4qd 4QD-300-36 Instruction Manual - Page 8

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10 Power Connections

Battery & motor wire size
This should be heavy gauge. For full output you will
probably use two motors. Battery drain is typically
about half the motor current (this depends on the
speed) so 10.0 mm² wire (which will carry about 70
amps continuously) will probably be adequate for the
4QD-300. Double strands of 6mm² would be better.

Battery wiring

WARNING be very careful with the battery wiring.
The 4QD is not polarity protected and any mistake
with battery wiring will destroy the controller. The
battery should be the last item you connect, and you
should disconnect the battery before changing any
other wiring. Reverse polarity protection can be
added simply by fitting a relay in the wiring if
required - see facing page - and this is strongly
recommended.
To avoid mistakes, chose a battery layout such that
the terminals cannot be wrongly connected. One
such layout is shown in the diagram
Cables anchored to chassis
Battery leads are clamped to the vehicle's chassis in
such a way that the positive lead can only reach the
positive terminal, and then only if the battery is fitted
the correct way round in the vehicle.
With incorrect battery fitting the –ve terminal (on the
left) cannot be reached by the positive cable
Be warned that, when you connect the battery, there
will be a rather large spark as the capacitors in the
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To 4QD
Keep the battery and motor wires as short as possible.
Excessive battery wiring length will cause reduced
voltage to the controller at full output, giving reduced
output current and degrading performance. Long
battery leads can also cause the 4QD's capacitors to
work harder when they may heat up, reducing their
life.
controller charge. This does not indicate a fault and
is quite normal. The capacitors are a very necessary
item (their purpose is to hold electricity to supply
current during the very fast switching of the
controller). The capacitors can hold their charge for
quite a time, so if you disconnect the battery then re-
connect it (even several minutes later) the spark may
not occur the second time. Fitting a reverse polarity
protection relay cures this spark.
Also: use good quality battery connectors. The 4QD
regenerates energy back into the battery during
braking. If the battery connection falls off at this
time then the regenerated energy cannot be dumped
and it will cause the voltage on the controller to rise
to a destructive level. Although this switches the
controller off, all control over the motors will be lost
Undervoltage protection
Undervoltage protection has two functions:
1
It can protect the controller from the effects of
a failed battery.
2
It can prevent damage to a battery which can
be caused by excessively discharging it.
Failed battery
If one cell in a battery fails, the effects at high
current an be unpredictable and can blow the
controller - since the battery voltage can disappear
very fast indeed!
Therefore adjustable battery undervoltage is now
fitted, It is adjustable (by means of a preset
adjustment on the base board) between about 14v
and 40v.
4QD series controller instructions.