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Trailer brake controller - ground current.

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I'm looking into the fitting of electric trailer brake controllers.

I know that there can be quite a lot of current in the trailer brake wire, especially if there are several axles.

Can anyone tell me what happens when the braking power is reduced? Does the brake controller work like an adjustable linear regulator, or like an adjustable buck controller, possibly using the brake coils themselves as the inductor? The linear regulator will get hot, while the buck controller will have quite a large ground current.

Are there freewheel diodes in the brake coils?

Or is the output of the brake controller a PWM output?

Have I misunderstood the situation?


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High-side PWM. The current through the wheel brakes returns through the trailer Ground wire. Probably a snubber diode (anode to vehicle Ground, cathode to Brake line) inside the Brake Controller (none in trailer).

I am using this one:


Your trailer design isn't stated. Will the intended trailer brake controller operate more than two wheels? You don't want to overload either the trailer or the brake controller and lose control of the situation.


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Usually it means that the brake fluid reservoir is low.

This can mean one of two things usually.

  1. Normal brake pad and rotor wear has allowed the brake pads to move closer to the rotors and pull fluid into the cylinders. This is normal but infrequent and usually toward the end of brade pad life, it usually is fixed by topping off the reservoir with fresh brake fluid, if the brakes are not worn past the point of safety.
  2. You have a brake system leak. You have no idea if it is a big leak or a small leak. A small leak can be tolerated for a short time but a big leak can result in total loss of braking power so the safe and wise thing to do is have it checked immediately after it comes on.

Whaaaaaat are you talking about?

I think Jonnywallter is a bot.
Last edited:


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He has disappeared. :rolleyes:
He was banned because he was a spammer, plain and simple.
As a result of this all his posts are automatically deleted.

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