Brake Controller Guide

Legal Requirements

Braking requirements for trailers in Australia are based on the weights of the trailer - specifically the ATM (Aggregate Trailer Mass). This is the maximum loaded weight of the trailer as specified by the manufacturer and is recorded on the VIN plate (vehicle identification number) attached to the van/trailer.

Trailer ATM No Brakes Requied Override Electric / Hydraulic Air / Vacuum Brake Away Required
0 - 750 kg
Very Light
750 - 2,000 kg
2000 - 3,500 kg
3,500 - 4,500 kg
4,500 - 10,000 kg
10,000 kg +
  • 0 - 750 kg (With a single axle): No trailer brakes required (this is the common size / weight of a 6' x 4' box trailer)
    • (Where a trailer has two axles less than a metre apart are regarded as a single axle)
  • 750 - 2,000 kg: Brakes fitted to at least one of the axles (normally the front). Override or electric braking is suitable.
  • 2,000 - 3,500 kg: Brakes fitted to all wheels, operated from driver's compartment, and brake-away system required (must remain applied for 15 minutes if detached). Electric brakes (or hydraulic or air) systems only. No override allowed.
  • 3,500 - 4,500 kg: Same as above
  • 4,500 - 10,000kg: Brakes fitted to all wheels, operated from driver's compartment, and brake-away system required (must remain applied for 15 minutes if detached). Air / vacuum systems only. No override OR electric allowed. Effective parking brake system required.
  • 10,000kg + : Same as above.

How Electric Brakes Work

electric brake animation

Image of an electric brake assembly (also known as a "backing plate").
This image is looking at the left hand wheel (kerb side of van), with the hub/drum removed.

Most caravans use electric brakes as pictured above. Disc brakes are available, but rarely used.

  1. When voltage is sent to the electric magnet (oval shape in lower centre of brake), it becomes magnetic is tries to stick to the inside face of the hub/drum.
  2. As the hub/drum rotates, it pulls to magnet rearwards.
  3. This in turn spreads the brake shoes where they make contact with the side wall of the hub/drum and provides the braking force
  4. When the voltage is disconnected from the magnet, the spring returns the brake shoes to their deactivated position.

The voltage applied to the magnet determines the braking force. More voltage = more braking. This is what your brake controller controls - how much voltage is sent to the electric brake magnets.

All brakes on a caravan are wired in parallel, which means they all operate at the same time, and at the same voltage. There is a single 12V cable which runs from the trailer plug near the coupling, to the brakes.

How an Electric Brake Controller Works

Your vehicle's electrical system normally operates at 12V DC. If you simply put in a switch in line between your vehicle battery and the trailer brake line, the magnets would power up to 12V immediately and apply maximum braking force with no control - most likely locking up the wheels. A brake controller (in its most basic form) allows you to adjust the voltage going to the caravan brakes - anywhere from 0V to 13.6V. The brake controller has two inputs:

  • 12V DC power from your vehicle battery
  • 12V DC sensor line from the vehicle stop lights or brake pedal

And has one output:

  • 0 - 13.6V DC to the trailer brakes

When you put your foot on the brake pedal in the vehicle, this sends a "signal" of 12V to the brake controller. The controller recognises that the vehicle brakes are active, then uses the 12V input from the battery (NOT the signal wire), and puts out a voltage of between 0 - 13.6V to the trailer brakes.

Proportional (Intertia Sensing) VS Non-Proportional Brake Controllers

There are two main types of brake controllers - proportional and non-proportional controllers.

Non-Proportional controllers are simpler - basically a dial that allows you to set the output voltage of the brake controller. ie, you might set it to 10.5V. When you put your foot on the brake pedal, and the brake controller activates, it puts out a constant 10.5V to the caravan brakes.

Proportional controllers are more complex and can sense the level of decellaration within the vehicle. They operate on a pendulum principle - imagine a weight suspended on a string from the ceiling of your vehicle. If you brake hard, that weight will fly forward very fast. If you brake lightly, the weight will swing forward gently. A proportional brake controller uses this pendulum concept to adjust the voltage going to the trailer brakes. While you still have the ability to set the maximum output voltage, and also the effect of the pendulum, the resulting braking force is a lot smoother, and more in sync with the vehicle. (These days the pendulum system is completely digital / solid state and there are no moving parts inside the brake controller).

Which Brake Controller to Choose

Non-Proportional controllers are cheaper but lack the finesse of a proportional unit. They do allow a higher level of manual intervention which is sometimes required by serious 4WDers.

Proportional controllers are generally recommended for most towing applications.

While most brake controllers are either one or the other, the recently released RedArc Tow-Pro brake controller gives you the options to set the controller into either mode. The best of both worlds!

Mounting and Installation of a Brake Controller

This really depends on the model of brake controller you choose. Or alternatively, sometimes you need to choose the brake controller based on how you are able to mount it. Due to dash layouts, air bags, and space for wiring, some brake controllers simply won't fit in your vehicle. Again the RedArc Tow-Pro brake controller is the most versatile for installation, as it has a small knob mounted on the dashboard, and the "black box" can be fitted either under the dash, or inside the engine bay.

Most proportional brake controllers need to be mounted in a specific orientation - so it is facing forward, and isn't tilted up or down too much - as this affects the pendulum operation. (The RedArc Tow Pro doesn't have this limitation even though it is a proportional controller).

Non-proportional controllers can be mounted in any orientation and is one of the reasons to go for this style of controller, as it is easier to fit in more places.

Electric Over Hydraulic Brake Controller

Some trailer brakes use a combination of an electric control over a hydraulic braking system. If your trailer has this type of brakes, you need to ensure that the brake controller supports that braking system.

Displays and User Interface

All brake controllers vary in this regard. It is important that you can easily access the controls on a brake controller to change the settings, or use the manual override in case of an emergency.

The more expensive controllers are simpler to use and setup. The units with digital displays give you very accurate read-outs of the settings. The units that just have coloured LEDs are much more difficult to setup. Many of the higher quality units have built in fault finding and will warn you of things like the trailer being disconnected, shorts in the wiring, overloaded currents etc.

Can I Fit a Brake Controller Myself

Generally a brake controller can be fitted by anyone with a good working knowledge of 12V systems. The things to be aware of are:

  • Cable size for appropriate current
  • Ensuring you have an auto-reset circuit breaker feeding power to the brake controller. (20A for up to 2 axles. 30A for 3-4 axles). (We prefer auto reset circuit breakers over manual reset or fuses as in emergencies it is better to have power availble to the braking system, even if it is intermittent).
  • Brake signal line pick up
    • This is where it gets tricky.
    • Most older vehicles are fine to tap into the cold side of the brake pedal switch or stop light.
    • However, newer vehicles - specifically the Ranger PX, Colorado and BT-50 - that have complicated ECU style signals for the stop lights - will have major issues if you do this. (You'll blow the existing vehicle ECU which is about $1,000 worth). The best bet with new vehicles is to get a qualified caravan service centre, or auto-electrician to fit them for you. If you want to do yourself, the major tip is to take the brake sensor line from the existing trailer plug on the vehicle. When a trailer plug is fitted to new vehicles, they are installed with their own ECU - not just tapped into the stop light / indicator light lines. Ensure you are working on the trailer side of the ECU for picking up your sensor line. If you don't have a trailer plug ECU fitted, you NEED to get one before going any further! (p.s. don't buy some of the cheapo ECU imports as they are a nightmare!) Brake Controller Recommendations

  • RedArc Tow Pro Brake Controller
    • We like this one for its versatility. You can switch it between proportional or non-proportional. It is a single knob on the dashboard, so it's easy to fit. It doesn't get in the way of air bags or your legs. The controller box itself can be mounted elsewhere.
  • Tekonsha Prodigy P2 or P3
    • These are great quality proportional controllers. They are mounted on a bracket normally under the dash, and provided they don't get in the way of your legs or air bags, they are easy to use systems. The P3 has advanced diagnotic capabilities warning you of any issues with the braking system.
  • Tekonsha Voyager
    • Budget, proportional controller.