4qd VTX Series User manual
“We're in Control”“We're in Control”
Office
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Burwell
Cambridgeshire, CB25 0AH
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Cambridgeshire, CB25 0AP
Instruction Manual
VTX series controllers
VTX-40 and VTX-75
4QD try to write a manual which is readable. If we
succeed and you don’t read it there is not a lot more
we can do. However if you try to read it and don’t
understand it (or even don’t like our style) - then we
have failed so please tell us. Only by means of your
criticisms and suggestions can we improve our
publications! To help you, we have marked the more
technical sections ¶ so that you may ignore them.
If you have any problems or queries, 4QD pride
ourselves on our level of technical advice and if we
put as much information into this manual as we could
many would find it too long.
If you require more information, 4QD have a very
full WWW site which has a large section giving
answers to commonly asked technical questions.
Even if you do not have easy Internet access, you will
find this well worth reading, so ask a friend who is
connected or go to your local Internet Cafe or public
library.
4QD’s VTX range of economy 4 quadrant controllers
have been engineered to replace the NCC series. As
well as improved circuitry, they benefit from surface
mount technology, which offers superior reliability
and is better suited to higher volume production.
The VTX controllers are very suitable for general
purpose speed control applications where reversing is
required. Amongst other applications our controllers
have been successfully used in the following:
Camera dollies
Caravan shifters
Carnival floats
Conveyors
Factory stores vehicles
Floor cleaning machines
Golf buggies
Invalid scooters
Kiddie cars
Miniature railways, 3”, 5” and 7¼ gauge
Mobile targets
Mountain rescue vehicles
Remote controlled vehicles
Ride on golf buggies
Winches
In fact wherever battery motor speed control - and
good value - is required.
Date printed: 13th May 2014
Foreword
Page 2 VTX series instructions
Contents
1 . . Introduction . . . . . . . . . . p. 2
2 . . Handling . . . . . . . . . . . . p. 2
3 . . Models . . . . . . . . . . . . . p. 3
4 . . Safety . . . . . . . . . . . . . p. 3
. . . . . . Reversing . . . . . . . . p. 3
5 . . Features . . . . . . . . . . . . p. 4
6 . . ¶ Specifications . . . . . . . . p. 4
7 . . Mounting . . . . . . . . . . . p. 5
8 . . Connections . . . . . . . . . . p. 6
. . . . . . Simple wiring . . . . . . p. 6
. . . . . . Control Fuse . . . . . . p. 6
. . . Battery Fuse . . . . . . . . . . p. 6
. . . . . . Push buttons . . . . . . . p. 6
. . . . . . Power Connections . . . p. 7
. . . . . . Battery wiring . . . . . . p. 7
. . . . . . Motor wiring . . . . . . p. 8
. . . . . . Fuse or Circuit breaker . p. 8
. . . . . . Battery condition meter. p. 8
9 . . Controls . . . . . . . . . . . . p. 8
. . . . . . Speed pot . . . . . . . . p. 9
. . . . . . Use as voltage follower . p. 9
. . . . . . On/Off switch . . . . . p. 9
. . . . . . Reversing . . . . . . . . p.9
. . . . . . Braking . . . . . . . . . p. 10
10 . Boxed version . . . . . . . . . p. 11
11 . Adjustments . . . . . . . . . . p. 11
. . . . . . Gain . . . . . . . . . . . p. 11
. . . . . . Ramps . . . . . . . . . . p. 11
. . . . . . RAT and MST . . . . . p. 12
12 . Expansion connector . . . . . p. 12
13 . Heat & Heatsinking . . . . . . p. 13
14 . Choice of motor . . . . . . . . p. 13
15 . Common faults . . . . . . . . p. 14
16 . Dos and Don'ts . . . . . . . . p. 16
. . . Other products . . . . . . . . . p. 16
. . . More information . . . . . . . p. 16
. . . Service & Guarantee . . . . . p. 16
The VTX series are open-card controllers. A very
high proportion of controllers returned for repair have
been damaged by mishandling!
Do not let any foreign body contact the board. That
includes water, dirt, screwdrivers, nuts and bolts.
Use only fully-insulated power connectors.
The controller can be damaged by foreign body
contact if the main capacitor is still charged.
Before handling the controller or unplugging the
power or motor connections, disconnect the battery,
then leave the ignition turned on for at least one
minute before handling the controller, to discharge
the main capacitor.
Otherwise, short out the battery inputs to the
controller, to discharge the capacitor to make the
controller safe to handle.
See also back page for dos and don’ts
2: Handling
Page 3VTX series instructions
It is normal practise, on passenger carrying vehicles,
to include some means of disconnecting the battery or
motor in an emergency. This could be a "kill switch",
or perhaps a removable link in the battery wire. This
is to guard against a failure in the controller or
wiring which, although very unlikely, could cause the
motor to run at an uncontrollable top speed. You
must not operate this switch with the motors moving
as (on rare occasions) this could damage the
controller.
Even without such additional safety features, the
VTX range controllers are designed so that failure,
and particularly dangerous failure is very unlikely.
Experience also shows that, in the improbable event
of a power device failing, the device normally acts as
its own fuse, removing drive from the motors.
Furthermore, notwithstanding a very unusual fault,
the motor can be stopped quickly by turning off the
ignition, or turning the speed down to 0. Either action
operates the relays to give full emergency braking.
Most dangerous faults have been due to water
splashes on the board - which is outside of our
control. No manufacturer, however careful, can
always guarantee what will happen in the event of a
failure.
It is important for the last word here be that the
constructor should fit a means of quickly
disconnecting the battery in the event of abnormal
control system operation.
All passenger carrying vehicles should, in any case,
be fitted with a mechanical braking system to
complement regenerative braking.
Reversing
On the VTX controller series, reversing is normally
‘dual ramp’. This means that, when the reversing
switch is operated at speed, the controller slows down
under control of the deceleration ramp, automatically
reverses and accelerates again under control of the
acceleration ramp. If the ramp controls are set for
quick response this process can be quite violent.
Also, reversing is done by monitoring the demand
speed, after the ramp circuit and not by measuring the
motor voltage so that, if the vehicle is reversed when
going down a hill, the motor will still be rotating and
the vehicle will be travelling when reversing occurs.
Reversing can therefore be accomplished on any hill
but it will be more or less violent if the gradient is
steep depending on the setting of the ramp controls.
The user is best advised therefore not to change
direction on steep hills!
Dual Ramp reversing can be deactivated, when the
reversing becomes pre-select. To disengage dual
ramp, alter the header shown in the diagram opposite.
4: Safety
Two models are available, for different current
ratings and with different options.
Each is available as 12v or 24v, but the 24v can be
supplied with resistors in the relays for 36v operation.
VTX-40 40 Amps nominal 55A max typical
VTX-75 75 Amps nominal 110A max typical
The nominal current is available for around 1 minute
(depends on mounting).
For some applications, e.g. double heading loco, two
standard units can be interconnected in tandem (if the
optional expansion connector is fitted).
The voltage is marked on the relays. Make sure these
are correct as 24v relays will not operate from 12v
and 12v relays will soon burn out their coils if used
on 24v.
The 36 version uses the 24v relays but with a resistor
in series with the relay coils and other components
changed as appropriate.
A boxed option is also available.
3: Models
Page 4 VTX series instructions
5: Features
The diagram above shows the VTX-75 which has
four MOSFETs and capacitors. The VTX-40 has two
only. Otherwise, the VTX-40 is largely the same as
the VTX-75.
Speed pot and reversing switch input is via a 6 pin
connector, supplied.
Power & Motor connections are by 6.3mm blade
connectors on top of the board. Spare power
connections are provided and can be used for control
wires or for extra motor wires as you wish.
Also available is an expansion connector option, see
page 12.
Regen brake defeat option, RAT and MST presets are
not normally fitted but are replaced by fixed resistors.
Parking brake and Thermal Sensor are standard on
VTX-75 but optional on VTX-40.
A version of the controller is supplied with fixed
acceleration, deceleration and gain: in this the presets
are replaced by fixed resistors.
Dual Ramp Reverse
Half Speed Reverse
MST Preset
ACC Preset
DEC Preset
Gain Preset
RAT Preset
B- Connection
B+ Connection
M- Connection
Parking
Brake
Controls
Expansion Connector
FETs
Heatsink
Forward
Relay
Relay
Reverse
Thermal Sensor
Capacitors
A
B
C
D
E
F
A
B
C
D
E
F
159mm
88mm
89mm
25.4
Supply voltage 12v, 24v, 36v or 48v different models.
Supply current 25mA at zero speed
Motor speed forward 0 to 100% full speed adjustable
reverse 0 to 50%/100% full speed selectable
Output current VTX-40 40A approx 1 minute 55A limit, typical
(typical) VTX-75 75A approx 1 minute 110A limit, typical
6: Specifications
Page 5VTX series instructions
The VTX series are designed for mounting via the
heatsink as in the diagram below. In most
applications, full current is only drawn for short
periods so little heating will be experienced.
However, the VTX’s heatsink is a thick block of
aluminium which won’t cool down quickly to the air.
In more demanding applications, good heatsinking is
important, such as a suitable metal plate which will
usually be the vehicle’s chassis. If heatsinking is
inadequate, the controller will give reduced
performance, and if allowed to overheat for too long,
may be damaged. The heatsink is completely
electrically insulated.
Mounting holes in the heatsink are tapped M4. Do
not drill these out larger. It is unnecessary and you
will contaminate the board with swarf, invalidating
any guarantees.
We recommend mounting only by the heatsink.
However if you want to use the corner mounting
holes as well, you must use insulating mountings.
Whatever you do, make sure the controller can’t get
wet and, if it does, don’t connect the battery until you
have dried the controller thoroughly. The water won’t
cause damage unless the unit is connected to the
battery, when electrolytic corrosion will occur.
Overheat temperature 95°C on heatsink
Overheat current 20 amps typical
Switching frequency 20kHz approximately
Size 153mm x 78mm x 45m Board version
198mm x 88mm x 43mm Boxed version
Weight 260g
Input 2k to 20k pot.
Pot fault detect greater than 25K
Input voltage 3v to 20v for full speed adjustable
Acceleration time 100mSec to 5 Sec adjustable
Deceleration time 100mSec to 5 Sec adjustable
Ignition input threshold 8v into 50k approximately
Reverse input threshold 5v into 10k approximately
Parking brake 1 amp max.
Thermal Sensor
Pot and direction switch via IDC connector.
Customer's heatsink
Main capacitors
Relays
6.3mm tags for battery and motor
Heatsink
7: Mounting
Page 6 VTX series instructions
Simple wiring
On the 6 way multicore control wire, yellow is
internally connected to battery +ve. White and black
may also be battery +ve (depending on the control
switches). Green is battery -ve and blue and red are
the control pot. A short circuit in the wiring between
these two groups will cause problems!
Boxed version: Wire colours are as shown in the
diagram above.
Control Fuse
Note the 1A fuse in the yellow wire. If this is omitted,
a mistake in the wiring can blow fuse tracks on the
controller. Controllers returned for repair with the
fuse tracks blown will be subject to a handling
charge. See page 15.
Battery Fuse
Note the fuse in the battery line: this is partially to
give a useful measure of protection against a reversed
battery. It will also protect against some other wiring
faults. The boxed VTX-75 has a 40 amp fuse (25A
for VTX-40) fitted but the controller may draw more
than this depending on the application. A larger fuse
can be fitted, but will give less protection. Use the
smallest value fuse which does not cause nuisance
blowing: if the controller is giving more current than
it can readily handle it will simply get hot. See also
pages 7 and 8.
Motor Capacitor
See page 13.
Push buttons
Instead of two switches (ignition and
forward / reverse) you may use two
push-and hold buttons. Wiring is
shown left: note the extra diode (any
small signal diode, e.g. 1N4148).
Without this, reverse will not work.
The diode's Cathode (the end with the
band) should be connected to White.
8: Connections.
Blue
Red or Brown
Permanent
magnet
motor
Black
6 core cable
Speed control pot
Reverse switch
Ignition switch
Cables anchored
to chassis.
Yellow
Yellow
White
White
Black
Black
Green
Green
Blue
Blue
Red
Red
1amp fuse
Fuse
A
B
C
D
E
F
Yellow
motor
capacitor
6 core cable
Speed control pot
Reverse
Forward
Black
Green
Blue
Red
Yellow
Yellow
Diode
White
Fuse, see text
Yellow
WhiteBlack
Green
Blue
Red F
E
D
C
B
A
The diagram shows the simplest
connections needed to use the
controller.
Fused yellow wire may be fed
from B+ if preferred.
green wire must not
connect to machine
chassis.
Page 7
VTX series instructions
Battery connections to the controller are shown in the
diagram opposite. Use only good quality battery
connectors: the controller feeds current back into the
battery during braking and if a battery connector falls
off when braking this regenerated current can pump
up the voltage on the dud battery connection.
Although the controller is protected against damage
from this, it is not advised. The same will happen if a
fuse or circuit breaker opens during braking.
Note that, if the battery is disconnected for a minute
of more, when the battery is re-connected, it is
normal for there to be a noticeable spark as the main
capacitors charge.
Polarity
Take great care: THE CONTROLLER IS NOT
POLARITY PROTECTED: BATTERY
REVERSAL WILL INSTANTLY DESTROY THE
CONTROLLER!
This will not be covered by the guarantee!
In practise a suitable fuse (opposite page) gives quite
effective protection. However a more positive
protection against reversed battery can be done by
wiring a suitable relay (one normally open contact) in
the positive battery lead. One end of the coil connects
to battery -ve and the other to pin B of the input
connector which is also connected to the ignition
switch. A resistor must be connected across the
contacts as shown. When the ignition is off, there is
no voltage on the relay coil and the relay contacts are
open. The VTX’s main capacitor charges through the
470 ohm resistor.
If the battery is reversed the VTX's MOSFETs short
out the capacitor, so no voltage is present and the 470
ohm resistor limits the current to a safe value. When
the ignition switch is closed the relay coil is
connected across the capacitor: if there is voltage
(battery correct) the relay operates and applies full
power.
Wire size. Use heavy duty wire for the battery and
make them as short as possible. This also applies to
the battery linking wire on 24v systems. 4mm
(12awg) wire is ‘officially’ rated to handle 41 amps
continuously. At 100 amps it gets too hot to touch
within about 60 seconds, so it is fairly well matched
to the controller. You may prefer to use 6.0mm²
(10awg) wire for the 75 amp version. Thicker wire
will cause no problems, so use the thickest you have.
Use of wire that is too long (and/or too thin) will
cause loss of power, but more importantly the
decoupling capacitor (see ‘features’ diagram above)
will heat up. Heat will shorten the operating life of
capacitors.
Crimp Contacts
It is VERY IMPORTANT that you use fully insulated
crimps: the power connections are close to the board.
Uninsulated crimps may short out and destroy the
controller. Best of all use ‘F type’ crimps with vinyl
covers shown in the drawing.
4QD can supply these pre-
crimped - they require a special
crimp tool.
Also be aware that the main
capacitor can store charge for a
long time (several minutes) so
the potential for damage is there
after the battery has been
connected.
Power Connections
Battery wiring
Relay 470 ohm
2 watt
Battery +
+ to controllerBattery -
+24v switched by ign switch
Page 8 VTX series instructions
Motor wiring
This is not so critical as battery wiring: too long
and/or too thin wire will cause a loss of maximum
current, will get hot and will waste battery power but
will not damage the controller. However, wire which
is too thick will do no harm either so we recommend
the same wire for the motor as for the battery.
Circuit breaker, fuse, isolator.
A circuit breaker or fuse may be fitted if required.
The main advantage is that it will enable the battery
or motor to be disconnected in the event of an
emergency or for security and it will give a measure
of protection should the battery be reversed.
Suggested fuse/breaker value:
50 amp max for VTX-75
25 amp max for VTX-40
Alternatively, you could fit a breaker in the battery
lead: take care not to increase the wiring length too
much. Also, certain types of breaker can have the
same effect as increased battery lead length.
A breaker in the motor may also be useful: it will
enable you to quickly disconnect the motor in an
emergency. If correctly rated, this can also protect the
motor against overheating due to mechanical
faults.Also with the motor disconnected, free-
wheeling becomes possible.
It is also possible to get a battery isolator switch.
These are normally fitted to lorries, buses and boats
to isolate the battery in an emergency.
Battery condition meter.
Pins A and F (yellow and green on the diagram) are
directly connected to the battery so that you may use
them to connect a battery condition meter.
The drawing shows 4QD's LED battery indicators.
6 way connector.
The mating connector supplied is suitable only for
the correct size of wire.
Acceptable wire sizes are:
. . . 7 stranded 0.22-0.25mm²
. . . Equivalent 24 AWG (7/32 AWG)
It is an Insulation Displacement Connector (IDC)
which 4QD have chosen because it is so very easy to
use and very dependable. - but only with the correct
wire!
Do not strip the insulation from the wires, simply
push them into the top part of the open connector and
squeeze it closed in a vice or with suitable parallel
action pliers. As you do this the tines of the contacts
bite through the insulation to make contact with the
conductors.
Wire which is too thin will not make contact. Wire
which is too thick will damage the tines.
Do not use single strand (telephone) wire: it will
make unreliable contact and easily breaks.
You can re-open a closed connector by gently
moving the tabs at the sides of the top cover outwards
to disengage the latches while lifting the cover
slightly, one side at a time.
11
Open Closed
1 1
1
D red: Max speed (7.8v approx)
E blue: Wiper
F green: 0v (Min speed)
C black: Reverse
A yellow: +24v to Ignition
B white: Ignition and reverse common.
A B C D E F A B C D E F
9: Controls
Page 9VTX series instructions
Speed pot.
We suggest a 10K linear pot, although other values
from 4K7 to 20K, linear or log, can be used.
The gain adjustment on the controller alters the
amount of rotation required before full speed is
reached: this enables a simple lever operated control
by means of a lever arm screwed onto a standard
rotary pot.
The simplest speed control is an ordinary rotary pot:
this won’t give any ‘dead man’ control as the pot
won’t return to zero when it is released. 4QD can
supply a spring return to zero hand control.
Alternatively 4QD can supply a plunger operated pot
(linear position sensor), suitable for incorporating
into a foot pedal.
The drawing shows the pot supplied by 4QD
With this pot you should only solder to the tips of the
tags: the holes shown are not for soldering but as
heat barriers to stop heat travelling up the tag and
melting the plastic body.
¶ Use as voltage follower
Instead of a pot, the input may be fed from a variable
voltage. 0v (common) to pin F, signal input (+ve) to
pin E. A resistor (10k) should be connected from pin
D to pin F to over-ride the internal pot fault detector
circuit.
Zero speed will be for zero voltage input and full
speed voltage may be adjusted (by the pre-set) to be
from 3v to above 20v. Input impedance is 100K.
If pin D is shorted to pin E (and the 10K present) the
gain control may be used as a pre-set speed control.
Ignition and reverse inputs are both high impedance
(voltage controlled). High activates. Thresholds are
around 5v and 7v.
On/Off switch
Circuitry in the controller switches it off (zero
current consumption) unless there is a voltage on pin
B or pin C.
The wiring is shown on page 6.
Beware of changing any switch when the motor is
running: the motor will brake to a halt more or less
quickly, depending on the deceleration ramp setting.
If the switch changed is the reverse, it will then
accelerate up to speed in the other direction. This
process is quite safe (for the controller).
With the ignition off, or even with the battery
disconnected, the relays short out the motor so free-
wheeling is not possible. To freewheel properly the
motor should be disconnected.
Reversing
Reversing switch
Reversing switch connections are shown in the
diagram above. Reversing is ‘dual ramp’ which
means that, if the vehicle is reversed at speed, it
automatically slows down under control of the
deceleration ramp then reverses and speeds up under
control of the acceleration ramp.
Whenever the vehicle is in reverse, a speed reduction
circuit operates, so that (if the gain adjustment has
been set up sensibly) full reverse speed is half of full
forward speed.
Reverse Speed reduction
¶ If half speed reverse is not required it can be
disabled by moving the header marked ‘HSR’ on the
board (and shown in the ‘features’ diagram). This is
a pinstrip with a shorting link which simply unplugs.
As shown (bottom pin free) reverse is at half speed.
Reverse threshold
If you are reversing the controller from, for instance,
a microcontroller, the threshold is around 5v. A
voltage above this selects reverse, below the
threshold selects forward.
front side back
Page 10 VTX series instructions
Dual Ramp Reversing
‘Dual ramp’ reversing can be disengaged by
removing the header marked Dual Ramp Reverse on
the diagram, page 4 (DRR on the board). Reversing
then becomes ‘pre-select’ so that, if the reverse
switch is operated at speed, nothing will happen until
the demand speed is reduced to zero.
Reversing will now occur when the demand speed is
turned up again. In this mode a push switch can be
used for reversing: push the switch as you move the
speed control from zero to engage reverse and release
it when the vehicle is moving. Then, when the speed
control is again reduced to zero, the controller will
drop back into forward.
Pre-Select reversing must be used for series-wound
motors or if regen braking is disabled.
Regenerative Braking
Regenerative motor braking is integral to the VTX
controllers. When the demand speed is reduced
below the actual motor speed, the controller starts
braking, returning as much of the braking energy as
possible back into the battery. The speed at which the
braking acts is adjusted by means of the deceleration
adjustment.
Regenerative braking does not work well at very slow
speeds, simply because it relies on the motor turning
to provide braking energy. If the motor is only
turning slowly then it cannot give a lot of braking, so
a vehicle will creep if parked on a hill. To stop this
you can get motors fitted with an electromagnetically
operated parking brake. When power is applied to
this, the brake is removed and when power is
removed the brake is applied by a spring.
There are few applications where regenerative
braking is deleterious and it should normally be left
engaged.
The ability to disable regen braking can be included
as an optional extra if requested at point of purchase.
When regen braking is disengaged :
1: the controller must be also switched to pre-select
reversing (see above).
2: Chose the longest deceleration ramp setting, as the
motor will brake only under friction.
Failure to do this will cause jerky performance and
may burn out the relays
Parking Brake
Some motors are fitted with a separate solenoid
released parking brake.
The VTX controller has a circuit to drive such a
parking brake brake: battery power is applied to the
solenoid as demand speed is increased above zero
and when the demand speed returns to zero, power is
removed.
Parking brake is via the 3 pin connector, shown on
the diagram ‘Features’. Wiring is as the diagram
below.
This feature is standard on VTX-75 but is an
optional extra on the VTX-40.
Pin A is battery +ve.
Pin C is 0v which can be used as you wish or can be
used for an off - auto - on switch as below.
Braking
1
A B C
Release
Brake
Normal
To brake
1
A
B
C
Page 11VTX series instructions
The adjustment presets are identified in the diagram
on page 4.
Gain
Set this so that, at maximum required pot range, the
controller just reaches full speed: this is easiest to do
with the motor unloaded. Set the speed pot to your
required maximum point (e.g. full up) then, listening
to the motor, adjust the preset. It it usually quite easy
to tell when the motor stops accelerating.
Maximum setting of the gain preset will give full
output for about 3v input.
Ramps
The VTX series controllers incorporate linear ramps
to control the maximum acceleration and deceleration
rates. These are user adjustable and, to get best
performance from your machine, you should adjust
them to best suit your application.
Acceleration ramp
This is labelled as ‘ACC’ on the diagram: it is present
to make the vehicle accelerate smoothly when the
speed pot is increased suddenly, so as to avoid
sudden surges and shocks to mechanical components.
As supplied it is normally at half setting so that the
motor takes about 2 seconds to accelerate. Adjust it
as you require to give smooth acceleration.
Clockwise increases acceleration (reduces time to full
speed), anticlockwise decreases acceleration
(increases time to full speed). If the acceleration is set
too high (anticlockwise) the acceleration may be
limited by the current limit, which does no harm but
means that acceleration is not being controlled
properly, so will be dependent on motor load.
Deceleration ramp
This is shown as ‘DEC’ on the diagram: it is present
to make the vehicle decelerate smoothly when the
speed pot is reduced suddenly. As supplied it is
normally at half setting (about 3 seconds). Adjust it
as you require to give smooth deceleration. You will
usually find you require a lower setting (more
anticlockwise) for DEC than for ACC. If the Decel
time is set too low (anticlockwise) then the relays
will drop out (and short out the motor) before
regenerative braking has finished, giving a jerk
before the vehicle stops completely. This will also
shorten the life of the relays.
Warning
Be careful not to set the ramps too fast: if reversing is
too fast the relays can arc, causing them to stick and
also shortening their life. This is fully explained on
our www site:
http://www.4qd.co.uk/serv/nccramp.html
11: Adjustments
10: Boxed Controller
Battery+
Battery–
Motor+
Motor–
198mm
88mm
Fuse
6 core
control cable
green
bluered
white yellow
black
locating notch
View on soldered pins
of Bulgin 6 pin
(option)
line mounting female
Page 12 VTX series instructions
RAT and MST
These two presets are not fitted on standard
production.
RAT. As the throttle is moved from zero, at a low
setting one or other direction relay engages
(depending on the selected direction). This is the
RAT (Relay Activate Threshold). At the same point,
the parking brake is released.
MST. As the throttle is further advanced then,
normally just above the RAT, the controller starts to
modulate: i.e. voltage is fed to the motor. This is the
MST (Modulation Start Threshold).
If you wish to adjust these parameters and are not
completely and utterly satisfied that you know what
you are doing, please contact 4QD.
Because of stiction in the motors, they need a small
voltage before they start to rotate: this will occur at a
lightly higher throttle setting.
This 6 way connector may be fitted as an option. This
expansion connector has two main uses:
1 'T' Version. To fit a board to work with a tacho
generator in a closed loop speed control system: this
gives far better speed control range and improves
performance (especially torque) at slow speeds.
2 'D' version. For ganging two VTX controllers
together, either for a two motor vehicle or for
occasional use, as when double heading a loco.
Double heading - D version
When two standard controllers are connected together
via the expansion connectors, one is used as the
master and the second becomes the slave. The master
should be connected normally and controls one motor
and its parking brake (if fitted).
The slave controller needs only battery connections
and connections to the second motor. It does not
require any controls to be connected to the standard 6
pin input connector: if any controls are fitted to the
slave, then a 'voting' system operates: If either
ignition is on, both controllers operate.
If reverse is selected on one, both will reverse.
If speed is non-zero on both controllers, then the
fastest selected speed will control both.
So to avoid confusion, simply plug nothing into the 6
way input connector on the slave!
The slave is to be connected to the master VTX via a
4 way cable between the two expansion connectors
wired as the diagram.
When connecting up the slave link, both systems
should be in an already operating state, i.e. with
batteries connected. Never connect the slave
connection before connecting the batteries.
This slaving system can be used as a permanent
controller for a two motor vehicle, when the two
motors will perform identically but with independent
current limits. If two motors are used off one single
200 amp controller, then the full 200 amps current is
available to drive either motor in stall conditions.
With the VTX system, each motor may only draw up
to 100 amps, limited by its own controller. The
system therefore offers more protection to the motors.
Also, if one motor gets disconnected the second
motor will still be protected. Lastly, if there is a
failure in one controller the chances are that the
vehicle may still be operable on the other controller,
providing an emergency ‘get you home’ service,
albeit at reduced performance.
Pin functions
Pin Colour D version T version
A Red ignition 9v1
B speed speed from tacho
C Blue speed speed to tacho
D do not connect not used
E Yellow reverse signal not used
F Green 0v 0v
12: Expansion connector
A
B
C
D
E
Fedge of board
pin A
pin B
pin C
pin D
pin E
pin F
pin A
pin B
pin C
pin D
pin E
pin F
(inside of board)
do not connect
(optional)
(on edge of board)
Master Slave
Page 13VTX series instructions
All speed controllers should only be used with good
quality motors. Old, dirty motors can have damaged,
worn brushgear and this causes arcing. On occasion
arcs at the brushes can cause seemingly random
controller failure. Fortunately this effect is quite rare,
but it’s best to be careful.
Motor capacitor: Ideally the motor should include
an internal suppression capacitor, a ceramic type of
10n value is suitable. If the motor does not include
this you are advised to fit one across the brushes as
close as possible to the motor body as shown on page
6. The controller will work without this capacitor, but
it can lengthen the life of the system.
A word of warning: many car type motors have the
chassis connected to one terminal. Take great care
with these as you could easily short the controller out
- which would be fatal. It is best to avoid these
motors. Otherwise either make sure the motor is
mounted on insulation (including the drive shaft), or
make certain that no other point of the control system
can be earthed to chassis. If in doubt contact 4QD.
Most modern d.c. motors use permanent magnets.
These are the best for battery operation. However,
other types can be used: at 4QD we regularly use a
12v car starter motor for testing (even with our 24v
150 amp drives) since these are a far worse load than
is ever likely to be met. Into such a motor (stalled)
the controllers simply deliver their maximum current
and get hot. It is virtually impossible to damage the
controllers by an unsuitable motor (the controller will
simply get hot quickly), so don’t be afraid to
experiment.
There is no reason why you cannot use a 24v motor
from 12 volts - it will only go at half its design speed.
Also, if you use a 12 volt motor from 24v, it will go
at twice its rated speed. Since the VTX is current
limited you won’t overload the 12v motor, provided
it can handle the available (limited) current.
Shunt wound motors can be used if the field
winding can be separated. Connect the field winding
permanently across the supply and control the
armature winding: the shunt would motor then
behaves like a permanent magnet motor.
Series wound motors may also be used but they
cannot give dynamic braking and are very inefficient
at low speeds so are not ideal. To use them with the
VTX series a modification must be made so the field
can be correctly connected into the relay circuitry:
contact 4QD.
You can reverse a field-energised motor by simply
swapping over the field windings. You should not do
this when the motor is rotating as armature currents
will then be very high. The field will draw much less
current than the armature so a much smaller switch
will suffice. A field energised motor, used on the
The rated current output of the controllers is with the
heatsink hot. When cold they will give considerably
more current. Thus the 40 amp version will in fact
give about 55 amps when cold. This is OK because
the MOSFETs used are rated at 60 amps continuous
with a case temperature of 25°C. As the MOSFETs
warm up their allowable current reduces so that at a
case temperature of 100°C they can (only!) handle
42 amps each continuously. The current limiting used
in 4QD’s controllers senses the MOSFET
temperature and automatically adjusts as the
MOSFETs heat up. However, running the controllers
at full current will cause speedy heating so the
allowable continuous current will depend on the
external heatsinking.
Steel is not a good heatsink material: heat does not
flow easily in steel. Aluminium or copper is far
better. If you have a steel plate, sandwich an
aluminium sheet between the steel and the VTX to
spread the heat. For really arduous use we suggest
heatsink compound between the VTX’s heatsink and
your own: this helps heat flow across the join. Make
sure both surfaces are flat and free of grit.
The VTX-75 incorporates a thermal sensor (optional
on other models) which cuts back the output current
if the controller gets too hot. The VTX-75 cuts back
to about 20 amps, when the MOSFETs will dissipate
about 20 watts. This is still enough to overheat the
controller if no external heatsink is used, so don’t rely
on it!
13: Heat & Heatsinking
14: Choice of motor
Page 14 VTX series instructions
wrong voltage, will normally still go approximately
at its designed speed. This is because its field current
reduces (or increases) in proportion and the motor
speed has to increase (or decrease) proportionally to
compensate.
The nameplate current quoted for motors is normally
a continuous rating: most motors will safely take an
overload of about 400% for short periods. The
current the motor actually requires is determined by
the mechanical loading, not by the controller or the
motor. If the motor is too small, it will overheat and
if the controller is too small, then it will overheat. For
more information on motors, contact 4QD.
Faults are not ‘common’: as soon as 4QD find a fault
which occurs often enough to recognise it as a
problem, we try to alter the design to eliminate it.
This policy makes it difficult to give you sensible
fault finding tips - but it does improve our product!
The vast majority of controllers returned have no
fault, or simply a fuse track has been blown by a
wiring fault (see back page for fuse information). Of
the rest, most failures are due to misuse, albeit often
through misunderstanding.
We cannot do a lot about external wiring faults
except to protect the controller as much as possible.
However if a bad fault occurs in the controls
(connected to the 6 pin input connector) the controller
has been designed to protect itself and minimise
damage. So there are weak points (fuse tracks) in the
controller intended to limit the damage- see opposite.
Sometimes wiring faults (e.g. a short between +24v
and the pot) will feed current back into the controller
and blow the 9v1 zener diode. This usually fails safe
(short circuit) so that there is no voltage feed to the
pot. This is probably a return to base repair - unless
you feel confident with a soldering iron, in which
case ask us for help.
The zener can also be blown sometimes by
mishandling, e.g. disconnecting the controller than
putting it down on a metal object: the main capacitor
stores charge for q considerable time.
Some problems are caused by the wrong wire in the
IDC connectors.
MOSFETs do fail occasionally: they are doing an
enormous amount of work and sometimes one simply
gives up: commonly the drive MOSFETs cause their
drive resistors to burn up - a sure sign the MOSFET
has failed.
An understanding of the internal powering
arrangements may help you find problems (both in
the controller and in your wiring).
Connecting the ignition to battery positive turns on a
current source (about 30mA) which powers all the
internal circuitry, using a 9v1 zener diode as a
regulator. This system is very reliable as it tends to
fail safe: zeners when overloaded usually fail short
circuit, which removes all internal power.
The 9v1 line is fed to the top of the pot via a
transistor (which detects open circuit pot wiring), so
when the internal supply is powered up you can
measure about 8.5v across the pot. Operating the pot
will, then, change the blue wire to pin E from 0v to
8.5v, depending on the pot setting.
Main capacitor:
Be aware that certain uses of the controller can cause
this to heat, particularly if the battery leads are long.
The main capacitor may get warm, but should not be
allowed to remain hot to touch for too long. Heating
will shorten the life of this capacitor and, if
excessive, can cause it to vent. When it vents, the
liquid electrolyte inside boils and vents. Although the
capacitor failing does not do any direct damage (the
controller simply looses power) the venting capacitor
can expel hot electrolyte: if this gets on to the wrong
9v1 zener
current source
battery +
ignition
reverse
pot top
pot wiper
pot zero (batty -)
pot fault detector
A
B
C
D
E
F
F2
F3
15: Common faults
Page 15VTX series instructions
part of the circuit board the controller may well fail.
The capacitor can only heat while the controller is
actually working properly so capacitor failure is
always simply down to overloading the controller in
one way or another.
Overheating
If any electrical item is worked hard it can get hot. If
it is overworked for too long it will simply get hotter
and hotter until something fails. Depending on the
nature of the installation and overloading, solder
joints can melt, the main capacitor can vent and the
MOSFETs may then fail. Fortunately such severe
overheating is not common.
Sustained overheating causes the varnish around the
heatsink and capacitors to discolour. This is not in
itself harmful but can indicate problems.
No reverse.
If the controller won't reverse there are two distinct
possibilities:
1 The motor still goes forward when reverse is
selected.
2 The motor is dead when reverse is selected
The first fault is likely to be a wiring fault: the
reverse signal is not getting to the controller. Measure
the voltage on the black wire to pin C (measure with
respect to battery –ve). If this is low (below about 6v)
the controller will go forward. When high (above
about 6v) the controller will reverse. The reversing
switch connects this pin to battery positive to apply a
voltage to reverse it.
The second fault is usually in the controller.
There are many more fault-finding hints in the
service manual available on our www site.
We can repair damaged controllers. But please be
sure that the controller is faulty before returning it as
we may make a charge for handling controllers which
are not faulty or which only have the fuse track
blown.
There is an additional handling charge made if
controllers are returned in boxes. The box itself never
requires and servicing!
Otherwise charges made will depend on the age and
condition of the controller and on the fault as we tend
to be fairly lenient in interpreting the guarantee!
A handling charge will be made if working
controllers are returned for test, or with only a fuse-
track blown.
Make sure you include your name, address and
details of the fault with the returned controller.
Fuses.
Three fuses are present to limit
damage to the controller in the event of a
major wiring problem to the control input.
The main 'fuse' is a zig-zag section of
track shown to the right. It is situated on the
underside of the board, just by the battery +
connection.
If it fuses, solder a fine piece of wire over
it - a single strand from 7/0.2 cable is fine, but
no thicker! Special pads have been placed for
this purpose. Or use FSR-090 (see 4QD www site).
There are also similar fuse tracks to pins A (F2) & F (F3) of the 6 pin input
connector (far right drawing). Best check these with an ohm meter as visual inspection can be misleading.
In practise fuse tracks are very fickle: it would be possible to design a board with 5 different fuses each
one of which could blow singly and separately under different overload characteristics: we cannot guarantee
therefore that the correct piece of track will always blow! So if in doubt, fit a separate fuse as page 6.
Service
main fuse
F2
F3
Other products
4QD manufacture a full range of controllers from
our Eagle and 1QD series through to our high current
4QD series (up to 300 amps, 36v) as well as a range
of extras such as LED voltmeters for 12v and 24v,
joystick interfaces and a timer for ‘stand-off’
operation in golf caddies. We also manufacture
controllers for golf caddies, golf buggies, kiddie cars,
wheelbarrows, conveyors and other battery motor
uses.
More information
A manual such as this cannot cover all the points
everyone may need to know. For more information
visit 4QD’s WWW site on http://www.4qd.co.uk
This contains a lot of information on battery motor
control.
If you don’t have access, you will surely know
someone who does - or visit your local library. You
won’t regret it!
A full service manual is available from our www site
http;//www.4qdtec.com.service/
Do not
Solder to the power connectors: it makes it
impossible for us to fit them to our test jig if it ever
needs repair. Solder is a bad conductor of electricity
and using it for power connections can be dangerous.
Remove the power connectors. Bolting to the
circuit board is less reliable - and the controller will
not be repairable as it won't fit our test jigs.
Let any metal object contact the circuit board.
Even with battery disconnected the circuit can still be
live as the main capacitor can store charge for several
hours.
Drill the heatsink or do any grinding, drilling
or filing near the motor or controller. Metal
particles in motor or controller can cause failure and
will immediately invalidate any guarantees!
Operate the controller for long if there is an
evident fault. It will survive a shorted motor but
only for a short time.
Disconnect the motor leads when the motor is
running. The resulting arc may destroy the
MOSFETs,
Do any work on the controller with the battery
connected!l
Do not
Try to test the controller with no motor
connected. You won't harm the controller but
reversing will not operate properly.
Pull the leads on the boxed controller - you may
disconnect them internally. This is mechanical
damage and a handling charge will be made for
fixing this!|
Short out the control pot. - a short red to
green (battery -ve) can damage the controller.
Do House the controller properly so it cannot be
contaminated by water, dirt or swarf.
Discharge the main capacitor before handling
or working on or near the controller.
Use fully insulated power connectors.
Fit a motor Suppression capacitor. A 10n
ceramic capacitor as close to the motor brushes as
possible will increase reliability.
“We're in Control”“We're in Control”
Office
30 Reach Road
Burwell
Cambridgeshire, CB25 0AH
Fax: 01638 744 080
Stores
Unit 6A
Heath Road Industrial Estate
Burwell
Cambridgeshire, CB25 0AP
4QD
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2
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