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First build failure..
Thank you, Allen. The "demand for power" makes sense, but.. doesn't? If it needs more power, wouldn't ET drop as it sucks up the heat?

Perhaps the issue is with the router speed control? If I understand correctly how it works, both voltage and current are reduced.. maybe the heating element doesn't like the drop in current, so it's not as effective or.. eh.. hmmm.

I guess where I'm confused is why are my roasts behaving differently now with the fan and heater split. Even when at max, I'm getting this leveling out into 1st crack, whereas with the unmodifed one, it'd go on a more straight line increase.

Your note on the differences in ET makes sense, however, after comparing a few graphs with other people, I don't think it's as much as 60F; my FC seems to occur at similar ET and BT temps as others. That said, maybe it will make sense to move the environment thermocouple closer to the bean mass, so it's right above it and see how the temps look then, as there's nearly a 35F difference before adding beans in just 3.5" space (BT vs ET).

What's even weirder, this time I momentarily turned off the fan early in the roast just to see what happened -- ET started to spike, but BT began to drop. Huh.

I'll keep playing. What is certain in this toasted-oats roast, no ashiness at all. It's kind of bland, but without tipping and scorching, it's better than before. That's why I'm trying to stay below 475F.
Edited by jedovaty on 01/07/2012 3:55 PM
A couple questions,

I'm assuming your fan isn't the type that has the DC motor fed from a very fine coil of nichrome within the area of the main heating coil as in some of the popcorn poppers of today? Or is it an AC universal motor?

Have you tried going direct to the heating element bypassing the router speed control. If losses through the speed control is the issue then you'll find out by this test.

Also, when you stated you momentarily turned off the fan did you still have the heater on?

Edited by allenb on 01/07/2012 5:13 PM
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
I remember a thread here about the Harbor Freight router controllers and that the maximum setting using the dial is not at full power.

I believe it was Chad's thread about the bread machine roaster. The fan speed of the heat gun was slower with the dial at maximum and when you flip the switch on the router controller to Full, the heat gun's fan increased it's speed/power.

Your graph shows a slow decrease (stall) in BT after FC where it should be a steady and slower RoR increase of about 7-8 deg/min.

I think the turbo oven fan should not be switched off too long as it also provides air flow to the upper case to prevent overheating.
Edited by JackH on 01/07/2012 8:12 PM


Your graph shows a slow decrease (stall) in BT after FC where it should be a steady and slower RoR increase of about 7-8 deg/min.

I think the turbo oven fan should not be switched off too long as it also provides air flow to the upper case to prevent overheating.

I was going to comment earlier about the stall on the graph and glad someone mentioned it.

I remember having a similar issue when roasting with my Poppery 1. The beans wanted more heat right at FC but the problem was I had no way to give it to them. I ended up letting it roast for another 7 minutes or so and gave up trying to reach 2nd crack. The coffee looked good but tasted like brown wheat water. My second attempt I put a plate on the top of the roaster's chimney at FC to try and keep the heat in and bingo I got to second crack three minutes or so after first. That coffee tasted like ash.

IMHO the most important temperature reading is the BT. FC tends to happen around 400?F and one can use that as a constant. As Allen mentioned ET can vary depending on many factors. If I were in your shoes I may try and move the ET to right above the bean mass to see what reading it gives during FC

Like Jack, I also wouldn't suggest turning the fan off on a TO. A convectional oven uses the fan to spread the heat out evenly. IF you turn the fan off then you are left with an element producing heat straight down onto the beans. That is why your ET when off the charts, The coffee would most likely be tipped and taste like ash.

All that being said you've made great progress since starting this thread so keep at it!



Turbo Oven Roaster w/ Variac, TC4Cw/ Bourbon | Bezzera Strega | Baratza Vario Grinder | Yama 5 Cup Syphon | Aeropress
Hey guys, thanks for the responses. I think my own posts are too wordy, and it's getting you all confused. It's hard not to write so much though sorry :(

Couple notes:
1. I only turned off the fan once for about 2 seconds in a roast I did today to see what happens (so doesn't show up on the past images). The fan in the TO is AC type, and it is on a toggle switch, not connected to the HF control unit.

2. I didn't mention this part previously: with the HF router control, I keep it on "full", then switch to "var" when the ET gets to about 465-470.

It might be easier to demonstrate what's going on in a single post with graphs here to compare... all beans guatemalan hunapu, 400g.

Roast 1:
This shows the roast before I modified the TO and no pot insulation. I "pre-heated" the beans at the low "thaw" setting on the TO. At the "B", I put heat on full and just waited the roast out. All the spikes and dips you see is the TO doing things on its own (except the one around 300-350, I fiddled with it but then set to max again). The ET TC was about 1" away from the beans. Slight stall around first crack. ET temps were around 500F max a few times, and there was ashiness. Again, TO was set to max. Every bean has tipping. Color is also pretty dark, expected at 2nd roast.

Roast 2:
This one is the modified TO, and also insulated the pot with silicone pad and towel. I preheated the chamber, then dropped in the beans. A little after the 9' mark, you see that blip? That's where I turned off the fan, saw the dip in BT, then turned it back on. The router control was set to "full" until I got to around 470F, then switched to "Var", and as you can see, the FC clearly stalled. At the end, I put the router control back to Full, and once ET broke 500F, the BT began to rise and I hit SC. ET TC same position as roast #1. Lots of neat little flaming chaffs flying around. Cupped this evening, tasted nutty, like toasted oatmeal. Thought I hit second crack, they look like they barely hit first crack.

Roast 3:
Same as Roast 2, but I preheated slightly more and I put the ET TC so it was just touching the beans. When ET hit 470F, I switched to var, and tried to maintain ET around that temp. Once FC, I immediately switched back to Full on the router control. Beans began to rise as I hit 500F again, then I backed off as I'm kind of afraid of going over 500F with those flaming chaffs. Still a little nutty, but not as much as #2, and there's some minor tipping. This one came out a bit uneven, and also seemed lighter than it should be.

Allen suggested I try a smaller batch. May try doing that. Any other thoughts?

Roast 1:
Roast 2:
Roast 3:
Edited by jedovaty on 01/08/2012 12:44 AM
If possible please shoot us a photo of your TO's heating element. I mistakenly thought they had a nichrome coiled element.

Are you using a master switch arrangement (fan being master)?

What were the batch weights of the last roasts you graphed? If tipping continues to be an issue I would definitely reduce batch size.

Keep plugging away, you'll be roasting great coffee in no time!

1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
Allen, 400g batches all around. Before the mods a few weeks ago, I tried smaller and larger batches (300 and 500), both ended up atrociously uneven, seems like 400 is about right.

Image of the heater bottom at end of this post. It's a deni, 1300W unit. I split the heating element and fan completely apart, and added a second AC plug to the back of the deni housing (made a little hole.. heheheh):


The toggle switches are beefy enough to handle the current, though I forget the specs. I plug the fan into a power strip, the heater into the router control, then the router control directly into the wall. The vacuum and roaster motor also go onto the power strip. The circuit these items are on is a 20A one, just double checked it. When ready to roast, I toggle the fan to on, then the heater, then switch the router control from off to Full.

This stalling kind of reminds me of high school physics, when the teacher put a flame under a paper cup filled with water... what would happen if I wired in the coil from the stir crazy right next to this one? I still have the ceramic holders and things... :)

What really confuses me is when I see other roasts, like Ed's here, the ET doesn't go any higher than the 475 yet his BT continues to rise. Why? His ROR graph is similar to mine, though. I understand our ET's may not be the same, but I... I'm having trouble believing that.
Edited by jedovaty on 01/09/2012 1:43 AM
The thing I see in all your plots is the RoR falling to 0 at the FC marker each time. (Almost like it does if I lift my turbo oven top). Ed's plot RoR drops but maintains the RoR at about 8-10 degrees per second.

If you switch from Full to Var at FC with the dial all the way up, these harbor freight units cut back. I would hook up a kill-a-watt to your heater AC and see what the current is at full on the switch and then in Var with the dial all the way up.

You might have a bad router controller.
You are correct, the ROR drops - I guess that's what we need to find out is why. I understand when going from Full to Var, they cut back -- but they don't cut back that much (at least, not mine). I actually do dial mine down a little, and you can see in Roast 2 and Roast 3 of post 55 above, the bit of wavering between 460 and 490, that's me using the dial. If I left the dial at max, ET temp would keep rising.

Note that roast 1 didn't have the router control, and it, too, dropped -- one could argue it was because FC occured during its cycling off.. and it's curious the BT began to rise though I was under 500F. Perhaps it's not a bad router control, but maybe the heating element needs to be at it's hottest to get a rise in the beans, and the only way I can accomplish that is to have the ET drop that much? Oh, this is confusing.

Settled then - next roast I'll remove the router control and just try flipping the heater's switch on and off manually, per Allen's suggestion earlier. If I can maintain a positive ROR after first crack, I'll return the router control and just get a stupid variac :p

Thanks for the help :)


jedovaty wrote:... I'll return the router control and just get a stupid variac :p

Sorry to beat a dead horse, but it would be a lot less expensive for you to buy a potentiometer and SSR and use the aCataui application (since you already have the TC4 up and running).

aCataui is identical to aBourbon, except that it also supports manual heater and fan control. You can control one, both, or neither as you choose.

Jim - if the full manual flip-on-off works, then I will consider this route as the benefit is that it'll reduce all the cables and weight and stuff to move around. It has many drawbacks for my situation, though:
1. I still don't understand it despite your time and efforts via pm
2. would have to take apart the roaster again
3. cost would be about the same, used variac will be $25-100
4. variac is just plug-n-play

But just so you know, a potentiometer and SSR should cost less than $20. And if you use aCatuai you would also get a record of heater output levels in the log file and on the graph.

Just confirmed the router control unit is not faulty. Same guat hunapu 400g, with the heating element plugged directly into the wall and no router control, manually flipping on/off switch to keep ET temp around 475. It's not until I get over 480 that I can get the BT into increasing rate and out of the stall. I learned I wasn't hitting SC in a couple of the prior roasts, the noise was the sound of the chaff.

I theorize any one or more of the following will help, in order of simplicity:
1. become convinced it's okay to let ET go up to 500F
2. smaller batch
3. move beans closer to heat source
4. add another heat source (deni not strong enough at 1300W)

#1: well, input? I have read conflicting info :)
#2: tough, as it leads to an uneven roast for me
#3: it'll be a minor pain but can be accomplished
#4: fun idea, but a little dangerous. I have that nichrome element from the stir crazy, just wire it in by the TO's element, but then I may be drawing more amps than my circuit can handle... yikes!

The results look clean, no tipping. A bit darker than I like. *shrug*
If you look at the traditional BT graph line it looks quite good during first crack. Having BT RoR puts it under the magnifying glass. It really shows the moisture exhaustion during the strongest part of the cracking. This release adds a cooler temp surrounding the beans as the temp inside will always lag by a few degree behind the surface reading. My theory on the level of drop in RoR has mostly to do with agitation. Getting the cooler moisture/air recirculated. The reason I say "agitation is important like grinder". I have variable speed on my agitation. If I slow the agitation during this part of 1st crack I get a more dramatic change than if I adjust the temp. If you look inside a commercial drum roaster the beans are flying around like a stirred up bee hive.
All this being said I don't think the drop in RoR shown above is actually damaging the roast much if at all. Adding too much extra heat to over come this is more damaging IMO.
Ed B.
DreamRoast 1kg roaster, Levers, Hand Mills
Ed: Makes sense -- moisture being released is like the ice cube melting in a glass of water. The stall being experienced does lead to a very even roast. Why wouldn't it be damaging to the roast? Popular opinion seems to believe stalling is bad..

The dramatic change during first crack with a slower agitation -- dramatic in what direction, reduced or greater ROR?

Would bringing the beans closer to the heat source be the same as adding more heat?
Edited by jedovaty on 01/11/2012 10:36 AM
Increased agitation will benefit getting that moisture/air recirculating and increase RoR significantly. Lowering the top or increasing heat will get tricky by possibly overheating the exposed surface but not necessarily getting the trapped moisture/air recirculating. A balance in trade offs must be considered. Lowering batch size can be a work around only if stirring/churning is not diminished by doing so.

Ed B.
DreamRoast 1kg roaster, Levers, Hand Mills
Okay, since I can't increase the speed of my motor without replacing it, I'll add another stirring arm across to make "4" and see what that does. Ran out of Hunapu, but have 10lb Yirg so that should get me by.

I cupped that most recent roast this morning, and thus far it's the most "normal" tasting, least amount of burnt/ash or grass flavor.

By increasing heat, I don't mean increasing temp, but more along the lines of intensity. The idea is to get just a few more watts, and the benefit would be maybe I could do slightly larger roasts, too. But path of least resistance, first :)
Anything that can increase the convection without increasing the MET will help.
TO tops put out enough btu's, it's getting the best heat transfer to the beans that will determine roast speeds and batch size.
Edited by farmroast on 01/11/2012 2:44 PM
Ed B.
DreamRoast 1kg roaster, Levers, Hand Mills


JimG wrote:And if you use aCatuai you would also get a record of heater output levels in the log file and on the graph.

This graph is posted as a follow up to our PM's.

The orange line shows the heater output level, 0 to 100%. The cyan line is a plot of the output signal to the fan motor, again 0 to 100%. This plot was made using aCataui and pBourbon with my Hottop.


PS - this turned out to be a really nice roast. Wish I knew why ......
JimG attached the following image:

Edited by JimG on 01/13/2012 4:28 PM
Success, I think! :) Took me a while to get there, got the flu real bad this year, finally recovered.

The issue is that my TO does not have enough heat. One way to solve it is by adding more, but as much as I wanted to do that, it would require major surgery, more wires and I'd be very close to needing a 220V outlet. So instead, I added two more stirring arms to make 4 per revolution, and went back to using the smaller colander, which puts the beans much closer to the heat source. It was dark so I couldn't get a good video of the beans roasting, next time if there's interest.

Below's the resulting graph.. sorry it's kind of messy, I accidentally hit spacebar and couldn't figure out how to get back to stuff. Preheated the chamber (the dips you early on was me playing with the router speed control) for about 5.5 minutes, then added the beans. To 300F in 4.5 minutes. The first snap of FC occured about 8'40", then rolling first crack around 9'20" (relative to when beans were added). Because there was continued "popping" until about 12 minutes I got confused whether that was indeed second crack so I pulled it, but as you can see, the roast did not stall at FC this time and I could keep ET maxed around 475F! The ROR did dip more than what I've seen for others (see the leveling out at the higher BT), and I will attribute this to the 1300W TO, however, I think I'm finally in the ballpark for getting some good roasts :)

This is an ethiopian yirg.. I know, you're supposed to take it only just past FC, but I ran out of the guatemalan last time, and wanted to see if I could overcome the prior stalling. Yeah!!
Koffee Kosmo


The issue is that my TO does not have enough heat.

I have designed for the KKTO roaster to work easily from a Turbo Oven with a 1300W - 1400W heat element

However you have to observe strictly the volumes required for it to work
7 litres for a 1300W 8 to 9 litres for 1400w in overall volume
There is a little over 1 litre in the glass dome of the TO

One more very important thing is, and it goes hand in hand with the volume is heat retention

Every bit of heat that is prevented from escaping is utilised for roasting

Edited by Koffee Kosmo on 01/26/2012 4:19 AM
I home roast and I like it. Designer of the KKTO
Roaster Build information
Blog -

Bezzera Strega, Mazzer Robur Grinder, Pullman Tamper Convex,
(KKTO) Turbo Oven Home Roaster.
KK: I was just around 7L volume with the large colander, including my extra piece for the raised floor but it was still too much for my TO, even with insulation (silicone mat and two towels). I could prevent the stall, but that meant I had to go to at least 500F ET, which was presumably causing the ashy taste. I guess I've effectively reduced the volume by bringing the beans closer to the heat source, since the smaller colander in my pasta pot set doesn't have as many holes and it's acting more like a SCTO/KKTO hybrid. The nice thing about the stall: it would make the beans quite even in roast color, but 7 days out the flavor was pretty lousy.

With this reverted setup, I'm still a bit lost as to when second crack occurs, I think I'm going to have to burn a sacrificial roast. Theory: The bubbling/popping sounds are caused by steam from condensation boiling against my false bottom, and the sound gets amplified as my motor housing unit / base is an old speaker. Pfffft.

Cupping the roast from last night yielded something decent, nothing epic, balanced, and consistent in flavor through the cooling. I guess that's what happens with a 2nd-crack yirgacheffe.


With this reverted setup, I'm still a bit lost as to when second crack occurs, I think I'm going to have to burn a sacrificial roast. Theory: The bubbling/popping sounds are caused by steam from condensation boiling against my false bottom, and the sound gets amplified as my motor housing unit / base is an old speaker. Pfffft.

put some foam inside to muffle the sound of the motor.

get some beans that you don't like that are really cheap and got from green to almost flames and you will learn a few things about your roaster I bet you don't know.

I pour Iron and roast Coffee BeansThumbsUp
If life seems normal your not going fast enough Mario Andrette


jedovaty wrote:... Below's the resulting graph.. sorry it's kind of messy, I accidentally hit spacebar and couldn't figure out how to get back to stuff....

Jedo and I have communicated already via PM.

But for the benefit of others reading this thread: after you press the space bar while logging with pBourbon, you have an opportunity to type a note that gets written to the log file. The note text appears overlaid on the graph as you type.

To save the note and exit the text entry mode, press ENTER. This also restores the function of the other hot buttons (B, F, S, E).

Hi, with the increased agitation and the more-or-less consistent results I'm finally getting with the beans closer to the heat source, I tried two new beans, one after the other (my roaster cools down between roasts). The first was a sumatra mandheling, second was a columbian. My goal was to get both to just the verge of second crack so I could compare flavors. The results? Got there, but the sumatra was unbelievably weird.. I got what looks like a stalled roast which I couldn't get out of unless I raised the ET higher to 490 (this is old behavior before my changes)?

Can different beans with the same batch size have such different results?

Almost days post roast the sumatra tastes very strange (bitter, burnt, fruity, sour) and I was forewarned that it would look weird: indeed, half the beans look scorched and the other half look okay, and there are a few very light ones. A local roaster has this bean sometimes, and it both tastes better and looks more uniform (granted on a deidrich machine). The columbian was the second roast, and it did what looks like an almost desired beginner's profile. In the cup it tastes like.. well.. decent coffee :)


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