High Current Motor Controller SM70

Features

• High current output - 400A. nom. for 24 & 36 systems (18 to 40VDC)
• Damped throttle action for smooth acceleration
• Supports both ‘Centre-Off’ Fwd/Rev control and ‘Zero to Max’ foot accelerators
• Electronic braking enables ‘hard’ Forward to Reverse direction changes
• Conforms to AS2359 Australian safety standards on Powered Industrial Trucks
• Water resistant electronics to IP65
• Robust chassis constructed from heavy duty Structural Grade aluminium
• LED display to indicate throttle position
• Output present for ‘FET Bypass’ contactor when throttle is at max.
• Forced air fan cooled, via software thermostat control
• Uses ‘short circuit’ and ‘stall’ protected semiconductor devices
• Ultra Low-spark contactor switching
• Unpluggable screw terminals for easy service
• Isolated chassis supports Pos/Neg or floating ground potentials
• Automatic fault diagnosis & reporting
• Continuously checks integrity of input sensors and switches
• High Temperature audible alert indicator.
• Very High Temperature forced shutdown
• Automatic power-up diagnostics
• Fuse fault indicator
• Key Switch ‘On’ safety alert during power up
• Accelerator ‘On’ safety alert during power up
• Emergency ‘Creep-forward 3-secs’ safety control for ‘Walk Behind’ style forklifts
• Hand Brake/Seat switch support for emergency stopping
• Adaptable to a wide range of throttle curves & profiles for retro-fit installations
• Clearance Height x Width x Depth needed : 85mm x 230mm x 205mm
• 100% Designed and Manufactured in Australia

SM70 Features In Detail

100% Designed and Manufactured in Australia
This unit was designed and manufactured in Australia with the latest stringent safety requirements in mind. It can be used to retro fit older electric forklifts and pallet trucks which do not comply with modern safety standards, or may be installed on new systems.

The image (right) features a 2 tonne, 30 year old pallet truck that had its crude ‘resistor’ speed control upgraded with an SM70 unit. It now supports fully proportional speed control in both directions. The conversion made it much more controllable at low speeds and allowed it to comply with current safety standards.

High current output - 400A. nom at 24VDC
The controller can handle between 18 to 40V, which makes it suitable for 24V and 36V systems. It supports series DC motors up to 400A on a 10% duty cycle or 250A on a 60% duty cycle. In its standby condition, that is when the throttle is released position, or the handbrake is on, the controller consumes a mere 50 milliamps from the battery.
Where a Bypass Contactor is fitted to a vehicle, much higher current levels and duty cycles are attainable. (Capacity is then limited only by the motor, battery and cabling ratings)

Note that a 48V versions of this controller are also available.

Damped throttle action for smooth acceleration
A ramped acceleration ensures that wear on tyres, drive transmission and motor components, is minimised. A ‘floored’ accelerator takes approximately three seconds to deliver maximum power to the motor. This is a one way dampening action, which means that deceleration changes can be close to instantaneous if needed.

Supports both ‘Centre-Off’ Fwd/Rev control and ‘Zero to Max’ foot control
There are two common types of accelerator profile for electric vehicles. The Centre off control is common to many walk-behind lift trucks where pressing a lever Forward moves the vehicle in that direction, pulling it back reverses the direction. Releasing the lever forces the control to spring return to an OFF position. Special software makes it safe to the controller and transmission to ‘crash’ between forward and reverse rapidly without causing damage. It does this without the need for microswitches to be fitted across the throttle lever to detect when the throttle is at rest.

A simple Zero to Maximum throttle profile may also be engaged. This is common for a foot pedal operation, similar to regular motor vehicles. An separate forward/ reverse switch can be added to the controller to determine the vehicle direction.

Most vehicles will not move until at least 20% of drive is applied to the motor. To avoid overheating motors without them moving and to reduce dead throttle rotation at the start of acceleration, drive levels between zero and 20% are not used.

Centre Off Profile                      Zero To Max Profile

Electronic braking enables ‘hard’ Forward to Reverse direction changes
The controller unit includes special braking routines, often referred to as plug braking. This feature is engaged whenever the throttle is brought to a halt, or passes through zero on a direction change. Put simply, it reverses the contactors that feed power to the motor and gently applies controlled power in the reverse direction until the motor has stopped. When the electronics has detected that movement in one direction has ceased, it the permits normal acceleration in the reverse direction. This permits the operator to flick the throttle control between forward and reverse rapidly without undue stress to the motor and drive systems.
The degree of the braking effect is automatically increased in intensity and duration as the load upon the vehicle is increased. This feature provides smooth operation for both light and heavy loads.

Conforms to Australian safety standards
This motor controller conforms to the following Australian Safety standards on powered industrial trucks...

AS2359.1.1.5.2 Electrical protection & isolation requirements
AS2359.1.9.5 Operator control systems and formats
AS2359.1.9.6 Emergency isolation switches
AS2359.1.9.9 Electrical drawings
AS2359.1.7 Safe reversing of pedestrian controlled vehicles

Water resistant electronics to IP65
The interior of the controller is divided into two compartments. There is a fully ventilated air cooling partition which can tolerate mild ingress of moisture and water spray, and a sealed compartment which houses the electronics and drive components. Note that while the electronics can withstand intermittently sprayed water, prolonged exposure to such moisture may cause corrosion on or around screw terminals and other wiring external to the sealed compartment.

Robust chassis constructed from heavy duty Structural Grade aluminium
The controller chassis is constructed from a solid cross section of aluminium channel. This provides considerable strength and rigidity for industrial environments and good heat distribution when the controller is under load.

The rear-view image shown here shows clearly the two partitions, the sealed electronics compartment and the forced air cooling section.

LED display to indicate throttle position
A small red LED display is located on the front of the control unit. It provides a relative indication of throttle position from 0 to 9 in both the forward and reverse direction. The display is blanked when the controller is turned off via the key switch or handbrake, and during various alarm conditions. The decimal point on the display remains on as long as power is connected to the controller. This is a safety feature to remind service staff that the system is still active prior to maintenance being carried out.
If desired, an LED display can be extended to a dashboard or similar position where the operator can see the display during normal use and get some visual feedback on how hard the vehicle is being driven.

Output present for ‘FET Bypass’ contactor when throttle is at max.
The controller provides for three contactors, a Forward contactor, a Reverse contactor and a Bypass contactor. Normally the motor speed is managed by high power semiconductors within the controller. When the drive to the motor accelerates to greater than 95% of maximum speed, a special output is activated to turn on a Bypass Contactor. This contactor effectively bypasses the electronic control and connects the motor directly to the battery. The bypass contactor is normally fitted where the vehicle is used frequently at maximum throttle. Like the forward and reverse contactor outputs, the Bypass contactor output is short circuit protected and can deliver up to 5 Amps to the contactor coil.

Forced air fan cooled, via software thermostat control
An integral fan keeps the electronics cool where it is used in a hot environment or under continuous heavy loads. It is thermostatically controlled by the microprocessor and a temperature sensor. Where the temperature remains high, even with the fan running, a double-beep will sound every seven seconds as an warning to the operator. Should the temperature rise to a higher level that places the electronics at risk, a shutdown will be triggered and an over temperature fault code will be announced. The main ON/OFF key switch can be used to reset the alarm.

Uses ‘short circuit’ and ‘stall’ protected semiconductor devices
The semiconductors used to control the motor are advanced FET devices with internal protection against excess current and temperature. These devices will internally fold back their output when stressed, unlike conventional FET semiconductors which would be destroyed under similar conditions. These devices also protect the circuits that manage the direction and bypass contactors

Ultra Low-spark contactor switching
Because all contactor operation is managed by software control, no current is flowing to the motor at the instants in time that contactors operate or release. Accordingly the contactors do not arc & spark as they may with conventional control systems. This feature minimises contact wear and the risk of contact sticking.

Unpluggable screw terminals for easy service
As may be seen on the front photograph, the three screw terminal strips used for external connections push on to the front panel. This is a useful maintenance feature as the controller unit may be serviced or replaced without the need to disconnect wires from the terminals. This removes the possibility of restoring a wire to the wrong terminal after equipment changeovers. The three screw terminal strips are of different sizes to prevent entire strips from being transposed in error during service.

Isolated chassis supports Pos/Neg or floating ground potential’s
The aluminium chassis of the controller is electrically isolated from supply or control potential’s. This means that the controller would not be affected if the chassis of the vehicle had a positive or negative ground.
(regardless of this feature, it is good wiring practice to ensure that all switch, sensor and potentiometer wiring is not bonded to the chassis. This ground isolation helps to increase noise immunity between motor current pulses and sensitive analogue inputs)

Automatic fault diagnosis & reporting
A number of potential alarm fault conditions are monitored by the controller. Some of theses are integrity checks that only happen when the battery is first connected, others are monitored continuously. Each alarm condition is announced by a unique sequence of ‘beeps’ emanating from within the controller. If the beep sound is not loud enough, provision has been made to extend the beeper to an operator dashboard or console.
Critical faults cause the controller to shut down. When this occurs, turning the key switch OFF then ON again will reset the alarm. If however, the cause of the fault is still present, the same alarm may be tripped again. A brief description of the tests is shown below. The full description of the various fault codes and sounds are located in another section of this guide.

Continuously checks integrity of input sensors and switches
If at any time the throttle wiring, temperature sensing or brake wiring should become shorted or open circuit, the controller will shut down and identify the problem with a corresponding beep code.

Automatic power-up diagnostics
Whenever power is first connected to the control system, it will perform multiple integrity tests to ensure safe operation. This includes checks on all contactors, motor and FET devices by briefly operating contactors etc and measuring the response against known profiles. If all tests are passed ok, the controller will beep three times as a successful start up confirmation.

Fuse fault indicator
Inside the controller is a small fuse to protect the electronics. Naturally if this should blow, there would be no power to the computer chip to report the problem. Instead a small red indicator is placed on the front of the controller near the display. Should a blown fuse condition occur, this indicator will glow to highlight the problem.

Key Switch ‘On’ safety alert during power up
If the key switch is left in the ON position while power is connected to the vehicle, a slow , steady beep will sound as a reminder to the operator. Should this occur, turning the key OFF and ON again will reset the reminder alert. The key switch control also provides two-level operator safety. As well as updating the microprocessor with operator activity, when turned ‘OFF’ the key switch also drives a quite separate safety circuit which inhibits any contactor operation independently of any microprocessor commands and functions.

Accelerator ‘On’ safety alert during power up
Similar to the key switch, if the throttle is not ‘at rest’ (zero speed) while power is connected, the controller will beep rapidly as a reminder to the operator. Should this occur, returning the throttle to the OFF position will reset the alert. This is a safety feature to prevent a runaway vehicle in the event that the throttle or foot pedal has been jammed into the ‘ON’ position.

Emergency ‘Creep-forward 3-secs’ safety control for ‘Walk Behind’ style forklifts
One of the risks to using the walk-behind style of forklift is the possibility of accidentally backing into a wall while moving backwards and having the throttle tiller sandwich the operator against that wall. In order to comply with Australian safety standards, the vehicle tiller must be fitted with a wide safety switch that will activate as it strikes the chest of the operator. If this switch is activated, the controller will force the vehicle forward for 3 seconds (at 40% throttle) and then halt. The three second timer is present to ensure that the vehicle will not operate ‘out of control’ if the creep switch were to fail or become jammed in the ON position.

Hand Brake/Seat switch support for emergency stopping
An input is reserved for connection to a hand brake or seat switch, or both. If the vehicle is fitted with a seat switch that will activate when the operator stands up or leaves the vehicle. Whenever this happens, the electronic braking routine will be engaged and the vehicle will come to a halt. Should acceleration be attempted while the switch is active, the controller will beep rapidly to alert the operator. This is a reminder to prevent the operator from running the vehicle while a brake is still engaged.
To ensure the integrity of this circuit at all times, a small resistor must be fitted across the rear of the brake switch. This is present so that the controller can pick the difference between a released switch and defective wiring. If the brake switch wiring is compromised, a critical fault will be triggered and the vehicle will shut down.

Adaptable to a wide range of throttle curves & profiles for retro-fit installations
Where a lift truck or vehicle is having its original control system replaced with an SM70 unit, it may be practical to connect to an existing resistive throttle circuit. Should this occur, there are a number of standard profiles available to match that control. If the throttle characteristics are non-standard then contact the distributor about creating a customised profile for that vehicle.

12 month parts & labour warranty
The SM70 controller carries a 12 month parts and labour warranty. The warranty does not cover transport costs for repaired or replaced equipment. The warranty may become void if the fault is the result of an incorrect installation.

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SM70 Connection Diagram

Note:
For an installation to be compliant with Australian safety standards, ensure that…

1. A prominent (norm.closed) Emergency Stop switch must be wired in series with contactor coils.
   
2. A suitably rated short-circuit protection fuse must be wired in series with the battery
   
3. A key switch must be fitted to prevent unauthorised access to the vehicle
   
4. The vehicle must be fitted with a warning horn to alert pedestrians.