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11-15-2018 13:26
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View Thread » BUILDING A ROASTER » Fluidbed Roaster
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Small roaster
Hi guys,

I've been lurking around here for a bit getting ideas for my roaster and have built one with a couple of iterations in between. Its about a 10cm diameter and I'm using a 2kW heating element


or so eBay says and a 600W vacuum motor. It's all hooked up to artisan via an arduino.

I've noticed that the max batch size is around 250g for most beans until I have to lower the blower down too much to pick up the temperature. My heater is essentially on 100% near the end of the roast at this stage. Could it be that my heater element is not actually 2000W? I've got separate circuits for blower and heater.

Will try some heat re circulation to see if that helps increase green bean load.
Edited by JackH on 10-15-2018 07:30
The column seems not having the right proportions... 250g of greens give me about 5 cm high at 10 cm dia cylinder. Too flat greens bed, imo...
So your blower will heat mainly a central column, and almost nothing near the walls...
You told us nothing about the hot air opening patern and funnel dimensions.
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I was going to go for the bake-around method but i'm down in Australia so I just used a large french press beaker from Kmart and cut the bottom off. Below that I managed to find a cocktail shaker from Avanti which fit nicely and has about 12 holes which i expanded to 5mm each if i recall correctly. The bottom of the cocktail fits nicely over the heat gun element case so it's about the same diameter as that.

I've done a couple of roasts and the beans appear to be very even, just wanted to bump up the capacity to 400-500g. Attached a quick video of how it all looks, i recently had a spontaneous change to my design hence the use of masking tape there

Edited by JackH on 10-15-2018 07:30
I think I have a similar set up to yours and typically do 330 gm batches. I found that the geometry of the air inlet to the roast chamber was a very important factor in blower effectiveness and wound up using portion of a funnel with ~60° sides. So the perf plate is about 4 cm in diameter at the base of the funnel, the upper edge funnel diameter is about 10 cm diameter and the perf plate is about 9 cm lower than the upper edge. I used a cheap aluminum funnel I picked up at a hardware store and cut it accordingly. My heater can do 2KW although I typically only operate it below 1.7KW and my blower tops out at around 500 VA (haven't checked the power factor). I use SCR's to control heat and blower. But one difference is that I do recirculate hot air back into the inlet for the blower motor, and that boosts heating capacity especially in colder weather.
So many beans; so little time....
I also do about 330 grams in my small air roaster with an 1800W element and 600W vacuum blower. I usually use about 90% heat in the later stages of the roast with the blower down to about 12%.

You might have to tweak the perf plate to increase the load over 300g. Your element may only be 1800W. I use elements from the cheap 200W hot air guns but the resistance I measure suggests they are 1800W.

And welcome to HRO from another Aussie!
Hi ChicagoJohn and Greencardigan! Thanks for the advice from the both of you, i've been watching both of your roasters progress over time and have definitely used them for some inspiration. I've bought some ss martini glasses so will try cut them to use as funnels as they have a much steeper side wall. Will also change my perf plate to a sink strainer with more open area and add some heat recirc.

ChicagoJohn, correct me if i'm wrong but I see in your video that you use copper pipes connected to some tubing? I was thinking of PVC but that seems like a good route to take too. Also thanks greencardigan for the welcome! it's nice to see some Aussies on here too.
jooi123 wrote:

ChicagoJohn, correct me if i'm wrong but I see in your video that you use copper pipes connected to some tubing? I was thinking of PVC but that seems like a good route to take too. Also thanks greencardigan for the welcome! it's nice to see some Aussies on here too.

I did use copper elbows. After that the tubes are high temperature silicone. I would be concerned at any structural load on PVC directly over the exhaust since the Vicat softening point is around 90°C.

One other thing I forgot to mention that could be something to check is line voltage. Not sure what the standards in Australia, but here we have 120VAC/60Hz, and I quickly learned that on the circuit I am using to roast, a circuit that has about a 30 meter run from the breaker box, there is a significant and variable voltage drop when I operate my equipment. Moreover, our local power company varies our voltages as a way of optimizing their profitability using smart meters.

So (at the suggestion of AllenB here on the forums) I added a 20A autotransformer / rheostat so that I could maintain the voltage to my equipment at 120VAC throughout the roasting process. This was crucial to my ability to obtain the heat I needed for 330 gm. My coils are around 7.3 Ohms so at 120VAC and 14.4A I get around 1.7KW but at 110VAC (and lower), I was only getting 840W. As long as we aren't operating anything else on that circuit, I can operate both the heater and blower without blowing the 20A fuse on the transformer.
So many beans; so little time....
Thanks for the info! will definitely look into those auto transformers
jooi123 wrote:

Thanks for the info! will definitely look into those auto transformers

If you put a voltage meter on another outlet of the same circuit you're roasting with, you'll be able to see if there is significant fluctuation associated with your roaster load. Hopefully you won't need any remedial measures. The transformer I got (made in China) was around $100. Not cheap.
So many beans; so little time....
Thought i'd do a quick update. I've revamped my roaster quite a bit taking parts of certain builds from the forum. I can do 250-300G of beans without recirc atm, however i do have to lower my blower all the way, which sometimes isn't enough. To fix this, i'll drill a couple of holes in the side of the blower as some people have done and hopefully it's all good.

What temperature is the cyclone exhaust air ?
Interesting to evaluate usage for heat recirculation ;)
haven't checked yet but will definitely check next time
Also, check how I fitted mine on a standard jar, by friction with a silicone sleeve, that ensure also tight sealing, maybe inspire someone.
renatoa attached the following image:
I am inspired!
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