Electric Brakes How do they work?

[Randylandy]

Dumb question but how do electric brakes work? I have a controller on my disco what happens between the time I put my foot on the anchors to having the brakes come on on the trailer. I understand how the actual brake part works just not the electrical side. ie is the controller hooked up the the brake light or is it driven by accelerometer? Is there a wire from the controller to the trailer or is it wire less? Are the brakes on/off or progressive.

I hired a car trailer the other day that had electric brakes but everything was self contained on the trailer so buggered if I know how it knew when to turn on or off.

[Lotz-A-Landies]

There is a positive wire from your battery to the trailer socket on the rear of your vehicle the controller sits in this line and varies the amount of current that can go to the socket based upon a number of factors, the setting the driver makes on the controller and for some types the G-Forces involved in the decelleration. The higher the setting/more G-forces the greater the current sent to the socket. Everething is activated by an electrical tap into the stop light switch/wiring.

For the trailer side, (mostly) you have special drum brakes on the trailer, they have both smooth braking surface for the shoes, just like normal drum brakes, and also the back of the hub is machined flat. A pair of electro-magnets are mounted close to this flat hub back. When current is applied to the electro-magnets they try to clamp onto the drum but because of the rotation of the wheels the magnets are rotated slightly within the drum, this movement drags on a mechanism connected to the shoes forcing them onto the braking surface of the drum. The more current applied the harder the magnets clamp and the more mechanical (braking) effort is applied to the shoes.

Electric drum brakes don't work in reverse and the mechanisms are sided.

[Yorkie]

i have a tekonsha p3 in mine and it is a simple case of connecting four wires, power, neg, brake switch, trailer blue wire. i hooked up the brake switch to my brake light at the rear as was easier, still works fine.
when you brake it detects the cars deseleration and applies the trailer brakes to match, you can fine tune how much braking is done by the trailer on the in cab controller.

below is from the tekonsha site


Proportional based controls offer a smooth braking response to almost any stop. Through the use of a sensing device, the brake control can determine the tow vehicle's rate of deceleration and then apply the trailer brakes to match. In other words, Proportional controls deliver power to the trailer brakes in direct relationship to the actual physical deceleration of the tow vehicle.

like you say some trailers have the unit fitted to the trailer, no experience with these but suspect work the same but without the one the move ability to adjust the settings.

[Lotz-A-Landies]

...I hired a car trailer the other day that had electric brakes but everything was self contained on the trailer so buggered if I know how it knew when to turn on or off.The hire trailer probably worked from your controller just like an electric braked trailer that you would own yourself.

However if it was a trailer that didn't require a controller on the car, it would operate like this. There would be a battery mounted onto the trailer and connected to this is a brake controller. When the car brake lights come on the trailer brake lights also come on via the trailer wiring, the brake controller has a tap into this brake signal and uses it the same way as the controller on the dash would work. It would likely have a charging circuit for the trailer battery possibly using the tail light current (did they ask you to keep the tail lights on?).

The disadvantage of this system is that you don't have an emergency over-ride to apply the trailer brakes from the drivers position. This is a requirement for trailers above 2 Tonne ATM and can save the car and trailer combination in the event of uncontrolled fishtailing event.

[Blknight.aus]

theres several parts to it...

the most basic uses a feed from the battery, a feed from the brake lights and a feed to the brakes theres a variable current/voltage limiter so you can manually dial the brakes to suit the load

more advanced ones have a g sensor fitted so that if you start braking hard the brakes are applied harder for you (works in the place of the current/voltge limiter)

even more ones tie into the vehicles systems and sense what the BECM and ABS system is saying and applies the brakes appropriately.


the second system is now by far the most common.

[ozscott]

I have mounted a new Hayman Reese with both delay and power adjustments for offroad use. Prefer that to G sensors for that stuff.

Cheers

[Pedro_The_Swift]

just to get your head around it--
the magnet grabs the inside face of the drum, directly behind the wheel studs.
The magnet operates an arm which twists a square block inbetween the top of the brake shoes. The design is not very efficient even for drums.

Do they make twin leading shoe electric brakes?:angel::angel::angel:

[Pedro_The_Swift]

I think the on-trailer module ones are only allowed in QLD??

[ozscott]

I stripped mine down the other day and serviced them. I need a new magnet and drum one one side. They actually work well if properly adjusted and are exceptionally powerful. Having said that electric over hydraulic discs are the bees knees.

Cheers

[Lotz-A-Landies]

I think the on-trailer module ones are only allowed in QLD??I know that the portable Tekonsha Prodigy RF that can be used in any car without the car being wired are not legal in Australia because the manual over-ride does not illuminate the trailer stop lights as required by ADR.

[weeds]

I know that the portable Tekonsha Prodigy RF that can be used in any car without the car being wired are not legal in Australia because the manual over-ride does not illuminate the trailer stop lights as required by ADR.

so the P3 manual lever should make the brake lights come on?.......i must try that when i next connect the trailer

[Graeme]

Electric drum brakes don't work in reverse and the mechanisms are sided.Not so for mine at least (ie working), although the linings are mounted to favour forwards direction. The lever swings in both directions, moving what is normally the trailing shoe instead of the leading one when reversing.

[Lotz-A-Landies]

I know that the portable Tekonsha Prodigy RF that can be used in any car without the car being wired are not legal in Australia because the manual over-ride does not illuminate the trailer stop lights as required by ADR.
so the P3 manual lever should make the brake lights come on?.......i must try that when i next connect the trailerI don't think it will work on my D4 either because they had to add a diode to the brake signal wire to stop feedback from the D4 electronics.

[Graeme]

I haven't fitted a diode to my D4 (yet) but no problems to date. I spotted today that using the manual lever with the ignition off only operates the van brake lights. I didn't check if the vehicle's lights operate using the lever with the ignition on but all lights work with the brake pedal with the igniton off. It was rego check time...

[Meken]

I haven't fitted a diode to my D4 (yet) but no problems to date. I spotted today that using the manual lever with the ignition off only operates the van brake lights. I didn't check if the vehicle's lights operate using the lever with the ignition on but all lights work with the brake pedal with the igniton off. It was rego check time...

Oh dear - late model landrover owners need to beware of ebc's - that dasterly red wire sensing the stoplight . - tekonsha have confirmed that when you use the manual lever - the tekonsha (p3 at least) sends current down the red wire to illuminate the brake lights. - yep that's all good in an old kingswood, but in modern cars with ecu's all over the place that's not good to have 12v current going backwards in the vehicle wiring.

My landy dealer is installing (on 2008 freelander 2) a diode protection 4 pin relay in the brake light wire that comes from the trailer ecu. the trailer ecu brakelight wire will pull the relay which will connect the constant 12v on the relay to the output, then the P3 red wire will be spliced in between the relay & the trailer socket. He said he normally does this at the brake pedal light switch but as i had someone else wire in the P3 (badly) and the wires are already run he is going to do it this way.


so the P3 still "senses" the brake light when brake pedal pushed, but when manual lever used on P3 all that can happen is current feeds through to trailer and cannot get back to ecu because relay is open.

a lot of auto elecs do not know this and will splice the wire in where they can. Installing the diode in the P3 red wire will make the installation not comply with ADR

He said stay well away from the cars stop light wires as they are controlled by fet's and it doesn't take much to upset them and they are not replaceable (IE whole new ecu required)

[Graeme]

It seems to me that LR has on the D4 fully catered for the likes of the manual lever on the P3 to ensure the trailer/van brake lights illuminate as required by law and that the locally recommended diode is not required.

FETs are replaceable but obviously not by your local mechanic and that warranty would also be voided. FETs for power switching are high current and robust devices that usually also have an inbuilt protection diode that cater for the reverse polarity current produced by a coil (eg driving a relay) when its power is removed, not that a P3 would be expected to be operating a coil/relay using the sense wire circuit.

[Lotz-A-Landies]

Hi Graeme

Not sure where the P3 was tapped in, I know that in the US there is a Tekonsha harness available to connect the P3 to the LR4 (D4).

I do know that the day after fitting the P3 I had a series of error codes, including special programs off, hand brake fail, esc off, hdc off etc etc, later that day the trailer brakes locked on and then a repeat if the full set of error codes.

Diana

[Graeme]

I won't hazard a guess at the reason why one D4's P3 installation works fine without a diode yet another doesn't, only that I fitted mine so I know how mine's connected.

Edit: I wonder if your one was connected to a brake switch wire and that wire was not the one for the lights but for the failed switch check circuit.

[Meken]

Hi Graeme - just for my interest sake? have you used the manual lever on your P3 whilst driving?

i would expect that the cars electrics are robust enough to support the connection of these add ons - considering the intention of these cars to go off road and with the towing capabilities they are engineered with!

[Graeme]

Yes I have - just recently at least to test that both van wheels locked (on dirt) at the same time to check that they are sufficiently evenly adjusted.