Learn the secrets and taboos of caravan and trailer electric brake magnets.

For many years, expert Auto Electricians and Manufacturers ran magnet cables across single and tandem axles. The industry believed this was the correct procedure.

There are many signs your magnets are failing.

  • Magnet wear holes have disappeared.
  • Low voltage at the magnet.
  • Magnet and electrical connections not soldered.
  • Magnets cabled across the axle.

Copper Losses

If the cable size installed is of sufficient cross section area then quite rightly, it is possible to run across an axle.

However, consider the length of cable running from the 7 pin plug to the 1st electric brake is 3 meters long and the length across the axle is 2.5mtr.

In total, the copper losses causing voltage drop is 5.5mtr.

If a cable were run down each chassis rail to the left and right magnet then the total copper losses would be calculated from 3 meters of cable and not 5.5 meters.

As a result of running a cable across the axle, the first magnet will lock during braking, In addition, the magnet across the axle will not lock.

Clearly, the two magnets are receiving different voltages.

The solution is to either run a larger cable across the axle or run a cable down the chassis rails.

During my apprenticeship, I wound thousands of miles of insulated copper wire onto bobbins similar to those within an electric magnet.

If you disagree about copper losses and how these losses impact on voltage, more than happy to talk to you.

Brake Controllers

What is the right brake controller or the most effective brake controller?

Couplemate prefers a brake controller that indicates the voltage being sent to the brake magnets.

In summary

  1. 12v x 10″ Magnets have Green leads protruding from the electric brake magnet.
  2. 12v x 12″ Magnets have White leads protruding from the electric brake magnet.
  3. 12v magnets with black leads are generally Dexter brake magnets.
  4. Al-ko does not make an off-road magnet to suit Dexter brakes. However, it is possible to file or grind the tip of the magnet arm to manufacture a fit.

View our Electric Brake FAQ here.

© Steve Wotherspoon 20th Jan 2019

Learn the Secrets of Electric Brake Magnets

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