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
B
+ to controller
Battery -
+24v switched by ign switch
