One of the best things that has happened to trailer braking, or particularly caravan braking, has been the development of the electrically operated braking systems. Although in Australia it has been in use on caravans for almost 30 years, electric brakes still seems to be shrouded in mystery as far as the components, operation and adjustment is concerned. In this article we will explain the benefits of an electrically actuated system, the best components to use and the best way to set it up so as to achieve reliable performance.
THE BASICS
Brakes are primarily a mechanism that converts energy from one form to another in order to slow or stop a vehicle. Any moving object has kinetic energy. This is sometimes referred to as energy of motion. If the speed of the object has to be reduced the amount of energy present also has to be reduced. However, laws of physics dictate that energy cannot be removed or destroyed, only changed from one form to another. In the case of a moving vehicle the kinetic energy has to be converted to heat energy in order to slow it down. This is the function of the braking system. By forcing brakes shoes against a drum, or pads against a disc, heat is generated. This heat is then dissipated to the surrounding air. The more efficiently this can be done, the quicker the vehicle is able to stop.
THE LEGAL REQUIREMENTS
Regulations only require brakes to be fitted on trailers that weigh more than 750kg. It is worth noting, however, that some vehicle manufacturers impose a limit of 500kg for towing unbraked trailers. Up to 2000 kg or 2-tonne any efficient braking system is acceptable as long as braking performance meets the requirements laid down by the State’s road transport authorities.
Unfortunately there is a loophole that allows a tandem or four-wheel trailer to be constructed with brakes on only two wheels as long as the trailer weighs less that 2000kg. In the interest of safety, owners of tandem trailers should adopt the philosophy that if it takes four wheels to carry the load, it needs four brakes to stop it. This means that anyone purchasing a tandem caravan should insist on brakes on all wheels irrespective of the size of the van.
If the trailer’s weight exceeds 2000kg, brakes must be fitted to all wheels. In addition the trailer must be fitted with an emergency braking system known as a ‘break-away’ system. A break-away system is designed to automatically apply the trailer brakes in case the trailer becomes accidentally disconnected from the towing vehicle. Once applied the brakes must stay on for 15 minutes. With electric brakes this is a simple process.
This self-contained Break Safe unit has an in-built battery that can be charged from an external source.
It is worth noting that in the case of the weights mentioned above that these refer to a laden or unladen trailer. If a small box trailer weighs, for example, 300kg when empty but 800kg with a 500kg load, it legally needs brakes. Similarly if a caravan has a tare or empty weight of 1800kg but loaded it comes to 2200kg it not only needs brakes on every wheel but also a break-away system.
HOW IT STARTED
Like most things in life, electric braking systems are not a recent innovation. As far back as 1927, Warner Electric developed the first electric brake for the ‘travel trailer’ industry in the USA. By 1963 three million electric braking assemblies had been produced. In Australia electric braking systems appeared on caravans in the mid seventies. Prior to this most had used an over-riding trailer coupling which applied the brakes by hydraulic or mechanical means. Although an over-riding system is a big improvement over not having any brakes at all, they require regular servicing, particularly the hydraulic type, to maintain efficient operation.
THE COMPONENTS
Broadly speaking there are two sections – the operating assembly and the control mechanism. The operating assembly consists of the backing plate, brake shoes and linings, magnet and lever and a brake drum. Bolted to a mounting plate that is welded to the axle, the backing plate holds the brake shoes, the lever and the magnet. The top of the lever is attached to a cam that expands the shoes while an adjuster joins the shoes at the bottom. The brake drum has a machined internal face which provides the contact surface for the magnet.
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The design of an electric brake assembly is similar to that of a hydraulic drum brake except that a lever and magnet is used to expand the shoes. |
The electric brake controller, which is usually mounted near the driver, automatically directs the correct amount of electrical current to the trailer’s brake assembly when the tow vehicle’s brakes are applied. Most controllers have an adjustment to compensate for different trailer weights as well as the number of wheels and a means of applying the trailer brakes independently should this be desired.
WHAT A BRAKE CONTROLLER HAS TO DO
The aim of a well-designed brake controller is to match the trailer braking to that of the towing vehicle under all operating conditions. If the driver applies the car’s brakes lightly the trailer braking should correspondingly be smooth and gentle. On the other end of the scale maximum braking should be achieved quickly when a rapid stop is called for. When this correct balance is achieved the trailer will take care of its own share of the braking without imposing additional load on the tow vehicle’s braking system.
The brake controller also has to be able to produce the correct amount of output depending on the number of trailer brakes and the weight of the trailer. Most controllers have what is known as a ‘gain’ control that can be adjusted to allow for different size trailers.
TYPES OF CONTROLLERS
In regard to operating principles, electric brake controllers can be classified under two headings. These are ‘Time Based’ or ‘Motion Sensing’. In the early days there was another design that was activated by hydraulic pressure. Recently this was re-introduced in the USA.
Seasoned caravanners are often of the opinion that the hydraulic unit was superior but modern car braking systems and regulations prevent this type being used on modern vehicles.
The Motion Sensing controllers can also be referred to as Inertia and Proportional controllers, depending on the manufacturer’s preferences. In turn the proportional ones can use a pendulum or accelerometer to determine the rate of deceleration.
CONTROLLER OPERATION
1. Time-based or solid state type
Like all controllers, the time-based unit receives a signal when the stop lights are activated. The amount of electrical current that is then directed to the trailer brakes is usually dependent on the adjustment of the power and time settings on the controller. A time-based controller always applies the trailer brakes in the same way each time unless the power or time adjustment is changed.
For normal or average braking conditions it may be possible to adjust this type of controller to provide reasonable braking. However, when the braking requirements vary from that for which the controller is set, the amount of trailer braking can either be too light or too severe as the controller has no way of knowing that the conditions have changed. Models include the early Hayman Reese solid state and RedArc controllers.
2. Inertia type
One controller that comes under this heading is the AccuTrac. Sometimes it is incorrectly referred to as a pendulum type as it has a lever on the side that has to be set in a vertical position. However, the lever adjusts an internal sensor that changes the output from a ‘Soft’ to a ‘Hard’ setting. Normal operation is not unlike a time-based controller but when the tow vehicle braking exceeds a pre-determined level, the controller is switched to a stage better suited to hard braking. The driver has to separately adjust the soft and hard setting.
3. Pendulum type controller
This type of controller uses an internal moving pendulum that determines the rate at which the vehicle is slowing down. Its movement can be compared to something dangling from the rearview mirror that swings forward when the car slows. The pendulum arm is attached to an electronic sensor that can determine the amount of electrical current that needs to be directed to the trailer depending on the extent of pendulum movement.
When the vehicle’s brake pedal is depressed far enough to make the stop light come on, an electrical signal is also directed to the brake controller. This serves to let the controller know that some braking may be about to take place and as a result the system is placed in a ‘stand-by’ mode. If the pedal is depressed to the stage that the vehicle’s brakes are actually slowing the vehicle, the pendulum inside the controller moves forward. This causes more electrical current to flow to the magnet inside the trailer brake assembly. The amount of electricity going to the trailer is dependent on the amount of pendulum movement which in turn is dependent on the rate at which the towing vehicle is slowing down. Consequently the amount of trailer braking increases or decreases proportionally to the rate at which the towing vehicle’s brakes are applied.
Commonly used pendulum types include the Hayes Energise III, Hayes Endeavour, Hayman Reese Guardian, Tekonsha Voyager and Tekonsha Sentinal.
The Hayes Energise III is a user friendly pendulum type controller that provides proportional trailer braking.
4. Accelerometer type
The accelerometer controller is similar in operation to the pendulum type described above in that it provided proportional braking. This design determines the rate of deceleration by an internal microprocessor rather than a moving pendulum. This does away with the need to adjust the pendulum position. Accelerometer type controllers are a recent innovation and usually have digital display that offers set-up, power output and diagnostic information.
Included in this range are the Tekonsha Prodigy, Hayes Genesis, Tekonsha Primus and the latest Tekonsha P3.
The Tekonsha Prodigy is a popular choice for those who like a visual display as well as offering proportional output.
THE TRAILER BRAKE ASSEMBLY
As we have established, the amount of electrical current that reaches the trailer and then the magnet is dependent on the output of the controller. The magnet is known as an ‘electro-magnet’, meaning that it has a magnetic attraction only when electricity flows through it. At the same time the strength of the magnet automatically increases or decreases as the amount of electrical current going through it varies.
When the brakes are not in use, the magnet lightly touches the inside face of the brake drum. Once the magnet is energised by electrical power from the controller, it will set up a magnetic attraction between itself and the brake drum. As the brake drum is rotating, it will try to pull the magnet with it. Consequently the lever to which the magnet is attached will expand the brake shoes out towards the brake drum. The more current sent by the controller, the greater the magnetic attraction and the higher the force that is exerted by the brake shoes against the brake drum.
Electric brakes are efficient and low maintenance.
So it can be seen that the amount of trailer braking is dependent on the output from the controller. Therefore it is important that the controller is able to vary the electrical current that is directed to the trailer’s wheels for the entire range of operating conditions from a gentle stop at a traffic light to an emergency stop on the highway. In other words, the trailer braking should be proportional to the arte at which the tow vehicle slows down.
LOCATION
Irrespective of the type of controller used, it should be located within easy reach of the driver to allow adjustment to be made or the independent manual brake lever to be used. Due to the design of modern vehicles it is often necessary to mount the controller on the lower instrument panel at the left hand side of the steering column. While this is not ideal, there is often no other option. Some drivers do complain about hitting the controller with their knee.
This is the normal location for a brake controller although further away from the driver’s knee would be preferable.
If there is a small compartment above or below the centrally mounted radio, a controller with the gain adjustment and manual lever on the front can be installed in this location. On some vehicles it is possible to remove the ashtray and use this space to fit the controller.
As the time-based controller has no moving parts it can be mounted in almost any position. Controllers that use a motion sensing pendulum or accelerometer must be positioned so that the back of the control module is towards the front of the tow vehicle. While the module does not have to be horizontal front to back, it must be level side to side. This ensures correct operation of the internal mechanism.
CONTROLLER INSTALLATION
Although the installation of a controller appears quite simple, it is not something that should be contemplated by the DIY handy person. As all modern vehicles have some type of electronic management or computer system, it only takes one incorrect connection of one of the four wires coming out of the brake controller to do considerable damage to the vehicle’s electrical system.
The installation is best left to someone with auto-electrical and brake experience. It is also very important that heavy cables are used, a good quality 20amp circuit breaker is fitted where the power is picked up from the battery and all connections are soldered. It is not a bad idea to check that the wires near the trailer’s wheels are not simply twisted together.
Also check that the earth connection between the car and the trailer is adequate. The normal earth wire that is used for the trailer lights can be too light. And the contact between the towball and the coupling cannot be relied upon to provide a good earth return.
For an electric brake system to function efficiently, all components, wiring and connections have to be of a high standard.
CONTROLLER ADJUSTMENT
The ultimate aim is to achieve a level of brake performance that allows the car and trailer combination to slow or stop with the same force on the brake pedal than that required to stop the car by itself. If more pedal force is needed than the trailer brakes are not doing enough. On the other hand if the trailer feels as if it is pulling up the car, trailer braking is too severe.
Apart from having the right equipment and installing the controller correctly the actual brake operation largely depends on the adjustment of the controller. Unfortunately most operating instructions supplied with the various controllers tend to confuse rather than enlighten. While the timed-based controllers are simpler in design, they usually have two adjustments that need to be set to allow for trailer weight, the number of wheels and the required output.
On pendulum controllers it is necessary to set the pendulum in a vertical position when the car in on level ground. Some controllers have an external levelling device which is normally positioned so that is points vertically downwards. Others use an indicator light in which case it is necessary to carefully read the instructions. Controllers with an accelerometer automatically make any adjust needed to compensate for the controller’s position. Once the initial settings are correct, the gain control or power output can be adjusted so that the braking performance is the same with the trailer hitched on than without.
With new caravans it sometimes takes a while for the brake linings to ‘bed-in’ and produce maximum efficiency. During this period it is sometimes necessary to reduce the output from the controller as the brakes wear in.
CONCLUSION
When it comes to choosing a brake controller, don’t automatically go for the least expensive. Just like these days you wouldn’t buy a car without ABS or airbags, you need to choose a quality controller that is easy to adjust, provides proportional braking under all operating conditions and makes towing, or stopping, hassle free.
If you are not satisfied with the operation of the brakes on your trailer consult someone who specialises in this type of work. Don’t accept poor brake performance as it has safety implications.
While many consumers adopt the philosophy that if all else fails, read the instructions, when it comes to electric brake controllers make sure that you read the instructions first. A brake controller is easier to set up and operate than a VCR or DVD player so should be within the bounds of most of us males to handle.
Thanks to R.V. Electronics, manufacturers of the Break Safe break-away systems, and ALKO International for their assistance in the preparation of this article.
For more information go to www.rvelectronics.com.au or www.alko.com.au.
AFTERWORD
The NSW situation
Although general braking requirements are the same throughout Australia, NSW takes a different approach when a Break-Away system is fitted. In addition to a 12volt supply in the trailer and a break-away switch on the drawbar, the tow vehicle needs to be equipped with an electrical circuit that will automatically maintain the trailer battery in a fully charged condition and can also warn the driver, by means of an onboard monitor, if the condition of the battery is such that it may not be able to maintain the brakes in an applied position for the required 15 minutes.
For more details about the NSW requirements visit www.rta.nsw.gov.au/registration/downloads/vsi/vsi22.pdf
An monitor is required that advices the driver from inside the car of the state of charge of the break-away battery in the caravan.
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