advance for your input.

Cheers,

CIV

Hello:

another_jim wrote:An exposed, fast roaster like a Probat sample roaster or a Huky is not going to be very efficient, and will run a lot higher.
Obviously, small powerful roasters are more profilable than large insulated ones, just as race cars are more maneuverable than trucks.

Makes much sense.

The thing I'm building has no insulation whatsoever, just a few kilograms of sheet steel to absorb/radiate heat and from my previous tests I can say it does get hot. Very hot.

The thing is to be able to control that much heat, quickly and predictably, lest the roast 'run away' on you and leave expensive charcoal behind.

Another important issue I envision is that, in order to have any success with it, I will have to get to 'know' my roaster very well so as to be able to properly gauge it's thermal inertia (see it coming, so to speak) and act accordingly on the needle valve / pressure gauge combo.

Thanks for your input.

Cheers,

CIV

I've heard some BBQ / Drum roasters throw a welding blanket over the BBQ for insulation. There's also lots of ideas on this site about insulating roasters, especially the Quest.

And, of course, insulation can have as much affect on the roast size as BTUs... If all the heat is radiating out to the world, only a small portion gets into the beans. If all the heat is reflected back into your drum the beans will absorb it much faster. What you need to be figuring with is not the BTUs of the burner as much as the BTUs directed into the bean mass.

[hint: you might want to rethink the 'no insulation' part of your design]