This is a simplified motor control circuit and shows the switching scheme used in our 4QD series full bridge [aka H bridge] motor controllers. The circuit shows a full bridge of four MOSFETs. In forward Read More

The battery current and motor current in a PWM controller can be very different.  Many people do not realise is that a PWM controller operates rather like a transformer (using the motor’s inductance) to deliver Read More

MOSFET is an acronym – I’ll give you the whole phrase, so you know why they’re always called MOSFETs.. Metal Oxide Silicon Field Effect Transistor. MOSFETs are very near to perfect semiconductor switches, capable of Read More

Our controllers use either a full bridge or a half bridge PWM circuit to to control the speed of an electric motor. In the half bridge configuration two sets of MOSFETS are connected across the Read More

All 4QDs controllers have a switching frequency of (around) 20 thousand times per second – 20kHz. This is high enough to give no whistle or whine from the motor but, more importantly, it means that Read More

Regenerative braking is a way of diverting the kinetic energy of a moving motor / vehicle back into the battery so that it re-charges the battery and provides a braking effect. Most of 4QDs controllers Read More

Current limit – drive Protection is fitted to all controllers so that the initial starting surge (or the current that would flow if the armature were locked) cannot exceed that which the MOSFETs can handle. Read More

When the controller is powered down (ignition turned off) but with the battery still connected, different controllers behave in different ways. There are, essentially, 3 possibilities: Open circuit Short circuit Diode Open circuit All semiconductor Read More

Acceleration Ramp Even if the throttle is applied sharply, the controller must accelerate the motor smoothly, without a jerk, so an ‘acceleration ramp’ is built into all controllers. This may be a an adjustable ramp Read More

A permanent magnet motor is reversed simply by interchanging its two armature wires. This can of course be done with any controller by using a suitable, high current, double pole changeover switch. However reversing should Read More

  If a vehicle is fitted with a hand or foot brake, it can be useful to disable the controller. This can be done with an interlock to ignition circuit on any controller. The problem Read More

Some controllers can be used with either a 3 position toggle or rocker to give forward/off/reverse or with two push buttons to give ‘go forward’ and ‘go reverse’ control. The DNO and Pro series need Read More

Undervoltage cutback – or Battery Discharge Protection When a battery is discharged its voltage falls. It is a widely known fact that discharging a battery too far can damage it, especially if it is left Read More

All 4QD’s controllers work on an input voltage, which is usually derived from a potentiometer. Gain adjustment This enables the top speed to be reduced, e.g. in a child’s car where the child is too Read More

A joystick (know in USA as a Wig-Wag control) is a lever operated speed and direction control. Move the lever forward to go forward, and pull it back to go backwards. The speed is controlled Read More

If the controller’s ignition is turned on while the throttle pot is not at zero the vehicle could accelerate to speed. High pot lockout [HPLO] prevents this by disabling the vehicle until the throttle returned Read More

If you inadvertently connect the battery up the wrong way round , then depending on which model you have, the controller may be destroyed in quite a spectacular manner! Only you can decide if this Read More

If you have read the page entitled Half-Bridge you will remember that the battery current is being switched on and off 20,000 times per second. Now electricity in wires has the equivalent of ‘mass’ – Read More

Most controllers are situated close to the user, e.g. in a ride-on golf buggy, so are controlled by a speed control pot wired directly to the controller. However some markets, such as Robots and some Read More

A tacho generator generates a feedback signal proportional to the speed of rotation, which can be used to provide closed loop control of a motors speed. Varying loads If such a ‘tacho’ is used and Read More

All controllers made by 4QD work with a voltage input, normally derived from a potentiometer. However it’s the voltage input that determines the speed. The controller cannot tell whether that voltage is coming from a Read More

Double heading is a term used by loco builders, it is where you have an engine on each end of the locomotive, so each end is a ‘head’, hence double heading. For double heading, you Read More

When choosing a controller, both it and the motor should be matched to the mechanical task that is to be done. So – you first of all need to understand the mechanics: What mass do Read More