caravan electric brake oval magnetCaravan Electric Brakes, magnets and optimising electrical connection methods is a trendy topic. Even auto electricians get caravan electric brakes wrong sometimes.

$32.50, click the image will take you to the buy page.

The electric magnet on the right is a 10″ electric magnet. This magnet is easily identified by the cross in the middle of the magnet.

This type of magnet has 3mm green leads. The 3mm refers to the copper cross-sectional area. A 3mm external cable is used to join the very small copper inside the bobbin or casing of the magnet.


  • Buy your electric brake magnets from well-known suppliers.
  • We have measured the resistance of many caravan electric magnets and found many magnets to be lacking enough copper wire turns.
  • This means less magnetism from your caravans electric magnet than you expected when braking.

Read on and I will explain the science in the equation for caravan electric magnets in relation to braking capacity.

When selecting your cable to wire your caravan electric brakes, you need 4mm or 5mm cable or if you are using an automotive type cable, use 6mm or larger.

Automotive cable is measured via the circumference.

Finally, do not wire across the axle as this creates copper losses and voltage loss. Wire the cable down inside each chassis rail, drill a hole near the magnet tails exit the frame rail, with the supply cable.

If you are finding it hard with wiring kits and want me to review making a kit specifically for wiring caravan electric brakes, please leave me a comment at eh end of this article.

10 inch OffRoad Electric Magnets RightAl-ko Off-road Caravan Magnet Upgrades

$45.93 click the image and go to the buy page.

The off-road magnets are essential when travelling on corrugated roads. There is no retaining clip to hold magnets onto the magnet arm. Al-ko recommends using a rubber band to temporarily retain the magnet into position until the 1st instance of braking releases the rubber band.

Consider a magnet upgrade before your trip to save you the expense of brake failure on your outback trip.

A few other spare parts like bearings, grease, white spirits to clean parts and a few extra wheel nuts are always handy spares.

An excellent article on why dirt roads destroy electric magnets. Click here.

caravan electric brakes Tekonsha Primus IQCaravan Electric Brake Controllers

Most brake controllers will not give you full voltage when stationary. Advanced braked controllers use the trailers or vehicle inertia.

$135.00, click the image will take you to the buy page.

Advanced proportional braked controllers use the trailers momentum or vehicle inertia.

A natural explanation may be to consider a pendulum inside your brake controller applies more voltage when the pendulum moves forward during braking.

When your vehicle is stationary, the voltage will be much less than 12v unless you have a dial resistor brake controller.

The proportional control in your brake controller only works when your car is in motion and braking.

You may, of course, activate your electric brakes by pulling the pin on your breakaway switch if your trailer is over 2000kg.

Important information on correct breakaway lanyard length.

Damaged Electric magnet caused by rough dirt roads.

Damaged Electric magnet caused by rough dirt roads.

Photos on the right are explained below,

  1. Standard magnet. Uses a clip to hold it into position and a spring to hold press the magnet square into the drum surface when braking.
  2. Off-road magnet has a spring but no clip. A rubber band has wrapped the magnet to keep it in place during assembly. The rubber band disintegrates upon the first application of the brakes.
  3. After 2 weeks on corrugated roads, a good magnet is destroyed. Vibrations have caused the metal tip of the magnet arm to slowing cut through the electric magnet. At this stage, the copper wire on the bobbin has been rendering the magnet non-functional. Now you can see an excellent reason to put off-road magnets on your rig.

My caravans electric magnets are drawing 1.5 amps each

The resistance of one magnet is 8 ohm.

I = V/R (I = Amps, V = Voltage R = Resistance)

Amps = 12v/8ohm = 1.5 amps

Car voltage is 12v x 3.0amp = 36 watts for two magnets or 18 watts for one magnet.

(a) The big mistake when wiring electric brake magnets, is to wire 3mm cable down one side then run more wire across the axle to the other magnet and connect.

Even manufacturers continue to make this mistake.

The long, additional run of the cable causes more voltage loss than is necessary. This cable is drawing 36.0 watts at something less than 12v.

(b) The correct method using 3mm cable or larger is to run a wire down EACH chassis rail and connect each magnet independently. This type of connection reduces copper losses and the resulting voltage loss.

(c) Proportional controlled electric brake controllers are most common in today’s market. The easiest way to explain proportional control is to think of a pendulum.

When your car is moving forward, the pendulum moves backwards and forwards according to the inertia of your vehicle. The more braking you apply (pendulum moving forward), the more current is supplied to your brakes.

Confused and just want the correct cable size?

If you are like me, you have read enough and just want the right cable size.

You will need the following

  • Distance from your car battery to your electric magnets.
  • Amps per magnet.

Then click here. This website will calculate the correct size cable for you.

If you think that was good, please goto the bottom of this page and give us a rating, please. Alternatively, contact if you require clarification.

10 inch Electric Brake Standard Assembly incl Park

I have a Master Craftsman electrical certificate issued by the NSW Electricity Commission.

TIP: Having problems replacing magnets or brake shoes? Replace the whole electric backing plate for $93.67. Click the image on the right and buy.

Caravan Electric Magnets Not Working?

It is not unusual for your caravan electric brakes NOT TO WORK when stationary. Quite often I will get a call about uneven braking, or one brake is stronger than the other brake.

Wiring magnets in series and using undersize cable is the cause of the problem.

Wiring electric magnets with cable size of 4mm for the single axle (2 magnets) and 5mm for tandem axles. (4 magnets)

A voltage drop occurs when an insufficient cross-sectional area of copper that causes the voltage problem of uneven braking.

Voltage loss in the cable is inversely proportional to the size of the copper. Ie the more copper, the less the energy loss.

If you are having problems with your brakes, then it is most likely to be a cable problem.

Wire your brakes in parallel, not in series.

Connecting electric magnets directly to your tail light will cause severe voltage losses.

Brakes still not working?

Here is a little-known cause of electric brake failure called magnetic induction in your drums.

You drums could be magnetised repelling your magnets thus causing ineffective braking.

Click here to read my article.

Love to here your comment if this articles fixes your problem.

Caravan Electric Brakes Tips:

  1. Adjust caravan electric brakes, so wheel spins between 1/2 and one turn.
  2. Brake shoes may be re-adjustment after the first 200km.
  3. Use good brand electric backing plate. Not all backing plates are the same.
  4. Chinese bearings are often the cause of overheating brakes. Overheated brakes create a lot of dust inside your drum.
  5. Check out the price for replacing both backing plates as opposed to magnets and shoes. You could save a whole lot of pain by replacing the entire backing plate. Just a small tip many folks overlook.
  6. 12″ electric magnets have a white coloured cable exiting the magnet body.
  7. Last tip, not all backing plates are the same. Al-ko and Couplemate make good backing plates you can trust and I yes, I am a little bias towards Couplemate.

12_inch_electric_brakeMechanical Problems can also develop with caravan electric brakes.

  1. Loose magnet arm causes uneven wear on the magnet and loss of braking power.
  2. Shoes not aligned correctly generate heat.
  3. Uneven adjustment on the left and right shoes causes loss of braking power.
  4. Bearings are a significant cause of overheating. Chinese bearings may be the problem. Quality bearings have the words Japan written on both the cup and race.

Alko Off-road electric brake adjustment guide.

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A good read is also “Electric Brakes made Simple”.

Finally, if you found this information helpful, please leave a review below.


* Life Time Guarantee on all Couplemate manufactured products provided those products are found to have been used according to the manufacturer’s product recommendations on our Terms and Conditions Page. If your purchased product cannot be located on our trailer parts store, then the product is not manufactured by Couplemate Trailer Parts Pty Ltd and is not covered by Couplemate’s Life Time Guarantee.