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Old 12-30-2020, 11:46 PM   #1
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Breakaway switch testing

When tripping a breakaway switch while connected, and the voltage back feeds the tow vehicle, will it damage the controller or on-board computer? Mine is factory installed on a Ford F150. But I recall warnings years ago in another RV group, that it would damage things.
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Old 12-31-2020, 12:44 AM   #2
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Since the breakaway system works either from an onboard dedicated battery in the trailer, or the house battery in the trailer, I don't see how it can back feed to the tow and cause a problem. The tow either makes the brake wire hot, or it doesn't, during normal breaking, but the negative from the tow doesn't complete the circuit in the emergency breakaway system. Typically, the negative from the tow, the negative from the trailer battery, and the negative from the breakaway go to one lug on the frame. And a brake negative goes from the brake magnets to the same lug. The circuit during a breakaway is completed in the trailer wiring.

I have tested my travel trailer breakaway system with my Ram connected. It skidded the trailer tires. But it didn't have any affect on the truck. I also damaged a breakaway switch while towing my dump trailer and all it did was turn on the trailer brakes. Again, no damage to the truck.

I'm curious how this could cause an electrical problem in the truck.
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Old 12-31-2020, 01:07 AM   #3
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Me too

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I'm curious how this could cause an electrical problem in the truck.
Thanks. I was recalling a post from a few years ago where someone said it would. The system will apply the RV battery voltage to the brakes while the Tow vehicle is still attached and there are sensors to indicate that the brakes are hooked up that would see the voltage. Hopefully that old post was for old controllers. I'll test it next summer.
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Old 12-31-2020, 02:33 AM   #4
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I don't want to claim it won't be a problem. I just don't see how it could be. Hopefully someone will chime in who knows more about it than I do.
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Old 12-31-2020, 05:56 AM   #5
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I have always tested my breakaway switch disconnected. You can hear trailer brakes humming when 12v power is sent to them. If they hum, they are getting full power, if not, there is a problem somewhere. But of equal importance the brakes have to be adjusted properly for them to work in a real world situation, whether the brakes are actuated manually or by the brake pedal when towing, or in an actual scenario that nobody wants to occur, an actual breakaway when they are powered by the in-house trailer battery.
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Old 12-31-2020, 07:44 AM   #6
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From the Tekonsha website: . WARNING Disconnect trailer plug
before testing breakaway unit. Failure to do so will result in severe damage to
electronic brake control.
look under breakaway controllers, instructions
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Old 12-31-2020, 08:59 AM   #7
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My 1996 Casita was built before breakaway switches were installed so I had to add it myself. Since they are designed to work without connection to the TV, I would definitely disconnect. The easiest way to test is to jack up the wheels one at a time, pull the plug, and see if you can turn the tire. Simple and easy.
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Old 12-31-2020, 10:23 AM   #8
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Quote:
Originally Posted by Joe MacDonald View Post
From the Tekonsha website: . WARNING Disconnect trailer plug
before testing breakaway unit. Failure to do so will result in severe damage to
electronic brake control.
look under breakaway controllers, instructions
Joe
I agree, my instructions say the same thing.
I don't want to risk destroying my brake controller so I'll follow the manufacturers guidance.
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Old 12-31-2020, 10:40 AM   #9
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Can't hurt!

Under normal operation, the brakes are powered by the controller. When you activate the break away switch you are also back feeding 12 volts to the controller which may or may not be powered. Without a schematic, there is no way to know what you are applying 12 volts to. My original Prodigy had the warning Joe mentions. If you're unplugged, you know the controller is safe.
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Old 12-31-2020, 10:43 AM   #10
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Breakaway Switch vs Chains

The breakaway brake switch seems to be totally redundant.
If the "safety" chains do their job, are properly adjusted for length, they will catch the trailer before the coil cord stretches enough for the breakaway switch to activate.
What are the chances that both the hitch comes off the ball, AND the chains break, or fall off.???
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Old 12-31-2020, 10:52 AM   #11
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Small chance, I agree, but considering the potential consequences, what's wrong with some redundancy?
My earlier trailers had the common S-shaped chain connectors. One time going down a particularly rough road, one of them bounced off, which suggests an answer to Wayne's question. Since then I've always made sure my chains are connected with safety gated hooks.

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Old 12-31-2020, 11:16 AM   #12
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In the event of a disconnect, would it be better to have the breakaway system activate while the chains are still attached, or have the chains catch the trailer without activating the breakaway switch?

It seems like it might be easier to make a controlled stop with the trailer brakes on, but it would force an immediate stop right in the lane. Trying to get stopped with the trailer hanging on the chains and not braking, seems like it would cause some damage and the trailer would only be slightly under control. If the brakes were not activated, one could pull over slowly and sort of glide to a stop.

I've never trusted those chain S hooks. Large safety hooks, or shackles are much stronger and more reliable.
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Old 12-31-2020, 11:22 AM   #13
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Quote:
Originally Posted by WaltP View Post
Small chance, I agree, but considering the potential consequences, what's wrong with some redundancy?
My earlier trailers had the common S-shaped chain connectors. One time going down a particularly rough road, one of them bounced off, which suggests an answer to Wayne's question. Since then I've always made sure my chains are connected with safety gated hooks.

Walt
There are rubber pieces that go on the S-hooks to keep them from bouncing off, listed as "Safety chain S-hook keeper / retainer. Usually less than $10 from a variety of places including Walmart, etrailer, and a dozen other suppliers. Could probably make your own easily.
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Old 12-31-2020, 11:25 AM   #14
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Thanks for jogging my memory

Quote:
Originally Posted by Joe MacDonald View Post
From the Tekonsha website: . WARNING Disconnect trailer plug
before testing breakaway unit. Failure to do so will result in severe damage
Joe
Yep, that's what I recall, but I could not find it in "print". I had a Tekonsha control on my 1997 f150, maybe that's where I read it.
TNX to every one.

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Old 12-31-2020, 03:34 PM   #15
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As I understand it the trailer's electric brakes are activated by the tug when hooked to the tug and by the house battery when the breakaway switch is activated. If the breakaway switch is activated while the unit is connected to the tug, the house battery may be able to send power through the wiring harness to the tug. Depending on the wiring arrangement and the setup of the break controller, this may, or may not be an issue. I check my breakaway switch frequently. I can hear the brakes activate. After leveling my unit in the back country I often have one or more wheels off the ground. An excellent chance to check the breakaway switch.
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Old 12-31-2020, 03:46 PM   #16
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Quote:
Originally Posted by Raspy View Post
In the event of a disconnect, would it be better to have the breakaway system activate while the chains are still attached, or have the chains catch the trailer without activating the breakaway switch?

It seems like it might be easier to make a controlled stop with the trailer brakes on, but it would force an immediate stop right in the lane. Trying to get stopped with the trailer hanging on the chains and not braking, seems like it would cause some damage and the trailer would only be slightly under control. If the brakes were not activated, one could pull over slowly and sort of glide to a stop.

I've never trusted those chain S hooks. Large safety hooks, or shackles are much stronger and more reliable.
Do a search on which should activate first and you will find arguments for both. Passionate arguments and long threads. Moderator head ache threads. . Like tires and tow ratings on here. I'm a safety chain first kinda guy. But what do I know.

And my chains are attached with threaded links. Slow but sure.
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Old 12-31-2020, 05:27 PM   #17
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Quote:
Originally Posted by Raz View Post
Do a search on which should activate first and you will find arguments for both. Passionate arguments and long threads. Moderator head ache threads. . Like tires and tow ratings on here. I'm a safety chain first kinda guy. But what do I know.

And my chains are attached with threaded links. Slow but sure.
I have no intention of wading into that morass. I'll just assume there is no clear answer.
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Old 12-31-2020, 06:42 PM   #18
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There's probably a lot of "it depends" based on wire sizing, layout, battery type, and brake size. I assume the problem is back-EMF from the solenoids in the brakes engaging/disengaging abruptly. That could definitely cause a voltage spike above the nominal 12V, though I'd be a bit surprised if it could get enough back to the controller to fry it given how long and thin the wires are.
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Old 01-01-2021, 08:08 PM   #19
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Originally Posted by CPW View Post
I have always tested my breakaway switch disconnected. You can hear trailer brakes humming when 12v power is sent to them. If they hum, they are getting full power, if not, there is a problem somewhere. But of equal importance the brakes have to be adjusted properly for them to work in a real world situation, whether the brakes are actuated manually or by the brake pedal when towing, or in an actual scenario that nobody wants to occur, an actual breakaway when they are powered by the in-house trailer battery.
Carl: Always thought the brakes hummed too but wonder if there are variables like temperature that matter. A few days ago I pulled the breakaway pin to test after doing some rewiring in the trailer and heard nothing at the wheels. Proceeded to jack up each wheel and they were locked. No humming.
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Old 01-01-2021, 08:28 PM   #20
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Quote:
Originally Posted by Raspy View Post
In the event of a disconnect, would it be better to have the breakaway system activate while the chains are still attached, or have the chains catch the trailer without activating the breakaway switch?

It seems like it might be easier to make a controlled stop with the trailer brakes on, but it would force an immediate stop right in the lane. Trying to get stopped with the trailer hanging on the chains and not braking, seems like it would cause some damage and the trailer would only be slightly under control. If the brakes were not activated, one could pull over slowly and sort of glide to a stop.

I've never trusted those chain S hooks. Large safety hooks, or shackles are much stronger and more reliable.
Breakaway should be taken literally in my opinion. This system is to bring the trailer to a stop if somehow it becomes completely disconnected from the tow vehicle. It’s to avoid a runaway trailer. If a trailer just jumps off the ball and down onto the chains the 7 pin is still plugged in and you can brake normally to a stop. If you are really good you can manually engage the brake controller and let just the trailer pull the rig to a stop as you pull over out of the traveling lane.
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