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6kW Electric Air Roaster
I finally got my new 3600W power circuit installed and was able to do an initial test roast with some old beans. Everything went reasonable well (ie I didn't burn the house down).

Although I'm hoping to roast 1.25kg green, I tested 800g for this initial test.

The 5400W of heat, combined with a completely different thermocouple placement caught me out, and I hit first crack at 5min 45s at BT of 190 degrees C. Second crack came soon after at about 7 minutes and about 208 degrees C.

Bean circulation was ok. A bit too energetic I think, but I could turn the fan down further.

Conclusion: I think I have enough power and airflow to try at least a 1kg green load. What do you think?

This looks first rate to me! Excellent circulation. I don't think you'll have any problem roasting a kg.

Nice work!

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
I roasted 1kg of decaf on the weekend reasonably successfully. Still need to do a few more roasts to learn the new temps.

However I've had a very annoying controller issue. I'm getting some blower cut outs and slow downs. I suspect I'm getting some interference that is mucking up the phase angle control. If I recall correctly I had a similar issue on a previous controller. EDIT: found it from back in 2012 https://forum.hom...post_40040

On the upside, the standard glass tube (not borosilicate) I'm using has not cracked with the heat yet.
Edited by greencardigan on 07/08/2018 10:36 PM
I've had that issue, but it involved slow writing times to a LCD or tft display. Found that the zc detection, and the triac firing times both have to be handled by hardware interrupts. The zc can be handled by Arduino / sketch, but the firing has to be done a level lower.
I think it might be a grounding problem. I noticed that the blower hicuped a bit when connecting my thermocouples. Connecting the TC4 ground to mains ground may have solved my problem, however I need to test a bit more before I'm certain. Seems like my roaster body was grounded but the TC4 wasn't.
I've just finished a successful evening of roasting without any controller/blower issues. It seems that grounding the TC4 was the solution.

I tried a few batch sizes ranging from 550 grams (1.2lb) up to 1.2kg (2.6lb) using decaf Colombian and all went well. The 1.2 kg batch was right on 1kg roasted so I've achieved my goal with this roaster. ThumbsUp

For the record, this was 5400W heating for 1.2kg or 4500W per kg with a bit of spare heat.

Next task is to build a chaff collector so I can roast non decaf without making too much mess.
Edited by greencardigan on 07/10/2018 7:35 AM
Another goal for this roaster was to be low cost. Excluding the controller it came to $235 AUD which is around $175 USD. Some parts were free from my junk bin.

- 3 x Heatgun - Ozito XU1 2000W - 3 x $23.50 = $70.50
- Vacuum Motor - ONIX 2 - in - 1 STICK & HANDHELD VACUUM 600W - $40
- 2 x Brass waste 40mm - 2 x $13.55 = $27
- Brass nuts to fit waste - Free
- 90mm PVC - Free
- 90mm PVC cap - $2.55
- 3D Printed manifold - Free
- RTV silicon - $31.55
- Liquid funnel stainless for heat gun joiner - $3.59
- Large funnel for base of roast chamber - $8
- Bin for roaster housing - Free
- Timber and aluminium supports for roaster - Free
- 1mm Aluminium sheet for various brackets - Free
- PCV mesh vent - $4.78
- Glass tube for Roast chamber - Free
- Threaded rod supports - Free
- Aluminium sheet 0.5mm for Roast Chamber extension tube - $35.75
- Aluminium tape - $11.95
- Power cables - Free
This roaster is proving to be a real workhorse. I'm really happy with it's performance.

I increased my bean load to 1.5kg (3.3 pounds) and the roaster handled it easily. A 12 minute roast required about 85% heater. Now I'm wondering if I could possibly reach 1.8kg (4 pounds) which would be 1.5kg roasted.

Cooling in the roast chamber is taking 3 mins to reach 100C.
Just a quick question about the power requirements. I was hoping to increase my roaster from 1 x 2000W heating element to 2 so that I have a total of 4000W available. Not sure what the best wiring would be and whether I would need a 15amp source in my house?
15 Amp 230V I guess...
Because 15 Amps @ 115 V make 1725W.
yeh thats fair enough, perhaps I can just run the two elements from different points and have a single SSR fire them both


greencardigan wrote:

Any thoughts on perforated areas? Funnel shape?

I drilled out a colander for a bean cooler and to get maximum air flow I drilled out all the holes to maximum and placed a piece of stainless steel screen over it. Only a thin framework is needed to support the screen which seemed to pass a lot of air.

"Espresso is a miracle of chemistry in a cup."
Andrea Illy
Hi greencardigan, i was wondering where you got the glass tube for the RC from? also did you seal the funnel which connects all 3 heating elements or is that open air?
Edited by Ooij01 on 10/21/2018 11:37 AM
The glass roast chamber was an unused vase that I 'borrowed' from work and cut the base off. It's standard glass but I have not had any issues with it yet.

It's all sealed with RTV silicon. The three heatgun nozzels go through an aluminium plate which is sealed in the upside down funnel.

My elements are all in parallel. Two are on one 15A circuit and the other on a separate 10A circuit. An SSR for each circuit.
JSA Coffee
Is there a link available for the funnel used as the base of the roast chamber?
It was from eBay. I don't have the exact ad any more but it was probably this one. Probably the 20cm one but I did order a few sizes and they're not very accurate.


greencardigan wrote:

Next task is to build a chaff collector so I can roast non decaf without making too much mess.

Hey Greencardigan,
Did you ever figure out how to add a chaff collector to this?
I tried and failed! Shock

I bought two of the small aluminium cyclones from ebay but i think I have too much airflow for them to work properly. I was getting a reasonable amount of chaff passing through the cyclones.

I'm now reverting back to a simple mesh basket sitting on top.
greencardigan attached the following image:
Nice dual setup ! Why not install mesh at the cyclone air exit too, keeping the chaff inside.
Or, another take, why not mount the cyclone as series instead parallel ;) I mean pipe the output of first cyclone to the input of the second.
I think my problem was I was forcing too much flow through even with two in parallel. Two in series would be worse I think with greater restriction.
I have a small amount of chaff escaping the exhaust on the transparent roaster as well. My blower is putting about 17-19 cfm through the cyclone. I think that is in the acceptable range for the cyclone specs.

The chaff escape problem may be from not having a large enough (larger diamter) chaff collection container... I'd say 99% is contained on mine, which has about an 86mm inner diameter chaff collector. Renatoa's idea of a mesh sounds good if the collection container can't be modified.
I am using this cyclone in a turbo oven setup, so air does not enter into cyclone by natural pressure from RC, but must be sucked using an external blower instead.
For this purpose I fitted a 10 cm / 20W inline hydroponics extractor fan that is rated for 140m3/hr ~ 82 cfm, that sounds enormous, but the feeling is not at all comparable with the airflow of a FB. Probably the specs of chinese ebay fan are fake.

Anyway, it does a good job as separation, no chaff thrown out until the chaff level approach the lower exit of the cyclone, that's the moment when it start to see sporadic flakes in the air. I am using a flour sieve in that moment, to cover the fan exit Grin.
I don't know what flow rate I get through my beans from my 600W vacuum blower, but the noise of the air whizzing around through the cyclones was probably louder than the roaster itself!
Greencardigan, you're right they can be loud. In Canada, our 3/4" threaded copper pipe coupling (male or female) has an outer diameter just under 25mm. One can be placed into the top exhaust and it acts kind of like a muffler... in some way it changes the turbulence on the way out and quiets the whistle or whizzing sounds.

Here's an image with the specs for these cyclones to work as intended.
CK attached the following image:

Edited by CK on 01/14/2019 6:21 PM
I don't understand the relationships between power and airflow, if any...
As I wrote, my exhaust fan specs are 20W only and 140 m3/h... completely off versus the cyclone.
So what fan should I use instead, for the best suction parameters ?
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