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Old 06-24-2011, 09:25 PM   #1 (permalink)
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FAQ: Timer Vs. Proportional Brake Controllers

Quite often in our towing forum questions regarding electric brakes appear. Many people report their model of brake controller only to discover that their controller is a "Time" based model.

Myself, and many others who understand these controllers, and their failings, consider timer based electric brake controllers to be dangerous - virtually an accident waiting to happen.

Here, I'll explain why.

Contemplate the following. You're cruising down the interstate at 70 MPH with thousands (or tens of thousands) of pounds of trailer behind you. All is well in the world.

Suddenly, there's an accident on the road in front of you. Cars go everywhere, smoke from locked tires, people smacking into the guardrails, cars spinning everwhere....and you're heading right for it with nowhere to go.

Instinctively, you mash your brake pedal....and the trailer braking reaction begins. Now, you go down one of two paths depending on if your tow vehicle is equipped with a good proportional electric brake controller, or a cheap (and arguably, dangerous) timer based controller:

Proportional Electric Brake Controller: The second you touch the brake pedal the brake controller wakes up. Immediately it senses massive deceleration of your tow vehicle due to the controllers built in inertial sensors. Since it detects rapid (emergency) stopping effort is being called for, it instantly answers the call and provides the same (maximum) braking effort to your trailer. Setup correctly, the trailer will provide the maximum physical braking effort it can provide just short of wheel lockup.

You stop rapidly and safely without becoming involved in the accident yourself. Whew!

Timer Based Electric Brake Controller: Since the setup of a timer based controller is based on maximum braking effort, and time delay to get there, you are very limited in functionality. You can't set the controller for more then the maximum amount of braking effort that provides a "comfortable" amount of braking from the trailer without causing the trailer to drag the tow vehicle uncomfortably hard during normal stops. Most people subsequently adjust the "delay" fairly long so that driving in stop and go traffic doesn't result in herky-jerky braking effort.

What MUST be remembered is the following:

- The "Maximum" brake power you setup will NEVER be exceeded. If you set the controller to provide only 6 Volts (~50% braking effort) to the trailer brakes, the controller will NEVER exceed 50% braking effort unless you manually apply the controller.

- The "Delay" never changes. The controller doesn't care if you're making a gingerly stop in town, or an emergency stop on the interstate - it'll still act according to how you set it up. If you set it to provide a 6 second delay to reach maximum, it'll always take 6 seconds to reach the maximum.

So, back to our accident scenario.

Your'e cruising along, the accident happens. You mash your brake pedal. What happens next with the timer based brake controller? Very little!

The controller is "Dumb". It has no inertial sensors that allow the controller to be able to see that you are in the midst of a critical emergency stop. It has no idea whatsoever, so it treats this stop as any other - a gentle, ramped application of the trailer brakes....but ONLY to the maximum you set it to!

So, the trailer begins to push you...HARD. You push the brake pedal in your truck harder and harder, but the trailer is only 2 seconds into it's "Ramp" up of the trailer brakes, and the trailer is still only providing 20% braking effort. A second later, maybe 30%. Did you set the controller for 40% maximum braking effort? Yep, a second later you reach 40%, and that's it - the trailer brakes won't apply any further, no matter what.

The trailer continues to PUSH...PUSH...and PUSH...providing totally inadequate braking effort...and SMASH..you become part of the accident due to your inability to stop. The trailer just didn't provide enough braking effort since the controller had no idea it was an emergency.

For all the controller cares you were still in stop and go traffic just tapping the brake pedal, not trying to push it through the floor board moments before an impending accident.

Ask yourself...what scenario do you want to be in?

If you have a timer based controller, they are DANGEROUS. Yes, they are better than nothing, but once you understand their failings you understand why they really should be replaced by a proper inertial based controller. Hopefully the example above will help you understand the situation better.

Questions, comments? Discuss below.
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Old 09-07-2011, 07:49 PM   #2 (permalink)
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I know this is old, but you have brought up a very good point. Can you share brand names of controllers that are time and those that are proportional?

In a recent trip coming down a fairly steep incline I had to stop quickly while pulling my 8.5"x24" enclosed trailer and though I stopped with plenty of space, I smoked my brakes on my truck, and got me thinking that the trailer brake controller was not set up strong enough....... I suppose it was a Time unit. I have since just traded the truck for a 07 LBZ crew cab short bed 4x4 with 33k miles..... I'll have to look at the brand controller that is currently in the truck....

Thanks
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Old 10-31-2011, 07:58 PM   #3 (permalink)
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Sorry for the delay, I had forgotten about your reply.

If you can provide the make/model details on the controller I'll be happy to tell members if it's a timer or porportional controller model. It is, however, unrealistic for me to make a full list of all models on the market.
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Old 10-31-2011, 08:01 PM   #4 (permalink)
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Well the one I have currently is a proportional unit, but the unit I had in my Dodge turned out to be a time based unit. I am much happier with my current brake controller.

I did not even realize the difference in controllers till I read this thread. Then search and read some more and now I have a much better understanding of brake controller designs.

Thanks
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Old 10-31-2011, 08:23 PM   #5 (permalink)
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:cheers: Glad to be of help.
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Old 10-31-2011, 10:33 PM   #6 (permalink)
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or even better, the 2007-2010 factory integrated brake controller that uses master cylinder pressure to control trailer brakes.

OR...the ultimate...the 2011+ factory integrated brake controllers that monitor master cylinder pressure, truck/trailer yaw rate, lateral and longitudinal acceleration, and have dynamic/active trailer sway control integrated through the ABS/stability-control module etc..
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Old 10-31-2011, 10:36 PM   #7 (permalink)
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Yep, the new factory controllers are, based on everything I've heard, hard to beat.
Given the level of integration some of them have with the rest of the truck (as mentioned above) that's not surprising.
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Old 11-01-2011, 12:37 AM   #8 (permalink)
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Ya they work very well till they go out.
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Old 11-22-2011, 12:22 PM   #9 (permalink)
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Quote:
Originally Posted by DURAtotheMAX View Post
or even better, the 2007-2010 factory integrated brake controller that uses master cylinder pressure to control trailer brakes.

OR...the ultimate...the 2011+ factory integrated brake controllers that monitor master cylinder pressure, truck/trailer yaw rate, lateral and longitudinal acceleration, and have dynamic/active trailer sway control integrated through the ABS/stability-control module etc..
Thank you for posting this, I was curious how the factory brake controller worked.

I noticed the first time I pulled my trailer that even sitting still, the harder you press the brake pedal, the higher the brake controller indicator would go. I was curious if it used some sort of pedal position sensor to determine what to output to the trailer. Now I know.

I have towed many different types of trailers, from 5th wheel toy haulers, bumper pull toy haulers, to goose neck equipment trailers and flatbed car haulers, and no way would I ever tow with a timer based brake controller again. I upgraded to a Prodigy proportional brake controller when we bought our 5th wheel toy hauler back in 2004, and it was one of the best purchases I have ever made. That being said, the factory controller in my LML works better than any of the others I have used.
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Old 11-22-2011, 03:04 PM   #10 (permalink)
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Quote:
Originally Posted by chatcr250 View Post
I noticed the first time I pulled my trailer that even sitting still, the harder you press the brake pedal, the higher the brake controller indicator would go. I was curious if it used some sort of pedal position sensor to determine what to output to the trailer. Now I know.

It uses a pressure transducer on the master cylinder, thats how it knows how hard you are pressing the brakes. If you have a tech 2 on the truck, you can see just how much pressure you are generating when you press the brakes...its pretty cool. Ive never read out pressure data on an HD truck, but I was looking at it on my buddy's 2006 yukon denali (yes, it has hydroboost from the factory just like the HD's, im not sure why though, most of the other half ton trucks are vacuum??) and with your foot hard on the pedal, you can generate almost 1900psi of brake fluid pressure...

Ben
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big thanks to...Eric @ Merchant Auto, Mike @ Inglewood Transmission, Guy @ SoCal Diesel, IdahoRob, Tim @ St. Joseph Diesel, RickDLance, McRat/team salad, BigDipper, Nathan @ MPI, Bobo/team twisted, Fingers, Tony @ RidgeRunner Diesel, EFILive
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LinkBack to this Thread: http://www.dieselplace.com/forum/76-speciality-forums/222-towing/425777-faq-timer-vs-proportional-brake-controllers.html
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