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Natural bean curve with air roaster
HoldTheOnions
So, contemplating preheating to 300 and then adjusting to final desired temp and only adjusting bean mass for desired length of roast would result in completely natural bean temp curve. Problem being I don't have the juice to get this done. To achieve final bean temp in one step and still agitate beans sufficiently I need to roast few beans and they cook too fast.

Anyone with powerful air roaster ever experimented and can comment on whether worthwhile endeavor or not?

Thank you.
JETROASTER
It's true. A right-sized air roaster can have a nearly perfect natural curve. Remind me again what you're working with? -Scott
HoldTheOnions
I have a 1440 watt poplite with external blower. To do that kind of roast I am figuring I need 300-400g, and mine tops out at 250g in summer (because of heater, not blower). Right now in 50f weather I can do 200-215g. To hit 400f on mine with cold beans requires about 150g, and goes from 300f to 400 in 2-3 minutes, depending. It gives flat roast.

My problem is the circuit, I don't think I can put 1800 watts on single circuit (is that even enough?), so need to split it up and need new roaster, which I don't really want to do at this point as I have other projects going.

That's why I am wondering if it is desirable or not, I don't want to waste time and money if it produces an ugly curve anyway.

Thanks for responding.
JETROASTER
I think I might be confused. Is this a heat problem or an agitation problem?
If you add the airflow to get needed agitation, you no longer have enough heat?


Cheers, Scott
HoldTheOnions
Yes, it's a heat problem. I can agitate as much beans as I want, I just can't get hot enough to skip straight to final temp without turning the fan speed down too low that the beans won't agitate. I can get to about 190c on mine with 200g in this weather, but that's it. I would have to get to around 230c with 300g+. I don't even know how much power I would need for that.
BenKeith
Don't know your skills and abilities to modify heating elements but if you have a 20 amp, 120VAC (if you even live in the US) I don't see where you should have a problem running more wattage. I typically wind higher wattage coils and replace the ones that come in my air roasters. I've never had a problem with coils at 6.8 ohms, which would be in the neighbor hood of 2,200 watts. The one I'm using now, I made a 6.8 ohm coil and it's running a 3.2 amp fan and it runs fine on a 120VAC 20 amp breaker. When it running it's dropping to approx. 116-117 VAC at the heating coil but that's still approx. 2,000 watts. Now, if you only have 15 amp circuits, that's not going to work because just the heating coil is pulling approx. 16 - 17 amps. If the blower and heating element are on different inputs you can plug the heater into one outlet and the blower into a different one, that will let you run more wattage on the heater.
Mine has enough air with a 200 gram load, I have to turn the fan back as much as 20% during the roast to keep from over agitating the beans, but even on high, my heater rarely runs over 90% with the blower on high and it runs down to 50-60% during the roast.
So, you if you have the know how, you could probably run a lot more heater if you wanted to. What you are running now, if 120VAC, is probably about a 10.5 ohm heater and that could probably be taken down to a 7 ohm and give you
almost 25% more wattage.
oldgearhead
I roast 420-450 gram loads every other day pulling 17 amps on a 20 amp, 120V (10 gauge wire) circuit. Both the roaster and the circuit are fused at 30 amp. However, I preset the heating wattage based on the ambient temperature and my history with the bean in the roaster. Recently the ambient temperature has been 50F and my heater is set for 1250 watts (unchanged) during a batch.

Two things I have learned running this fluid-bed roaster are:
1) Re-claiming hot air from the roast chamber works. The temperature at my blower inlet has been running 100-150F for over 4 years now with no failures of either the blower or the heating element.
2) The temperature of the air exiting a heat gun element, or any heating element, is inversely proportional the the air flow. In my case the starting flow rate, depending on load size, is close to 50CFM, to fluidize the bean mass. However, because the beans get lighter as they lose moisture I can
lower the flow rate 3-4 times during the roast and achieve much higher temperature after drying. In my case control of the flow rate is paramount.
No oil on my beans...
BenKeith
Recirculated exhaust air like oldgearhead is talking about is another way to get around adding more wattage. Raising the intake air to the roaster to 150 degrees F, will make a huge difference in the amount of heat I'm not sure I would personally want to go as high as 150 degrees, 130 would be closer to my comfortable max, but I guess that would also depend on the type blower motor. Most small vacuum motors generally have a 135 degree or less ambient temp rating. Anyway, just adding you a recirculation system may give you that extra boost you are looking for. When I first started this mess, I started with the good old Poppery II and used recirculated air on it to get the heat up. Doesn't have to be anything fancy. I just made me a wooden box, sat the roast over inside of it and rigged a 3" flex vent pipe from the exhaust air into the box and fixed me two slide gates, on for the air into the box and one for the flex vent pipe. The hardest part of the whole thing was making a T at the top of the roaster just to pull some of the exhaust air, because you don't want to dump it all into the box. It also can be a smaller recirculation pipe, it was just that 3" was the smallest Home Depot had in that metal type flex vent. If he is running a recirc system, he may have some details posted on how he did his.
Edited by BenKeith on 12/16/2015 4:48 PM
oldgearhead
The entire build is here:

All Foruma/
Building a roaster/Fluidbed roasters/'Brewer to Roaster'

http://forum.home...rowstart=0
Edited by JackH on 12/16/2015 11:57 PM
No oil on my beans...
HoldTheOnions
I have don't have 20 amp, but two 15 amps, so was thinking I could maybe add smaller element on separate circuit, I don't know if it would fit though in current roaster, have to look at it. Probably something like 800watts would do the trick, if there is such a thing. A new build will be at least $100, so trying to avoid that, but maybe can't.

Thought about recirculation before and didn't think I could do it because I have blower in separate room, but this got me thinking again that might work ok, just need to run a tube back in the room...somehow :-). I need about 40c, which would be 72f, so for recirculating to solve the problem completely I would need to be around 130-140f intake.

Thanks a lot for the feedback, have to think about it a bit.
BenKeith
Make sure they are on separate circuit breakers. Builders will put several outlets on one breaker, so if they are not separate, won't do you any good.

As for additional heaters, there on tons of places online you can buy heat gun elements in all types of wattages. Bunches on ebay, and eparts probably has them.
scotthal
I'd suggest cannibalizing a cheap harbor freight heat gun (< $10), & using the element for preheat. Link might give you some ideas http://forum.home...#post_4640
Food for thought; coffee for concentration
HoldTheOnions
I do have two circuits, so two stage heat gun is a good idea, I am pretty sure there is room to mount one of the elements in there and not cost much. Thanks for good idea!
HoldTheOnions
So it's not good, you have to manage it for nice curve.
BenKeith
I'm don't see why it has to be a "curve".

The profiles I'm using now are basically four straight lines and how steep those lines are is based on the time I want to reach a certain temp.
For instance, the one I just used from some Brazilian beans, 300 degrees in 240 seconds, after about the fist 30 seconds, (takes that for the PID to get locked in) it's a straight line then it makes a sharp dogleg and another straight line to 340 at 360 seconds, then another slight bend and a straight line to 398 at 570 seconds, with another little bend to 414 at 700 seconds. Which is when it was set to turn off the heat and kick the fan on high for cooling. During each of these phases, it's maintaining a fairly even ROR that's is less than the previous ROR so it's maintaining a steady decline at each phase.

Doing this, I hit each one of my phases within a couple of seconds, something that's pretty dang hard to do if you are shooting for a steady arch and it's the same every time. Does not matter if I'm roasting 120 or 200 grams.
oldgearhead
An electrically heated fluid-bed roaster will have a basic curve that is favorable for coffee roasting. If fact the pioneer of the fluid-bed roaster (not the inventor), Michael Sivetz, didn't even believe in the concept.
However, if you can control the rate of bean heat rise, you can change the flavor...I do it by changing the time between blower turn-downs. Keep them moving with a positive rate of rise...
No oil on my beans...
HoldTheOnions
To be more specific, I got a really big jump from 311-349 in 30 seconds, like a jet fighter, then pretty bad flick at the end of 7degrees. If I had pulled it early then it would have been too light for my tastes. I was really only able to try it because it was 108 degrees outside. Was trying to think if I could do a smaller charge and turn down heat and air, but seemed like I would just end up in the same place and did I mention it was 108 degrees outside? So I wasn't really up for doing it a bunch of times in that heat.

That said, I probably should have reserved my judgement until I drink it and I could thoroughly test it with upgraded roaster, but it doesn't look like it's going to be very good to me. I will let you know if it is somehow magically tasty though. ;-)
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