FIXED OUTPUT, TIMED, OR PROPORTIONAL
What type of brake controller should you use?
WORDS BY JOSEPH VAN WOERKOM PHOTOGRAPHY BY CARAVAN & MOTORHOME
Most caravans are equipped with electric drum brakes because of their simplicity and low cost. To activate these brakes the tow vehicle must be equipped with an electric brake controller.
Before choosing a brake controller it’s helpful to understand how electric drum brakes work. Inside the brake assembly is a lever which forces the brake shoes against the brake drum whenever it is moved. The amount of force applied to this lever determines the amount of braking achieved. The force on this lever is determined by the current flowing through an electromagnet which rests on the outside face of the brake drum. When energised the electromagnet tries to rotate with the brake drum and moves the brake lever.
The job of the brake controller is to control the current flowing through the electromagnet and hence the amount of braking achieved. The real difference between brake controllers is how they control this current.
It turns out that there are three main types of electric brake controller; fixed gain, timed and proportional. While all three types can vary the amount of brake current by varying their output voltage, it’s important to know the differences between them in the way they change this voltage.
The fixed gain controller is the most basic and simply outputs its preset voltage whenever the brakes are applied. This means that the amount of braking done by the trailer is the same no matter how hard the tow vehicle is braking, from gently coming to a stop in bumper-to-bumper traffic to a full on emergency stop. To my mind this type of controller is simply not suitable when towing a heavy trailer like a caravan.
Timed brake controllers (aka solidstate controllers) differ from fixed gain controllers in that their output voltage starts low and then ramps up over time to the preset maximum voltage when the brakes are applied. Therefore, the longer you hold your foot on the brake, the harder the trailer brakes are applied. The ramp timing (aka Sync) can be controlled independently of the output voltage. Again, I don’t recommend this type of brake controller when towing caravans.
This leaves us with proportional brake controllers. The great thing about these is that they automatically vary their output voltage in proportion with the deceleration of the towing vehicle. They do this by using an accelerometer (pendulum or solid-state) to determine how quickly the vehicle is slowing down and vary their output voltage accordingly. In other words, the harder you brake, the harder the trailer brakes. To me, this is the only type of brake controller that is suitable when towing heavy trailers like caravans.
Some proportional controllers are also equipped with ‘Boost Control’ which activates the trailer brakes immediately when the brake pedal is depressed and before the tow vehicle starts slowing down. This increases stability when towing heavy trailers by ensuring that the trailer does not push the rear end of the tow vehicle around under heavy braking.