TL33 Work Platform 5-5
5.3 D.C. Motor Control - General Information
What is it ?
DC motor control is one way to achieve smooth proportional control of an electrically powered work platform.
Most of you are familiar with the “constant rpm electric motor” turning a hydraulic pump at a constant speed. The speed
of the function is controlled by the proportional valve, allowing more or less hydraulic fluid to the e.g. lift cylinder
depending on the angle of the joystick.
With DC motor control we are doing the opposite, but still achieving the same objective. By controlling the r.p.m. of the
electric motor we are controlling the amount of hydraulic fluid the pump will deliver, or the speed at which the elevating
assembly will e.g. lift.
On electric drive machines, i.e. SP37, the DC motor gives the operator the ability to drive at various speeds depending
on the angle of the joystick.
How is it done ?
The basic DC motor controller has three connections: Positive (B+), Battery Negative (B-) and Motor Field Negative (A).
The electric motor has continuous battery positive (B+) over the main fuse. Inside the DC motor controller we have high
current MOSFET transistors & capacitors and the low current control circuitry, made up of integrated circuits (IC’s).
By controlling the amount of time when Battery Negative (B-) and Motor Field Negative (A) is “connected” - the electric
motor will turn at an r.p.m. equal to the same. Or simply:
• If (B-) and (A) are connected all the time - then the motor will turn at 100%
• If (B) and (A) are not connected - then the motor will turn at 0%
• • Anything in between will turn the motor at any speed between 0 to 100%.
Some of the benefits of this type of “proportional control” are:
• • Energy efficient - preserves battery power.
• • Smooth and Precise - allows safe and easy precision control.
• • Quiet operation - the motor only “hums”, no high pitch scream.
• • Compact - no bulky equipment.
What is the difference ?
We are using two types of DC motor controllers: the PUMP controller and the TRACTION controller (Self propelled units
only). Typically we call them: a TRACTION MOS90 or a PUMP MOS90. They are not interchangeable and the
fundamental differences are as follows:
PUMP MOS90:
• A Pump MOS90 only controls hydraulically powered functions.
• Can only control a “pump motor” (single direction)
• Has two (2) or three (3) proportional speeds.
• Has up to four (4) fixed speeds (non-proportional)
• Identified by three (3) big terminal connections at the front.
• Currently there are five (5) different models covering the TL33/49 and SP37.
TRACTION MOS90:
• A traction MOS90 only controls the electrical drive functions on the SP37
• Can only control a “traction motor” (bi-directional D.C. motor)
• Has three (3) proportional speeds
• Has an electric “plug-braking” system (similar to hydraulic counter balance valve)
• Identified by four (4) big terminals at the front.
• Currently there are two (2) different models covering all SP-37’s.
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