HomeRoast Digest


Topic: heater load calculations (83 msgs / 1826 lines)
1) From: AlChemist John
If someone with some electrical load knowledge could answer this, it would 
be appreciated.
I am sizing various heater coils for the drum roaster I am designing.  They 
are listed at 400 W.  To calculate amps, I realize you divide by the 
voltage for approximately 3.3A @ 120v.  My question is what happens if my 
voltage drops?  Which part of the system is constant?  If it drops to 100 
V, do I have 4A to worry about in my load calculations or only 300W of 
power being consumed (and emitted through the heaters).  I think the later 
happens, but I have over thought it, and am now not sure.
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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2) From: Dan Bollinger
John,  You already know the answer, you just haven't realized it yet. Take
one step backward and look again.  Given: Watts=Amps*Volts.  You know that
if you reduce the voltage (like with a Variac) the energy (Watts) is also
reduced proportionally.  So, if Watts and Volts are reduced the same amount
and they are on either side of the = sign, then Amps stays constant. Of
course you'll want to include a safety factor in that, but most electrical
equipment is sized for 'working amps' already, so you don't have to worry,
the safety factor is designed in.  Dan
<Snip>
They
<Snip>
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3) From: AlChemist John
Sometime around 07:58 11/24/02, Dan Bollinger typed:
<Snip>
Right you are.  I was "thinking" but not looking at the equation.  Ok, the 
element lists watts, I calculate the constant amps (I'll verify this once 
the elements are in hand), and size my loads accordingly.
Thanks for pointing out what I knew ;-)
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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4) From: sho2go
John, the Ohms law calculations are at once simple and complicated.
Watts=E^2*R  where R is resistance.  If we were to assume the resistance of
nichrome stays constant, then the power will vary by the square of the
change of voltage.  So in your example, 400 W /120V=~3.3A, then R=V/A=~36.3
ohms.  So if V decreased to 100V, then W=(100)^2/36.3'5 watts.  The
stickler here is that the resistance of nichrome will vary by power (heat)
but I don't remember the numbers.
Mike

5) From: Dan Bollinger
Mike,  Right you are, it is not linear. Not only do you need to know the
resistance curves for Nichrome, you need to know them for the specific
alloy!  There are about a dozen commonly used nichrome elements in use.  I
didn't want to confuse John with the finer points.  Since he was talking
about voltages near the design voltage, then amperage will appear to be
linear.  Any slight increase will be handled by the safety factors in
switches, relays, cordsets, etc.  Dan
<Snip>
of
<Snip>
R=V/A=~36.3
<Snip>
would
<Snip>
my
<Snip>
100
<Snip>
later
<Snip>
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6) From: Eric Fesler
John is correct here.  Current is a function of voltage and
cannot be held constant when you vary voltage.  Accordingly,
W= V*I but since I=V/R W really equals V*V/R.
Cheers,
Eric

7) From: AlChemist John
Sometime around 08:39 11/24/02, Dan Bollinger typed:
I
<Snip>
And I thank you for this!
<Snip>
What are relays used for BTW?
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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8) From: dewardh
John:
<Snip>
are listed at 400 W.  To calculate amps, I realize you divide by the
voltage for approximately 3.3A @ 120v.  My question is what happens if my
voltage drops?  Which part of the system is constant?  If it drops to 100
V, do I have 4A to worry about in my load calculations or only 300W of
power being consumed (and emitted through the heaters).
The equations that apply are Ohm's law (E) and the "power law" (P).  The 
"assumption" one makes is that although the resistance of heating element wire 
does vary some with temperature it is essentially constant *over the range of 
operating temperature in question*.  The rated "watts" of the heating element 
is *not* a constant except at some specified constant voltage . . . the actual 
wattage varies as the square of the applied voltage for any particular element. 
 If you double the applied voltage (across a resistor (heating element)) the 
current doubles as well, so the power increases by four.  If you cut the 
applied voltage in half the current is also halved, so the power is reduced to 
one quarter.  Lowering the voltage across a resistor *will not* increase the 
current through the resistor (to keep the "power" constant).
This leads to the (somewhat) counter-intuitive "reality" that shortening a 
heater coil (lowering its resistance) *increases* its power dissipation (up to 
the point that the shorter coil burns up) if the supply voltage is kept 
constant (something that your utility company is paid plenty to do ).
Another "illuminating" example is light bulbs  . . . two of them wired in 
parallel (the way we usually do it) use double the power of a single bulb, 
expressed as twice as much light.  The same two bulbs wired in series 
(effectively doubling the resistance, and cutting the voltage across each in 
half) use half the power of a single bulb (1/4 power each bulb), expressed as 
two bulbs glowing dull orange.
Deward
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9) From: Rick Farris
John wrote:
<Snip>
Actually, wrt household appliances, it is indeterminate to what a "power
rating" (in this case 400W) refers.
I would wait until I got the element, measure it's dc resistance
(disregarding ac impedance effects), and then use the formula "power =
(voltage * voltage) / resistance" to calculate the power dissipated at each
voltage of interest.
-- Rick
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10) From: Dan Bollinger
<Snip>
John, Sometimes heavy electrical loads are switched on and off with relays.
Common in home ovens and dryers.  Commercial ovens use relays. For the amps
you are talking about heavy duty switches will work and they are cheaper.
Dan
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11) From: AlChemist John
Sometime around 11:04 11/24/02, dewardh typed:
<Snip>
I am not even going to pretend to understand this.  Your right, it is 
counter intuitive.  On that note, I won't go shortening the coils (as I had 
considered, if there was a need to lower my heater load a little)
I know chemistry is not, but I was rather hoping other sciences were 
straight forward and intuitive 
(30 minutes later)
Ok, I wasn't going to ask, but WHY doesn't the amount of heat drop by half 
if you cut a coil in half??????  That really doesn't make sense.
<Snip>
Good, I had already planned to wire  the coils in parallel so I can control 
them individually in the R&D phase.
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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12) From: sho2go
Take it to the limits: if the coil is infinitely lengthened, would the power
be infinite?  Don't forget the resistance of the heating coil is in the
divisor, and assuming constant voltage,  the pertinent equation is:
P=V^2/R.
<Snip>
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13) From: Andrew J. Lynn
AlChemist John wrote:
<Snip>
<Snip>
This does not make less sense than chemistry. :)
Think of the wire in the heating coil as a resistor - the amount of 
resistance is controlled by the length and the cross-sectional area. 
 The longer wire = more resistance, shorter wire = less resistance. 
 Here's the diagram:
+120V ----------^^^^^^^^^^^^---------Ground
(OK, I labelled the voltage source as if it were DC, but it works either 
way and this is just easier.  The ------- is a wire, which has 
negligible resistance, and the ^^^^^^^ is the resistor/heating coil.)
On one side of the coil the voltage is +120, on the other side it is 0, 
so it has to drop by 120V over the coil.  This is true regardless of the 
coil length/resistance.  The math is:
V
P
where V is voltage, I is current, R is resistance and P is power.
When you drop resistance (by shortening the wire) while keeping voltage 
constant, your current increases proportionally.  Less wire means less 
resistance means more current when voltage is the same.
In the power equation V is a constant 120 while I doubles when you cut 
the coil length in half, so the amount of heat you're generating doubles.
Andy Lynn (who was an EECS for a while long ago)
<Snip>
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14) From: dewardh
John:
<Snip>
<Snip>
if you cut a coil in half??????  That really doesn't make sense.
It's simple . . . (really ).  If you cut the coil in half (shorten it) the 
resistance (of the shorter coil) is cut in half.  That means that for a 
constant voltage double the current will flow (I=E/R) in the shorter coil. 
 Double the current at the same voltage means double the power (P).  The 
effect *at the coil* is that the coil will run "hotter" (more power dissipated 
over less surface equals higher temperature) *and* produce more "heat" (which 
is just "power" in thermodynamic terms) in total.
When considering "power" it is best to consider the coil as a "black box" . . . 
the only thing that matters is its resistance.  Long coil of thick wire, short 
coil of thin wire, nichrome, tungsten, none of that matters . . . only the 
resistance determines power (for constant applied voltage).  How "hot" (temp  
erature) the coil gets *is* a function of its size and the thermal conductivity 
of its surroundings . . . but the amount of heat (how much air it can bring to 
250C how fast, for example) doesn't change.
<Snip>
them individually in the R&D phase.
It really is a *lot* easier to control power by adjusting voltage . . . 
somewhere around the lab there *has* to be an old variac that used to be used 
with heating mantles or oil baths . . . and with an amprobe and a voltmeter you 
can determine power easily at any setting (not to mention the convenience of 
adjusting the roast air temp at the twist of a dial . . .).
Deward
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15) From: Tom Gramila
On Sun, 24 Nov 2002, AlChemist John 
wrote:
<Snip>
OK, I'll venture a stab at this...
	It comes down to which parameter of the problem is held constant.
	In an electrical circuit, there are two related "measures" of 
things electrical, voltage and current.  The first is how hard you "push" 
the electrons, and the second is how many electrons travel by in a given 
time.  The relationship between them is fixed by the resistance of the 
circuit.   V/I = R  (or equivalently: V = I*R)
	One analogy that may be helpful is water pressure and flow in a 
pipe.  for a given pipe size, more pressure (like voltage) results in a 
bigger flow (aka current).  changing the pipe size changes the 
relationship etween the pressure and the flow.  A large resistor 
corresponds to a small pipe, and a small resistor is lake a big pipe.
	In your home, the voltage is essentially fixed.  Cutting the
resistor in half is like making the pipe twice the size: the "resistance"
to current flow is reduced.  Now you have a bigger current flow with the
same voltage. So ..... you are pushing just as hard on twice as many
electrons, thus using up twice the energy.
	I hope this is helpful rather than more confusing......
		Tom Gramila
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16) From: David Westebbe
<Snip>
So how does this translate into the temperature of the coils, and the btu
output of the coils?
While we need to be interested in the power characteristics for safety
purposes, we also need to focus on temperature for profiling purposes, and
on btu output for purposes of maximum load size/time.
Can you give any hints?
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17) From: AlChemist John
Sometime around 19:07 11/24/02, Andrew J. Lynn typed:
<Snip>
That was the key bit of knowledge I needed.  With that in hand, it does 
make sense why a shorter coil could burn out. I'm suddenly glad I am 
purchasing heater coils (as heater coils) instead of just the nichrome wire 
and wrapping them myself.
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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18) From: AlChemist John
Sometime around 19:59 11/24/02, dewardh typed:
<Snip>
Yeah, but I have never done things the easy way.   We don't have extras 
around the lab.  If anything, we are in need of about 8 of them.  At this 
moment I am planning on maintaining control over the heat by venting 
"excess" heat with a built in fan (whose speed is a lot easier to control 
(read less expensive)), vents and baffles.  It may not be by the numbers 
roasting, but it seems right to me, shall we say "roasting by gestalt" .
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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19) From: Dan Bollinger
<Snip>
1 BTU = .29 Watt-Hour
<Snip>
Sivetz, in his patent, says that the supply air is usually 450, but never
more than 530F for a fluid bed roaster.
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20) From: David Westebbe
<Snip>
I like the way you think.  I took it to the other limit in my head:  With
the coil infinitely SHORT, the power would indeed be infinite, as you would
have a dead short circuit
 Don't forget the resistance of the heating coil
<Snip>
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21) From: dewardh
David:
<Snip>
output of the coils?
As Dan summarized so succinctly . . . "heat" (BTUs) and "power" (watts) are 
interchangeable terms, more "power" produces more "heat".  It is a direct 
equivalence . . . more "power" makes either more "hot air" (at some specified 
temperature) or it makes the same amount of air "hotter" (higher temperature). 
 Or, converted to "beans", more power will increase the temperature of more 
beans at the same rate or of the same mass of beans at a faster rate.
In an air roaster (in any roaster, actually, but "air" is conceptually 
"cleaner" and easier to understand) the rate of heat transfer from the air to 
the beans is a function of the difference in temperature between the air and 
the beans (what the beans "do" with that heat is a function of their 
temperature . . . i.e.. the "progress" of the roast).  Small (home) air 
roasters are typically quite inefficient thermally . . . they produce an excess 
of hot air and then "waste" it out a vent after a single pass through the roast 
chamber (where it has given up much, but not all, of its heat content to the 
beans).  It is thermally more efficient to re-circulate the exhaust air and 
retain the heat not transferred to the beans on the first pass (the Rosto does 
this, to some extent, which partially accounts for why it can roast 150 grams 
of beans with the same power input a Hearthware uses roasting 75 grams).  The 
two home "drum" roasters (Alp and HotTop) manage more beans still (at similar 
power input) because they vent (relatively) little air during the roast cycle . 
.. . with the Alp it's just enough to carry away the evaporated moisture, you 
can sometimes actually see condensed "steam" in the exhaust during the "drying" 
cycle, indicating that the exhausted air is nearly saturated as it exits the 
roaster.  The PRO1500, which both recirculates its roast air and is well 
insulated, is able to manage 1500 grams of bean with not much more power (~1500 
Watts), but it takes it quite a while (~15 minutes) to dry the beans and get 
them up to roast temperature (once they get to first crack and exothermy begins 
the roast proceeds quickly, unless deliberately slowed).
But back to "air" roasters . . . one controls the "roast profile" (the 
temperature/time curve of the beans) by controlling the temperature 
differential between the air and the beans, and thus the rate of heat transfer 
into the beans.  There are some limits . . . if the air temperature is too high 
the beans will "scorch" on their surface before their interior reaches roast 
temperature, if it is too low (below the temperature necessary to initiate 
exothermy, in particular) the roast will "stall" and the beans will "bake" 
rather than proceed through subsequent roast stages.  This leads to the biggest 
single difference in "profiling" with an air roaster compared to a drum . . . 
the air can cool the beans as well as heat them, at any stage during the roast. 
 In a drum roaster once exothermy begins the roast can "take off" and develop a 
"momentum" of its own as the heat released by the beans heats both the beans 
and the drum/roast chamber itself.  In an air roaster (one without a lot of 
re-circulation, anyway) the air begins cooling the beans as soon as the beans 
get hotter than the air.  The more re-circulation there is in an air roaster 
the more it behaves like a (closed) drum (thermally, anyway).  That is the key 
to Seivetz's insight . . . he noted that large commercial "drum" roasters, 
which heat not the drum but air passing through the drum, are essentially "air" 
roasters using the drum as a stirring mechanism . . . and that by fluidizing 
the bean mass he could dispense with the drum altogether and gain greater 
control over bean temperature and roast development.
<Snip>
purposes, we also need to focus on temperature for profiling purposes, and
on btu output for purposes of maximum load size/time.
<Snip>
It's all in the numbers  . . .
Deward
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22) From: Rick Farris
Alchemist John wrote:
<Snip>
Oh?  How shall you control the speed of the fan?  With a variac?  :-)
I think you're making a big mistake by varying air speed.  Remember, the
speed of the air will change several things in your system -- the
temperature of the air, the fluidization of the bed, etc.  Consider also
that when you slow down the air, the temperature goes up at the same time
your fluidization goes down, probably the opposite of what you want.
No, the correct way to go is to change the amount of heat applied to the
system (with a variac on the heater coil).  That way you're only changing
one variable at a time.
Now you may wish to vary the air speed to adjust the fluidization for
different load sizes, but that would be a static adjustment, not the dynamic
adjustment you need for temperature during the roast.
-- Rick
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23) From: Jim Schulman
On 25 Nov 2002 at 23:14, Rick Farris wrote:
<Snip>
The weight of the beans is declining throughour 
the roast, so ideally the airflow would reduce 
continuously. 
I've been taking Ken Mary's results to heart and 
trying to reduce the heat continuously throughout 
the roast, and still control the roast timing (not 
easy). With a variac on the whole unit, the heat 
reduces as a square of the voltage ( V^2/R), and 
the airspeed linearly with voltage (V^2/R = E = 
MV^2/2), so the air temperature also drops 
linearly with voltage. This makes the variac on 
the whole unit fairly convenient for this style of 
profile.
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24) From: AlChemist John
Sometime around 22:14 11/25/02, Rick Farris typed:
<Snip>
No, a small rheostat.
<Snip>
Remember (or note), I am not making a fluidized bed, it is a drum roaster 
(or maybe a hybrid at most).  The air flow is specifically for movement of 
hot air.  With this in mind, I believe it is the only variable in the 
system that is being changed.  If the system is running hot, I will turn up 
the fan, down if it is too cool.
<Snip>
See above.  Besides, I really cannot afford a variac.
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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25) From: David Westebbe
<Snip>
Well, yes and no.  Keep in mind that the beans get MUCH lighter towards the
end of the roast.  Unless you can turn down the airflow, the air temp will
cool off due to the lightweight beans allowing a faster flow.  So slowing
down the air to achieve a constant airflow, and therefore a constant temp,
is exactly what you DO want as the roast progresses.
I find that the best strategy is to load the popper to just under the max
"wet" bean capacity.  That way, I have leeway after the beans dry and
lighten to control the temp up and down.
<Snip>
I agree that is good to be able to control the coils.  But I found that with
my airvents opened up, I really had to install a fan speed control, or else
the air got too cool at the end of the roast (unless I loaded the popper up
with a very heavy load of beans, forcing me to stir at the start of the
roast).  So both types of control would be optimum, but if I had only one, I
would  (and did) choose the fan control.
I can turn the heat down using the heater coil on/off switch like a human
thermostat, which is not all that hard to do.
<Snip>
I dunno about that.  The load "size" varies during the roast, as the beans
dry out and lighten.  I find that I need to constantly adjust the airflow to
maintain the level of fluidization. But so long as they move sufficiently
and don't just sit there, the level of fluidization is not really critical,
except to the extent it affects temperature.
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26) From: David Westebbe
<Snip>
You might want to use a triac-style dimmer switch instead.  That is the
standard way of doing it.
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27) From: AlChemist John
Sometime around 06:56 11/26/02, David Westebbe typed:
<Snip>
What is the advantage?  Why not a rheostat, practically?
<Snip>
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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28) From: dewardh
David:
<Snip>
standard way of doing it.
This is where one of those $15 "router motor speed controllers" that people 
were burning up earlier this year trying to control the heater would work fine 
.. . . and with the addition of a little 12V "boost" transformer (maybe $5) it 
would let you overspeed the fan as well, useful both with the heavier beans at 
the start of the roast and (possibly) for cooling.
Deward
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29) From: dewardh
David:
<Snip>
"wet" bean capacity.
Same with the Rosto . . . at 150g the beans barely move initially (leading some 
to "rock" the roaster to help mixing . . . I don't find it necessary), but 
after drying (and especially after "first crack") the beans whirl like they're 
in a tornado.
<Snip>
temp,
is exactly what you DO want as the roast progresses.
In the Rosto this happens "automatically" (sometimes) . . . as the too-small 
chaff filter clogs up the airflow goes down and temperatures rise.  With high 
chaff beans the effect is pronounced, and the roast duration is appreciably 
shortened (compared to low chaff beans, which can take minutes more to reach 
second crack).  One learns to "adjust" . . . 
I'm coming to think that a single mechanical airflow control (valving the 
exhaust) might be both the simplest and most elegant (from a control 
standpoint) way to manage a Rosto (and it could be easily "automated" with a 
stepper or some linear actuator).  Because of the way a Rosto is built such a 
device could be mounted using the two existing screws on the lid assembly, with 
no other changes to the roaster (except the holes for air and bean temperature 
probes, of course ).  With the exhaust completely closed all the air would 
recirculate (and get *very* hot), wide open and it would be cooler than the 
present design even with the heater on full, and give even better than the 
already excellent cooling with the heat off.
Oh scat . . . another "project" . . .
Deward
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30) From: Dan Bollinger
<Snip>
John, A rheostat is a heavy-duty, variable resistor.  What it does is drop
the voltage to the motor by creating heat.  Lots of heat. If your motor is 2
amp, then the rheostat to control it will be about 2 amps.  That's about
200W.  A motor-speed control hardly gets warm and costs about the same and
is more readily available.  Dan
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31) From: David Westebbe
<Snip>
Rheostats are variable resistors, and they work by converting the electrical
energy into heat energy.  They get hot (duh) and must be made pretty heavy
duty if they are to handle much current.  Heavy duty (generally) =
expensive.
Dimmer switches use a solid state device called a triac to slice the AC
waveform into pieces.  If the dimmer is set on 1/2, for example, only half
the waveform, and therefore half the current, is applied to the load.  They
do not get nearly as hot, and they save electricity.
You might need a special fan dimmer if you use an AC motor (I'm not sure)
but for any typical DC motor, a standard el-cheapo dimmer from Home Depot is
fine.
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32) From: AlChemist John
Sometime around 07:57 11/27/02, David Westebbe typed:
<Snip>
Well, I am/was mainly considering a rheostat because it would do the job 
and not expensive since it is from a surplus source (C&H supply).  I may 
still use one for initial R&D, but may well go with a regular dimmer for 
the final version.
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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33) From: David Westebbe
<Snip>
Well, Tom...Now for something completely different.
What If I used some nicrome wire from a hair dryer?  What should I expect
for heat and temperature output from say, an 1850 watt blow dryer?
Any info?  Any guesses?
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34) From: dewardh
David:
<Snip>
blow dryer?
Heat . . . about 1850 watts . . . temperature . . . testing my wife's 1875 watt 
(rated) dryer I found "hot zones" in the airflow directly at the exhaust as 
high as 300F+, but in the "blended" airstream 5-6 inches away it was more like 
160-170F, which probably more accurately reflects the average exhaust air 
temperature.  Cutting the airflow would increase the air temperature in 
proportion to the flow reduction, up to the point that the heater burned out or 
the housing melted or some "safety" device shut it off (I didn't try, I just 
bought her this one last year ).  My "shop" heat guns (of comparable 
wattage) have a substantially lower airflow, and are all metal . . . maybe 
later tonight or tomorrow I'll see what they do . . .
Deward
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35) From: dewardh
David:
More numbers . . .
With a "Kumas Stripper" (rated 12A at 120V, but running probably closer to 
110V) of unremembered provenance I was able to see air a couple inches from the 
exhaust at close to 500F, though mostly it seemed a bit cooler.  With a 
"Chicago Electric" (Harbor Freight #35776, rated "1500 Watts") I measured air 
at 650F (at least in some spots) in the same circumstance (far short, though, 
of the rated "1000F").  In both cases the heating element was visible, glowing 
toward the dull orange, which was not the case with the hair dryer, on which 
the notably longer and larger coil did not glow at all.  Neither "heat gun" 
moved anywhere near as much air as the hair dryer.  I suspect that more stable 
(and more accurate) readings would be had (with the "heat guns" anyway) by 
blowing into a length of inch or inch and a half tube and measuring the more 
fully blended air ten or twelve inches "downstream", and that would make air 
volume/velocity more easily measured, too, but I don't have an air flow meter 
handy, and it would take more hours than I want to spend jerry rigging one just 
for this test.
Of the two "heat guns" the "Chicago Electric" unit seems the better built (or 
the more sturdy, anyway, its almost twice as heavy) but I doubt that its fan is 
strong enough to loft any beans (in something like the Sivetz "heat gun" 
roaster) without the air temperature rising too high.  There might be some way 
to modify it, though, perhaps adding an additional fan.  The lighter (an 
advantage if you're on a ladder stripping trim ) Kumas unit seems to move 
more air, and might work to roast as is with some sort of roast chamber/chimney 
to hold the beans.
Deward
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36) From: Dan Bollinger
Hair Dryers are kept cool so they won't ignite hair.  Hot Air Guns come in
two temperatures, usually, 500 and 750.   Sivetz and others use them for
sampling roasters and they will agitate a small amount of beans.  Hot Air
Blowers have a slower air speed and won't agitate beans, but will roast
them.    Graingers sells the replacement heating elements.  Dan

37) From: Tom Gramila
On Sat, 30 Nov 2002, David Westebbe wrote:
<Snip>
Since deward has already given some good specific examples, I'll try 
answer the question in general terms.
If the heater is 1850 wats, you should expect to get close to that much
heat when plugged in.  (You can vary this by changing the supply voltage,
as some in the list do by using a variac.)
To figure out what temperature you will get is a complicated question.  
What you are doing is applying a fixed amount of heat to an unspecified
system and trying to determine the temperature rise.  Essentially what you
need to know is the volume (or mass) of air that absorbs this amount of
heat, and its heat capacity.
Temperature increase = heater power / (air mass flow rate)*(air heat capacity)
Knowing this is a bit harder than it may appear, since the air flow can be
influenced by lots of things, apart from the details of the fan in the
unit.  If you want a rough idea of the temperature, these variables dont
matter much, but I would expect that if you are trying to roast,
repeatability would be an issue.  Air flow would be affected by the
ambient temperature, the humidity, and, importantly, anything that
physically obstructs the flow field (like vents, or coffee beans!).  The
heat capacity is also influenced quite a bit by the humidity.
So the temperature of the air is tricky to determine, but the amount of
heat carried by the air is not.  Assuming that the heat gun is well
designed, the air carries away close to 1850 watts of heat -- regardless
of its temperature.  This is because the amount of heat that you geneerate 
has to "go" soemwhere, the gun is designed so that almost all of it goes 
into the air.  The temperatures of the heater element and of the air 
are forced to "conspire" to get this right....
Now a few specifics.  It is possible to get as high as 1000 F from an 1800
watt heater. The heat guns that I prefer for the lab are made by Master
appliance:http://www.masterappliance.com/There is lots of good info in there.  I'm pretty sure that one of their
guns is used in the Sivetz roaster. Their products are sold by grainger,
including replacement heater elements, which are pretty inexpensive.  
(the guns are of order $100).  Depending on the model, air temperatures at
the nozzle exit run from about 500 to 100 F.  They even have units which
temperature regulate the exit air temperature (vt-750c). the master
appliance pages include specifics on heater current (which can give you
heater power), and air flow in CFM.
I like to think of my popcorn roaster as a heat gun with a coffee chamber 
attached......
Tom G.
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38) From: David Westebbe
<Snip>
So that is just about perfect for roasting coffee.  With a few in parallel,
in order to supply more btu's, a large batch could be done in a reasonable
amount of time, no?
 With a
<Snip>
So that one would allow for a MUCH stronger fan, or cooler ambient temps, I
would imagine.
What seems to be the physical differences between the two?  Do the heating
coils look to be the same gauge?  Different lengths?
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39) From: Dan Bollinger
<Snip>
parallel,
<Snip>
From the description, it sounds like this stripper is the same as a hot air
gun.  If heat loss is reduced, then the roast size can increase.  There is
no reason you can't roast 1 pound using a 110V/20A circuit, but probably not
using a fluid-bed roaster which pumps heat away at a huge rate.   Dan
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40) From: Simpson
Exactly. Unrecirculated hot-air roasters are as inefficient as they can be,
but they are easy for us to build. And most of us are constrained by 110v,
20a. That's why most air roasters have similar and small roasting
capacity... the Zach and Danni's is a bit larger capacity but they have
added mechanical agitation.
I've said it for awhile... a gas fired air roaster using 110v for blower
and gas for heat is the way to go if you aren't going to recirculate.
Or you can go the drum route which the hottop made pretty attractive. Has
anyone used a sealed box with some 500w halogen lamps as a drum roasting
enclosure?
Ted
*********** REPLY SEPARATOR  ***********
On 12/1/2002 at 10:37 AM Dan Bollinger wrote:
snip
<Snip>
<Snip>
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41) From: dewardh
Dan:
<Snip>
Both the "hot air guns" have "hi/lo" settings . . . the HF item "claims" 600F 
and 1000F.  A quick search on "Kumas" suggests that they claim even higher.   I 
tested the "hi" setting on both.
Sivetz and others use them for sampling roasters and they will agitate a small 
amount of beans.
I presumed that anyone interested would have already seen the Sivetz roaster . 
.. .
<Snip>
roast them.
Some may, some may not . . . the HF unit would scorch the beans, due to its 
high air temperature (which would only get higher if airflow was restricted by 
beans).  Of the three the hair dryer would seem to have the most promise as a 
"roaster", since it has the most powerful fan (and the most "headroom" on its 
normally cool-operating heating element).  Airflow would be reduced by the bean 
mass, and that could bring the air temperature up enough to roast, without 
burning out the heater.  The "problem" is that the plastic housing is clearly 
not designed to support the higher temperature, and would probably fail, so one 
would have to "gut" the unit and mount the parts in some other enclosure.  Both 
the "hot air guns" would benefit from a suplemental fan.  Still, any one of 
them might be an easy place to start on a home-brew home roaster . . . the HF 
"air gun" typically sells for under $20, and I didn't pay much more for the 
hair dryer.  But it makes more sense to just get a popper, or a purpose built 
roaster . . .
<Snip>
For what ? ? ? The three units I examined all have different (substantially 
different, not easily interchangeable) coils and coil support assemblies . . .
Deward
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42) From: dewardh
Dan:
<Snip>
probably not
using a fluid-bed roaster which pumps heat away at a huge rate.
A fluid-bed roaster "pumps heat away at a huge rate" only if you don't 
re-circulate the air . . . that's a design choice, not a characteristic of 
fluidized beds.  Agitating the beans and heating the beans are separate (or 
separable) issues . . . one can agitate with a drum, or some other mechanical 
stirring method, or with air, as in "fluidized bed".  In all cases (except, 
perhaps, for "stovetop" poppers loaded only one bean layer deep) most of the 
heat enters the beans from the surrounding hot air, not from mechanical contact 
with the agitator (drum or whatever).  A solid drum, with heat applied only to 
the drum exterior, maximizes "contact" heating but still most of the beans are 
not in contact with the drum most of the time but rather with the hot air 
inside the drum.  Perforated drums or drums with "assisted convection" are just 
air roasters with mechanical agitation.
A "fluidized" design puts more constraints on airflow, making "design" more 
complicated, but can be mechanically simpler and has all the parts in place for 
rapid cooling.  If one is willing to "waste" excess heat it can be smaller as 
well . . . all of which probably accounts for why most "home roasters" are 
fluidized bed designs.
Deward
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43) From: Tom Gramila
<Snip>
	Grainger's replacement heater units are for Master Appliance heat 
guns.   Lots of data at: http://www.masterappliance.com/		Tom G.
<Snip>
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44) From: Tom Gramila
On Sun, 1 Dec 2002, David Westebbe wrote:
<Snip>
	I think that part of the problem with using heat guns to roast
coffee is that you still need to design a roast chamber that can support a
fluidized bed.  Just geting alot of heat in isnt enough, you need to have
the flow designed properly for mixing and thermal contact. You want the
air to move fast enough to "float" the beans, but not so fast that much of
the heat ends up dumping outside the roast chamber.
	Popcorn poppers have already done this, to varying degrees of
success.  I think that the bed design is part of why some recommend the
"flow in from the side" chamber approach.  The Sivitz giant commercial
roaster does air roasting efficiently, I believe, because it has really
high airflow, but recirculates the air so less of the applied heat is
"wasted".
Tom G.
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45) From: Dan Bollinger
<Snip>
will
<Snip>
I tested the Master Appliance Heat Blower and it won't fluidize and amount
of beans under any condition.  It just doesn't generate the static pressure
required.
<Snip>
(substantially
<Snip>
.. .
<Snip>
Check www.graingers.com catalog for the replacement heater specs.  Dan
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46) From: Ed Needham
I think a heat gun, pointed downward into a stainless bowl, so as to make the
beans agitate in a circular pattern, would be a great, cheap roaster.  No
fluid bed needed.  If I had a heat gun and a stand to hold it, I would try it
for sure.
Ed Needhamhttp://www.homeroaster.comed
****************************************
**********************************************

47) From: Tom Gramila
It may be just semantics, but if you are agitating the beans into a 
circular pattern, you have made a fluidized bed.  Of course this may be a 
very clever way to make one.....
I'd love to hear if someone tries this out.
 Tom G.
On Sun, 1 Dec 2002, Ed Needham 
wrote:
<Snip>
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48) From: Dan Bollinger
Tom, A fluidized bed is one where the mass is supported by a flow of air.
Dan

49) From: Ed Needham
Does 'fluidized' mean that air agitates the beans, or does it mean that air
lifts the beans on a fluid bed?  I've never been sure of the definition.
Maybe what I need to do is take the term out of my idea all together and say
'Use the air from the heat gun to agitate the beans sufficiently to get
constant motion of all beans'.
Ed Needhamhttp://www.homeroaster.comed
****************************************
**********************************************

50) From: Tom Gramila
Dan,
	Which model master appliance did you try?  some of their heat guns
have as little as 5cfm (of course this is rated with no obstructions like
coffee beans...).  But they have a unit that claims to push 47 CFM at 2200
FPM.  Thats alot of air.  Its name is a Masterflow heat blower, which is
very similar to the name you mention.  I would have guessed that this
puppy could make coffee beans dance!  -- And would love to know if thats 
not true......
Tom G.
On Sun, 1 Dec 
2002, Dan Bollinger wrote:
<Snip>
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51) From: dewardh
Dan:
<Snip>
Oh?
How, then, would you describe what happens in a Caffe Rosto . . . where the 
bean mass is agitated ("fluidized" ?) by air, but not "supported" by air ? ? ?
Deward
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52) From: dewardh
Tom:
<Snip>
coffee is that you still need to design a roast chamber that can support a
fluidized bed.  Just geting alot of heat in isnt enough, you need to have
the flow designed properly for mixing and thermal contact. You want the
air to move fast enough to "float" the beans, but not so fast that much of
the heat ends up dumping outside the roast chamber.
<Snip>
success.  I think that the bed design is part of why some recommend the
"flow in from the side" chamber approach.
All of which (and more ) is why I find the Caffe Rosto almost ideal as a 
"roaster test bed" . . . it has the "side flow" chamber, making airflow less 
critical, and it already re-circulates some "exhaust" air, so the flow 
recirculation "plumbing" is already there.  It takes only a minor modification 
to gain complete control of the re-circulation/pass-through ratio.
And you can always re-set it to "stock" and roast coffee  . . .
Deward
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53) From: Simpson
And the bowl. Don't forget the bowl. Oh! And the coffee... You'll need
coffee...
8^)
Ted
*********** REPLY SEPARATOR  ***********
On 12/1/2002 at 12:47 PM Ed Needham wrote:
<Snip>
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54) From: Simpson
I think just pushing some beans about in an airstream while they are
resting on a steel plate isn't a fluid bed roaster at all. It's a "pushing
some beans about in an airstream while they are resting on a steel plate"
roaster.
A fluid bed refers, I believe, a medium which completely supports and
surrounds the material to be handled/heated/cooled whatever. A Sivetz
roaster is a fluid bed. OTOH, the roller-roaster isn't, it's just using a
hot air stream to move some beans about. Doesn't mean it doesn't work
great, its just not a 'fluid bed'.
Ted
*********** REPLY SEPARATOR  ***********
On 12/1/2002 at 12:59 PM Tom Gramila wrote:
<Snip>
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55) From: AlChemist John
Sometime around 08:04 12/1/02, Simpson typed:
<Snip>
And here I was designing for 15a.  I just checked the circuit I would roast 
on and it is 20 amps.  Yeah, 25% (or 33%) more power to play 
with.  That  is really useful.  I was at 14.6 amps.  A little close for my 
comfort.
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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56) From: Tom Gramila
On Sun, 1 Dec 2002, Simpson wrote:
<Snip>
Maybe I have misunderstood the term.  My understanding for fluidized bed
was that it meant flow happenned, not necessarily that floating was
required.  But physicists (whose brains I picked to get this impression)  
often have very broad definitions for some things ...
Tom
<Snip>
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57) From: Dan Bollinger
Tom,  Yes, that's the one I have, the AH-501, it's 500.   I tried it and it
barely makes beans dance, let alone fly.  It's not the cfm or velocity, but
the static pressure.  Simply put, the static pressure must exceed the bean's
gravity.  I am going to use it for hot air roasting, but not a fluidized bed
roaster.  Dan
<Snip>
amount
<Snip>
pressure
<Snip>
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58) From: Dan Bollinger
<Snip>
the
<Snip>
? ?
<Snip>
Deward,  From what I know, I would call the CR a hot-air roaster, but not a
fluidized bed, hot-air roaster.   Dan
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59) From: Dan Bollinger
<Snip>
Tom,  Physicists probably won't know much about it.  Fluid Beds are used in
industry and it a piece of processing equipment. This quote was taken from a
fluidized bed mfgr. website: "An fluid bed sends a powerful stream of air UP
THROUGH your particulate material, SUSPENDING and circulating the particles
like a boiling fluid."  Emphasis, mine.  Using air to move beans around in a
wok is more like 'pneumatic stirring'.  ;)
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60) From: dewardh
Dan:
From what I know, I would call the CR a hot-air roaster, but not a
fluidized bed, hot-air roaster.
OK . . . but . . . then the Hearthware is also "hot air" roaster (the air 
stream only impinges on a small part of the bean mass at any given time), and 
so, realistically, is the Alpenrost (and probably the Hot Top).  So are we left 
only with the clumsy "air stirred hot air roaster" vs. "mechanically stirred 
hot air roaster"?  And if the swirling bean mass in the Rosto is not to be 
called "fluidized" what, again, *is* the "proper" term for a bean mass swirling 
(flowing) like a liquid but not "suspended" on air ? ? ?
Deward
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61) From: Dan Bollinger
<Snip>
Not so fast, bucko!  The HWs are true fluid beds. Many fluid beds have a
'return' path so the granules circulate down to the bottom and then back up,
improving processing.  Pharmaceutical tablet making used fluid beds that
circulate, just like the HWs.  The only processing I know of that uses a
totally fluid bed is powder coating.  It is not the amount that is supported
by the air stream, but whether or not the granules are supported at all.
<Snip>
Pan Roasting.  ;)
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62) From: Mike McGinness
From: "Dan Bollinger" 
<Snip>
The back & forth semantics are interesting. I call it "Variable Variac
Rockin' Rosto Roasting"...:-)
MM;-)
Now back to Christmas lights!
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63) From: Tom Gramila
Wow.  I guess this is why the sivetz "sample roaster" with a whimpier heat
gun claims only to do a 30 gram batch!
  Tom G.
  PS -- thanks for the info on  fluidized  beds.
On Sun, 1 Dec 2002, Dan Bollinger wrote:
<Snip>
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64) From: dewardh
Dan:
<Snip>
'return' path so the granules circulate down to the bottom and then back up
You seem to be assuming that a mass of particles is only "fluidized" if it is 
lifted against gravity by an air stream.  Such thinking is "directionally 
challenged" . . . and ignores the fact that snow and ice in an avalanche is 
"fluidized" (as is the descending bean mass in a Hearthware, even though it is 
not, while descending, being "supported" by air).  One look at the swirling 
bean mass in a Caffe Rosto should be enough to convince *anyone* that it is 
"fluidized" . . . (until you come up with an alternate word, of course . . . 
).
Deward
Ps. if you manage to convince anyone that the Rosto is a "Pan Roaster" do let 
us know  . . .
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65) From: Dan Bollinger
That works for me, and much more poetic too boot!

66) From: Dan Bollinger
<Snip>
up
<Snip>
is
<Snip>
Yes, see below...
<Snip>
is
<Snip>
I suppose you could say it is fluidized.  But that's neither here, nor
there...
(as is the descending bean mass in a Hearthware, even though it is
<Snip>
swirling
<Snip>
is
<Snip>
I suppose you could say fluidized.  But that's neither here, nor there...
The term we are discussing is Fluidized Bed.  B-E-D.  There is no bed in an
avalanche.  The mfgrs. definition I posted earlier said air comes from below
(through the porous bed) and suspends the granules.  If the CR doesn't
support some of the beans by an air stream YOU will have to come up with an
alternate word.  :)  Dan
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67) From: dewardh
Dan:
<Snip>
Then I shall . . .
<Snip>
By all means yes . . . let's go with what the manufacturer says . . .
Caffe Rosto uses a "fluid air bed" roasting system which allows constant 
rotation of the coffee beans as it roasts, and when it cools.http://www.brightway.com/features.htmlGuess that settles it then . . . 
Deward
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68) From: Dan Bollinger
<Snip>
What ever you say, Deward.     Dan
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69) From: Ed Needham
Everything is soooo complicated! 
Ed

70) From: David Westebbe
<Snip>
Can we simplify this, and just consider the temperature of the nichrome in
still air?  It was mentioned that the wire glowed in certain applications,
while it did not in a hair dryer.  I'm wondering if that is some inherent
quality of the hairdryer setup, or a mere artifact of the increased airflow
in the dryer.
My real underlying goal is to find out whether I can get nichrome wire from
a thrift shop hairdryer to put in parallel with what is already in my
popper, in order to increase the heat output.
If that wire will never get hot enough, then it would be a waste of time.
But if it were to heat up to a known temperature with a known amount of
juice, then it would be a cheap source of wire to experiment with.
Maybe the answer is to buy a hairdryer, stall the fan, and see what happens?
If the wire  glows cherry red, then likely it is hot enough.
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71) From: Les & Becky
I wasn't going to get into this discussion, but I am finding it to be
interesting.  I have two heat guns and a stainless bowl, so tomarrow, I may
just give this a try!  All this discussion just fuels the thought that
someone needs to make a good roaster for a good price!
Les
Popcorn Popper Roaster extraordinaire!  Who likes to dabble with roasting
over coals!

72) From: Tom Gramila
On Mon, 2 Dec 2002, David Westebbe wrote:
<Snip>
	^
	I think that your misconcepton is here.  What matters is not the 
temperature that the wire gets to, but how much heat the wire generates.
	Consider two identical wires, driven by the same power.  one is in 
a stream of rapidly moving air, and in the other the air moves at a tenth 
the speed.  The former wire will not get nearly as hot as the latter, BUT
they will both deliver the same amount of heat to their respective 
airflows.  
	
	The temperature of the wire is sort of a free variable here.  A 
step by step view of the process might be:
	
	* You turn on the power
	* The wire, initially cold, heats up
	* When the wire reaches a temperature hot enough that it can 
	reach a balance between the amount of heat that is coming in,
	and the amount of heat that it sends out, its temperature stops 
	going up.
	If you are trying to add heat generating capability to your
popper, adding any heater wire (that does not self destruct) in parallel
with the original heater will increase the amount of heat delivered to the
air.  You will need to worry more, I would suspect, about the current
limitations on you electrical circuit.  These can be determined through 
standard electrical approaches: V = I*R, and P = V**2/R = I**2*R = V*I
	Do you have an idea if you need a little more heat, or alot?? I
typically run my poppery II with a voltage greater than 120, which also
increases its heating power, by using a variac.  Variacs tend to be a
little pricey, but I have been able to roast outdoors in 26 degree
weather, and I have not melted its heating element, at least not yet!!
			Tom G.
<Snip>
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73) From: John Abbott
Make sure you wear goggles :O)

74) From: David Westebbe
<Snip>
But aren't both factors important?  If we were to have a mile of nicrome,
which we supplied with voltage and current sufficient to make it heat up to
100F, we would have massive amounts of heat.  But we would not attain
sufficient temperatures to roast coffee.
By the same token, if we had a little tiny piece of nicrome, and finagled
the electricity so it were to heat up to 500F, we would have sufficient
temperature, but we could only roast one bean at a time, due to the low heat
output.
<Snip>
Well, "need" is a pretty harsh test.  If the truth be told, I don't need
anymore heat.  However, I'd love to have the ability to do larger batches,
and I'd love to have the ability to crank the air temperature up to 525 or
so to play with extreme profiles.
I
<Snip>
I've done some winter roasting - not much.  My popcorn pumper will roast 3/4
cup nicely, but it seems to take a long time.
I'm looking for headroom, and power.
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75) From: Tom Gramila
On Mon, 2 Dec 2002, David Westebbe wrote:
<Snip>
The two factors are not independent.  The temperature of the wire is
dependent on how much heat you put into it, scaled by its thermal coupling
to its surroundings.
<Snip>
			Yes
<Snip>
What is important for roasting coffee is the temperature of the AIR and 
not the temperature of the wire, since the air is in thermal contact with 
the coffee, but the wire is not.  
Lets make this example work for coffee, without changing the amount of
heat we generate, ie. trying to keep the voltage and current the same:  
This mile of wire is going to be inside a pipe, with airflow along the
tube.  Now all the heat eventually goes into the air, and makes its
temperature well high enough to roast coffee.  (as long as we dont melt
something!)  For this same amount of heat, the temperature of the wire
will no longer be 100F, because it is cooled less effectively.
 > 
<Snip>
	^sufficient in the wire, but likely not in the air  
<Snip>
Lets go back to my prior claim.  Any nicrome wire that you add in parallel
which is heated, will increase the temperature of your air.    The wires
temperature will be ABOVE the temperature that the air would have been had 
it not been present, as long as it is being heated.  
One way you could try to raise the heater output would be to shorten the
heater wire that you already have.  If it doesnt self destruct from
overheating, it will give you more heat.  Of course, if it does self
destruct, you will likely have to get a new popper.....
Good luck, and send word of what you end up using!
Tom G.
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76) From: dewardh
David:
<Snip>
while it did not in a hair dryer.  I'm wondering if that is some inherent
quality of the hairdryer setup, or a mere artifact of the increased airflow
in the dryer.
The increased airflow is undoubtedly part of it, but probably the major 
contributor is that the hair dryer coil is both longer and wound to a larger 
diameter (both the coil itself, and the "coil of coil"), so it is losing heat 
to the air over a much larger surface.  Also no doubt, though, that if airflow 
across it were stopped it would "reach a glow" quite quickly (absent some 
thermal interlock to disconnect it) . . . 1875 Watts is a lot of heat in a 
(relatively) small bit of wire.
<Snip>
a thrift shop hairdryer to put in parallel with what is already in my
popper, in order to increase the heat output.
Not unless you used the whole coil (and had a supply circuit of sufficient 
capacity to feed it and the existing popper heater without blowing a breaker). 
 If you used less than the whole coil it would dissipate even more . . . (see 
previous discussion in this thread).
<Snip>
How times change . . . it used to be (when I was a lad ) that you could get 
various gauges of nichrome wire, straight or coiled, at the local "appliance 
repair shop" at very reasonable prices.  It was speced by resistance (ohms per 
foot) and you just decided the wattage you wanted, calculated the appropriate 
resistance, and then picked a wire (or coil) that gave the physical length you 
wanted to fit your burned out toaster, or hot plate, or hair dryer, or 
whatever.  At least the straight wire must still be available somewhere . . . 
I've seen several discussions of homemade "hot wire" cutters for shaping foam 
wing cores in "Sport Aviation" . . .
<Snip>
If the wire  glows cherry red, then likely it is hot enough.
Not to worry, it will (if you bypass the "safety") . . . first red, then 
orange, then yellow, then white, then "poof" . . . .
Deward
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77) From: Prabhakar Ragde
<Snip>
This discussion is starting to remind me of the "roasting coffee on a
jet plane" post -- a classic, and one that Tom should have on his
website, except that it would probably scare people away since the
Internet is known to be the world's biggest irony-free zone. 
--PR, counting the days until his first in-person visit to SM, and
  thankful that they don't sell the Mazzer Mini yet, because the old
  Rancilio Jacky still has some life left in it...
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78) From: David Westebbe
<Snip>
Hmmm.....That's an idea.  So for any given airflow, keeping all other
factors the same, if I shorten the wire, will the temperature of the wire
(and therefore the temperature of the air) increase?
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79) From: AlChemist John
Sometime around 11:55 12/2/02, dewardh typed:
<Snip>
I have found some coiled nichrome wire in three different gauges and 
lengths.  I think two of the three were 400 W and 600 W.  I figure I am 
going to be ordering some in the next week of so.  I will order extra and 
pass it along for cost plus shipping.  It is in the $1-2 per coil 
range.  If anyone is interested, let me know and I will list your choice of 
wire here.
--
John Nanci 
AlChemist at large
Roasting and Blending by Gestalt
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80) From: Tom Gramila
On Tue, 3 Dec 2002, David Westebbe wrote:
<Snip>
Thats right.  Ignoring other influences (like airflow changes resulting
from changes in temperature, blown fuses, etc) if you cut the reistor in
half, you will get twice the power, and a resultant rise in temperature.
I would probably start smaller, like a 10 or 20% reduction in length,
which is less likely to burn up on you...
Good luck!
	Tom G.
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81) From: David Westebbe
<Snip>
I would imagine that using a piece of copper wire to short the coil would
work just as well. Maybe I'll make up a heavy duty jumper with some small,
sturdy, heatproof clips and experiment with "short"ening the main heater
coil.
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82) From: Ken Mary
<Snip>
It will work for a *short* time then oxidation will ruin the connection. I
have already tried this. I did have better success using 1/8 inch copper
tubing as a crimp-on connector for the ends of the nichrome wire. Fold the
nichrome back on itself to make a small "hairpin" so it will not twist out
of the tubing. I suggest that you cut off a small section of nichrome if you
want to increase the power consumption. I think this has already been
suggested, but do this in small increments. If you assume 120 volts, 11 ohms
heater resistance is 1300 watts, 10 is 1440, and 9 is 1600. Do not go beyond
1600 watts unless you have plenty of airflow to protect the heater coil.
--
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83) From: David Westebbe
<Snip>
These sound like excellent suggestions.  Thanks, Ken.
I've got an old popper that I don't care about.  Maybe I'll experiment using
it.  It never really got hot enough before.  Maybe I can get it to work at
sub-zero ambient with a little work?
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