HomeRoast Digest


Topic: nichrome wire (8 msgs / 314 lines)
1) From: Peter Zulkowski
Ben can correct me on this, but I seem to remember that he had problems 
with Nichrome elements burning out quickly on a P1 when connecting them 
to a PID.
It was reason enough that I was happy to find the thicker, electric oven 
type heaters in the Turbo Oven I use with my Pretty Good Roaster (PGR).
That said, I am now wondering how responsive these heating elements 
really need to be. Dan says he does well with Nichrome wire, and it is 
very responsive, but I figure that since the idea is to ramp to a 
certain point, hold it for a while, and then ramp some more, possible in 
several stages, that it doesn't really matter how responsive the element 
is to cooling.
Heating response time will get over run by the mass of the beans anyway, 
it seems. I know that if I try to roast a Kg of beans it takes quite a 
bit longer than if I just want to do enough for an espresso shot.
I did a lot of roasts with hot air poppers, and my main concern with 
them was some chaff getting to the element and causing a hot spot, 
shortening the life. That never happened to me, and I just retired my 
poppers. They did not die (other than I had a hard time toward the end 
avoiding breaking glass chimneys. They either fell over or I dropped 
something on them.)
Anyway, the PGR sees a lot of chaff in its heating element, because it 
all recirculates around and around. A lot of it burns against the 
heater, and it continues to work fine.
I did bring a spare bread machine and a spare Galloping Gourmet, 
camping. You just never know. I bet I have roasted a hundred pounds with 
it (just a guess, could be more) and it still does fine, but I DO love 
spares! Spare bread machines cost over 30 bucks here in MA. Only five in 
LHC.
Stainless Steel mixing bowls just last forever.
PeterZ
Catching up on email, camping, here in MA.

2) From: Dan Bollinger
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Concerning longevity.  Nichrome oxides. When it does, it loses some metal.
As it loses metal the diameter of the wire reduces. As it reduces resistance
goes up until such time that it fails. The higher the temperature it is
operating at the faster the oxidation rate. And, the more times the wire
cycles between hot to cool (delta T) the sooner it fails.
Controlling the heater with a on-off percentage cycle timer cycling the
heater for a portion of a 10 second cycle the heater will not last very
long, a month or two.  (The same is true for a PID set to cycle 5 seconds or
greater)
Controlling the heater with a PID set at 1 second helps a great deal since
the heater is cycling so fast that it doesn't have time to heat up very much
or cool down very much. The wire will last about 6-8 months.
Controlling the heater with a SCR/TRIAC, or other continuously variable
device like a VARIAC, will give you the greatest life from a bare nichrome
heater. About a year or so.
Jeffrey and Doug have done some cupping that says the latter also produces
better tasting coffee. I have no reason to disagree with them and will
eventually run my heater with a TRIAC.
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Yes, I'm convinced, after a year of use, that bare, coiled nichrome is the
way to go if you want to profile roast in a small roaster.  Your assessment
is incorrect.  First, I find no advantage to programming a soak period into
a PIDs ramp profile. I don't use that feature.  But that's a moot point.
Even during a soak period, where you are maintaining a constant temperature
in the roaster, the heating element is still cycling on and off for a
portion of a second or more, depending on how you are controlling it. This
Delta T leads to nichrome failure. However, like I said before, using a
continuously variable controller is the way to go and all but eliminates the
cost of replacing heaters.
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Did you know?  These are nichrome heaters, too.  They are called tubular
heaters. What they do is encase the nichrome in a mineral filled steel tube.
This keeps oxygen away from the heater and lifespan goes up dramatically.
The downside is a horrible heater response time. The heater lag is so great
that a controller has great difficulty following a ramp. However, it is
possible to use them to maintain a steady state temperature in an
environment with few external factors effecting the oven.  Is use fuzzy
logic PIDs to control a bank of 15KW ovens at work using tubular heaters. We
have no problems bringing the ovens up to temp, without overshoot, and
maintaining plus or minus one degree.
When I first made my electric sample roaster I used a tubular heater. It
cost $100.  I did not like its response time, even when operated by the
percentage timer in a manual mode.  Sure, you can jury rig an element made
for another appliance, but still, they aren't cheap. After it burned out, I
replaced it with a $1.35 piece of coiled nichrome.  A person can do the math
in their head to see that nichrome is the best value.  When you add the
responsivity factor bare, coiled nichrome is the clear leader.
Dan

3) From: Peter Zulkowski
    Hi Dan,
            Thank you for your response, and your input on NiChrome
            wire. You have enlightened me on the subject. I did not know
            that that I was using is tubular nichrome. So far I have not
            seen that this slower response is significant in the PGR.
            When I adapt it and make it a CCR the quicker response may
            be more important. Right now I am happy that the tubular
            version seems safe in the chaff recirculation  environment
            it exists in.
            The  PGR has no controls other than the thermostat switch
            which I have found to be useless to determine the actual
            temperature.
            It is just easier to use it, but I monitor the TC and vary
            the ramp time by adjusting said thermostat switch. When I
            want the element off, I rotate the know until the indicator
            light goes out, rotating the other way makes it go on, and
            the heat goes on.
            When I get to 320 F, I turn the heater off and the roast
            'coasts' up another seven or ten degrees. This is the slow
            response of the element I guess.
            Not so between first and second crack.
            If I cut the heater power towards the end of first, it will
            coast in several minutes, all the way to second. Heater
            response lag, and exothermic reaction I suppose. The better
            the roaster is insulated, the more you can see this.
            Right now, I have used the PGR enough that it is very
            predictable, and I can roast coffee to suit me and C (she).
            It would be nice to have *better* control.
            I would love to super insulate, add more heater, use a
            larger mixing bowl, and experimentally determine how much
            coffee  can be roasted with a 20 amp circuit, 110 V.
            Not with my current PGR though. It serves me well.
            Since I have all the parts, I will need to make a Super PGR,
            computer controlled, and maybe coiled NiChrome wire.
            I agree that cost is the issue. The Galloping Gourmet comes
            with a tubular heater built in. Other convection ovens have
            the coil wound heater. I have the GG, and it is the most
            powerful. So I chose it to use. I have lots of nichrome
            wire, recycled from other heaters, and that may be a next
            step, but so far I am too lazy to modify what is working
            well, for me.
             From what you said if I were going to buy this stuff new,
            the wire would be the way to go.
            The way to determine how fast a heater response time is
            needed would be to somehow evaluate how quickly the beans
            absorb the heat that is applied to them. With the air popper
            I found that I could generate 1000 degree F temperature,
            resulting in scorched beans and lots of divots, but the
            beans would not be cooked all the way though in some cases.
            The need to have time in temperature, but how fast do you
            need to accelerate this temperature increase?
            I do not know this, but I do know that I can and have
            applied too much temperature with an air  popper. With the
            PGR also methinks.
Dan Bollinger wrote:
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Some folks have been trying to let the roast set at certain temps for a 
bit. I have been delaying the temp rise by cutting power. This seems to 
make the coffee taste smoother.
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My cycle time is very slow. Almost a minute off. I  turn it off a few 
degrees before I want the temp to stop rising, and do not turn it on 
again until I see it level off and hold for a few seconds.
<Snip>
The slow response helps maintain temp also, while the power is off.
<Snip>
When doing small batches, less than 70 gr or so, it is easy to roast too 
quickly with my set up, it *is *more difficult to get a 13 minute roast. 
That is why the computer would help I am sure, but you may be correct 
and I may have to switch to wire even with that. Small batches are 
doable, just need to be cautious.
PeterZ
Just did 1.4 lb of Harrar with no problem, wonderful coffee, here in 
Gloucester, or anywhere.
<Snip>

4) From: Dan Bollinger
Peter, You can see the response time in this test I did. The electric
heaters are self-explanatory. You can see why I went with nichrome.
I added the gas data over the weekend. While gas responds very quickly, it
can never go to zero since you must keep the burner lit by turning it to LO.
Danhttp://www.claycritters.com/coffee/heater_response_time.htm<Snip>
since
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much
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nichrome
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produces
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assessment
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temperature
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unsvbscribes) go tohttp://sweetmarias.com/maillistinfo.html#personalsettings<Snip>

5) From:
Ahem- 
The humble toaster uses bare nichrome wire as the heating element, as
does the hair dryer. Also true of electric clothes dryers.
In electric stoves, the actual heating element is nichrome wire,
encased in compacted alumina, in an Inconel or similar protective
tube. Industrial  U-shaped elements with fins are made for heating air
flow in the curing ovens for screen printing. Coaxially in the center
is the nichrome wire.
Curing temperatures for the common screen printing inks is 325 degrees
F. You wouldn't want to get your hair or your clothes that hot.
The point is- if you can see the heater glowing, it's up around 1,000
degreesF. You can multiply the life of the nichrome heater element if
you can run it, say, 100 degrees cooler.
Suppose you wanted an absolute maximum air temperature of 450 degrees
F for a fluid bed roaster. You have that now, but your heater burns
out annually. That's not bad, but you could extend the Mean Time
Between Failures (MTBF) to at least 10 years if you made the heater
physically larger, and ran it at 750 degrees instead of 1000.
How so, you ask? You van get nichrome heater coils at appliance repair
shops, and they probably get them from Johnstone Supply. W. W.
Graingers probably has them too. Any shop that handles temperature
instrumentation (Omega Engineering, etc) either has this stuff or can
tell you where to call.
[ The downside is a horrible heater response time. The heater lag is so gre=
at
 that a controller has great difficulty following a ramp.]
If you're using a PID controller, it compensates for the hysteresis lags.
Cheers -RayO, aka Opa!
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ribes) go tohttp://sweetmarias.com/maillistinfo.html#personalsettings<Snip>
-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the
Wichita WurliTzer

6) From:
$100.00 for a tubular heater? They saw you coming!
On 7/5/05, raymanowen  wrote:
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reat
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scribes) go tohttp://sweetmarias.com/maillistinfo.html#personalsettings<Snip>
-- 
"When the theme hits the bass, I dance the Jig!" - -Virgil Fox at the
Wichita WurliTzer

7) From: Dan Bollinger
<Snip>
You haven't priced industrial heaters in awhile!  The heater was about $75,
I seem to recall, but the company has a $100 minimum order. What really
pissed me off was when it burned out after about 30 roasts.  I expected it
to have the life of a heater element in my oven.
Dan

8) From: Alchemist John
I have a number of tubular heaters that were shipped incorrectly to me at 
some point.  If someone wants some to play with, I will let a few go for 
cost (under $10 apiece) plus shipping.  I will look up wattage if there is 
an interest.
At 07:24 7/6/2005 -0500, you wrote:
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John Nanci
AlChemist at large
Zen Roasting , Blending & Espresso pulling by Gestalthttp://www.chocolatealchemy.com/


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