Pro-120: Reversing, 24V, 120A.


The Pro-120 is a mid-size controller, suitable for currents up to 120A. Commonly used in mid-sized locos and golf buggies. It has been replaced by the newer PRO-150 digital controller, but is still available for some niche applications.


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The Pro-120 Mk2 is the culmination of the analogue Pro and NCC series development. It is designed principally for 24V operation but variants for 12V, 36V, and 48V have been produced.

The Pro-120 has been fitted to a multitude of applications including, mobility scooters, golf buggies, miniature railways, childrens electric cars, floor cleaners, caravan shifters and vehicle loaders.

Pro-120 key features are:

  • Adjustable acceleration and deceleration ramps.
  • Gain adjustment [for setting top speed].
  • Selectable dual ramp or pre-select reverse switching for a smooth transition from forward to reverse.
  • Selectable half speed reverse.
  • High pot lockout.
  • Thermal overload protection.
  • Low battery voltage protection.
  • Reverse polarity protection.
  • Built-in heavy duty reversing relays.
  • Integral box and heatsink.
  • Expansion connector for double-heading locomotives.
  • Peak current 120A. 1 minute current 80A. Continuous current 60A [heatsink dependant].
  • Parking brake driver for vehicle applications.
  • Regenerative braking.
  • Input 4k7 ohm to 20k ohm potentiometer, direct voltage control, or PWM control by Pi or Arduino etc.
  • 3 and 6 way IDC control connectors are included.


Model 120
Nominal voltage range 24 [12 possible as special order]
Minimum / maximum voltage 20 – 30
Motor current A [max] 155
Motor current A [1 minute] 100
Motor current A [continuous] 30 [depends on mounting / cooling]
Reversing Y
Half speed reverse Link selectable
Regen braking Y
Gain adjustment Y
Dimensions [mm] 181 x 121 x 46 [boxed]
Weight [g] Board = 320g, boxed = 630g,
Power connections 9.5mm push-on blades
Input 5k – 25k pot, 0 – 3V [adjustable via gain]
Reverse polarity protection Y
Over voltage protection Y
Under voltage protection Y [20V, can be disabled]
Pot fault protection Y [>30k]
Thermal protection trip @95’C
Current limit – drive Y
Current limit – regen Y
High pot lockout Y
Joystick/Wig-wag input Via joystick accessory board
Radio Control Via DMR-203
Selectable dual ramp reversing Y
Pre-select reversing mod
Ramping Acceleration and deceleration adjustable between 0.3S and 7S
Parking brake Yes [1A max]
Inhibit function N
Powerdown state (motor) shorted
Tacho feedback Via tacho interface board
Ignition, Electronic Y
Heatsink Integral with boxed version
Double heading opt
Switching frequency 20 kHz
Quadrants 4



The manual provides full instructions on setting up and operating the controller. The manual is available in two formats, one for reading on screen, and one for printing as a double-sided booklet:

Adobe_PDF_file_icon_32x32   Read manual                                                                        Booklet icon  Print booklet (double-sided)

Wiring Diagrams

There are several wiring diagrams available:

  • A typical wiring diagram.
  • With Dual channel Interface as used in Robots.
  • With pushbuttons for forward and reverse.
  • Wiring for a model loco with horn relay board etc.


We have a page here that lists issues that we have found with the Pro-120.

12v controllers

A 12v version is possible subject to a minimum order quantity [10], but see our thoughts on 12v systems.

Double Heading

For double heading these controllers an optional expansion connector must be fitted. This can be ordered factory fitted or instructions for user-retrofitting are available. Wiring instructions for this expansion connector are in the instruction manual.


You may need some or all of the following

Additional Photos

View of cased version of controller.

PRO-120 box drawing with dimensions

This is mounted on a Base of 4mm thick aluminium with a vacuum formed cover.

View of uncased (bare board version) controller.

PRO-120 Mark 2 top view of circuit board

Section through cased version

Cross section PRO 120

Showing mounting and heasinking arrangement.

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