An electric trailer brake controller is a device that supplies power from the tow vehicle to the trailer brakes. Many styles of trailer brakes are available that differ from how they look, to the number of trailer brakes they can power, but all of them can be divided up into two main groups, Proportional or Time Delayed.
The With proportional brake controllers, if the trailer brakes pedal is stepped on, a motion sensing device knows how fast the tow vehicle is going to stop. It then applies power to the trailer brakes equally as fast (or slow) as the towing vehicle. This allows the trailer to stop at the same rate as the tow vehicle. Therefore, in an extreme stopping situation where the vehicle brakes are slammed on, a proportional controller will then immediately send the maximum preset power to the trailer brakes.
For time Delayed trailer brake controllers, once the trailer brakes pedal is stepped on, the pre-determined amount of power (which is set by the user, based on trailer weight) is sent back to the trailer brakes. On time delayed controllers, a delay always exists from when the brake pedal is pushed to when the unit reaches the user set, maximum power output.
A wide range of trailers will contain trailer brakes. Smaller trailers may not contain trailer brakes. It is highly recommended that if the total trailer weight is over a couple thousand pounds, the trailer needs to have some sort of braking system and the tow vehicle be equipped with a brake controller.