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my first roaster
marce
Hello fellow home roasters.
I have been working at building a drum roaster for a while.
I have roasted about 10lbs in it so far and I am working to improve the design/efficiency of the roaster. I find that I have not quite enough power to control the ramp up speed. As it is now, it runs on 110V it has 3 sets of 700W elements for a total of roughly 2000W and a total of 6800btuh.
The drum is a stainless compost bin 7? diameter by 9? long. It is fairly thin so it doesn?t have a great thermal mass but I suspect it does transmit heat fairly easily. The walls are solid with perforations through the back for convection. The front and back of the roaster are ?? steel.
I currently load the roaster with 300gr at 400F and roast to FC FC+ in 13 min or so. I?d like to gain more control over the ramp up speed and profile of the roast. So far the only way I can control the roast is by changing the load temperature. I can cool off the roaster quickly with the fan but I am unable to speed the ramp up.
Would a perforated drum help? Or do I need more btuh? As it is now it?s maxed out for 110V in order to get more heat I?d have to go to 220V or gas. I would be tempted to go with gas rather the 220V.
Here are a few pictures
marce attached the following images:
roaster_4_2.jpg roaster_3_2.jpg roaster_2_2.jpg roaster_1_3.jpg drum_3.jpg roaster_15.jpg
 
allenb
Very nice looking build! Can you provide a little more info for us to kick around?

-Have you measured the amps drawn by the heater bank? If not, let us know the resistance in ohms of each tubular element.

-Are the tubular heaters mounted underneath the drum or on top?

-Are you able to reduce air flow to a small amount during a roast or is it all or nothing?

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
snwcmpr
That does look good.

Ken in NC
--------------
Backwoods Roaster
"I wish I could taste as well as I wish I could roast."

As Abraham Lincoln said "Do not trust everything you read on the internet".
 
marce
Thank you for the comments!
I have 124V at the outlet, 7.1 OHM total resistance for the 6 tubular elements. They are wired in pair. 2 elements in series and the 3 pairs in parallel. According to my calculations, that amount to 2166W and a total of 7390 BTUh.The elements are from toaster oven bought from a thrift store and are at the bottom of the roaster, there is 1" of space all the way around the drum. As mentioned earlier, the drum is 7" x9" and the roaster is 9"x 14". So there is a lot of empty space at the back of the roaster in order to accommodate the cheap elements.... Might not be a good thing.
The fan is controlled by a SSVR and a potentiometer. It is not quite working right though, the fan is off a Jennair down draft range. It is huge but design to to work with a specific back pressure intake resistance. The motor is to weak to suck from a 2" hose. So it is not ideal but it does pull the chaff out. The fan suck from the bean chute at the top front and there is a series of hole at the bottom front for intake.
The elements are controlled by a PID, simple without ramp program.

What else, the drum turn at 60 RPM. I use Artisan with a Phidget to send data to a laptop.

I plan on making an other drum. This first one has fins that are too big and it make it difficult to get a good BT probe placement. With 300 gr, it is not quite fully immerse in the beans mass. Also the drum got distorted when I welded the fins in it, the next one I will use rivets to fasten them in and maybe have room for a trier.
I am tempted to drill hole in the original drum walls just to see how it would behave. What do you guys think about perforated vs solid drums?
 
allenb
Here's a few thoughts,

With 2100 watts you should easily be able to roast a pound of coffee in 10 to 12 minutes.
What will help tubulars is having a shiny reflector behind them to reduce energy directed to the outer skin of the roaster. This can eat a bunch of heat even with insulation. The extra volume behind the drum adds to your square inches of heat sink which, as you mentioned, eats more btu's.
An important part of drum roaster design is making sure your incoming air is absorbing as much heat from the heat source as possible prior to entering the back of the drum to ensure you aren't passing air across the bean mass that's lower in temperature than the beans at any time. If this happens, you end up heating the beans via drum skin and then cooling them as the air passes through the drum. Have you measured the temperature of the air entering the back of the drum?

On the drum vanes, it's important to keep anywhere between 1/2 to 3/4" between the front end of the vanes and the face of the roaster to reduce the tendency for beans to get crunched as the vanes pass by openings. This also allows getting a thermocouple low enough in the bean mass without encountering the vanes. My sensor is about 3/4" from the drum wall at about 8 o'clock.

Hope this helps,

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
marce
Good idea on the reflector. I'll get some in soon.
As far as the air entering the drum, I'll try to take a measurement would a exhaust temp be a good indicator? or should I place a probe behind the drum?
I had 3/4 of space between the face of the roaster and the vanes but when I installed a sight glass on the door I noticed that the beans against the glass where not moving much, so I added extensions on the vanes as you can see on the picture. At the same time I grounded the face's opening at a 45* angle so beans would not get hung up on the 1/4" face thickness. It might have done the trick without the vanes extensions...
Any thoughts on perforated vs solid drum?
Thank you so much for the feed back!
Marce
 
allenb
FYI, for a low cost and effective reflector, some have just taken heavy duty aluminum foil, shiny side up, wrapped around a piece of sheet metal and works very well. The sheet metal can be mounted on stand-offs in between the tubular elements and the outer skin of the roaster.

The only way to know if you're heating the incoming drum air effectively is to measure at the rear of the drum.

Perforated drums work fine although will give a slightly different flavor profile depending on % of open area. Large open area where medium wavelength IR can have easy access to the beans will give you different results versus the very long wavelength IR coming from the solid drum. Sort of the difference between heat transfer from a Behmor and a solid drum roaster.

Another potential issue is small chaff particles falling onto your tubular elements will create burning chaff smoke which could alter flavor.

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
marce
Last night I have installed heat reflector made of stainless, I will try a batch later on today and I will post my observations
Thank you!
 
ginny
marce:

that is one great looking build an thank you for posting the pictures.

i agree with Allen and I think the shield/reflector will help.

please let us know how i all goes.

way cool roaster; you should be very proud of this baby.

ginny


Grin
 
marce
Thank you ginny for the compliments!
Wow What a difference! The reflectors sure increased efficiency. I just finished roasting some Yemen Mokha Harasi A coffee that I had a hard time getting enough heat to roast and not bake. my first attempt tonight had the first crack done at 7min! so on my second batch I increased the load to a full pound of green and got it done in a little over 13 min. For some reason Artisan did not record the event time and temp. So I have no recollection of the timing of all the phases...
I now need to get a better fan, finish the chute/vent with a hopper and a permanent cooling tray.
I'll keep posting my modifications.
Marce
 
marce
well I got lucky today, driving by a heat ventilation contractor's shop, I saw they had an old hot water tank in the yard that was marked for recycling. I went in and asked if I could have the draft fan off of it and they gave it to me!
I now have a better fan to work with and for free...woohoo
 
Erik

Quote

marce wrote:

well I got lucky today, driving by a heat ventilation contractor's shop, I saw they had an old hot water tank in the yard that was marked for recycling. I went in and asked if I could have the draft fan off of it and they gave it to me!
I now have a better fan to work with and for free...woohoo


Good score.

Nice work on this. What are you using for the insulation?
 
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