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Improving your Caravan Brake Wiring Ability

by | Apr 25, 2020 | Repairs & Maintenance | 0 comments

Improving Your Caravan Brake Wiring Ability

Improving Caravan Electric Brake Wiring for many owners is near impossible. Although I have written many, many articles on this same subject, the concept of voltage drop remains elusive.

Some trailers and caravans are very long and therefore incur more voltage drop than usual. Measure the voltage drop from the car battery to the last electric magnet.

We recommend auto electricians install a proportional brake controller to power electric drum brakes on caravans and electro-hydraulic disc brakes on boat trailers.

“Voltage drop does not concern me as I do not have braking problems.”

Fair enough but do yourself a favour and get under your vehicle to measure your magnet volts. Your wife can push the override on your electric brake controller rather than pull the breakaway pin.

These days most cars have proportional control such as tow pro elite or similar controllers. This type of controller increases the amount of power from the tow vehicle to the trailer braking system as the driver increases pedal pressure.

What voltage should I see at my electric magnets?

The minimum voltage you should see is 12vdc. If lower then your cable is too small. (Run your car as the battery may be under 12v, with the car running  the battery voltage should be more than 13v)

If your manufacturer has run a cable across the axle, then it is almost impossible to get identical voltages at each magnet.

Another example of mega failure occurs when connecting a stoplight directly to electric magnets. The braking force or current required to run through trailer wiring is 6.4 amps per axle.

How do I get even voltages?

Run a cable down each chassis rail so that the same length of cable feeds each magnet.

What Size is my electric cable?

Herein is the problem, there are two calculations for cable sizes.

  • Most automotive outlets use American wire gauge.
  • Electrical Outlets use the cross-Sectional area calculation method.

Narva_CableThis comparison chart below removes a lot of confusion.

To improve caravan electric braking systems, start by measuring the cable size (copper size) of the electric magnet, it is 1.15mm diameter or close to it.

Caravan braking and camper trailer braking are all improved when increasing cable size.

Narva advises the 3mm Size of this cable in this photo is a stock number only. The 3mm is not the correct size of the wire. The 1.13mm nominated is the actual cross-sectional area size of this cable.

So please ignore this 3mm Size.

Two sizes are identified in the chart below

  • 17 AWG or
  • 1mm Cross-Sectional Area


caravan cable size comparison

Is 17 AWG or 1mm cable sufficient Size for a single axle trailer?

A 17AWG almost gets it right with correct voltages, however, if you upgrade the cable to 15AWG you will feel your electric magnets come back to life.

Is 15AWG  of sufficient Size for my tandem trailer?

Unfortunately not. Use 14 or 13 AWG for the ultimate braking experience.

Voltage Drop

For those of you that are technically minded and wish to calculate voltage drop in a copper wire, use the following formula:

Volts= (Length x Current x 0.017) /   Area

  • Volts= Voltage drop
  • Length= Total Length of wire in metres (including any earth return wire)
  • Current= Current (amps) through wire
  • Area= Cross-sectional area of copper in square millimetres

What if changing the cable does not work?

At times, changing cable may not work due to a little know phenomenon known as drum polarisation.

I will write more on this subject in a few weeks, but here is a brief overview:

Caravan Electric Brake Problems Simplified

Electric Drum Polarisation

The connection of 2 wires determines if the magnet surface has a North pole or a South pole. By looking at the cables, one cannot tell the correct polarisation.

The drum face can become polarised accidentally if the brake magnet is engaged by say a breakaway switch for a period of more than 15 minutes.

In this case, the drum face is magnetised to the same polarity as the magnet.

When the magnet re-engages, it will repel instead of attracting onto the drum face.

Slow brake response is also a symptom of polarisation. In this case, the tow vehicles brakes provide most of the braking power.

The remedy in the past was to change the polarised drum for a brand new drum. As a result, braking returned to normal. Note: Brake shoes are not damaged during polarisation.

Finally, an alternative is to interchange the wires, to reverse the magnet polarity. Initially, a robust connection will occur when a north polarity magnet is attracted to a south polarity drum or visa versa.

©Steve Wotherspoon 25th April 2020. Images and text may be copied, provided a link back to the copied page and the source is displayed where the content or image is located.


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