HomeRoast Digest


Topic: FR mod for heat control (2 msgs / 200 lines)
1) From: Kevin DuPre
Recently this past week I did a test to determine if
it was worth modifying my Fresh Roast to be able to
stall the roast at a given temperature and thus
lengthen the roast.  My test involved using the timer
to alternate between heat and cool at a given
temperature to stall the built-in or "stock" roast
profile and thus lengthen it.  The resultant coffee
was so different from that roasted with the stock
profile that I decided to do the modification.
Contrary to what I read on a previous message there is
no "slider" in my Fresh Roast to do this. In fact this
thing is so simple inside there isn't much needed to
accomplish what I needed to do.
As it turns out the heater module has 3 wires coming
out of it - a red wire, a black wire, and a white wire
which I determined must be a tapped wire heating
element with one part being the actual heater and the
other part being a dropping resistor to lower the
voltage to the fan motor to 12 volts.
The fan motor, a 12 volt DC motor has a full wave
bridge rectifier "around it" with the inputs to the
bridge coming from AC neutral and the resistor side of
the heater module, and the outputs of the bridge being
soldered directly to the terminals of the motor.
My modification involves putting a relay with 10 amp
switching contacts in series with the white ac neutral
wire going to the heater module.  I used the normally
closed contact of the relay so that not controlling
the relay would give me the stock profile that the
unit came with.  My relay's coil actuates with 12
volts DC and I piggybacked off the DC fan motor
voltage, put a 1/4" phone jack in series with this to
control the relay with a musical keyboard sustain
footswitch.
The relay was constrained to the base by passing a
tie-wrap through the vent holes in the base and up and
over the relay to hold it in place.  A 3/8" hole was
drilled in the base to accommodate the phone jack.
While alternating between heat and cool with the timer
dial works, using the footswitch to actuate the relay
and interrupt the current to the heater actually
allows tighter control over the temperature.  In
addition, once I add a thermocouple and a control
circuit I can fully automate this if I was so
inclined.
With this modification I was able to recently get a
Pacific-Northwest style dark roast with the developed
body and suppressed acidity characteristic of that
roast. My profile basically involves stalling the
roast at a given temperature for a given time to delay
the onset of 1st crack, followed by stalling at a
second temperature to delay 2nd crack and allow the
darkening to take place over a longer time than the
stock FR allows.
The actual profile used will be posted in a subsequent
e-mail.
As soon as I can figure out how to send an image with
this, I'll try to get a schematic of this modification
online.
Regards,
Kevin
=====
--
Kevin DuPre
obxwindsurfhttp://profiles.yahoo.com/obxwindsurf"The real voyage of discovery consists not in seeking new landscapes but in having new eyes -- Marcel Proust"
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2) From: Steve McKinney
I think the missing 'slider' was a feature of an older model of FR.  My
brother has an old FR with a 'Roast Control' slider, which is missing
from my newer FR+.
I for one would be very interested in seeing an image of your mod.  Your
description is excellent but I am not really electronically inclined
enough to feel confident hacking into my FR+ without a comforting
picture.  I have been playing around with the roast profile on my FR+
using the timer and have had some success but it sure is a bit of a
pain!
Steve


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