Print Thread
Attempt at a 1/2 pound hot air roaster
StarryNightDave
I'm designing my own hot air coffee roaster to roast about 1/2 pound of beans at one time. And, I found some electrical parts at Grainger.com, but I'm not sure how to make them work together. I was wondering if anyone here has electrical experience?

I found this blower for just $17.00.

images.grainger.com/B296_25/images/products/1C982.JPG

And, I found replacement heat gun elements for just $25.00.

images.grainger.com/B296_25/images/products/1A503.JPG

So, how do I wire these things together? I'm going to build a chamber out of sheet metal and have the blower force air over the heating element into the chamber. At least that's the plan. I have an interesting idea for the roasting chamber which I'm going to draw and post later.

So, is this possible, or am I a contender for a Darwin Award? :)
Edited by StarryNightDave on 12/03/2009 8:39 AM
 
John Despres
Nah, no Darwin award for you! We got your back.

Off the top of my head, I'd say yes, but the size of your chamber will make a big difference.

Does the heater work off straight 120 volts?

Wiring it will be pretty easy. I suggest you find a coffee drinking friend who is electrically knowledgeable and get them interested. If you wire the heater and fan separately on different switches, you'll have better control.

Sheet metal? Don't forget the ground!

Are you planning on blowing the air over the heat element? I wonder if the fan may move too much air and cool the heater rather than move as much hot air as you might expect.

You can control the air flow by limiting the air going into the fan by just screwing a piece of sheet metal over the inflow and simply opening and closing it by rotating the sheet metal on the screw.

Are you planning on a tube for the heater? You'll want a protective sleeve between the heat element and the tube. If you didn't get one with it, I may have one in my heat gun bone yard. (Don't ask, when I get the time, I'll post the whole story and pictures with a request for help)

In the meantime, let's se who else offers some thoughts.
Have fun!
John
Respect the bean.
John Despres
Fresh Roast 8, Gene Cafe, JYTT 1k, Quest M3, Mazzer Mini, Technivorm, various size presses and many more brewers.
 
seedlings
DAVE! Hold the phone! Hopefully you saved your receipt for the blower because you'll need to return that one. You must read:

http://forum.home...#post_9660

To see that I've already failed with that blower. Now, if you want to incorporate that blower into a bean cooler, that's a different story, but it will not loft enough beans.

However, I think that heatgun element is great, but you'll need a second one... wait... maybe not to do 1/2 pound...

Finally, when you get to building the "hopper" I highly recommend using RoasterRob's proven design (http://forum.home...#post_6964).

Let us know how else we can help. I've tried to help by discovering more ways it can't work Grin

CHAD
seedlings attached the following image:
13hoppers13hoppers.jpg

Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
StarryNightDave
Thanks for letting me know about the blower. I haven't bought anything just yet. Fortunately I have a Grainger store just 15 minutes from my house.

www472.pair.com/ccadmin1/images/SNDRoaster.JPG

I tried this in Paint and it is crude. My idea was to have an inner V-shaped chamber that would be controlled using a small door flap at the bottom. (See red circle) The plan is to turn on the heater and blower, then open the door flap. The beans fall down, get heated and blown up the left side, and return back to the pile while the chaff and smoke exit. A thermometer will be placed through to the center of the bean pile to get an accurate reading of the pile.

This is why I was asking about the vanes in the drum. I was thinking that they naturally pile up beans to some degree. So, if the door flap is open wide enough, the beans will rotate quickly so they won't stay in the pile for more than a few seconds, similar to what would happen in a drum roaster.

I would also like to put a piece of fireproof glass in front of the pile to view the color.

So - what do you guys think? :)
Edited by StarryNightDave on 12/03/2009 3:43 PM
 
StarryNightDave
Well, till I figure this out, I just bought one of these at Target for just $18.00 and roasted up some espresso beans tonight.

ecx.images-amazon.com/images/I/41E3W0WEPFL._AA260_.jpg
 
seedlings
Dave, I love the concept, however the problem I see with this design is the potential to lose too much heat from the time the beans are heated in the tube, then blown back on top of the pile. This circulation will have to be vigorous, and the design will need to be tweaked.

CHAD
Roaster: CoffeeAir II 2# DIY air roaster
Grinder: Vintage Grindmaster 500
Brewers: Vintage Cory DCU DCL, Aeropress, Press, Osaka Titanium pourover
 
RoasterRob
Hey Dave you need a pressure blower to blow beans around. I am running a 2.3 kg roaster off a 1000watt vacuum cleaner blower. I am looking to do a sample air roaster, for which i bought a 230v airbed inflator. This is 130watt and although is is a similar design to the vacuum blowers it barely moved 150grams of green beans. Looks like there is too great a gap between the intake side plate and the impellor.
The blower you show from graingers is very low pressure and will not move the beans.
I use a 1kw triac based dimmer to control the vacuum cleaner motors, works really well. It is possible to use a triac dimmer on universal electric motors up to 2kw+. Thats how the speed controllers on vacuum cleaners work.
Just managed to roast 4kg recently using my larger conical RC using only one vacuum cleaner motor. I will be able to do 6kg if i run it off 2 VC blowers. I am looking to have a roaster up and running in the not too distant future that will do between 5 & 7 kg not the conical RC - (think I have been saying that for the last year or 2)

Rob vL
NZ







VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
 
endlesscycles
Rob,

How does your conical chamber look/work? I am blow away by the function of the asymmetric chamber, and I assume that is the design you too prefer.

I am building a 6" diameter chamber any day now. (I've been saying that about this pile of bits for the past two months!)

Do you have a chamber diameter / bean mass relationship figured out?
My 4.7" diameter seems to be limited by its height more than anything, but does excellent roasts of 2lbs / 1kg finished.

FYI: I've got a beastly burner that works great below designed range. In fact I dry with it nearly off and have no flickering problems.
-Marshall Hance
Asheville, NC
 
RoasterRob
Hi Marshall

The conical RC works well, i roasted 4kg with it using 1 only 1000watt VC blower and the 7kw sievert burner. I know I can move 6kgs in it using 2 blowers. The reason i went for the conical RC was i tested an 8" asymmetrical RC with 2 blowers and could not get much more than 3kg moving well in it. Also the beans fell back in the middle of the pile not across the other side of the RC. Because of the perceived problems with this RC I kept the perfed area of the conical Rc small - less than 2" dia.
Today i revisited the 8" asymmetrical RC. I redrilled the holes from 3mm to 3.3mm, broke the drill half way thru and finished the last half with a 3.2mm drill bit. Tested it cold with the 2 blower roaster that is almost complete. I had 6 kg of green dancing right up to the edge of the RC. Could probably do 7kg with it except once roasted it would be blowing out the top. Could look at a curved deflector to sort this.
The really good thing about this RC is that by just turning down the dimmer/controller on the VC blower the beans are roasted at a reasonable roast profile.
The height of the bean mass is limited by the airpressurre available and the how the beans behave once roasted. Any more than 2.3kg in my 6" Rc and I have roasted beans bouncing out the top toward the end of the roast, again a deflector at the top would probably mean i could do closer to 3kg. My earlier 6" RC would only do 1.9kg of green because it was shorter.
Problem now with 2 blowers and still only a 6" dia "furnace" section of the roaster is that the extra airflow snuffs the burner out. Something i need to work on.

Rob vL
NZ
VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
 
StarryNightDave
So, have you guys determined the CFM (cubic feet per minute) rating required to float various weights of beans? That $17 blower above has a rating of 160 CFM. If that's too light, then how high do we need to go?

This is a little confusing to me because some actual vacuum motors seem to have less CFM ratings. For example, this one from Grainger has a CFM of just 60.

images.grainger.com/B297_43/images/products/2M429.JPG

But, it does qualify this by saying @ 2-in. orifice. I guess that has more power than the other blower at 160 CFM?
Edited by StarryNightDave on 12/06/2009 11:53 AM
 
RoasterRob
CFM is volume. You need pressure, the VC cleaner blowers have plenty of that. From memory I measured one at about 18" water, the blower at the top of the page would be lucky to have 2". Even a small VC blower would be good for a kg of coffee even more.
If you read some of the earlier threads about blowers and air roasters there is alot of info there about this.

cheers

Rob vL
NZ
Edited by RoasterRob on 12/07/2009 12:21 AM
VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
 
StarryNightDave
Sorry - I didn't mean to rehash the blower topic. I'm more interested in what you guys think about the inner V chamber design. With the proper wall thickness and insulation, I think the flow of beans will have a similar heat/rest cycle as found within some drum roasters. Beans are heated when they contact the walls of the drum, but then pile up for a short time before coming in contact with the drum again.

I think the drum contact/heating will be simulated by the beans entering the hot air flow. I'll see if I can draw this up better to explain how I want this to function.
 
RoasterRob
Hey Dave try mocking it up in cardboard and plastic and testing it cold.
Looking at the design it could and should work. But You are pushing the beans up and to the left then trying to steer them back to the right. If they were going straight up it would be easier to make them throw to the side. You need a reasonable gap were the beans fall back into the airflow ( the red circled area) JMO. There is a roaster using a similar design, the roller roaster or something similar.

Rob

VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
 
StarryNightDave
Now that's a great idea. Thanks! I'll do that.
 
endlesscycles
Rob,

Would you foresee a certain diameter necessitate conical design? In past posts you've suggested an advantage over friction in the asymmetric roaster; would you imagine bean-bean friction less an issue at a certain scale? What are your thoughts on conical RC diameter vs. perf diameter vs. bed height?

These are just some questions that arise.


Quote

RoasterRob wrote:
Hi Marshall

The conical RC works well, i roasted 4kg with it using 1 only 1000watt VC blower and the 7kw sievert burner. I know I can move 6kgs in it using 2 blowers. The reason i went for the conical RC was i tested an 8" asymmetrical RC with 2 blowers and could not get much more than 3kg moving well in it. Also the beans fell back in the middle of the pile not across the other side of the RC. Because of the perceived problems with this RC I kept the perfed area of the conical Rc small - less than 2" dia.
Today i revisited the 8" asymmetrical RC. I redrilled the holes from 3mm to 3.3mm, broke the drill half way thru and finished the last half with a 3.2mm drill bit. Tested it cold with the 2 blower roaster that is almost complete. I had 6 kg of green dancing right up to the edge of the RC. Could probably do 7kg with it except once roasted it would be blowing out the top. Could look at a curved deflector to sort this.
The really good thing about this RC is that by just turning down the dimmer/controller on the VC blower the beans are roasted at a reasonable roast profile.
The height of the bean mass is limited by the airpressurre available and the how the beans behave once roasted. Any more than 2.3kg in my 6" Rc and I have roasted beans bouncing out the top toward the end of the roast, again a deflector at the top would probably mean i could do closer to 3kg. My earlier 6" RC would only do 1.9kg of green because it was shorter.
Problem now with 2 blowers and still only a 6" dia "furnace" section of the roaster is that the extra airflow snuffs the burner out. Something i need to work on.

Rob vL
NZ

-Marshall Hance
Asheville, NC
 
RoasterRob
Initially I came to the conclussion that you would need to go conical over 6" dia. But after getting 6kg lofting in an 8" asymmetrical RC I don't know if there is an upper limit.
I do believe there is an advantage using the asymmetrical design in minimizing bean to bean friction. I tried something random the other day. had 5kg of green in the conical RC, it wouldn't loft with the blower on full noise so i pushed a 2" ss pipe down the middle of the RC to about an inch or so from the perf plate, the beans started to flow up and spout out of the pipe. Seems the pipe directed the air flow and cut down the friction/engulfment of the surrounding beans.

The perforated area should be related to the total area of the RC say 20%. Hole size and distribution is linked to the pressure and air flow. Too many holes for a given area and the you lose pressure & velocity and get a random bean flow and bean bed height is limited. If the holes are too small (or too few for a given area) again your bean bed height will be limited. Greater pressure can over come this but is probably not an option due to limited options for blowers. Also heat/air density will no doubt be affected.

Your bean height is affected by air pressure. If your air pressure is 18" of water, beans weigh approx 70% of water so you should be able lift more than an 18" column of beans. However because the beans don't form a tight seal in a pipe you get alot of slippage (airflowing past the beans). Plus you need surplus airflow to throw the beans around.

So my ball park bean bed height is around 8" give or take.

Check out this alt.coffee thread from Andy S post

http://tinyurl.co...g?

Ok the tiny url didn't work try the less than tiny one.

http://groups.google.co.nz/group/alt.coffee/browse_thread/thread/c3245d35efffdbf2/3940f02c30d4f7d5?hl=en&q=stainless+steel+pipe+roaster&lnk=nl&

Quote

endlesscycles wrote:
Rob,

Would you foresee a certain diameter necessitate conical design? In past posts you've suggested an advantage over friction in the asymmetric roaster; would you imagine bean-bean friction less an issue at a certain scale? What are your thoughts on conical RC diameter vs. perf diameter vs. bed height?

These are just some questions that arise.



Edited by RoasterRob on 12/16/2009 3:52 AM
VBM Minimax 2gp, 1gp Reneka Techno, 2 gp la Pavoni Pub, la Cimbali M28, SJ Maz, FB 6kg HM roaster and other stuff
 
endlesscycles
The spout pipe is genius.
Thank you for your input!
-Marshall Hance
Asheville, NC
 
Dan
A hot-air roaster needs a medium-volume/medium-pressure blower. Problem is, most are either high-volume/low-pressure or high-pressure/low-volume. Seem my blower spreadsheet in the Downloads section.

A vacuum motor like above will work.

Dan
 
Jump to Forum: