CARAVAN ELECTRIC BRAKES

Caravan Electric Brakes are a very popular topic. Even auto electricians get it wrong sometimes.

Caravan Electric brake magnets have no positive and negative leads.

A copper wire is wound around a bobbin several thousand times to generate the EMF (Electromotive force) in a magnet.

The two cables you see on a brake magnet are the start of the winding and the finish of the winding.

Caravan Electric brake Magnets cannot operate in reverse if wired incorrectly.

Electric brakes are electromechanical. When energised, the magnet attaches to the drum’s inner face; the spinning drum face applies pressure to the magnet arm, which in turn energises the brake shoes.

Why is one wheel hotter than the other?

It would be reasonable to think the problem is located at this hot wheel, yes?

The answer is actually NO, but let me explain.

The step is essential. With the car running and someone manually operating the brake controller (not putting their foot on the brake), engage the brakes. Voltage should be around 14v at the battery, the trailer plug and magnets.

Measure voltage on all magnets.

All voltages should be the same.

The lowest voltage shouldbe at the last magnet in the wiring system.

*** The opposite magnet to the hot one on the same axle is LAZY and low-voltage. ***

It is considered lazy because it is not receiving sufficient voltage. The solution is to double the wire size for all undersized voltage readings.

Wiring Size

It is not uncommon for manufacturers to fall into the trap and install cable the same size as the magnet. Your actual cable size should be double this size.

The wiring exiting the magnet is the largest cable size the magnet manufacturer can install in the magnet bobbin.

Finally, on this point, an auto electrician told me I was wrong and that he had been using his cable methods for 40 years.

I explained to him that I was a Master Craftsman Electrical and that I had held an Electrical Fitter/Mechanic Licence issued in NSW in 1976. (Stephen Wotherspoon). I offered to send him the voltage drop calculation for his trailer build, but he said it was unnecessary.

The points above are the primary causes of the electrical braking issue we receive at Couplemate.

Myth Busted

10″ Electric brake Magnets draw 3.2amps and 12″ Electric Magnet draw 3.4amps

The car voltage is 12 V at 3.2 A, for a total of 38.4 W per magnet.

The biggest mistake when wiring electric brake magnets is to run 3mm cable down one side, then run additional cable across the axle to the other magnet and connect them.

The longer the cable run, the larger the voltage loss.

This cable is drawing 76.8 W at less than 12 V.

(b) The correct method using 3mm cable or larger is to run a cable down EACH chassis rail and connect each magnet independently.

This type of connection reduces copper losses and the resulting voltage loss.

Proportional Brake Controllers

(c) Most electric brake controllers are proportional controlled. The easiest way to explain proportional control is to think of a pendulum.

When your car is moving forward, the pendulum moves back and forth due to your car’s inertia.

The more braking you apply (the pendulum moves forward), the more current is drawn by your brakes.

It is not unusual for your brakes NOT TO WORK when stationary.

Quite often, I will get a call about uneven braking or one brake being stronger than the other.

This problem is often caused by undersized cable wiring in a series.

Wiring the electric brake magnets with a cable of a larger size.

3mm for single axle (2 magnets) and 5mm for tandem axles. (4 magnets)

Voltage drop is caused by insufficient copper cross-sectional area, leading to uneven braking.

Copper in the cable is inversely proportional to the cable’s cross-sectional area. ie the more copper, the less the voltage loss.

If you are experiencing brake problems, it is most likely a cable issue.

Wire your brakes in parallel, not in series.

Do not connect your taillight to your brakes, as it is wired with a very light cable. Voltage losses occur when taillights are connected directly to your magnets.

TIP:

1. Adjust brakes so wheel spins between 1/2 and 1 revolution.
2. Re-adjust after 200 km to allow for the shoes to be properly bedded in.
3. Use a good brand electric backing plate. Not all backing plates are the same.
4. Overheated brakes can often be worn Chinese bearings. If there is not much dust in your drums, the hot brakes are likely faulty bearings.
5. Check the price to replace both electric backing plates rather than magnets and shoes. You could incur significant pain by replacing the entire backing plate. Just a small tip many folks overlook.
6. Last tip, not all backing plates are the same. AL-ko and Couplemate make a good backing plates you can trust and I yes, I am a little bias towards Couplemate.

Mechanical Problems can also develop in electric brakes.

1. A loose magnet arm causes uneven wear on the magnet and loss of braking power.
2. Shoes not aligned properly cause 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. Only use bearings labelled “Japan” to ensure high quality.