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Stir-Crazy Popper - no TurboOven
Do you like the suggested mod? Do you like the suggested mod? 33%[1 Vote]
Are you planning to make one like this? Are you planning to make one like this? 33%[1 Vote]
Did you make one like this? Did you make one like this? 33%[1 Vote]
Total Votes : 3
 Print Thread
Stir-Crazy popper without TurboOven
xengineer
Hi all PopperRoasters! I am a new member, and would like to share the details of my modified Stir-Crazy popper for coffee roasting.

INTRO: Being a retired electrical engineer, I started with an evaluation of the Stir-Crazy that I bought second-hand, but essentially new condition. I measured the power consumption, which was found to be just under 600 W. I also measured the heating/temperature profile in time, using a precision Platinum resistive sensor (see attached plot). I found that the achievable temperature is more than sufficient for coffee roasting (>250C/482F). The built-in thermal switch will turn off the heater at that temperature in about 4-5 minutes, then let it fall to about 180C/356F before it switches it back on, repeating the cycle, though it will not reach the previous high again due to improved thermal equilibrium. Therefore the long-term average will be about 200-210C/392-410F. This is why previous attempts were unsuccessful using its built-in heater for coffee roasting (reports of >60 minutes roasting time).

I concluded that if the electrical power to the heater can be maintained at a controlled, lower level after the thermal switch turned it off, it could provide the required temperature for coffee roasting. Since the power consumption was found to be below 600W, I connected a standard incandescent rotary dimmer parallel with the thermal switch, which controls the heater power depending on its setting. Granted, this is not a feed-back control based on sensing the temperature, just input power control, it provides reasonably stable temperature for coffee roasting. Precaution must be made not to set the dimmer too high as the popper can self-destroy by reaching too high temperatures.

WARNING: I recommend the modification described below only to those who understand electrical circuits and are capable of doing safe and reliable electrical and mechanical projects.

MATERIALS for the Coffee Roaster:
1. qty. 1 Rotary Incandescent Dimmer, 600W (no switch needed);~$6-7
2. qty. 1 Suitable electrical box, e.g. Iberville Model: 1110-CRT
3. qty. 1 face-plate for dimmer
4. qty. 4 standoffs, e.g. ~1/4"HEX x 0.5"..1", F-F
5. qty. 8 plastic washers, ideally of soft and heat resistant mat. (Teflon)
6. qty. 2 "FastOn" "Y" F-M-M terminal, available in auto-parts stores, or online at DigiKey.com, P/N A27891-ND; (qty. 10 min) $3.20
7. qty. 2 "FastOn" insulated female crimp terminal
8. qty. 12" high-temperature insulated 16-18 awg flexible wire
9. nuts and bolts
10. Materials for shaft modification (details can be found on the Internet)
11. Stir-Crazy popper, new or in good condition

THE MOD:
A. Open up the bottom of the Stir-Crazy, carefully remove the wires from the power input connector posts, or from the heater and thermal switch (small ceramic disc pressed against the heater, with two terminals) so that the plastic body can be safely worked on. Make sure you remember what goes where!
B. Attach four stand-offs to the side of the electrical box at ~1"x2" spacing, and remove the bottom-center cover plate.
C. Drill matching holes for them on the side of the Stir-Crazy plastic body (round!!), near the thermal switch location. Gentle! Don't crack the hard plastic!
D. Drill additional two holes, ~1/8" dia and ~1/2"-1" apart, near the thermal switch, for the high-temp wires.
E. Attach the electrical box with the stand-offs to the Stir-Crazy body.
F. Attach a female FastOn insulated terminal to one end of two pieces of 6" high-temp wires.
G. From the inside of the StirCrazy body, thread the two wires through the two holes on the body and the bottom-center hole on the electrical box.
H. Using the wire-connectors supplied with the dimmer, attach the 6" wires to the dimmer wires. Make sure all wires and connections are properly insulated!
I. Carefully Mount the two FastOn "Y" terminals onto the the thermal switch.
J. Re-assemble the Stir-Crazy electrical connections.
K. Connect the two extended dimmer wires to the two extra terminals of the thermal switch on the "Y" connector (THE ESSENCE OF THE MODIFICATION: dimmer is connected parallel to the thermal switch).
L. Shaft modification may not be necessary, although the plastic shaft may not be able to withstand the extended exposure to the required temperature. (I replaced most of the shaft with a stainless steel screw and various washers and bits and pieces.)
M. Replace the motor and the bottom plate.

CALIBRATION (you need a suitable thermometer, e.g. IR):
i. Turn on the Popper with the stir-arms removed, and wait until the thermal switch clicks it off the first time (4-5 minutes)
ii. Measure the surface temperature: Starting with the lowest dimmer-setting (CCW), slowly, step-by-step rotate it CW, and measure the Popper temperature. Stop at each setting, and wait for the temp to stabilize. Make sure you notice if the thermal switch comes back up again, which shouldn't happen in the desired roasting temperature range.
iii. Make markings at the dimmer settings within the desired temperature range.

READY TO ROAST!

I have posted additional pictures of the Roaster at: https://picasaweb...directlink

CONCLUSION: I have done 5 batches up till now in the 100-200 g batch size, with consistent results. The roasting took typically 20-21 minutes, to reach my desired medium-light roast of Costa Rican Tarrazu, at ~230C/446F. I use the original transparent lid, without the cap, so fumes can escape. Stirring is not perfect, so I pick up the Roaster with the lid and shake it up every minute or two.
I have also made a simple cooler/chaff-blower, using a strainer-basket and a little fan removed from a failed heat-gun, powered by a plug-in power supply of an old gadget (see posted pictures).
xengineer attached the following image:
p1050334a.jpg

Edited by seedlings on 02/21/2012 7:22 PM
 
allenb
Great first post!

From hearing about previous failed attempts of folks trying to use the stir crazy base as a primary heat source I thought a lack of wattage was the issue.

I'm glad you dove into the innards of one to find the root cause.

I wonder how small of a batch would you need to drop to in order to shave a couple of minutes off the roast?

Allen
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
xengineer
Hi Allen,

The batch size at this point is not the determining factor in the roast time. I can still raise the temperature and shorten the time, but I am concerned about the uniformity of the roast in the cross-section (and among) of the beans. What would you consider the ideal roast time is?

Charles
Edited by xengineer on 02/21/2012 9:07 PM
 
allenb
Ideal roast time? That's a tough one! With my various rigs I've found the best results when not exceeding 16 minutes but, many have found excellent results going up to 20 minutes.

It depends on many factors including the characteristics of the particular roaster and the varietal so again, hard to pin down and it's best to experiment with various profiles long and short to find what you feel is the sweet spot for your roaster.

I would suggest going through the "Roasting Coffee" forum in our Discussion Forums which will show you profiles from many here at HRO as well as some basic getting started tips on roasting.

Also, if you find uneven roasts when trying higher heat levels you'll want to read up on different stirring paddle options and speeds under Turbo Oven Roasters.

Allen
Edited by allenb on 02/21/2012 9:55 PM
1/2 lb and 1 lb drum, Siemens Sirocco fluidbed, presspot, chemex, cajun biggin brewer from the backwoods of Louisiana
 
kurt_hulst
Do you think this would work by bypassing the thermal switch and controlling the heat gradually with the dimmer switch to get it to desired roast temp? I would think similar to the air poppers.
Kurt Hulst

Equipment: Modified Presto Poplite roaster, Modified Stir Crazy, Saeco Aroma espresso machine, Ascaso i-3 Mini espresso grinder.
 
DavidG
Impressive innovation, xengineer!!

N.B.: West Bend recently came out with a new model called West Bend 82386 Kettle Krazy Popcorn Popper and Nut Roaster. It sports a metal shaft and heavier-duty elements. http://www.amazon...B002JM100Q It retails for less than $40. Any guess whether the same mods would work?

Is this the newest entry-level coffee roaster?

Cheers,
David
europiccola | yama + coryrod | chemex | AP | clever
wbp1 | wepp1 | bm/hg | co hybrid (still coming soon...)
 
kurt_hulst
Well I have modified the Stir Crazy (found it on clearance $25) to the specifications above with a few small modifications of my own. Still in the works as I tweak things (finding a good spot for the thermometer). I do not have a thermocouple but a prob rod that reaches 550F that I used with my air popper. I have roasted 3 full cups (3 separate roasts) now with great results. The Ethiopian Harrar and Brazil FAF Bourbon Sweet Yellow came out real nice. My last roast was today. I am contemplating drilling a hole through the base of the SC horizontally so that the temperature rod can rest just above the heating plate and just below the swing arms and rest in the bean mass. I have had it setting just above the bean mass and was getting a reading of 350F when I started to hit first crack at 9 min and finished at approx 13-14 min just starting at second crack. I have contemplated getting a thermocouple and coming in through the bottom like many have done, but funding is limited so going a low tech route right now.
Kurt Hulst

Equipment: Modified Presto Poplite roaster, Modified Stir Crazy, Saeco Aroma espresso machine, Ascaso i-3 Mini espresso grinder.
 
fullofdays

Quote

DavidG wrote:

Impressive innovation, xengineer!!

N.B.: West Bend recently came out with a new model called West Bend 82386 Kettle Krazy Popcorn Popper and Nut Roaster. It sports a metal shaft and heavier-duty elements. http://www.amazon...B002JM100Q It retails for less than $40. Any guess whether the same mods would work?

Is this the newest entry-level coffee roaster?


Cheers,
David


I just ordered this new roaster from target.com and will be using it in combination with a supentown SO 2007 turbo oven. i am just going to disconnect The heating element or perhaps rewire The heating element to run off The switch. more to come next weekend
 
kurt_hulst

Quote

fullofdays wrote:

Quote

DavidG wrote:

Impressive innovation, xengineer!!

N.B.: West Bend recently came out with a new model called West Bend 82386 Kettle Krazy Popcorn Popper and Nut Roaster. It sports a metal shaft and heavier-duty elements. http://www.amazon...B002JM100Q It retails for less than $40. Any guess whether the same mods would work?

Is this the newest entry-level coffee roaster?


Cheers,
David


I just ordered this new roaster from target.com and will be using it in combination with a supentown SO 2007 turbo oven. i am just going to disconnect The heating element or perhaps rewire The heating element to run off The switch. more to come next weekend


With xengineer modifications it works without the TO. However, I have not heard from xengineer how long his heating element might last. I have only done 3 roasts with a fourth coming today having found a new placement for the thermometer. With the inaccurate temperature readings from the previous roasts I have gone by sound, sight, and smell and they have come out real nice regardless. The chaff I blow away after dumping into a colander with a fan as I cool the beans. I like this mod because it is a cheap solution to roasting and it works with out the Turbo Oven's.
Kurt Hulst

Equipment: Modified Presto Poplite roaster, Modified Stir Crazy, Saeco Aroma espresso machine, Ascaso i-3 Mini espresso grinder.
 
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