Need stronger brakes, what can I do?

[Rock Crawler]

I know next to nothing about trailer brakes but if the whole using the friction to apply the brakes harder is true, wouldn't they not release until the trailer came to a stop.

Incorrect. Here is why.
You have a puck style magnet that gets energized and when this happens it slaps itself into the flat face of the drum. When it has energy and goes to the face, it drags radially on that machined surface and applies force to a cam bracket that provides the expansion energy to the drum shoes.

The more energy applied to that puck, the more drag is created, and the more resulting cam expansion energy is applied to the shoes.

When you release the brake pedal in the vehicle and electrical/magnetic energy is removed from the puck, the puck drops free of the drum face and everything returns to the resting position due to the drum return springs.

The rotational force in the shoe friction surface is not what gives the brake force, it's the friction on the magnetic puck.

This is also why the magnetic puck is a normal wear item and should be inspected at least annually, often times you'll note that the friction face if the puck will take on more wear than the friction face of the shoes.

I have always replaced the magnets along with the shoes, I consider them to be standard fare on doing trailer brakes.

Also note that if the face of the drum is worn and/or grooved, that new magnet will be weak due to lower surface area contact and the air gap will be increased causing jerky braking.

There jerking happens because as the air gap gets excessive, the puck will not softly pull to the drum face with mild excitation. Instead it will lay dormant until you build enough electrical/magnetic energy to attract to the face where the puck will slap violently causing abrupt and jerky application of the braking force.

 

[ovrszd]

And his perfect explanation also explains why trailer brakes have limitations. Also why you can't apply them harder as needed. With most add on controllers a voltage max is determined by the operators settings. Once that voltage is applied that is all the braking effort you are gonna get.

Some high dollar systems tie into the vehicle brake system and apply more voltage the harder you push on the brake pedal.

My add on controller is timed. If I have it set on 8V for example, it will start on 4V or 5V and steadily increase until it reaches the maximum setting. This softens the application and takes that jerk of the trailer out of the equation.

 

[Fallon]

And his perfect explanation also explains why trailer brakes have limitations. Also why you can't apply them harder as needed. With most add on controllers a voltage max is determined by the operators settings. Once that voltage is applied that is all the braking effort you are gonna get.

Some high dollar systems tie into the vehicle brake system and apply more voltage the harder you push on the brake pedal.

My add on controller is timed. If I have it set on 8V for example, it will start on 4V or 5V and steadily increase until it reaches the maximum setting. This softens the application and takes that jerk of the trailer out of the equation.

All the decent controllers will put out up to full vehicle voltage. Every time you hitch up you should check your brakes & adjust the controller. Keep raising the voltage until the brakes lock up when you manually apply them at 10-30mph. Then back things down until they just barely don't lock up. That way the controller knows the maximum braking force (voltage) it can apply. Inertial based controllers will adjust the voltage based on how hard you brake so that the trailer matches the trucks braking force.

Applying more voltage just below what locks up the brakes is counterproductive. You loose most of your traction when tires lock up. It's the same reason we have ABS in all modern cars. Only in this case its pre-set manually. And as loads change you need to change the max voltage on the controller. It takes me about 30-60 seconds these days to kick on the trailer brakes after I turn out of the driveway & adjust things for max braking force.

 

[ddbackhoe]

All the decent controllers will put out up to full vehicle voltage. Every time you hitch up you should check your brakes & adjust the controller. Keep raising the voltage until the brakes lock up when you manually apply them at 10-30mph. Then back things down until they just barely don't lock up. That way the controller knows the maximum braking force (voltage) it can apply. Inertial based controllers will adjust the voltage based on how hard you brake so that the trailer matches the trucks braking force.

Applying more voltage just below what locks up the brakes is counterproductive. You loose most of your traction when tires lock up. It's the same reason we have ABS in all modern cars. Only in this case its pre-set manually. And as loads change you need to change the max voltage on the controller. It takes me about 30-60 seconds these days to kick on the trailer brakes after I turn out of the driveway & adjust things for max braking force.

well, yeah but...12 VDC at 1 amp is not the same as 12 VDC at 16 amps (about 4 amps per magnet). Without the proper amperage, a brand new set of brakes will be weak. So you really need to see the amp draw at each wheel to truly diagnose what is wrong (magnet, controller, wiring, grounding path)

 

[Fallon]

well, yeah but...12 VDC at 1 amp is not the same as 12 VDC at 16 amps (about 4 amps per magnet). Without the proper amperage, a brand new set of brakes will be weak. So you really need to see the amp draw at each wheel to truly diagnose what is wrong (magnet, controller, wiring, grounding path)

Ya, but amp draw is a function of the magnets being properly wired & in good shape as opposed to the controller. Controllers dont vary the amperage they put out, they vary the voltage. Amps is a result thanks to ohms law (current = voltage / resistance). Resistance is a fixed value more or less if the wiring & magnets are in proper shape. That just leaves the current varying depending on the voltage comming out of the controller.

Assuming the brakes are properly installed & functional, a decent controller should be able to lock them up (or more properly get them to just below lockup). If not, either the controller is junk, the installed brakes are inappropriate for use or broken.

 

[oliver1555]

Ya, but amp draw is a function of the magnets being properly wired & in good shape as opposed to the controller. Controllers don't vary the amperage they put out, they vary the voltage. Amps is a result thanks to ohms law (current = voltage / resistance). Resistance is a fixed value more or less if the wiring & magnets are in proper shape. That just leaves the current varying depending on the voltage comming out of the controller.

Partial misinformation here.


As voltage increases, so will amperage. My MaxBrake controller display shows the amperage and voltage being delivered/used by the magnets in the brakes. As I apply more pressure on the brake pedal, the controller delivers more voltage and amperage. Amperage is what does the work. I tried to link a Dexter Axle article, but their web site is having problems. Here is one that explains how to troubleshoot brakes. It clearly states, "System amperage is the current flowing in the system when all the magnets are energized. The amperage will vary in proportion to the voltage."
TROUBLESHOOT ELECTRIC TRAILER BRAKES

 

[ovrszd]

Wish I had that controller. I've always heard good things about them.

 

[oliver1555]

Wish I had that controller. I've always heard good things about them.

It's a shame they quit making them. They were pretty pricey, and that made it hard to compete, is my guess. They really help with troubleshooting, by displaying amperage and voltage. Plus, they have a nifty little parking brake mode which will apply full power to brakes. I use it when loading and unloading machinery and when opening the gate, on a hill, going into our barn lot and corrals. I never leave it set for too long, as I'm not sure if the magnets should have that kind of current for an extended time. Another nice thing is that since it ties into the braking system, I don't need to constantly adjust my controller to different trailers. I can pull my gooseneck flatbed, with four brakes, loaded and my little two horse trailer, with two brakes, empty without changing anything. Very smooth operation, as opposed to other controllers I have used that either feel like they aren't working, or make the trailer jerk every time you brake.

 

[Fallon]

Partial misinformation here.


As voltage increases, so will amperage. My MaxBrake controller display shows the amperage and voltage being delivered/used by the magnets in the brakes. As I apply more pressure on the brake pedal, the controller delivers more voltage and amperage. Amperage is what does the work. I tried to link a Dexter Axle article, but their web site is having problems. Here is one that explains how to troubleshoot brakes. It clearly states, "System amperage is the current flowing in the system when all the magnets are energized. The amperage will vary in proportion to the voltage."
TROUBLESHOOT ELECTRIC TRAILER BRAKES

No, as I said ohms law is a fundamental law of nature. Current (amps) equals voltage devided by resistance. Increase voltage & current goes up. Increase resistance (bad wiring or bad magnets usually) & current goes down when the voltage stays the same.

You can either regulate voltage or current, but not both. The other one varies according to the resistance of the circuit & ohms law. Brake controllers along with most electronics regulate voltage.

 

[oliver1555]

No, as I said ohms law is a fundamental law of nature. Current (amps) equals voltage devided by resistance. Increase voltage & current goes up. Increase resistance (bad wiring or bad magnets usually) & current goes down when the voltage stays the same.

You can either regulate voltage or current, but not both. The other one varies according to the resistance of the circuit & ohms law. Brake controllers along with most electronics regulate voltage.

I know what the display on my MaxBrake controller tells me. I know what my multi-tester will show when checking individual brakes, and I know what Dexter Axle shows on page 21 of their troubleshooting guide:
https://www.dexteraxle.com/docs/default-source/default-document-library/medium-duty-electric-brakes.pdf?sfvrsn=0

All done here.