Quest M3 consequences of excessive MET

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
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Peppersass
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Postby Peppersass » Jun 04, 2019, 6:23 pm

While I'm on the subject of dumb things I've done with my roaster...

I've read that it's bad to let the MET get much over 600F in a Quest M3, but it's not clear to me exactly what the risks are.

I'm asking because during my last session somehow the heater duty cycle got stuck at 100% while I was doing other things (grinding a sample of the previous roast to check color), and MET got over 1000F before I smelled a bit of plastic in the air, realized what was happening, and turned off the heater. I let the roaster cool way down, then brought it back up to charge temp for another roast. It looked as though chaff dust on the walls of the drum was a bit charred, so I ran some seasoning beans through to clean it off. That seemed to work, so I proceeded with one more roast, which went OK.

I don't believe the temperature probes were seriously affected, though the relationship between MET and BT wasn't quite normal at the start and I had to wait for a while for the relationship to return to what it usually is (e.g., when MET idles at 475F in an empty roaster, BT=350F, etc.) As I've just torn down the roaster for a thorough cleaning, I plan to test the probes with ice water and boiling water to make sure they're OK, and recalibrate them in Artisan if needed.

I had painted the drum black with several coats of Char-Broil grill paint, properly baked. The overheating turned it into a completely white layer of ash that was still adhered to the outer surface of the drum but brushed off easily. The metal in some areas inside and outside the drum is slightly discolored (bluish-purplish) in places, particularly around the strut weld marks on the outside of the drum. The inside surface of the roaster is also slightly discolored near the elements, though it could be that it's always been that way. The copper tube I added for better airflow had some black paint deposited on it, which wiped off easily, and solder on a fitting I attached to it looks like it's been overheated -- grainy not smooth like it was when I did the solder job.

So... what sort of damage could have resulted from the overheating? What, if anything, should I look for?

samuellaw178
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Postby samuellaw178 » Jun 04, 2019, 7:09 pm

In my understanding, the worst case scenario is you'd be shortening the lifespan of the elements with excessive MET.

Since you have Arduino/TC4 mods (correct me if I am wrong), you can try adding an alarm to kill off the heat for events like this (if you haven't had one set already). If the 100% heat output was due to software crash/bug then no dice. :P

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another_jim
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Postby another_jim » Jun 04, 2019, 8:45 pm

Peppersass wrote:I'm asking because during my last session somehow the heater duty cycle got stuck at 100% while I was doing other things (grinding a sample of the previous roast to check color), and MET got over 1000F before I smelled a bit of plastic in the air, realized what was happening, and turned off the heater.

So... what sort of damage could have resulted from the overheating? What, if anything, should I look for?


They must have really upgraded the heating elements; the early ones fried at 600F. The elements end in the back, square section where the controls are. You might want to open it up and visually check if the heat transmitted to the connectors and their insulation, damaging them.

It sounds like you didn't warp the drum or the outer case; so you got lucky there.

Reason: Closed quotes
Jim Schulman

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Peppersass
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Postby Peppersass » Jun 05, 2019, 6:48 pm

samuellaw178 wrote:Since you have Arduino/TC4 mods (correct me if I am wrong), you can try adding an alarm to kill off the heat for events like this (if you haven't had one set already). If the 100% heat output was due to software crash/bug then no dice. :P

Truth be told, I can't recall if it was a software crash, or more properly my MacBook Pro hanging up with the dreaded spinning wheel (could be due to running Windows under Parallels on that machine, where I have another copy of Artisan to evaluate the last roast while the Mac version is getting the roaster ready for the next batch, but I've never had a problem doing that.)

I'm thinking it might have been a hang because I do have an alarm set to do PID OFF when temp is over 600F. That said, I think the roaster has gotten over 600F in the past and it didn't shut off. Maybe I need to try setting a slider like in your example. Some experimentation is warranted.

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Peppersass
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Postby Peppersass » Jun 05, 2019, 6:54 pm

another_jim wrote:They must have really upgraded the heating elements; the early ones fried at 600F. The elements end in the back, square section where the controls are. You might want to open it up and visually check if the heat transmitted to the connectors and their insulation, damaging them.

It sounds like you didn't warp the drum or the outer case; so you got lucky there.


My roaster went over 600F many times before I painted the drum black, though usually not much more than 625F. After painting the drum and installing the copper tube mod, I can get a well-developed roast with MET no higher than 500F.

I have the case open because I'm doing a complete clean (fan and its mounting plate removed.) The heaters, ends, connectors and wires all look pristine. No evidence of melting, discoloration or anything else. So I don't think they were damaged. The drum isn't perfectly round, but I don't think it ever has been. I think if it had changed shape the strut welds would have broken.

EddyQ

Postby EddyQ » Jun 05, 2019, 6:56 pm

Are your bearings ok?

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another_jim
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Postby another_jim » Jun 05, 2019, 9:04 pm

Peppersass wrote: After painting the drum and installing the copper tube mod, I can get a well-developed roast with MET no higher than 500F


IMO, that's ideal for the Quest for most beans. You might want to try finishing at 525F - 550F and minimal air with SL28s or Bourbons; this gets the classic roast tastes -- blackcurrant, molasses, cloves, spice cake -- that I quite like (although it has gone out of style).
Jim Schulman

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Peppersass
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Postby Peppersass » Jun 05, 2019, 9:16 pm

EddyQ wrote:Are your bearings ok?

I think so. They seemed OK on the last roast before I tore down the roaster. I'll check them when I put it back together.

Are the bearings sealed? Can they be lubricated? If so how and with what?

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Peppersass
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Postby Peppersass » Jun 05, 2019, 9:25 pm

another_jim wrote:IMO, that's ideal for the Quest for most beans. You might want to try finishing at 525F - 550F and minimal air with SL28s or Bourbons; this gets the classic roast tastes -- blackcurrant, molasses, cloves, spice cake -- that I quite like (although it has gone out of style).


When you say finishing at 535F-550F, is that the MET at drop or is that the peak MET and you reduce from there -- say, a minute or so before 1C? Generally, I have to reduce heat well before 1C or RoR takes off like a rocket in 1C.

OT: I recently went up to somewhere in that range trying to get a fast roast of some Ethiopian Worka greens that I got from Northbound (there's a large thread here about the roasted version -- very blueberry.) I boosted the temp above 500F trying to get 3 min DE, but couldn't get it below 3:30. But this was an entirely different roast that I dropped before the end of FC, at around 14% development. I had to roast it that way to get close to the cinnamon color of the Northbound roast. It actually worked pretty well as espresso - the blueberry aroma was quite distinct and it wasn't too grassy (though some.) My biggest issue was not getting as even a roast as Northbound, which hasn't been a problem when I go darker. I think they might have screened the greens for more uniform size.

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another_jim
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Postby another_jim » Jun 05, 2019, 10:06 pm

This is at the end of the roast, from the beginning of the first crack on, for a medium roast taken to just ahead of the first pops of the second (you'll be able to smeel the roast tastes). The fast finish (around 3 minutes) keeps the medium roasts clean and snappy. A basic rule is that regardless of how light or dark the roast, the time from 1st crack start to the end should stay roughly constant. This means for medium or dark roasts, you do not drop the ET.
Jim Schulman