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What should be observed when adjusting the air flow?
The flow of air circulates the coffee beans and carries the heat. Everything seems simple at first glance. But in the case of a given pid controlled profile, changes in air flow will also affect the air inlet temperature (ET). Is the air flow regulated so that the inlet temperature does not exceed 260C?! Anything other than not blowing the beans away?
Well I use Air flow to fine tune temp and bean movement. So more control over your curve and ROR. Keeping those beans moving is critical in my FB in keeping those beans roasted evenly. Too slow and beans get burnt and too high and they take too long to roast.
In my roaster combination, the blower is limited by keeping the beans in the roasting chamber. The 3.3 kw heater can keep the processes in line. Now there is a choice of which intensity to blow. So far I have only learned that too slow circulation raises the temperature of the ET unacceptably high (up to 400C about). Hence the question, what else to watch? Is there any need to change the amount of airflow during roasting if the circulation works, the beans stay in the chamber and the pid can hold the line?

I am replacing the heater with a 2.1 kw one, because more than 250g of coffee beans cannot be kept in good circulation in a chamber with an internal diameter of 80mm.
What device controls your roast?
What is the range/resolution/(steps count) of the airflow and heater control?
The TC4+/Artisan combo, brushless motor controller is controlled by IO3. 1/100 steps default, Artisan pid
I made buttons: +1Fan, +5Fan, -1Fan, -5 Fan and +1Heater, +5 Heater, -1 Heater, -5 Heater
Edited by walk on 04/18/2023 2:11 AM
An aside.
Blowers have very different characteristics and there is no clear line between them. Some (Example A) move more air, but in the presence of resistance, the flow does not have much force. The second (Example B) moves less air, but the flow has force and is harder to influence with resistance. I believe that this should be taken into account when planning the FB roaster.
In my own roaster (Example B, 24000 rpm) I can circulate the green beans at 90% Fan and I can roast them all the way without changing it, because the air flow is pretty constant. I think that with Example A blower, the flow should be increased a lot during roasting?!

Example A:


Example B:


I have both. 600W vs 144W can be very misleading here!
Edited by renatoa on 04/18/2023 3:27 AM
I use something similar to the example A blower.
I start my green beans at 42% and eject the beans at 45% fan. Roast chamber is 76mm ID and 80mm OD.

I'm limited by my heater at 1400 watts so I roast 227g to keep even roast weight when only buying 1 pound samples.

I use a fountain spray pattern, one spout in the middle. I try to keep this bean movement just above what I might call a bubble bed speed.

I have moved more beans then I roast but never tried to max out the roast chamber but can test that if needed?
Now in air flow tests the blower I use was run at 60-65% and I thought that was very high and I would never need to run it in that range? I never did test an asymmetrical base pattern but one of these two patterns might allow more control over the beans?
Just to see if I could float more beans, this is a pick of 454g or 1 pound of green beans using 57% and ejected at 60%.
The bean movement was more like asymmetrical but I think this is due to how the air is forced into the chamber, would play a bit more but no time right now.

I just wanted to see if the blower would float them and it can.
Quick video moving 1 pound of Green Beans.
HarryDog attached the following image:

Edited by HarryDog on 04/18/2023 9:25 PM
Indeed, the so called leaf blowers motors rated for 500W are capable of one pound and even more.
I have one and same experience, when used (at full power) for cooling a pound of roasts there was a beans rain in all my kitchen... Shock
The A model pointed by @walk is described as a computer tool, maybe is a tiny version of our blowers, and the Watts figure could be inflated by seller, or a copy paste error from other product.
I understand that blowers have two important parameters - air flow in m3/h and air pressure in kPa. In example A, the air flow is high, but the air pressure is not very high. In example B, the air flow is not high, but the air pressure is. I can close the air flow of the 500W blower with my palm without difficulty, but not on the 144W blower. Both examples can do the same job in the roaster, but there must be differences in character. So I think example A is more sensitive to changes and needs more adjustment in operation.
Edited by walk on 04/19/2023 3:38 AM
The simplest test you can do: get a 2 litres PET drink bottle, cut the bottom, and mount its mouth to the blower output, with duct tape, or a rubber gasket.
Then start blower at 10% and add beans until they bubble, increase blower, add beans, etc, until you are satisfied.
This way you can have an idea about the blower capabilities, before starting any costly build.
Check below an example video of such frankentest, 110W inflatable pool pump and 200 grams of greens, at 100%.

If you can close with the palm, definitely that is not 500 Watts, but a toy blower.
Return it to the seller, and go to a gardening mall, where you can test live the power of a real 500 Watts leaf bower.
Edited by renatoa on 04/19/2023 5:58 AM
This blower is about half the size of a leaf blower and I was not sure it would get the job done when I first saw it in the store.

Mastercraft Cordless 20V Workshop Blower delivers up to 240 KPH (150 MPH) air velocity, Delivers up to 90 cubic feet per minute air volume.

Specs are very limited so I wanted to make sure it could lift 1 pound, it can probably lift 1.5 pound but it handles 1 pound well.

This motor is responsive but my heater is too small to roast 1 pound easily.

Walk I think you have an advantage with all that available heater but what type of base are you using (Drill pattern)?

I don't think I saw that anywhere and it will make a difference in controlling the beans.

You can see the hole pattern that I use on the right side.
It is a good idea and recommendation to do tests before the final construction!


If you can close with the palm, definitely that is not 500 Watts, but a toy blower.
Return it to the seller, and go to a gardening mall, where you can test live the power of a real 500 Watts leaf bower.

I will measure the current of the blower with clamps and let you know. It is not surprising if the given power is taken into account at the moment of starting the engine... And maybe the efficiency can also be different.

But the point was different. Blowers have different constructions and characteristics, and for FB roasters some combinations of parameters (m3h@kPa) should be more suitable than others. But in any case, it's worth testing on the model first! I was lucky when building the first FB roaster, it started working. (250g/green beans, 90% Fan, max 60% Heater)
As few English as I know, for me there are two categories:
- leaf fans, usually using induction motors, low RPM, in the 1500-3000 ballpark, thus very silent, but low starting torque, and low pressure. Flow depends on the fan/leaf size.
- turbine blowers, using universal/brushed or brushless motors, high RPM, over 10.000, thus noisy, high starting torque, high pressure.

Both examples you posted are turbine blowers, the fact that one of them is weaker than the other is simply because probably is a fake labelled product, as a lot of chinese stuff. Probably underrated motor, or a toy build turbine.
Or maybe they fitted inside an induction motor, which is not appropriate to drive a turbine.

As operating principle there is no reason that a turbine blower not outperform a leaf blower having same motor power rating.
This is how the current is measured, 230VAC.
walk attached the following image:
15.000 RPM points to an universal motor, so the turbine build remains the only culprit to check for the low pressure.
Or, the turbine - shaft lock screw, maybe the tightening has weakened and turbine is freewheeling.
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