This is only a preview of the August 2024 issue of Silicon Chip. You can view 45 of the 104 pages in the full issue, including the advertisments. For full access, purchase the issue for $10.00 or subscribe for access to the latest issues. Items relevant to "The Styloclone":
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Items relevant to "180-230V DC Motor Speed Controller Part 2":
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180-230V DC Moto
Controls 180-230V DC motors rated from 1A
to 10A (¼HP to 2.5HP)
Controlled by four common op amp ICs
with one opto-coupler and three linear
regulators
Zero to full speed control
Safe startup procedure
Emergency cut-out switch facility
Automatic over-current switch-off
Optional reversing switch capability
PWM, Live and Power indicator LEDs
Rugged diecast aluminium enclosure
Current and back-EMF monitoring for speed regulation under load
Initial setup adjustments can be done with a low-voltage supply
M
otors rated at between 180V and 230V DC
are supported; they are driven by
PWM-chopped rectified mains.
Motor load/speed feedback is via current and back-EMF monitoring. The
circuit is based on analog techniques
and is designed to be robust and easily
adjustable. Most of the active devices
are common types of operational
amplifiers (op amps).
The motor speed is controlled by a
rugged IGBT (insulated gate bipolar
transistor). Most parts are throughhole types except for a few resistors
and the opto-isolated IGBT driver. It
all fits in a convenient diecast aluminium case.
Having already described the overall
design and how the circuit works in
the first article published last month,
let’s move on to building it.
Construction
Most of the parts are mounted
on a double-sided, plated-through
PCB coded 11104241 that measures
Warning: Mains Voltage
This Speed Controller operates
directly from the 230V AC mains
supply; contact with any live component is potentially lethal. Do not
build it unless you are experienced
working with mains voltages.
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Silicon Chip
201×134mm, which fits in a 222 × 146
× 55mm diecast aluminium enclosure.
The only off-board parts are the GPO
socket for the motor, the speed potentiometer and the IEC mains input socket.
Some of the PCB tracks connecting
to Q1, BR1 and CON1 on both sides of
the PCB are tin-plated so they can handle more current. Before installing any
parts, they should be covered with a
layer of solder to thicken the tracks and
further reduce their resistance (shown
in red in Figs.3 & 4). However, be careful to avoid getting solder in the component through-holes when doing so.
Fig.3 shows the layout of the topside parts on the PCB, which you
can use as a guide during assembly.
Begin by fitting the surface-mounting
opto-coupled Mosfet driver (IC5). You
will need a soldering iron with a fine
or medium tip, a magnifier and good
lighting. It’s also a good idea to have a
syringe of flux paste and some solder-
wicking braid on hand.
Solder IC5 to the PCB pads by first
placing it with its pin 1 locating dot
to the top left and the IC leads aligned
with the pads. Solder a corner pin and
check that the IC is still aligned correctly. Soldering the small leads will
be easier if you apply a small amount
of flux paste on top first.
If it needs to be realigned, remelt the
solder and gently nudge the IC into
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alignment. When correct, solder all the
IC pins. Any solder that runs between
and bridges them can be removed with
solder wick.
Following that, mount diodes
D2-D10 and zener diodes ZD1-ZD3.
Ensure each is orientated correctly and
that the correct diode or zener diode
is installed in each location before
soldering their leads. Diodes D2 and
D6-D8 are 1N4004 types, while the
remainder (except for the zeners) are
1N4148 types. ZD3 has a different voltage rating from ZD1 and ZD2, so don’t
get them mixed up.
TVS1 can also be installed now; it
is bi-directional, so it can go in either
way around.
Follow by soldering the SMD resistors in place. These mount on the
underside of the PCB, as shown in
Fig.4. They are the 10kW resistor under
IC5 and the four 0.022W resistors under
inductor L1. If you are building the
speed controller for a motor rated at
5A or less, see Table 1 for the required
number and value of these shunt resistors. Otherwise, fit all four.
Install these by soldering one
end first, then the other after you’ve
checked that the part is aligned correctly and the first solder joint has
solidified.
The low-wattage (½W) throughhole axial resistors can be fitted now.
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or Speed Controller
Our new High-voltage DC Motor
Speed Controller, revealed last
month, can control motors
commonly used in lathes and
treadmills. It can operate
such a motor from stopped up
to full speed and maintains
a constant speed even with a
varying load. This article covers the assembly,
testing and setup of the Speed Controller.
They have colour-coded bands and the
codes were shown in the parts list last
month. However, you should also use a
digital multimeter to check each resistor before soldering it, as the colour
bands can be difficult to distinguish
(especially brown, red and orange).
The remaining ICs can now be
installed, taking care to get the correct
one in each place and with pin 1 in the
proper location (double check that!).
Sockets can be used for each of the
ICs, although they can also be soldered
directly to the PCB, which is likely to
give better long-term reliability.
The 1W and 5W resistors can be
mounted next. When fitting the 5W
resistors, leave a gap of around 1mm
between the body and the PCB to allow
air to circulate.
Regulators
REG1-REG3 mount horizontally
with their leads bent by 90° to fit into
the allocated holes in the PCB. Each
Part 2 by John Clarke
regulator is secured to the board using
a 6mm-long M3 screw and nut before
the leads are soldered. Make sure you
don’t mix up the three different regulator types.
Diode D1 is mounted horizontally
with its leads bent by 90° so you can
insert them into the PCB holes. Secure
it with an M3 screw, washer and nut
before soldering.
The capacitors can now be installed.
There are four types used. The
630V-rated 47nF capacitors operate at
rectified mains voltage, so make sure
the correct types are used in the upperleft corner of the PCB. The other types
are ceramic, MKT polyester and electrolytic. The 100nF and 1μF ceramic
capacitors are placed near IC5.
The electrolytic capacitors need to
be orientated correctly since they are
polarised. The longer lead indicates
the positive side, while the negative
stripe down one side of the capacitor
indicates the negative side. One 100μF
(just above IC3) and 10uF capacitor
(above D4) is rated at 25V, so ensure it
is located correctly, or it will be damaged when power is applied.
For the MKT and ceramic capacitors, the 10nF capacitor is likely to
be marked 103, the 100nF capacitors marked 104, the 220nF capacitor
marked 224, and the 1μF capacitor
marked 105.
Solder in the three PCB-mounting
spade connectors (CON5-CON7), then
bridge rectifiers BR1 and BR2, ensuring correct orientation. BR1’s positive
lead is spaced further from the others,
so it will only fit in one way. Mount it
so there is about 1mm of lead length
below the PCB for soldering. For BR2,
the longer lead is positive. The AC
and + terminals will also be marked
on the package.
LED1-LED5 can be fitted now. Be
sure they are correctly orientated with
the longer lead placed into the anode
(A) hole in each case. The power LED,
Table 1 – shunt resistor values depending on motor rating
HP ¼
½
¾
1
1¼
1½
1¾
2
2¼
2½
kW 0.18
0.36
0.54
0.72
0.9
1.08
1.26
1.44
1.62
1.8
A 1
2
3
4
5
6
7
8
9
10
2S*
3
3
3
4
4
4
4
4
913W
764W 645W
0.022W
W shunts 2S*
VR2 value (R1) 4.95kW 2.25kW 1.95kW 1.36kW 1.47kW 1.36kW 1.1kW
IC1b gain 12.5
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6.25
5.55
4.16
3.33
4.16
3.57
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3.125 2.77
2.5
* S = in series.
Alternatively,
you can use two
0.05W resistors in
series and set R1
to 1.93kW (¼HP)
for a gain of 5.5
or 752W (½HP)
for a gain of 2.75
August 2024 79
Fig.3: most components mount on the top side of the PCB. T1 and L1 are heavy, so both are secured to the PCB using cable
ties. The large relay, RLY3, is attached to the board using screws and nuts, and will later be wired to CON1 and CON3.
This diagram and Fig.4 are both shown at 90% of actual size. The red areas are where extra solder is added.
LED2, is green while the remainder
are red.
LED1 and LED3 can be mounted vertically with 5mm of the leads projecting above the top PCB surface. LED2,
LED4 and LED5 display the Power,
Reset and Run status on the front
lid via fibre-optic light transporters.
Before soldering each LED, clip the
LED bezel end piece for the fibre optic
connection onto the LED, then solder
it in place with the clip touching the
PCB surface.
CON1 to CON3 can be fitted now.
CON1 can be installed either way
around, but CON2 and CON3 must
be orientated correctly. That is most
easily done by plugging the screw
terminal plug into each socket before
mounting it to the PCB. For the 3-way
terminal, CON2, the wire entry faces
toward diode D5. For the 2-way terminal, CON3, the wire entry faces away
from diodes D7 and D3.
The next step is to install the relays.
RLY1 and RLY2 directly mount onto
the PCB, while RLY3 is held to it using
M3 screws, washers and nuts, with
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Silicon Chip
each screw inserted from the underside of the PCB. The washers go under
the nuts on top of the relay’s mounting feet.
T1 can now be mounted onto the
PCB. Its pins hold it in place, but we
use a large cable tie to ensure it cannot move and break the transformer
pins if it is dropped. There are slots
in the PCB to accommodate the cable
tie, to wrap around the transformer
body and under the PCB after soldering it in place.
Winding inductor L1
L1 is made using two powdered iron
cores side-by-side. Use epoxy resin to
glue the two cores together. Once the
glue has set, wind on seven turns of
1.25mm-diameter enamelled copper
wire. The winding direction is not
important.
The finished winding and core are
mounted on the PCB with a cable tie
securing the toroid to the PCB. This tie
is fed through the slots in the PCB to
wrap around through the centre hole
of the core and under the PCB.
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Trim the wires to sufficient lengths
to solder to the PCB pads, then strip
the insulation off the ends of the enamelled wire. It’s generally best to do that
with a sharp hobby knife (be careful not to cut your fingers!) or emery
paper. Depending on the enamel used,
you may be able to burn it off by holding a blob of molten solder over the
wire ends.
Make sure the enamel is entirely
removed so you can make a good solder joint, then solder the wire ends to
the pads for L1.
Q1 can be installed now. Stand it
above the PCB so there is about 1mm of
lead projecting below the PCB to allow
soldering. Because the PCB tracks near
the IGBT are thin, the exposed, tinned
PCB tracks at the emitter and collector should be built up with solder to
lower the resistance.
Final assembly
The PCB is secured inside the enclosure base using M3.5 screws into the
integral standoffs in the base. However, before attaching the PCB, the IEC
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Fig.4: if all four 0.022W shunt resistors are soldered to the board, as shown here, the Controller will suit motors rated at
6-10A (1.5HP+, 1.08kW+). For lower-powered motors, fewer resistors are fitted, as per Table 1. For ¼HP and ½HP motors,
make sure the two resistors are in series, not parallel. If three resistors are required, any three can be fitted.
connector cutout will need to be made
in the side of the enclosure.
You will need to drill and shape
holes in one end of the case for the
IEC connector and Earthing screw. You
might as well prepare the lid at the
same time, which needs holes made
for the GPO socket, Earthing screw and
speed control potentiometer.
Fig.5 is a guide for the required cutouts; it can be copied or downloaded
and used as a template. The large cutouts for the mains GPO and IEC connector can be made by drilling a series
of small holes around the inside perimeter, then knocking out the centre piece
and filing the job to a smooth finish.
Alternatively, you can use a speed
bore drill to remove a large portion of
the required area and then file it to the
final shape.
The Earth screw positions are not
critical. Use the wiring diagram (Fig.6)
to decide where to place the holes. One
4mm hole is required on the lid, and
one in the enclosure base. Two 3mm
holes are needed to secure the IGBT
(Q1) and BR1 against the side of the
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The underside of the Motor
Speed Controller’s PCB. There
are five components that are
soldered to this side, the four 0.022W shunts (shown
in the left insert) and the 10kW resistor (shown at
right). The extra through-hole resistor shown at the
bottom of the PCB was only for our prototype, and is
fitted on the topside with the final PCB.
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August 2024 81
Fig.5: the
required
holes in the
lid and base
of the diecast
aluminium
case. Ensure the
IEC and GPO
socket holes
are shaped
correctly (filed
carefully to
size) so they
are not loose.
The exact Earth
screw positions
are not critical,
so they are not
marked.
enclosure. Temporarily place the PCB
into the enclosure and mark where
the holes for Q1 and BR1 are needed.
The holes for Q1 and BR1 need to be
slightly countersunk on the inside of
the enclosure to provide a flat mounting surface. There must not be any
sharp edges around the hole or any
remaining swarf that could puncture
the silicone insulating washer.
3.5mm diameter holes are needed
for the fibre-optic LED bezels on the
front panel. These are not directly
above the LED position on the PCB
to give the fibre optic cables room to
flex in an ‘S’ shape when the lid is
attached.
Once the drilling and filing is complete, install the IEC connector using
countersunk head 10mm-long M3
machine screws and nuts. The PCB
can then be placed inside the case but
wait to secure it to the corner posts.
Q1 needs to be insulated from the
enclosure using a TO-247-sized silicone insulating washer. Its package
has an insulated hole, so no insulating bush is required to insulate the
package from the screw. A 12mm-long
M3 screw and M3 nut can be used to
secure Q1 to the side of the enclosure.
Check that the enclosure is insulated
from all three of Q1’s leads by measuring the resistance between each lead
and the enclosure. There should be
high resistance reading in each case,
in the megohms region.
BR1 does not require an insulating
washer since the metal tab on the back
of the package is insulated from the
internal diodes.
Before attaching the mains GPO,
you can print out the front panel
label (Fig.7), available to download
from our website at siliconchip.au/
Shop/11/436 Details on making a front
panel are found at: siliconchip.au/
Help/FrontPanels
Now wire everything up per Fig.6.
All wiring must be run using mainsrated cable. Be sure to use 10A cable
where indicated, and note that brown
wire is used for the Active wiring and
blue for Neutral. Green/yellow-striped
wire must be used for the Earth wiring only, and the Earth lead from the
IEC connector is attached via a crimp
eyelet to the enclosure Earth.
The wiring not marked as 10A can
be lighter-duty 7.5A mains wire, such
as for the speed potentiometer VR1, or
use 10A wiring throughout.
The IEC
socket and
Earth screw
are on the lefthand side of
the case.
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Australia's electronics magazine
The terminals on relay RLY3 will be
too tall for the lid to fit, so they need to
be cut down, with the wires soldered
directly to the shortened terminals
and covered in heatshrink insulation.
These terminals are brittle, so hold the
lower part of the terminal with small
flat-nosed pliers while you break off
the top part with another set of pliers.
The terminals will break at the wire
hole location.
Be sure to insulate all the connections with heatshrink tubing for safety,
and cable tie the wires to prevent
any wire breakages coming adrift, as
shown in Fig.6. The Active and Neutral leads are secured to the GPO using
cable ties that pass through the holes
in its moulding.
Use neutral-cure silicone sealant
(eg, Roof and Gutter silicone) to cover
the Active bus piece that connects the
Active pin to the fuse at the rear of the
IEC connector.
Take great care when making the
connections to the mains socket (GPO).
In particular, be sure to run the leads
to their correct terminals; the GPO has
the A, N and E clearly labelled. Do the
screws up tightly so that the leads are
held securely. Similarly, make sure
that the leads to CON1’s screw terminals are firmly secured.
Warnings
Almost all of the circuitry operates
at mains potential, so it is dangerous
to make contact with any part of the
circuit when it is powered. The speed
potentiometer connections are also at
mains potential.
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Fig.6: all wires must be mains-rated;
the wires marked with an * need to
handle 10A, while the others can be
rated at 10A or 7.5A.
Some adjustments can be made
more safely by disconnecting the
mains supply from some parts of the
circuit. This leaves the circuit floating
at mains Neutral potential instead of
Active. You still need to be very careful, but the risk of electrocution should
you touch the circuitry is much lower.
Some adjustments will need to
be made when the circuit is live.
We recommend using a 1000V-rated
screwdriver with a 0.4mm-thick,
2.5mm-wide flat tip. That size of
screwdriver suits the trimpot adjustment screws and has a sufficient voltage rating to protect against electrical
shocks. We used a Wiha 1000V screwdriver that has an insulated shank.
Similarly, when measuring voltages
in the circuit, use a 600V CAT III (or
higher, eg, CAT IV) rated multimeter
and probes.
We provide indicator LEDs that
show when the circuit is powered and
live. So don’t touch the circuit when
any LED is lit, and always unplug it
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from the mains before working on it
(except during the part of the setup
where it needs to be operating).
Another LED shows the PWM duty
cycle by varying brightness with PWM
duty. A separate LED shows when the
speed potentiometer is rotated fully
anti-clockwise. Finally, there is one
LED that shows when the motor can
be started.
Testing
Ensure that the mains power point
you connect to when testing and
adjusting the 180V DC Motor Controller is connected to an Earth-leakage
core balanced relay, also known as
a Residual Current Device (RCD)
or mains safety switch. This can be
installed in the fusebox, as a separate
unit within the power point or as a
plug-in device.
The RCD is designed to cut the
power should you receive an electric
shock that passes through your body
to Earth. However, an RCD will not
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Errata: in Fig.2 last
month, the labels for
REG1 and REG2 were
transposed. The top
regulator should be
REG2 (7815), while
the middle one should
be REG1 (7812).
protect you if current flows through
your body from Active to Neutral (eg,
by touching two points in the circuit
with different hands).
Thus, it is a good idea to use one
hand only when there is any possibility of making contact with the live
circuitry within the Motor Controller.
If you are building the Controller
in a different arrangement than the
one we described, eg, with the motor
hardwired to it, any wiring that goes
outside the enclosure must be run in
sheathed mains-rated cable that is
secured to the enclosure with cordgrip
grommets. This includes the safety/
emergency stop switch wires.
The safety/emergency stop switch
must be mains-rated and enclosed in
an Earthed enclosure with its contacts
covered in heatshrink tubing and the
wiring cable tied together. Treat all
connections to it as if they are live!
Additionally, the wires from the safety
switch need to be secured to its enclosure with a cordgrip grommet.
August 2024 83
Fig.7: this panel label is also available as a PDF download from the Silicon Chip website. It can be printed, laminated and
attached to the lid. This panel is shown at 83.3% actual size, and so needs to be enlarged by exactly 20%.
Initial settings that can be made
with the power off include setting the
torque trimpot to near 0W. This resistance can be measured between the Vt
and Rt test points.
IC1b’s gain is set by varying VR2’s
resistance (referred to as R1) to provide
the required current measurement output voltage at the rated current of the
motor that’s used.
Table 1 shows the resistance setting for R1 versus motor ratings and
shunt resistances. We show values
based on ¼HP increments from ¼HP
through to 2½HP. This closely corresponds to 1A to 10A motor ratings in
1A steps. That’s because, for a 180V
DC motor, each amp is 180W. Since
1HP is 746W, 180W is 0.24HP or near
enough to 0.25HP.
resistors in series to form a 0.1W shunt
instead of the 0.022W shunts used for
other ratings; in that case, less gain is
required from IC1b.
The gain for IC1b is set so that, at
the full rated motor current, its output
sits at 0.55V. For example, when the
current shunt is 0.022W, and the motor
is rated at 10A, the voltage across the
shunt will be 0.22V at 10A. IC1b needs
to amplify this to give the 550mV output, meaning a gain of 2.5. The formula
for the required R1 resistance is (gain
– 1) × 430W. That works out to 645W
in this example.
With the power off, connect your
multimeter probes to the two R1 test
points on the PCB and adjust VR2
for the value required for R1. Now
insert IC1 and the remaining ICs in
their sockets if you have not already
done so.
Shunt values
Overload setting
Note that the shunt resistance
comprises series and parallel resistors to provide the required overall
shunt resistance. For the 1A and 2A
rated motors, you can use two 0.05W
At the motor’s rated current, IC1b’s
output delivers 0.55V. IC3d amplifies this by 4.68, giving a 2.57V output. VR6 provides adjustment of
the current threshold (It) for motor
Setting IC1b’s gain
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Australia's electronics magazine
overload. To set the motor overload
to 1.6 times the rated current, the ‘It’
setting should be 1.6 × 2.57V = 4.1V.
This value assumes that the Vovl offset output from IC3d is set to 0V using
VR5, which we will do later.
The overload trip voltage needs to be
set with the power on. Before applying power:
1. Check your wiring carefully and
ensure all mains connections are covered in heatshrink tubing and the wiring is cable-tied.
2. Check the Earth connection
between the enclosure and the Earth
pin on the IEC connector. The reading
should be steady and under 1W.
3. Install the fuse inside the fuse
holder.
Testing
The initial testing and setting up can
be done more safely by disconnecting
the Active wire to BR1. This is done at
CON1, by removing the wire between
terminals 4 and 5 and only connecting the Active wire to terminal 5. Also
disconnect the spade connector wire
loop between CON5 and CON7.
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The large relay’s
terminals are cut down and
the wires soldered and covered
with heatshrink so the lid will fit.
Because the circuit operates at
mains potential, it is unsafe to make
contact with any part of the circuit,
including the terminals of VR1, when
it is switched on, despite the above
measures. Do not touch any part of
the circuit except with the multimeter
probes and 1000V-rated screwdriver.
Attach the enclosure lid before
switching on power for the first time.
That will make it safer if something
is wrong, such as a reverse-connected
electrolytic capacitor or if a 16V capacitor is installed in a 25V position. Still,
check those aspects again before fitting
the lid and applying power.
If all is quiet when power is applied
(except for relays clicking), switch off
the power and open the lid. Wearing
safety glasses, switch on the power
again and measure the AC voltage
between Neutral (at terminal 3 of
CON1) and the mains Earth connection to the enclosure. The reading
should be no more than a few volts.
You should read close to 230V AC
between Earth and terminal 5 of CON1.
If the Neutral reading is instead
close to 230V AC, check that you have
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wired up
the IEC connector correctly.
If the wiring is correct,
your mains supply may have the
Active and Neutral wires transposed.
Have this corrected by an electrician
before proceeding with testing the
motor controller.
Switching on power again, you
should be greeted with power LED2
lighting to show that the +12 and -12V
supplies are up. Check the regulators
for the correct output voltages. There
should be +12V between the 0V and
+12V test points. Similarly, there
should be +15V at the +15V test point
and -12V at the -12V test point. These
voltages should be within 5% of the
designated voltages.
That means between 11.4V and
12.6V for 12V, -11.4V to -12.6V for
-12V and between 14.25V and 15.75V
for +15V.
Verify that when VR1 is fully
anti-clockwise, LED4 is off and only
switches on once the speed pot (VR1)
is rotated clockwise slightly.
It is important to test the Controller
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initially using
a filament light
bulb. A halogen
25-100W bulb is
sufficient, eg, in a
table lamp. This way,
nothing bad will happen
if the ‘motor speed’ oscillates; any
changes in ‘speed’ can be seen by
observing the lamp brightness.
Setup and adjustment
With the lamp connected, perform
the following tests and adjustments.
All voltage measurements below are
with respect to the 0V test point.
1. Adjust VR3 for -7V at Vt.
2. Adjust VR1 for 0.5V at Vc.
3. Adjust VR7 so that LED3 is just lit,
then back off anti-clockwise until the
LED is off. Vs should measure 0.4-1.0V.
4. Adjust VR5 for a reading at Vovl
as close to 0V as you can manage.
5. Adjust VR6 for 4.1V at ‘It’. This
sets the motor overload threshold to
1.6 times its rating.
Now switch off the power, unplug
the unit and restore the Active connection between terminals 4 and 5 of
August 2024 85
The assembled module,
ready for mounting in the case.
CON1. Also reconnect the crimp spade
lead from CON5 to CON7. Make sure
VR1 is set fully anti-clockwise and
connect the lamp. Apply power and
wait for RLY1 to switch off (indicated
by LED4 switching off).
Check that the lamp begins to glow
at low speed settings and reaches full
brightness with the potentiometer
fully clockwise. Once the operation is
successful with the lamp, switch off
the power and test it with the motor.
Verify that the motor speed can be
controlled, noting that the motor will
not start unless the speed potentiometer is rotated fully anti-clockwise
first (LED4 off). Wait for RLY3 to be
powered (LED5 lit) before bringing it
up to speed.
Test the motor under load at around
25-50% of full speed and adjust the
Torque trimpot, VR4, so that the motor
does not drop markedly in speed when
a load is applied.
Anti-clockwise rotation of VR4
increases the feedback control, meaning that more torque will be applied
when the motor is under load. Too
much speed compensation can cause
the motor to speed up under load, so
minor adjustments between tests are
necessary to get it right.
Note also that the torque adjustment will affect the Vs value set with
VR7, which ensures the PWM output
is zero when the speed potentiometer
is brought fully anti-clockwise. Check
this by repeating steps 2 and 3 above
after adjusting VR4.
Suppose the motor drops in speed
too much under load even with
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Silicon Chip
maximum torque adjustment. In that
case, the output from IC1b (current
feedback) can be boosted by increasing the gain of this amplifier via clockwise adjustment of VR2. Again, make
small adjustments between load tests.
Increasing the gain of IC1b will
also require increasing the overload
threshold (It) using VR6 by the same
percentage.
Adding a reversing switch
If you need a motor reversing
switch, you can use a 3PDT switch, as
shown in Fig.8. One suitable switch is
the “Lovato 3PDT 3 Position 60° Motor
Reversing Cam Switch”, rated at 20A.
It has a knob actuator and is available
from RS Components (Cat 8405624).
Two poles of the switch are used
to reverse the motor polarity. The
third switch pole ensures the motor
is disconnected from power during
the switching. It does this by opening
the safety switch connection at terminals 7 and 8 of CON1. This prevents
the motor from being switched into
reverse while the motor is running.
After reversing, the motor can
only be started once the speed pot is
returned to its anti-clockwise position.
If a safety/emergency stop switch is
also used, this will need to connect in
series with the reversing switch pole
at terminal 8 of CON1.
There is insufficient room inside
the enclosure to install a reversing
switch. Consequently, mains wiring
for the motor connections and safety/
emergency stop switch will need
to run outside the enclosure using
10A sheathed mains cable, with the
cables secured to the enclosure using
cordgrip grommets.
The reversing switch must also
be enclosed in an Earthed metal
enclosure with cables secured using
cordgrip grommets. Altronics H4280
grommets are suitable.
Note that if you have an on/off
switch in series with the motor wiring,
the switch needs to be a double-pole,
double-throw type (DPDT) so that
one pole connects or disconnects the
power to the motor, with the second
pole connected in the same way as
shown for the third pole in the reversing switch. That way, the motor can’t
suddenly be reconnected, which could
SC
damage the Speed Controller.
Fig.8: a 3PDT
or 3P3T switch
can be used
to reverse the
motor. The
third pole
(terminals
9-12) is used
to shut down
the Controller
when the
direction is
changed. The
speed pot needs
to be reset to
zero each time
the switch is
thrown before
the motor will
be powered
again.
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