HomeRoast Digest


Topic: Question About Popper Temp Readings (7 msgs / 442 lines)
1) From: Andy Thomas
I'm wondering whether anyone else has observed this phenomenon. I've never =
seen it mentioned. I have a WB Poppery, modified so the heater is switched.=
 I use a Craftsman multimeter with a K type thermocouple to measure tempera=
ture. The TC is placed through a hole that I drilled in the side of the pop=
per so the bead is just below the surface and in the center of my typical=
 load of green coffee (130-150g). =
When the temp reaches about 230°F, I begin slowing the roast by switching=
 the heater off and on. But, when I switch off the heat, the temp spikes 10=
-12 degrees before dropping. As the roast progresses, this spike and drop h=
appens every time I kill the heat, until about 300°F or so, when the spik=
e gradually diminishes until barely noticeable.
This has been happening ever since I began using the modified popper with t=
hermometer, several years ago, and it happens whether I use a bimetal dial =
t-meter or one of two digitals. My question is: What causes the temp readin=
g to apparently spike when I kill the heater? Is the spike and drop pattern=
 normal? Do others notice it? Is it just a measurement phenomenon -- a fals=
e reading of some kind -- or does it reflect something that is actually h=
appening to the roast? I'm just curious. As far as I can tell, it doesn't a=
ffect the outcome of the roast in a negative way. (OTOH, if it did, how wou=
ld I know?;-)) TIA for any insight.
Andy
      =
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2) From: Brian Kamnetz
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3) From: Andy Thomas
OK. I'll buy that.
----- Original Message ----
From: Brian Kamnetz 
Subject: Re: [Homeroast] Question About Popper Temp Readings
Just a guess, but I'm guessing it has to do with the fan suddenly
spinning faster and moving a bit more of the built-up heat in the
metal. The heat is in equilibrium at the slower fan speed, but the
sudden faster fan speed sucks away a bit more of the heat.
On Thu, Aug 21, 2008 at 7:20 PM, Andy Thomas  wrote:
<Snip>
<Snip>
ng the heater off and on. But, when I switch off the heat, the temp spikes =
10-12 degrees before dropping. As the roast progresses, this spike and drop=
 happens every time I kill the heat, until about 300°F or so, when the sp=
ike gradually diminishes until barely noticeable.
<Snip>
ill the heater? Is the spike and drop pattern normal? Do others notice it? =
Is it just a measurement phenomenon -- a false reading of some kind -- or d=
oes it reflect something that is actually happening to the roast? I'm just =
curious. As far as I can tell, it doesn't affect the outcome of the roast i=
n a negative way. (OTOH, if it did, how would I know?;-)) TIA for any insig=
ht.
<Snip>
      =
Homeroast mailing list
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4) From: Martin Dobbins
Hi Andy,
 
A lot depends on what the cycle period of on and off is, I follow the tempe=
rature but often find I'm into a ten seconds on five seconds off cycle.  =
Since I have the same equipment as you I know the fan will run faster once =
it doesn't have to share the current with the heater.  This combined with=
 the fact that the wire in the heater doesn't immediately cool down from re=
d heat when you hit "off" means that you are immediately measuring a faster=
 moving airstream which is carrying more (by virtue of speed) of the resi=
dual heat from the coils.  Something as sensitive as a thermocouple is go=
ing to show you every nuance of the temperature profile even if it only las=
ts for a short period of time.  =
 
Logic would suggest that the longer the heater is on the more residual heat=
 it will build up and the longer it will take to cool when switched off. =
 Thermodynamics 101 was a long time in the past for me, but I seem to remem=
ber that it takes a lot more energy to raise the temperature of air (or cof=
fee beans) from 300F to 301F than it does to raise the same from 70F to 71F=
.  If that is correct it would explain why the spikes disappear at high=
er temperatures, in effect you have created a "heat flywheel" that damps wi=
ld temperature swings. 
 
Cheers,
 
Martin
--- On Thu, 8/21/08, Andy Thomas  wrote:
I'm wondering whether anyone else has observed this phenomenon. I've
never seen it mentioned. I have a WB Poppery, modified so the heater is
switched. I use a Craftsman multimeter with a K type thermocouple to measure
temperature. The TC is placed through a hole that I drilled in the side of =
the
popper so the bead is just below the surface and in the center of my typi=
cal
load of green coffee (130-150g). =
When the temp reaches about 230°F, I begin slowing the roast by switching=
 the
heater off and on. But, when I switch off the heat, the temp spikes 10-12
degrees before dropping. As the roast progresses, this spike and drop happe=
ns
every time I kill the heat, until about 300°F or so, when the spike gradu=
ally
diminishes until barely noticeable.
This has been happening ever since I began using the modified popper with
thermometer, several years ago, and it happens whether I use a bimetal dial
t-meter or one of two digitals. My question is: What causes the temp readin=
g to
apparently spike when I kill the heater? Is the spike and drop pattern norm=
al?
Do others notice it? Is it just a measurement phenomenon -- a false reading=
 of
some kind -- or does it reflect something that is actually happening to t=
he
roast? I'm just curious. As far as I can tell, it doesn't affect the
outcome of the roast in a negative way. (OTOH, if it did, how would I know?=
;-))
TIA for any insight.
Andy
      =
Homeroast mailing list
Homeroasthttp://lists.sweetmariascoffee.com/listinfo.cgi/homeroast-sweetmariascoffee=.com
Homeroast community pictures -upload yours!) :http://www.sweetmariascoffee.com/gallery/main.php?g2_itemId=7820      =
Homeroast mailing list
Homeroasthttp://lists.sweetmariascoffee.com/listinfo.cgi/homeroast-sweetmariascoffee=.com
Homeroast community pictures -upload yours!) :http://www.sweetmariascoffee=.com/gallery/main.php?g2_itemId=7820

5) From: Eric Faust
Because you are working with such a small amount of coffee in the popper you
are going to be able to see the effects of releasing moisture more quickly
than if you were working with a higher volume. In my experience it is best
to put the heating elements on seperate switches. There is an inner and
outer coil. I have always left the outer coil on throughout the entire roast
so there is a constant heat source and used the inner coil to determine my
profile. Also, the fan will speed up with modifications, but should stay the
same speed throughout the entire roast.
On 8/21/08, Andy Thomas  wrote:
<Snip>
hing
<Snip>
op
<Snip>
pike
<Snip>
t?
<Snip>
st
<Snip>
 in
<Snip>
ht.
<Snip>
ee.com
<Snip>
-- =
Eric Faust
(651) 357-6272
16420 7th St Ln South
Lakeland, MN 55043
Homeroast mailing list
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6) From: silascoelho
Andy
I do have a popper modiffied as well (not WB), and I have not observed this =
effect so far. I dont know exactly your setup, my assumption is thatyou are =
turning off the full heater only. In my case , I need to have a small =
transformer to source the dc motor+diode bridge, because the heater is =
splitted in two parts: one step for the motor (low voltage, and the end of =
heater to the AC, and my intention was really to turn off totally the heate=
r =
(both portions), in order to keep motor running I used the travo 12Vx1A.
Can you (or someone) describe the wiring diagram of WB (assuming is not the =
same as my popper)?
regards
Silas

7) From: Martin Dobbins
Hi Silas,
 
WB Poppery 2 pretty much the same wiring setup you're describing for your=
 popper with DC motor running off a diode bridge and "thermal fuse" that =
prevents overvolts to the motor.
 
See:http://www.geocities.com/Athens/Oracle/8104/popper.html 
Poppery 1 not a DC motor at all but an AC motor, one substantial heater wit=
h thermostat.  No "thermal fuse" provided or needed since motor is not DC.
 
See:http://homepage.mac.com/dparham_is/PhotoAlbum31.html 
Hope that helps?
 
Martin
--- On Fri, 8/22/08, silascoelho wrote:
Andy
I do have a popper modiffied as well (not WB), and I have not observed this =
effect so far. I dont know exactly your setup, my assumption is thatyou are =
turning off the full heater only. In my case , I need to have a small =
transformer to source the dc motor+diode bridge, because the heater is =
splitted in two parts: one step for the motor (low voltage, and the end of =
heater to the AC, and my intention was really to turn off totally the heate=
r =
(both portions), in order to keep motor running I used the travo 12Vx1A.
Can you (or someone) describe the wiring diagram of WB (assuming is not the =
same as my popper)?
regards
Silas


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