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3D Printer
Filament
Drying Chamber
This enclosure can store up to four 1kg reels of 3D printer filament, keeping them dry
and ready for use at any time. You don’t even need to remove them – the filament can
simply be fed to the printer through a small hole in its lid!
Part 1 by Phil Prosser
T
he ability to produce functional 3D
parts, either standalone or as part
of a larger project, is incredibly useful. Over the last few years, 3D printer
prices have fallen remarkably. You can
now find some amazingly-priced 3D
filament printers on the market.
The major Australian electronics
stores (Jaycar and Altronics) both stock
“Creality” products, which I think are
excellent. There are plenty of other
good alternatives available online.
My grandson, who wanted to buy
printed parts, drew me into this. I
pointed out that for the price of a
handful of ‘bought bits’, we could
buy our own 3D printer. So I did. I
quickly found that being able to manufacture complex 3D parts was incredibly handy.
Like most of these technical things,
once you start, there is an amazing
range of extras you might want or
need. One surprising accessory is a
filament dryer. It had not dawned on
me that plastic filament can absorb
moisture. However, PLA (polylactic
Photo 1: the surface of the black boat
is not smooth due to moisture in the
filament. The white filament was dry,
giving a much better result.
20
Silicon Chip
acid), probably the most common filament these days, is sufficiently hygroscopic that moisture can become a real
problem.
3D printers work by heating the
plastic filament to around 200°C (or
much hotter for materials like ABS)
and extruding it through a small nozzle, typically 0.4mm in diameter.
The printer acts like an X-Y plotter
and deposits lines of melted filament
where required, in layers, thus building the part.
It is incredible to consider that a
large print may have the printer laying down material in this manner for
12-24 hours, all without error.
If that sounds too complicated to be
reliable, well, you need to get many
things right for the printer to work
well. However, when set up correctly,
reliable results can be achieved. I
would say that most electronics hobbyists would have the inclination, skill
and inquisitiveness to learn the tricks
and tips required to keep a 3D printer
running, but they certainly are not ‘set
and forget’.
When I first ran the printer, things
went swimmingly well. However, I
later realised that even a little moisture in the filament can cause problems when it is heated in the extruder.
The moisture boils into steam, which
pushes filament out of the extruder and
causes ‘blobs’ on the print.
Photo 1 tries to show the difference
between fresh new filament (white)
Australia's electronics magazine
and some that had been lying around
(black).
All the printer knows is that it has
driven the correct length of filament at
the right time, but the ‘blobs’ mean it
doesn’t end up exactly where it should
be. So surfaces can get ‘blobby’, and
you hear small popping noises during
printing.
While PLA certainly suffers from
these problems, other materials, such
as Nylon, also have a terrible reputation for being hygroscopic and hard
to print with.
While the printers themselves are
competitively priced, I was not really
into spending hundreds more on a
fancy filament dryer. Some people
use a food dehydrator, which, while
cheap, does not handle multiple reels
or allow you to feed straight from the
dryer to your printer.
I was convinced that I could easily
make something to do the job with a
handful of bits from the spares box,
a leftover laptop power supply and
maybe a microcontroller. We can even
customise the size and shape to suit
our workspace and needs. So, while
we provide a complete parts list here,
you can modify the design to reuse bits
you already have, saving a few bucks.
There does not seem to be a specific
‘right way’ to dry or, perhaps more
correctly, dehydrate filament. All
approaches use an elevated temperature and some form of timer. Some add
air circulation, while a few incorporate
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a mechanism to change the air in the
box periodically.
The idea of heating the filament in a
sealed enclosure is that when the air in
the enclosure gets hotter, it can hold a
lot more moisture, so relatively speaking, the air is dryer. In other words, the
relative humidity of the air in the box
reduces as it is heated.
Fig.1 shows that for a typical room
at 20°C and 40% relative humidity
(RH), there is about 6g of water per
kilogram of air. If the box is sealed,
there is always the same amount of
water in the box. So, at 42°C, we see
the relative humidity will be about
10%. Because the air is now quite dry
(for its temperature), it pulls moisture
from everything in the box.
PLA filament that has absorbed
moisture does not dry out quickly; drying times are typically 6-9 hours. By
keeping the dryer sealed and including some desiccant, such as silica gel,
in the enclosure, we can keep the filament dry and ready for use. If you will
not use the dry filament for a while,
it remains a good idea to seal it in a
vacuum bag.
and substantial protection circuitry.
The second part is making an enclosure for the filament. There are several
possible approaches, ranging from
very simple to quite complicated.
Choosing your approach to the container is probably the most critical
choice, as the controller is not that
complicated.
We built two enclosures. The first
was a custom one optimised for our
needs and just a little bit fancy – see
Photo 2 and the image above. The
second was an 18L plastic tub into
which we installed the controller and
heater (Photo 3). The latter proved to
be quick and simple to assemble and
quite effective. It must be said that it
looks a lot like a plastic tub, though.
We will provide an overview of how
to build the custom enclosure but will
not go into great detail. If you are not
confident in filling in the details yourself, stick to using the off-the-shelf
plastic tub.
Both enclosures use the exact same
controller, but we have arranged the
heating plates quite differently to suit
the differing enclosure shapes. In both
cases, we found that without adding
insulation to the enclosure walls, we
could achieve about 47°C inside with
50W of heating.
Adding a layer of Corflute to the
bottom and walls of the enclosures
increased the temperature at that
power level by well over 5°C, effectively reducing the amount of power
needed to keep the enclosure at a given
temperature.
The unit is powered by either a 24V
DC 4A plugpack or an 18-24V 3A+
DC laptop power supply. Is it just
me who has a growing collection of
these things, which seem to outlast
the laptops they powered? Either way,
it drives a resistive heater in the box
via a control board, much of which is
safety circuitry.
We put a couple of small bags of
silica gel in the box to absorb any
The design
This project has two distinct parts.
The first is a filament dryer controller
board. This is a standalone thermostat
controller board that could equally be
used to control an incubator or curing
oven for painted parts. The board is
essentially a thermostat with a timer
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Fig.1: water in the air plotted against temperature for a range of different
relative humidity (RH) values, from 10% to 90%. You can see how hotter air can
contain a lot more moisture for the same RH figure.
Australia's electronics magazine
October 2024 21
moisture released by the filament and
occasionally change the air in the box
to expel excess moisture. Cat litter
crystals are simply silica gel, so for
$10 at the local supermarket, we got
a huge bag of silica gel from which
we make our own drying sachets. We
just put it in paper envelopes to pop
in the dryer.
Our filament dryer hangs the reels
on a rod and allows you to draw the
filament straight from inside the dryer
box.
We decided to omit a fancy display,
which technically is not hard but adds
construction constraints and cost.
During development, we noted that
even with a fan circulating air in the
dryer, the temperature throughout the
box varied significantly. So, a temperature display may feel important, but it
would only be indicative. Leaving out
the display also avoids the need for a
humidity sensor.
This decision was hard but it keeps
things simple and cheap. If the box is
warm and you have fresh silica gel,
after a couple of cycles, your filament
will be as dry as it will get. Some really
cheap humidity sensors are available
online that you can pop in the box if
you want to monitor it.
Because we are making potentially
combustible materials hot, we have
taken a very conservative approach to
the design to ensure that it is as safe as
reasonably possible. Refer to the text
box on safety analysis for a discussion
of how key design drivers were arrived
at. If you are designing your own enclosure, you should consider the hazards
we list and satisfy yourself that your
approach mitigates all hazards.
The design presented here is mostly
about implementing the control and
safety systems identified in Table 1,
which mandate the following inclusions:
• A controller that maintains the
Dryer in a safe state until the user
deliberately starts a cycle.
• A thermostat, allowing the temperature to be set from room temperature to 50°C.
• A timer that allows a six- or ninehour drying period, then shuts the
heater down.
Table 1 – Hazard & Risk Assessment
Hazard
Initial Risk
Mitigation
Final risk
High
Implement a temperature control system.
Limit the maximum energy available so the
ultimate temperature without control is safe
(50W gives a maximum of around 60°C).
Low
Short circuit or critical
component failure
Low
Integrate thermal switches/fuses that disable
the system at a safe temperature. Include
a fuse in the design, to blow in case of a
catastrophic short.
Low
Excessive heating since the
control system does not
sense the real temperature
Moderate
Include a fan to circulate air throughout the
enclosure.
Low
Failure of fan results in loss
of thermal control
Low
Integrate a ‘fan operating’ sensor and shut the
heater down if the fan fails.
Low
Heating element contacts
personnel
Medium
Mount heating resistors inside a plenum
or behind sheet aluminium to minimise the
likelihood of contact with personnel.
Low
Personal
injury
User touches energised part
Medium
Operate the dryer from an isolated plugpack
with a low voltage output.
Low
Electric Shock
Long-term heating results in
auto-ignition of material
Low
A timer shuts the unit down after six or nine
hours
Low
Fire and
uncontrolled
energy
Enclosure operates
unexpectedly
Medium
The system starts in an idle state. Force the
user to press a start button to commence
drying.
Low
Inadvertent
operation
Software fails
Low
Critical controls (thermal- and energy-related)
are to be implemented in hardware.
Low
Inadvertent
operation
Heating element touching
combustible material
Medium
Limit the heating power such that the element
does not exceed 80°C. Mount the heating
element so it is not in permanent contact
with timber. Use polypropylene Corflute
for insulation, which has an autoignition
temperature of 288°C (flash point 260°C).
Low
Fire
Misuse – user fills the
enclosure with rags or paper
Medium
Integrate thermal cutout on heater plates at
90°C (high but safe).
Low
Fire
Misuse – user covers the
dryer with a blanket
Medium
Use a thermostat to control the internal
temperature, with a safety shutdown & timer.
Low
Fire
Uncontrolled heating,
causing the enclosure to
become excessively hot
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Silicon Chip
Australia's electronics magazine
Consequence if
not mitigated
Damage or
combustion
of filament or
enclosure
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• Onboard fusing.
• A thermal cutout on each heater
element.
• A thermal fuse on the controller board.
• The maximum heating power is
limited to 50W.
• A ventilation fan that is integral
to the controller board, ensuring airflow in the box.
• An interlock that shuts down
the heater if the ventilation fan
stops.
We have spread the heating across
six 25W resistors, which dissipate 8W
each into the large aluminium heating element. Even if everything fails,
they will never get hot enough to create a hazard. We tested our two boxes
with all controls disabled and determined that 50W of heating resulted
in a maximum box temperature of no
more than 60°C.
Looking at what is on the market and
having read a lot of tests on commercial filament dryers, most make wild
claims as to the temperatures they
achieve. We feel that 50-55°C is a good,
safe temperature. If you want it to get
hotter, you would need to increase
the power or reduce the size of the
box. The controller will accommodate
that, but we advise you approach any
changes with appropriate caution.
You may have your own spin on
how to build this; you could design
a box that better suits your needs
and use a surplus power supply.
You could even reuse some different heating resistors. That will let you
build a dryer for a fraction of the cost
of a ‘bought one’, but make sure you
follow our safety tips so everything
goes well for you.
We will first describe the controller and then present a couple of way
it can be used.
Photo 2: this DIY
timber box can be sized
to suit your needs. It has a rod
for hanging the reels and convenient
handles. The lid is removable and has a hole
for feeding filament through.
The controller
The controller can operate from
18-24V DC, so you can recycle a laptop supply or similar power brick. It
must deliver sufficient current for your
resistor bank. The input is fused; select
a fuse rating an amp or so above your
expected maximum operating current.
There is also a polarity protection
diode that will dissipate about 2W;
we have included heatsinking fills on
the PCB, and this ‘extra power’ simply adds to the overall heating in the
system.
The controller is expected to be
siliconchip.com.au
Photo 3: this box
from Bunnings
doesn’t look as elegant
and may be a little large
for some people, but it’s
much less work to prepare
and does the job well.
Australia's electronics magazine
October 2024 23
installed inside the Filament Dryer,
as that simplifies the wiring, and the
temperature sensor is on the board.
This means the controller will be
operating at up to 50°C, perhaps a little more. That fine for most electronic
components, but you will notice that
we have specified high-temperature
electrolytic capacitors and allowed for
heatsinks on transistors Q1 and Q2.
Circuit details
The circuit is shown in Fig.2. An
8-bit PIC16F15214 operates as the
timer, while an LM336-2.5 voltage
reference (REF2) is used to produce a
2.5V reference, which is buffered by
half of an LM358 op amp (IC1a). This is
used in the temperature measurement
circuit. The reason we have chosen the
LM336-2.5 is it produces a reference
voltage that is very stable over a wide
temperature range.
The LM336-2.5 has a variation of
just 6mV over 0-70°C, so we can expect
to see an error of less than a degree in
temperature control over our operational range.
The temperature sensor itself is a
simple 1N4148 silicon diode (D6),
using its -2.1mV/°C temperature coefficient. This is stable, reliable and used
in many measurement circuits. The
controller is a ‘Bang-Bang’ style, which
simply turns the heating element on
and off rather than implementing
fancy control loops. This choice is
again to keep things simple and cheap.
The controller comprises half of
the LM358 (IC1b), which compares
the voltage across the sense diode to
the temperature set voltage. We use
the 2.5V reference voltage to set the
current through the sense diode via
a 4.7kW resistor. The same reference
Fig.2: the circuit of the Filament Dryer Controller. REF2 and IC1a create a 2.5V reference (trimmed
by VR1). This biases diode D6, the temperature sensor. The voltage across D6 and the setpoint from
VR2/VR3 are compared by op amp IC1b to drive Mosfet Q2 for powering the heating elements. Microcontroller IC3’s timer
limits the heating time and powers the fresh air fan periodically.
24
Silicon Chip
Australia's electronics magazine
siliconchip.com.au
voltage generates the set voltage using
trimpots VR1 and VR2 plus a couple
of padder resistors.
By using this very stable 2.5V reference, we can be assured that the current through the sense diode and the
set voltage are constant over time and
temperature.
At room temperature, there is 400μA
flowing through the sense diode, giving 0.56V across it. With the 12kW and
2.7kW padders and two 500W potentiometers, we get a temperature set point
range of about 20-50°C. The reason we
have included two pots is to allow us
to use one (VR2) to set the minimum
temperature to room temperature,
while the other (VR3) is used to choose
the temperature setpoint.
With trimpot VR2 at the nominal
value of 220W, the minimum voltage will be 0.489V (2.5V × 2.90kW
÷ [12kW + 2.92kW]). The maximum
voltage will be 0.554V (2.5 × 3.42kW
÷ [18kW + 3.42kW]). The difference is
0.065V, and at 2.1mV/°C, that gives a
spread of 31°C.
Even using 1% resistors, the errors
in the voltage divider are significant.
If one is 1% high and the other is 1%
low, the setpoint could move as much
as 7°C. By adjusting VR2 so the minimum setpoint is room temperature, we
can calibrate such errors out.
The output of IC1b is low when the
sensed temperature is below the setpoint and goes high when the temperature exceeds the setpoint. The 8.2MW
resistor adds about 2°C of hysteresis
by feeding back the output voltage to
slightly shift the setpoint voltage.
The ratio of the 8.2MW and 4.7kW
resistors results in a shift of just a couple of milivolts, which is what we
need. This stops IC1b from oscillating
once the setpoint is reached.
With the controller being flat out on
or off, and the degree or two of hysteresis, the temperature control is not
super precise. But for warming the filament to dry it out, that is OK.
For the timer, we started by considering simple CMOS timer circuits and
the venerable 555. To get a nine-hour
period from these is not easy, so the
cheapest way to make the timer was
to use a PIC. These cost nearly $1.50
in single units, a fraction of the cost of
the discrete solution, and can be programmed to do a huge range of jobs.
We consider the timer to be an integral part of this design and strongly
recommend against omitting it.
Parts List – Filament Drying Chamber
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1 double-sided PCB coded 28110241, 126 × 93mm
1 18-24V DC 3A+ power supply (eg, laptop charger)
2 12V DC 40mm fans, 10mm-thick [Altronics F0010A]
1 40mm fan grille [Altronics F0012]
2 PCB-mounting M205 fuse clips (for F1)
1 5A 250V M205 fuse (F1)
1 77°C axial thermal fuse (F2) [Altronics S5631]
5 2-pin vertical polarised headers, 2.54mm pitch (CON1-2, CON4-5, CON7) [Altronics P5492]
5 2-pin polarised header plugs with pins [Altronics P5472 + 2 × P5470A each]
1 5-pin header, 2.54mm pitch (CON6; optional, for programming IC3 in-circuit)
1 PCB-mounting DC socket, 2.1mm ID or to suit power supply plug (CON8)
1 PCB-mounting 90° miniature SPDT toggle switch (S1) [Altronics S1320]
1 PCB-mounting 90° sub-miniature SPST pushbutton switch (S2) [Altronics S1498]
1 10kW side-adjust single-turn trimpot (VR1)
1 500W side-adjust single-turn trimpot (VR2)
1 500W 16mm single-gang linear potentiometer (VR3)
2 TO-220 micro-U heatsinks (optional) [Altronics H0627]
2 90°C normally-closed (NC) thermal switches/breakers (S3, S4) [Altronics S5612]
Hardware (common to both versions)
1 3D-printed vent (“Vent Rotor.STL”, “Vent Rotor Base.STL” & “Vent No Fan.STL”)
1 3D-printed fan cover (“Fan Shroud.STL”)
6 M3 × 25mm panhead machine screws
18 M3 hex nuts & 32 M3 flat washers
1 3m length of high-temperature (90°C+) heavy-duty hookup wire
1 250mm length of 6mm diameter heatshrink tubing
1 2m length of 5-10mm wide open-cell foam adhesive tape
1 small tube of thermal paste
Hardware (for plastic box version)
1 polypropylene box [Bunnings 0171464]
2 1.5mm-thick aluminium plates, 210 × 180mm
Panhead machine screws: 8 M3 × 6mm, 32 M3 × 10mm, 8 M3 × 16mm, 6 M3 × 25mm
Tapped spacers: 4 M3 × 15mm, 16 M3 × 25mm male/female hex spacers [Altronics H1243]
Other: 58 M3 shakeproof washers, 46 M3 hex nuts
Hardware (for timber box version)
2 3D-printed handles (“Filament Dryer Rail Tall.STL”)
1 sheet of 12mm MDF or plywood
1 1.5mm-thick aluminium plate, 330 × 225mm
Panhead machine screws: 6 M3 × 6mm (30 if building lid), 16 M3 × 10mm, 4 M3 × 16mm,
24 M3 × 25mm, 1 M4 × 10mm (for attaching handle to lid)
Tapped spacers: 12 M3 × 6mm (for lid), 10 M3 × 15mm
Other: 42 M3 shakeproof washers, 38 M3 hex nuts
Capacitors
1 470μF 35V 105°C electrolytic [Altronics R4865]
2 10μF 50V 105°C electrolytic [Altronics R4767]
7 100nF 50V multi-layer ceramic or MKT
Semiconductors
1 LM358 dual single-supply op amp, DIP-8 (IC1)
1 LM336BZ-2.5 voltage reference diode, TO-92 (REF2) [Altronics Z0557]
1 PIC16F15214-I/P 8-bit microcontroller programmed with 2811024A.HEX, DIP-8 (IC3)
1 LM317T adjustable positive linear regulator, TO-220 (REG1)
1 BD139 80V 1.5A NPN transistor, TO-126 (Q1)
1 IRF540(N) 100V 30A N-channel Mosfet or similar, TO-220 (Q2)
2 BC548 30V 100mA NPN transistors, TO-92 (Q3, Q4)
1 BC338 25V 800mA NPN transistor, TO-92 (Q5)
1 BC558 30V 100mA PNP transistor, TO-92 (Q6)
4 1N4004 400V 1A diodes (D1, D3, D11, D13)
1 R250H or 6A10 400V 6A diode (D2) [Altronics Z0120A]
3 1N4148 75V 200mA diodes (D4-D6)
1 12V 0.4W or 1W zener diode (ZD10)
2 5mm red LEDs (LED7, LED8)
1 5mm green LED (LED12)
Resistors (all ¼W 1% axial unless noted)
1 8.2MW
1 100kW
1 12kW
12 4.7kW
1 2.7kW
3 1kW
1 330W
1 47W
6 39W (18V), 47W (19-20V) or 68W (24V) 25W aluminium body resistors [Ohmite HS25 series]
October 2024 25
Our dryer includes two fans. The
first is to circulate air inside the box
and it runs full-time. There is also a
ventilation fan that runs briefly every
10 minutes. This is intended to draw
fresh air into the box and to exhaust
the hot (and possibly moist) air. This
ventilation fan is driven by the PIC
microcontroller.
We do not want to continuously
change the air in the enclosure, as it
would require a lot of power to keep
the temperature elevated. So our tiny
PIC microcontroller drives the vent
fan sparingly.
Software
The program in the timer is quite
simple. At power-up, the PIC goes into
an idle state, disabling the heater and
ventilation. It stays in this state until
the user presses the start button. This
requires a deliberate action by the user.
Once the start button is pressed, the
timer moves into the running state. If
IC3’s RA4 digital input is low, the timer
drives its RA2 output low and counts
nine hours. If RA5 is low instead, the
output is low for six hours. After the
selected time, the heater is switched
off and the system goes back to the
26
Silicon Chip
idle state. If the input is invalid, it
remains idle.
The PIC includes a secondary
timer that drives digital output RA1
to switch on the ventilation fan every
10 minutes.
The timer output and the output of
the temperature sensor comparator
are combined using open-collector
transistors Q3 and Q4, which disable
heater drive transistor Q2 when they
are on. When the box is up to temperature, the output of IC1b goes high,
switching on Q3, which disables the
heater. Green LED12 is in series with
this output, and lights showing that
the set temperature has been achieved.
Switching the load on is implemented using an IRF540 or similar power Mosfet with a gate pullup
resistor to 12V. The gate drive pullup
is derived from the ventilation fan
power supply, which might seem an
odd choice. The ventilation fan draws
current through D11, D13 and the parallel 47W resistor.
The specified fan draws 60mA in
operation and develops 1.2V across
these diodes. This voltage switches on
Q6 on via its 4.7kW base resistor, which
forms the Mosfet gate drive.
If the fan stalls, its internal controller reduces its supply current to
2mA and attempts to restart it every
few seconds. This 2mA current only
generates 94mV across the 47W resistor, which is not enough to switch Q6
on, and consequently the Mosfet gate
drive is removed. Thus, we disable the
heater if the ventilation fan is stalled
or not working.
For Q2, pretty much any TO-220
package, low-RDS(ON) N-channel Mosfet will work. They virtually all have
the same pinout. If you want to use
a different Mosfet from our recommended part, look for one with an
RDS(ON) under 0.1W.
For example, the MTP3055V has an
RDS(ON) of 0.18W and for a load current of 3A, it will dissipate 1.6W (3A2
× 0.18W). That would demand the use
of a flag heatsink; there is room for this
on the PCB. The recommended IRF540
has an RDS(ON) of 0.077W and will
dissipate 0.7W at 3A (or 0.4W for the
IRF540N version), which will make it
warm but it won’t require a heatsink.
Photo 4: the top side of the prototype PCB. The fan is mounted to the underside
using four M3 x 16mm machine screws with matching hex nuts.
Australia's electronics magazine
siliconchip.com.au
There are two headers for wiring up
the heater resistors. This allows you
to run separate wiring to two banks of
resistors, making the wiring and layout easier in some builds. The current
rating of the recommended Altronics
P5492 headers is 3A, so you could get
away with using just one.
We have included a thermal fuse in
the power supply to the Mosfet. The
specified fuse has a current rating of
10A AC but in our application, we are
breaking nominally 2A DC. The fuse
does not have a DC rating but that is
well within its capacity. This device
will fuse at 77°C, and will hold at 55°C
continuously. Should your enclosure
exceed 55°C for extended periods, you
may trigger this protection.
The heater
We performed a number of tests on
the boxes we’re presenting and determined that we need 50W to heat our
enclosures to 50°C reliably in a 20°C
room. This is also a good maximum,
as per the safety considerations we
touched on earlier.
To allow us to spread the power
around the enclosure, we are using
six 25W resistors mounted to large
heatsinks. We have used 68W devices,
which at 24V will dissipate 50W in
total. To spread the heat, we used a 330
× 225mm aluminium sheet folded to
fit inside our timber box, or two 210
× 180mm panels for the plastic box.
If using a 19V supply, the heating
resistor values need to be reduced to
47W to keep that 50W target.
We recommend the cheapest aluminium case power resistor we could
find, mentioned in the parts list. The
cost is around $20 for six, so you
can save some decent money reusing
parts you have. It is important that the
devices you select can be bolted to the
heat spreader, as this ensures they do
not get hot enough to create a hazard.
We tried using 10W ceramic resistors each dissipating 5W. While they
were operating within their specification, their surface temperature of over
130°C would have the potential to create a hazard if combustible material
fell onto them.
Safety considerations for the Filament Dryer
In designing the controller, we undertook a hazard assessment and developed controls for each hazard we identified, seeking to mitigate these hazards as much as
reasonably practicable. This in broader engineering often forms part of a “Safety
Engineering Program”. This process involves identifying credible hazards them
applying the ‘hierarchy of controls’ which, in order, are:
● Eliminate the hazard
● Substitute to avoid / minimise the hazard
● Apply engineering controls
● Add administrative controls (how it is used)
● Use Personal Protective Equipment (PPE)
In safety engineering, there is an important differentiation between a hazard,
which is a potential outcome, and the risk this represents, which considers the
likelihood of this occurring. The intention of applying the hierarchy of controls is
to mitigate and minimise the overall risk of a system.
Our hazard assessment was undertaken to inform the design of the project and
to shape the solution, both to minimise the underlying hazards in the design and
also to apply substitutions, engineering and administrative controls to further mitigate residual risks. By keeping a record of the approaches to managing safety, and
building those into the design, we can then test the project to ensure that these
controls do what we expect.
The hazards and controls we identified for the filament dryer are shown in Table
1 (Hazard & Risk Assessment). Some significant changes in design were implemented. Those practised in the safety art will note that we have picked parts of a
larger process to document here, as a full safety program is comprehensive and at
times less than fascinating. We have, however, included some important elements
for your consideration when making your own version of this.
Next month
The second and final article next
month will have the construction
and testing details, including building or adapting and then insulating
the container.
SC
Photo 5: the Filament
Dryer in use, showing
how filament is drawn from the container.
siliconchip.com.au
Australia's electronics magazine
October 2024 27
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