PDA

View Full Version : OT Electric Trailer Brakes



Fasttrack
02-04-2010, 12:51 PM
So my BIL has bought a new trailer and generously allowed me to use it whenever I need to haul machinery. I want to outfit my K2500 to pull it and so I started desinging my own brake controller.

The question I have is regarding current draw. I understand that these brakes can draw up to 6 amps per axle and we have two brake axles.

Does my brake controller need to be able to source 12-15 amps? Or does the signal from the brake controller go to some electronics on-board the trailer?

I can easily add an "old school" 1970's mil surplus transistor that can handle large currents to bump my brake controller output, I don't want to do that if it isn't necessary.

Thanks!

fredf
02-04-2010, 01:16 PM
Does my brake controller need to be able to source 12-15 amps? Or does the signal from the brake controller go to some electronics on-board the trailer?

I can easily add an "old school" 1970's mil surplus transistor that can handle large currents to bump my brake controller output, I don't want to do that if it isn't necessary.

Thanks!

There are no electronics on the trailer, just a coil on each wheel. Having said that I have read about brake controllers that mount on the trailer. . . Plan on a diode to suppress reverse EMF. There is a battery that goes across the coils if the breakaway cable is pulled, so you can get a back feed during testing. HOPEFULLY the battery is connected correctly . . . .

Generally controllers do not apply breaking all at once, but ramp up gradually (use pwm). The real fancy ones use an accelerometer to match the braking force to the deceleration of the vehicle

camdigger
02-04-2010, 01:26 PM
Generally controllers do not apply breaking all at once, but ramp up gradually (use pwm). The real fancy ones use an accelerometer to match the braking force to the deceleration of the vehicle

The cheap ones (like mine) have a plumb bob hung inside a circular contact.

mcskipper
02-04-2010, 01:28 PM
Yes, the electric breaks suck a ton of power.
I have had these systems on my SUV's for 30 years.

The electronic controllers you can buy that do not tie into the trucks breaking system are all trash.

They have ckt's that sense the decelaration of the truck then add breaking to the trailer.

My last three SUV's have a provision to plug a controller into the trucks break system. This is the best way to do it.

The VERY OLD Borg Warner break controller was the BEST system I ever had.

The one thing I do to this day is I check the current draw of the trailer.
Over the years wires get lose or disconnected.
A full voltage test will pick up this up.
A hard stop is no time to find out half the breaks don't work.

A test will pick up a problem.

Mike Burdick
02-04-2010, 02:25 PM
Okay looks like your question is answered.

But... a little something to think about before borrowing, especially from FAMILY!

If you MUST borrow, take a look at what your Brother-in-law is using for his braking and buy the exact same thing! If you think his unit is not adequate then talk it over with him and then BUY two units that you both agree on and GIVE one to him! Perhaps you can build one that's better than anything on the market but this is not the time to show off your design skills!

Keep in mind your Brother-in-law's situation: He's trapped between you and your sister and is kind of forced to loan you his trailer. Of course he may be glad to help, but either way you'll never really know for sure!

Jim Caudill
02-04-2010, 02:41 PM
Just buy one! They are not that expensive and you can even find them used. There are about 3 different ways to apply the brakes. One is purely time-based. You set the max voltage you ever want the brakes to get, with a variable wheel or knob; then, the control will ramp up to that voltage over a time interval that you also set. You need to be able to set the max voltage based on load and conditions. Too much voltage and you'll lock the trailer brakes when empty - too little voltage with your mill on it, and you'll have almost no trailer brakes.

Another method is to try and sense the deceleration of the vehicle using a pedulum or some other "g-force" sensor. The voltage will be sent according to the sensor's output, and will still be "upper limit" set by the driver. Units with a pendulum will have a "level adjustment" somewhere on the box, so that the pendulum hangs somewhat "plumb".

The older units used a rheostat that was moved by hydraulic pressure from the master cylinder, with a small handle for driver "over-ride".

I believe that some of the newer vehicles with the factory towing packages can actually get a variable voltage signal from the braking system. Sort of an electronic version of the old hydraulic "tie-in".

They all work as designed. You have to figure out how sophisticated you want it to be, and how smoothly you want it to work. Do a search for some of the RV trailer towing groups and you can get as educated as you want. The Airstream trailer guys are probably at the top of this heap.

Falcon67
02-04-2010, 04:16 PM
Good ones cost $$$ and will save your azz. Both trucks here are fitting with digital controllers and they are not cheap. Ours are adjustable on the fly for road conditions. The Ranger tows 5500 regularly and the F-150 about 6000+. The race cars on the trailers cost a hell of a lot more than a hundred something bucks for a decent controller. Besides, if you are dragging something on the trailer and the trailer gets away from you, guess who's on the hook. Don't "rig" it - if you plan to use it safely, buy the right stuff to handle it. Besides, if it has electric brakes, it's probably rated to handle a weight that would put you in a state requirement for a certain level of control. And that is usually based on capacity, not actual towed load.

Both trailers here use 7-way RV connectors for commonality. Either truck can pull either trailer. The F150 had a harness for a controller in the glove box, the Ranger cost about $200 for the controller and wiring since it only comes with a 4 way connector. There are adapters for various trailer connections.

PS - I DONT loan trailers in general. Period. I will to a very good friend that tows regularly and knows how to handle a trailer and that I have seen how the person cares for equipment. Everyone else gets a NO, go rent one. OR - I go with it for a fee. You can get mad about it, then go get one for $2600 and do what you like. Family same deal. SIL has used one once, but it was covered by his company's insurance and used for work. And I didn't like that at all either. The wooden floor trailer gets used every year in the homecoming parade and I pull it.

Jim Caudill
02-04-2010, 04:55 PM
Hey Falcon, I used to live in Abilene when I flew C-130's; over on Bob-O-Link, just west of 277 on the Southeast side of Abilene. They used to have a big steer on top of the meat shop you could see from the highway: Rancher's Beef, IIRC and jsut north of Southwest Dr.

Doozer
02-04-2010, 05:22 PM
I have some experience with this. My dad has a 1 ton dump truck that pulls a 18,000 capacity trailer with electric brakes. At the time I set it up, there were no decent electronic controllers available. So I used an old Kelsey-Hayes controller that has the brake line that goes to the master cylinder. The KH controller worked well, in sync with the brake pedal, but the trailer wheels always wanted to lock up. I tried to drop the voltage with the KH resister tap box, but the voltage was still too high. I finally bought a big honkin wire-wound reostat from Allied electronics and mounted it under the dash. This worked well to set the brakes just right. So, it was now a decent working system, with the KH hydraulucly actuated controller and that running through the reostat. A lot of pissing around though.
I also set up a Tekonsha hydraulicly actuated brake controller in our 1977 Lincon for pulling a camper. That worked well, and no reostat was necessary. Fast forward to present day, my dad now has a Dodge megacab with the Cummins motor. His camper is a 35' fifth wheel. The brake controller is a Prodigy electronic, inertia sensing top of the line gizmo. Let me say that it works great! Very adjustable, no brake line to the master cylinder, no need for a huge reostat, it just works.
Bottom line, your time and effort is worth something. I spent a bit of time in developing the KH unit in the dump truck to get it to work right. If a controller like the Produgy was available then, I would have used it. I do like the robustness of the old Kelsey-Hays or Tekonsha brake units, but there was a lot of fiddling around to get them to work right. And if you pull a different trailer, you might have to fiddle with them some more. With the electronic Prodigy unit, just change your max setting, and the inertia sensing will take care of the ramping. That's it. I think it was $200 or so, but really, just buy it. I also can make things with electronics and such, but just because I can, does not always make sense that I should. Just buy an electronic one, and a good one.

--Doozer

Fasttrack
02-04-2010, 06:14 PM
Okay looks like your question is answered.

But... a little something to think about before borrowing, especially from FAMILY!

If you MUST borrow, take a look at what your Brother-in-law is using for his braking and buy the exact same thing! If you think his unit is not adequate then talk it over with him and then BUY two units that you both agree on and GIVE one to him! Perhaps you can build one that's better than anything on the market but this is not the time to show off your design skills!

Keep in mind your Brother-in-law's situation: He's trapped between you and your sister and is kind of forced to loan you his trailer. Of course he may be glad to help, but either way you'll never really know for sure!

:) I have known my brother-in-law since second grade. We are best friends. I told him I was going to buy a trailer and asked if he'd be willing to let me keep in on his farm for the next year until I get a place of my own. He called about a week ago and said, "well I bought you a trailer". Factory made, brand new and everything. He said they'd license it and keep it on the farm but any time I wanted to borrow it I could. He's not too concerned with the brakes. For "real" hauling he has his Peterbilt and dropdeck trailer ;)

While your advice is excellent in general, it doesn't really apply here :)

Falcon67 - I aggree. My BIL are very good friends. He taught me how to drive, actually. He then taught me how to drive an 18 wheeler, a combine, and numerous other pieces of expensive equipment. If he can trust me with a 200,000 dollar piece of equipment, I hope he can trust me with a 4000 dollar trailer.


My brake controller will tie directly into the brake hydraulics via a transducer to read pressure. My design also incorporates the ability to output a pulsed "ABS" signal to the trailer in hard braking conditions or slippery conditions. This will be cued via either surpassing a certain pressure threshold or from the Kelsey-Hayes RWAL system on my truck.


EDIT:

Doozer - my controller looks like it will cost me about 30 dollars. It will be extremely "robust" but also sophisticated. More importantly, it will give me something to do when I'm away from my machine shop. I have a very nice electronics lab here, but the machine shops is ... sub-par compared to my 2D and Pacemakers ;)

Your Old Dog
02-04-2010, 06:39 PM
$94.99 and you're good to go with something you can trust. It's the same one I have on my RV and it's a dream to use. Not only that, something goes wrong and you don't have to blame yourself. Your truck may already be equipped to use it, my 2002 F350 was. I wouldn't dink around re-inventing the wheel unless it was taking food off the table.

Let me look tomorrow and if I can find my old one I'll send it off to you. It was a Reese unit if I recall correctly. Not nearly as good as the Prodigy but free!

EDITED TO ADD: http://www.rvwholesalers.com/catalog/prodigy-brake-control-by-tekonsha-17-0101.html

John Stevenson
02-04-2010, 06:46 PM
Get one off a Toyota, plenty about, just throw the mat away.

Knowing the crap electric you have over there I'm guessing these things are only 110 volt ? ;)

.

mooney1el
02-04-2010, 07:22 PM
Perhaps I am paranoid, or I live too close to my neighbors (the lawyers), but I would be concerned with the liability and exposure associated with installing anything "shop made" in my braking system. In an accident, your insurance company will cover nothing, including the other guy's injuries and damages. And hope there is never a death. Even if I had the skill set and tools to make such a device, the exposure would far overrule the $100-200 for a commercial brake controller.

Doozer
02-04-2010, 07:41 PM
FT- Using a pressure transducer and having the ability to pulse an ABS signal to the trailer sounds C:cool::cool:L! I was envisioning some old linear rheostat like the old KH setup, but you idea sounds super neat. Perhaps you have a patent idea in the works. I don't think the best trailer controller has ABS. I know big rigs do, but nothing in the 2 ton and under market. Keep us informed.. and include pics.:D
I dunno if you have a sensor already, but I have used GEMS sensors in the past for inputting to analog PLC cards. They are made in Italy I think, and around $200 new, but there is always ebay.

--Doozer