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Learn the Secrets of Electric Brake Magnets

by | Mar 13, 2019 | Repairs & Maintenance | 0 comments

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

  1. Incorrectly installed electric brake magnets will not stop your caravan quickly.
  2. For years, expert auto electricians and manufacturers ran magnet cables across single and tandem axles.
  3. 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 are not soldered.
  • Magnet cabling is installed across the axle.

Read on, and we will go into more depth.

Learn about polarised electric drums here.

Copper Losses

If the cable size installed has sufficient cross-section area, it is perfectly possible to run it across an axle.

However, consider that the cable from the 7-pin plug to the first electric brake is 3 metres long, and the distance across the axle is 2.5 metres.

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

Install a cable down each chassis rail to the left and right magnets; the total copper losses would be calculated from 3 metres of wire, not 5.5 metres.

Running a cable across the axle causes the first magnet to overheat during braking and the opposite magnet to become cold.

Copper losses between the two magnets cause different voltages and inefficient braking.

The solution is twofold:

  • either run a larger cable across the axle or
  • run the wiring down each chassis rail.

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 voltage, I am more than happy to discuss this with you.

Brake Controllers

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

Couplemate prefers a brake controller with a voltage indicator.

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 brake magnet
  3. 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.
  5. Purchase Dexter Off-Road brakes here.

View our electric brake FAQ here.

Secrets and Mysteries of Electrical Brake Systems

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