4qd Mark 2 Series Instruction Manual - Page 14

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The cover is a vacuum forming which is waterproof.

The cased assembly is best mounted with the

heatsink at the bottom: water may run over the

aluminium base with no problem - in fact water on

the base would have to be about 10mm deep before it

touched anything electrically live.

In the mouth of the cover you should fit a splash

plate (supplied with the cover) in the position shown

in diagram 6. The splash plate should be

sealed/glued in place with suitable silicone rubber

(Dow Corning 734 RTV) between plate and circuit

board. Run a fillet of rubber along the top edge of the

plate and push it up to the relays. Leave the assembly

board-side down while the rubber sets so that it runs

down to the circuit board forming a seal. When

supplied as a controller with case, 4QD will ﬁx the

splash plate in position.

All speed controllers should only be used with good

quality motors. Motors with damaged, worn

brushgear will causes arcing. On occasion brush

arcing can cause seemingly random controller

failure. This effect is quite rare, but be careful.

Ideally the motor should include an internal

suppression capacitor, a ceramic type of 10n value is

ideal. If the motor does not include this you are

advised to fit one across the brushes as close as

possible to the motor body. The controller will work

without this capacitor, but fitting 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.

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)

Page 14

15 Waterprooﬁng

The cover has a strip of foam already ﬁtted to help

sealing between cover and board. However you must

not let water get onto the board - at the very least

electrolytic corrosion will occur - so take a moment

to consider what will happen if water runs down the

leads to the controller: put a kink in the leads so

water drops off at that point.

If mounting the controller on its side, remember that

if water gets into the mouth it could sit inside the

controller and could easily touch the circuit board.

Either make sure water cannot enter or else drill a

drainage hole in the bottom side of the cover, at the

mouth, so water can escape. We also suggest you

seal the splash plate to the side of the cover with

silicone rubber.

16 Choice of motor

the controllers simply deliver their maximum current

and quickly 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 Pro is

current limited you won't overload the 12v motor,

provided it can handle the available (limited) current.

Shunt wound motors are suitable - they react as a

permanent magnet one.

Series wound motors are not suitable for the standard

controller because they will not reverse by normal

armature control.

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 see our

www site

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