Control Board Jumper Positions

This picture shows the factory default control board jumper positions, these allow single ended operation. For joystick [wig-wag] operation move J1 and J2 to the opposite positions.

Ampflow motor

We recently encountered a strange issue with a 4QD-300 driving an Ampflow A28-400-F24 motor. Forward operation worked as expected but in reverse a very slight pulsing or oscillation of the motor speed could be detected Read More

Damage From Blown Mosfets

It doesn’t happen often but when the mosfets in a 4QD series controller do blow they can take a number of other components with them. If you are attempting a DIY repair this photo shows Read More

Battery Contactor

This optional battery contactor arrangement can be fitted as part of the 4QD-200/300 installation to provide reverse polarity protection and also an emergency power disconnection. The relay should be chosen so that it is capable Read More

Adjustment for 48V

Unless specifically requested for 48V, we usually configure the 4QD series for 24V operation. When operating at 48V the acceleration ramp control may need to be adjusted as well as the gain control in order Read More

Overheating in Boats

If you are using the 4QD series in a boat then you should pay particular attention to airflow and cooling to prevent the controller from overheating. It’s not kind to shut your controller away in Read More

Use with Series Wound Motors

Our controllers are principally designed for Permanent Magnet motors, but they can be made to work with series wound motor with some modifications to the wiring. To control speed and direction of a Permanent Magnet Read More

Converting Parking Brake to Brake Light

The 4QD series has a Parking Brake solenoid driver. Optionally controllers can be supplied from the factory with this converted to a ‘Braking’ Light driver. This page describes the modification. Warning. The parts that need Read More

Inhibit Ramp Modification [4QD series]

The inhibit input on the 4QD controllers is designed to be used in conjunction with a microswitch sensing the foot brake on an electrical vehicle. Our features area explains this operation of the Foot-Brake inhibit. Read More

Deadband values and removal

This page specifically refers to modifying pre issue 15 boards. From issue 15 onwards there is an on-board jumper to alter the deadband. With issue 17 boards, the half-speed reverse feature was changed to make Read More

How to dismantle the 4QD series

Hopefully you’ll never have to do this, but if the need arises then here is how to do it. Top board removal. Remove the top board by loosening the four corner screws. Disconnect the 14 Read More

Fault finding on the 4QD series

4QDs policy on all controllers is one of continuous modification. If we find a mechanism whereby a user can blow a controller, we modify the design if possible, to prevent it happening. This means that Read More

Testing the 4QD Base Board and MOSFETs

Bridge testing Method All testing of faulty controllers should be done on a current-limited bench power supply: testing a faulty controller from a battery will almost certainly exacerbate the fault, causing yet more damage. The Read More

Current limit resistors

Notes on the current limit resistors for the 4QD series. The control board current limit resistors have changed frequently, as MOSFET improve the Rds generaly decreases. This increases the current, but it has to be Read More

Use with Tacho Feedback Board

The circuit of the standard tacho-generator feedback board is described on the 4QDTEC.com site and a drawing with other information is available. Mechanically, this board is designed to plug into the NCC and Pro series Read More

Control Board Modification [Pre June 2010]

Control board modification This page details two modifications The first part should be done to all controllers with serial numbers below 4028. After that, the modification was included in production. Modification is to the top Read More

Reverse Speed Modification [pre issue 17]

How to adjust the maximum reverse speed on earlier 4QD control boards. This information applies to earlier 4QD series only. With issue 17 control boards the method of incorporating half speed reverse changed. It is Read More

Mixing 4QD 150 / 200 / 300 series boards

With several ‘caveats’, the control boards and base boards of the 4QD series are interchangeable and may be mixed and matched. However – it is important that you understand the potential problems. 4QD 300: This Read More

4QD version history

This page lists the different versions of the 4QD series circuit boards, and their date of introduction. This listing was originally generated for 4QD internal use only so the descriptions may not be as full Read More


These notes apply to the inhibit function of the 4QD series controllers. If a vehicle is fitted with a hand or foot brake, it can be useful to disable the controller. This can be done Read More

Multiple Controllers [Double Heading]

This page describes wiring that allows multiple Pro-150s and 4QD series controllers to be controlled from a single speed potentiometer. This is useful when double heading model locomotives. As the Pro-150 is a programmable controller, Read More