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Topic: Hot Alpenrost Problem Diagnosed! (13 msgs / 456 lines)
1) From: David Liguori
Some time ago my Alp started running hot: with most beans it reaches 
first crack in about 10 minutes, or else the thermal cutoff shuts it 
down altogether.  I've been in touch with Craig Andrews about this 
problem, have read all his posts and others, and have adjusted RV1 all 
the way from one end to the other, little by little.  I've concluded 
that this adjustment has little if any effect.  Also, I noticed that 
apparently after the unit returned from the last warranty so-called 
repair, the trace was cut to the ground end of RV1 and another 2.2K 
connected in series with it, in an attempt to bring it back into range, 
instead of diagnosing and fixing the actual problem.
In Craig's posts he says there is a thermocouple spot welded to the 
heating element, but I had never been able to locate it.  I didn't 
realize I had to remove a clamp to see it.  Just now I did so, and sure 
enough it has come detached from the heating element: no thermal 
contact, entirely consistent with the problem.
Unfortunately, my welding experience is zero.  I don't suppose these 
relatively delicate and valuable parts are the place to start learning. 
  So my options are either take it to someone who can re-attach the 
thermocouple or try to attach it mechanically.  I was thinking of just 
twisting some wire around it--preferably something that won't corrode 
too severely from all the heat and whose expansion rate is similar to 
the heating element's--or else some kind of spring clip. Any 
suggestions?  I guess any thermal contact I can get is better than none 
at all.
Of course, I also have to undo the factory circuit board kludge, or I'll 
end up with a cold roaster!
David Liguori

2) From: Mike Coppola
Hi David,
My first disclaimer...I'm not familiar with the Alp, but:
Is it possible to reattach the thermocouple with a proper adhesive.  
Some thermocouples are designed to be attached with a "thermo-cement".  
Here's an example of a company that sells high temperature cement: http://www.omega.com/pptst/CC_CEMENT.html. They also sell the 
thermocouples that are designed to be used with it (in case yours is 
damaged). 
If this isn't possible, then could you replace the thermocouple with one 
that is designed to be strapped on with a hose clamp?  There are thermo 
gels that are available to help with the heat transfer if that is an 
issue. 
Hope this helps.
Mike
David Liguori wrote:
<Snip>

3) From: Michael Dhabolt
David,
The first thing I checked when reading your post, was the info at
Omega that Mike Coppola referenced.  Unfortunately this particular
adhesive will not deal with the temps that the heating element will
reach (1000 F at times, if my information is correct).  His
suggestion of a mechanical attachment would probably provide enough
heat transfer from heater element to TC to be functional.  I am not
aware of a heat transfer compound that wouldn't degrade at theese
temperatures, a good mechanical attachment would probably circumvent
the need for it.  A phone call to the tech folks at Omega would
certainly get you all the state of the art information that is
available - these guys are really knowledgeable and super helpfull.
You might want to query Craig about what 'type' TC is used (K, J etc.)
in case you decide to take Mikes other good suggestion to replace the
TC with one that is designed to be mechanically attached.  If the type
is unknown, you can usually figure it out by attaching it to any TC
thermometer - check boiling water and ice and extrapolate to whatever
'type' TC the thermometer is set for (use the charts on Omega.com for
different TCs).
Mike (just plain)

4) From: Craig Andrews
Hi David & Mike,
I don't think that Thermo-cement will work as the temp ratings I saw on 
the linked website aren't high enough. The element glows bright orange & 
internal temps in the roasting chamber can get as high as 800F, when the 
overlimit thermosat shuts down the roaster!, & will reset in approx 15 
minutes.
I've measured air temps just under the drum at approx 450 - 475F. An 
electrical element glowing  that bright orange would have a surface temp 
pretty astromomical, who knows?, 1000F plus? My DVM will only read to 
1000F.  A small pipe clamp wouldn't work either, as I suggested this to 
someone to try as a last resort. The clamp sucks the heat out of the 
element in that whole contact spot & changes the element temp to 
drastically, not orange hot., but a dark cool black spot that obviously 
is much cooler & will give erroneous readings to the IC chip.
It was back on March 12 - 14th 2006 when you emailed me on the Alp & 
Sept/05 before that. {:-)
You'll have to spot-weld it on.
Cheers!
Sincerely,
Craig Andrews.
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5) From: Mike Coppola
The Omega spec doesn't indicate a maximum temp (that I could find); 
however it does reference 1475 F when indicated dielectric strength.  I 
agree with Michael that I call into Omega would clarify.  Actually, that 
brings up another point regarding the cement...it will act as a 
dielectric.  Not sure if this will cause problems with the measurement.  
Obviously, if the previous thermocouple was welded to the heating 
element, then it was electrically connected.  Maybe a mechanical mount 
is the way to go.
Another way to figure out the type of thermocouple would be to check the 
individual wire colours (inside the jacket) if you can get a look.  In 
North America, Yellow and Red are type K.  J is White and Red.  Omega 
has a nice reference chart if it's not K or 
T..http://www.omega.com/techref/thermcolorcodes.html.Mike
Michael Dhabolt wrote:
<Snip>

6) From: rnkyle
Snip:
You'll have to spot-weld it on.
Not having seen what you are attempting to weld, I will take a guess that if 
it can be spot welded which tends to melt two metals together, You should be 
able to Tig weld it without using a filler rod, and accomplish the same 
thing with more control.
 Any good welding shop should have a tig welder and could most likely do the 
job for you. Just a thought.
RK

7) From: Dave Brandes
I just noticed this post and have not followed the previous messages, so =
my
reply may be off base.  Just wanted to let you know that a Thermon type =
T-63
is good to 1250 deg F.  It's primary application is resistance heating
elements.
Dave

8) From: David Liguori
Thanks to all for chiming in.  I think something heated to where it's 
spectrum peaks in the visible red is going to have a temperature in the 
thousands of degrees (K, C or F).  The specs for the adhesive on the web 
site gave some expected lifetimes at various temperatures, the highest, 
I think, being 575F.  It doesn't exactly say it will fall apart at glow 
temperatures, but it doesn't sound promising.
I think a small enough clamp would not sink that much heat, but what I'm 
concerned about is either loss of contact or damage due to different 
expansion rates.  Also, I realize now that any kind of spring would have 
its temper ruined quickly.
Craig, I'm curious about the semi-circular clamp on that one corner of 
the heating element.  It seems to serve no purpose other than to hide 
the TC from my view, which it did for a long time.  It makes no physical 
contact with anything except where it is screwed to the bottom of the 
roaster.  Is it possible there was a ceramic spacer under the heating 
element and thermocouple that went up the Shop Vac?  If not, do you 
think installing one would be an option (pressing the thermocouple and 
heating element up against the clamp)?
Another thought is that the element *is* cycling.  It is not on all the 
time.  So the TC circuit is doing something, and any thermal contact I 
can get will tend to lower the temperature.  However, a mechanical 
kludge will likely shift around a lot and not be consistent.
I will show it to the people in my academic machine shop and ask for 
their recommendations about welding.
Craig Andrews wrote:
<Snip>

9) From: Mike Coppola
Hi Craig.  Just saw your post.
I rechecked the spec for the Omega CC High Temperature cement that I 
provided an example link.  It's max service temperature is 1550F.  Not 
sure how this will relate to life expectancy of the bond when mounted on 
a heater element where we don't know the exact temperature.  There are 
other manufacturers that go higher.  Aremco is an example of one.  They 
have a thermally and conductive product that goes to 1700F, but who 
knows how much their product costs.  Spot-welding is definitely the sure 
and simple solution.  Let us know how you make out, David.
Mike
Craig Andrews wrote:
<Snip>

10) From: David Liguori
Mike Coppola wrote:
<Snip>
Yes, in addition to the unknown factor of whether the adhesives would 
work at glow temperatures, the prices did give me pause.
OK, here's where I am at this moment.  First of all, the thermocouple is 
nothing fancy, just two wires in a white sleeve.  No "type K" or "W", 
unless that simply refers to the metals used.  The machinist at my 
university, who services the physics department I work for as well as 
the other science departments, and has seen plenty of thermocouple work, 
said he could do it, no problem.  He also said the proper way to make 
one is to weld the end of the two wires into a ball (like you see in 
Omega and other brands of commercial thermocouples).  When I described 
what's in the Alp, wires crossed and joined in an "X" he said that's the 
way most people do it.  He can do it for me any way I want, he says. 
Finally, he said that if I just tie it to the element with some wire, 
which was my first idea, it would work just fine.  He was right!  I did 
that, put 225  g of Colombian Buchamaraga in, and away I went.  After 10 
minutes, instead of first crack the beans were not even tan.  That was 
what I predicted, but I didn't want to change more than one variable at 
a time.  Next, after an hour or so of cool-down, I took out the 2.2k 
resistor someone had added and bridged the cut trace back together, and 
set RV1 to 500 ohms, the half way point.  I tried a fresh batch of 
beans, and I'm at first crack in 12 minutes.  (When I first got the Alp 
I reached first crack at about 14, a little hotter than nominal but I 
was living with it).  I re-adjusted RV1 to 700 and will try another 
roast tomorrow with the thing stone cold.  I'm sure I can reach 
finishing in about 18 minutes, the design center, with a little 
patience.  Of course, it would be easier if I knew the nominal 
temperature inside the drum, and had a way to measure it (Craig, are you 
listening?)  After I get that set I'll be watching for signs of 
changes--the Alp used to be very stable and consistent--and will take 
that as a sign the wiring job has come loose from thermal cycling.  In 
that event I will take the machinist up on his welding offer, maybe in 
return for a few pounds of some of the best coffee he's probably ever 
tasted.
Thanks to all for your advice and suggestions.
David

11) From: raymanowen
David-
A type K thermocouple uses the proprietary names of Chromel/ Alumel for the
two wires used used at the measuring junction. "Chromel" is the name derived
from an exact combination of chrome and nickel, or Nichrome, the same as the
heater's composition!
The original design is so bad that ridiculing it is about like shooting fish
in a barrel. There are absolutely NO "delicate and valuable parts" in the
roaster, least of all the nichrome heater element or the thermocouple. Hair
dryers and toasters use the same heater element.
If the thermocouple is "open," just make a new junction. Strip the wires for
a few mm and shine them with steel wool. Twist together tightly for a couple
of turns, and you have a brand new thermocouple. The thermocouple  the
junction of the two wires.
The temperature of the junction is what you're reading. The physical
installation errors can be huge, but the intermediate junction errors are
mostly insignificant and pointless to find and correct.
Roasting requires only heat and time. If your roaster is a machine, and the
failure of any little part stops your roasting, it's not a good machine.
Cheers -RayO, aka Opa!
Got Grinder?

12) From: Michael Dhabolt
David,
Congratulations on the fix.  Even if you have to re-do the fix after
awhile, it sounds like it will be easily accomplished.  Did you get a
picture of the modification? If so - a link to it?
<Snip>
inside the drum, and had a way to measure it <
A solution to the above question that I used is the Cooper thermometer
that SM sells for $18.90.  It required drilling a 1/8" hole through
the lid, a picture of my modification is at:http://tinyurl.com/kfhm4I can't remember who I copied with this mod, or I'd give them credit.
Mike (just plain)

13) From: Craig Andrews
Hi David!
Great it's working out for you!! I measured the temps in my new Bravi 
below the drum approx 1/16" away from it with my thermocouple between 
the 2 ends/arms of the heating element. I've measured air temps at 445F 
@ 1st crack & 2nd crack air temps @ 455F - 475F, starting @ 470F.
It may/should be similar in the Alp, but I haven't measured.
Cheers,
Craig.
Message: 12
Date: Fri, 02 Jun 2006 22:52:50 -0400
From: David Liguori 
To: homeroast
Subject: Re: +Hot Alpenrost Problem Diagnosed!
Reply-To: homeroast
Mike Coppola wrote:
<Snip>
Yes, in addition to the unknown factor of whether the adhesives would
work at glow temperatures, the prices did give me pause.
OK, here's where I am at this moment.  First of all, the thermocouple is
nothing fancy, just two wires in a white sleeve.  No "type K" or "W",
unless that simply refers to the metals used.  The machinist at my
university, who services the physics department I work for as well as
the other science departments, and has seen plenty of thermocouple work,
said he could do it, no problem.  He also said the proper way to make
one is to weld the end of the two wires into a ball (like you see in
Omega and other brands of commercial thermocouples).  When I described
what's in the Alp, wires crossed and joined in an "X" he said that's the
way most people do it.  He can do it for me any way I want, he says.
Finally, he said that if I just tie it to the element with some wire,
which was my first idea, it would work just fine.  He was right!  I did
that, put 225  g of Colombian Buchamaraga in, and away I went.  After 10
minutes, instead of first crack the beans were not even tan.  That was
what I predicted, but I didn't want to change more than one variable at
a time.  Next, after an hour or so of cool-down, I took out the 2.2k
resistor someone had added and bridged the cut trace back together, and
set RV1 to 500 ohms, the half way point.  I tried a fresh batch of
beans, and I'm at first crack in 12 minutes.  (When I first got the Alp
I reached first crack at about 14, a little hotter than nominal but I
was living with it).  I re-adjusted RV1 to 700 and will try another
roast tomorrow with the thing stone cold.  I'm sure I can reach
finishing in about 18 minutes, the design center, with a little
patience.  Of course, it would be easier if I knew the nominal
temperature inside the drum, and had a way to measure it (Craig, are you
listening?)  After I get that set I'll be watching for signs of
changes--the Alp used to be very stable and consistent--and will take
that as a sign the wiring job has come loose from thermal cycling.  In
that event I will take the machinist up on his welding offer, maybe in
return for a few pounds of some of the best coffee he's probably ever
tasted.
Thanks to all for your advice and suggestions.
David
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