Trailer Breakaway Switch

[SuiteSuccess]

I have a 2017 DRV trailer that has a two wire emergency breakaway switch for the brakes.  It’s the one that has the lanyard that activates the brakes if the trailer becomes disconnected from the hitch.  The present factory one is ESCO and I’m wondering if a generic, Curt, or Hobbs replacement should work (I can get those locally)?  

[Jim & Wilma]

Functionally they’re all the same; contact closes when pin is pulled out.  If you’ve got hydraulic brakes, it’s pretty low current and any switch should work fine. If electric/magnetic brakes, each wheel is 3 amps and I’d try to check and make sure it’s rated for the amp load.  
 

In either case, it’s a good practice to routinely pull the pin to make sure it works. For electric brakes, a clamp on amp meter will tell you if all the magnets are working; total current = 3 amps times # of wheels. 

[SuiteSuccess]

54 minutes ago, Jim & Wilma said:

Functionally they’re all the same; contact closes when pin is pulled out.  If you’ve got hydraulic brakes, it’s pretty low current and any switch should work fine. If electric/magnetic brakes, each wheel is 3 amps and I’d try to check and make sure it’s rated for the amp load.  
 

In either case, it’s a good practice to routinely pull the pin to make sure it works. For electric brakes, a clamp on amp meter will tell you if all the magnets are working; total current = 3 amps times # of wheels. 

Thanks Jim.

[NeverEasy]

Yep, concur with Jim.

Clamp on a DC clamp on meter on only one of the two black wires at the breakaway switch.  Like Jim said, 3 amps per wheel if you are electric brakes.  From my experience, you only get .8 amps if you are running an electronic over hydraulic setup.  

 

[SuiteSuccess]

10 hours ago, NeverEasy said:

Yep, concur with Jim.

Clamp on a DC clamp on meter on only one of the two black wires at the breakaway switch.  Like Jim said, 3 amps per wheel if you are electric brakes.  From my experience, you only get .8 amps if you are running an electronic over hydraulic setup.  

 

Chet,

Reason for replacement is the “plug” connected to the lanyard has become fused to the body of the switch so I can’t pull on the lanyard and remove it.  Going to probably have to put vice grips on it to get it out.  Want to have a new one available cause I’m sure it’s probably going to break.  If so couldn’t I just cut and connect the two wires to complete the circuit, reconnect the battery and test with the clamp on meter?

[GlennWest]

Subject I hadn't thought about in years. I have air over hydraulics. No air brakes lock. 

[NeverEasy]

Carl, Yes the wires connected together would be the same as pulling the plastic plug.  Of course, disconnect when complete.

I have had breakaway plugs get stuck in a couple of trailers in the past.    Both appeared to be welded to the contacts by the 12 VDC.  Appears something got in there with enough conductance to cause enough heat to do the welding.  I can't explain it.

Those two black wires run into the connection box under the hitch.  One goes to the 12 volt  battery source (usually red) and the other goes to the trailer brakes wires (usually blue).  

I say that here because it is tempting to cut the black wires and splice in the new breakaway when it is pretty easy to connect the new ones directly into the connection box. 

[phoenix2013]

2 hours ago, GlennWest said:

Subject I hadn't thought about in years. I have air over hydraulics. No air brakes lock. 

Ah, my young padawan, wisdom have you acquired, the force of air is with you in abundance.

No stinkn' brake controller, no stinkn' brake away switch.

[rpsinc]

5 hours ago, GlennWest said:

Subject I hadn't thought about in years. I have air over hydraulics. No air brakes lock. 

But if the trailer breaks away then air will be disconnected and as such with air failure, does a system like Blu Dot cause brakes to fail ON like in a commercial trailer??

[rickeieio]

1 hour ago, rpsinc said:

But if the trailer breaks away then air will be disconnected and as such with air failure, does a system like Blu Dot cause brakes to fail ON like in a commercial trailer??

Yes.  There's a tank supplied with the BluDot to apply the brakes should the supply line become disconnected, same as on a commercial trailer.

Recently, I was moving our trailer after having unhitched several days earlier.  Since I was only backing the rig into the shop, I didn't bother hooking up the lines/electric cord.  The trailer brakes were dragging, so I dove under and opened the tank drain.  It still had perhaps 15 psi, enough to lightly apply the brakes.  

Since installed the BluDot, 7-8 years ago, it had always leaked down in 12-15 hours.  Why it now holds air is a mystery.

[Jim & Wilma]

8 hours ago, SuiteSuccess said:

Reason for replacement is the “plug” connected to the lanyard has become fused to the body of the switch so I can’t pull on the lanyard and remove it.

@SuiteSuccessCarl, I had a similar issue years ago. I would often test the switch and measure the current, sometimes taking a few minutes in the process. One of the times I just couldn’t pull the plunger out. Got me curious why it stuck.
 

So I did a forensic exam of the switch. I found the plastic plunger, that separates the spring loaded contacts, had melted into the contacts. My conclusion was the contacts had previously made poor contact and became rather hot, probably glowing. When the plunger was reinserted to separate the contacts, the contacts also melted into the plastic plunger.

After that experience,I paid a bit more attention to switch current handling capacity, though that data can be a challenge to find.  It was one more reason I changed to electric over hydraulic  

 

[SuiteSuccess]

1 hour ago, Jim & Wilma said:

@SuiteSuccessCarl, I had a similar issue years ago. I would often test the switch and measure the current, sometimes taking a few minutes in the process. One of the times I just couldn’t pull the plunger out. Got me curious why it stuck.
 

So I did a forensic exam of the switch. I found the plastic plunger, that separates the spring loaded contacts, had melted into the contacts. My conclusion was the contacts had previously made poor contact and became rather hot, probably glowing. When the plunger was reinserted to separate the contacts, the contacts also melted into the plastic plunger.

After that experience,I paid a bit more attention to switch current handling capacity, though that data can be a challenge to find.  It was one more reason I changed to electric over hydraulic  

 

I am electric over hydraulic.  Interesting finding on your forensics. Makes sense though.  I’ve ordered a new switch and when installed will tear apart the old to see if what you describe might be a reoccurring issue.  If so two solutions come to mind.  1. Slip a pared down popsicle stick between the contacts to let them cool for awhile, then quickly change with the plastic plunger. OR 2. Put an on/off switch on the 12 volt wire. (Not ideal but should work).

[Jim & Wilma]

13 minutes ago, SuiteSuccess said:

popsicle stick

Smiles and reminds me of a story.

Technicians maintaining critical ground support equipment were using “graduated” popsicle sticks to apply and measure application of an adhesive.  Use once and throw away the sticky sticks (sorry). Made lots of practical sense to them . . . but not to Quality.

Quality went into orbit over use of non-calibrated measuring devices and made quite an issue of it. They argued, with some logic, failure to apply the adhesive to spec could result in system failure with potential for catastrophic consequences. I got unenviable task to address and resolve this but that's another story. 

[phoenix2013]

7 hours ago, rpsinc said:

But if the trailer breaks away then air will be disconnected and as such with air failure, does a system like Blu Dot cause brakes to fail ON like in a commercial trailer??

Emergency valve in the BlueDot system which puts full air pressure (from the storage tank) into air over hydraulic actuator in case bad things happen to the hoses.

 

[GlennWest]

Works real good too. I lost air once on my truck due to a valve bypassing. It only went to trailer brake system though. All 3 axles locked down. electric never worked this good. 

[NeverEasy]

1. Slip a pared down popsicle stick between the contacts to let them cool for awhile, then quickly change with the plastic plunger. OR 2. Put an on/off switch on the 12 volt wire. (Not ideal but should work).  

Carl,

I agree that you should open the old breakaway and see if the plastic plug is melted.  Just consider this:  The original electric magnetic brakes used about 12.6 AMPS via the house battery(ies) to engage the brakes.  Read that, 4 brake magnets each have a resistance of 3.4 ohms.  Those in parallel work out to close enough to 1 ohm. 4/4 =1  Therefore, the AMPs required to engage those brakes are just about equal to the battery voltage  I=E/R or 12.6/1 - 12.6.

Ok, that's enough to generate heat if the contacts in the breakaway do not create a dead short across the contacts. On a system using electric brake magnets, it would be good to put some contact cleaner on your popsicle stick and push it in and out a few times.

Now, consider your system on Electric/Hydraulic.  The controller for that system only requires enough current to operate itself.  I have that system on my rig.  My testing shows no more than .8 amps (yes, 8/10s of an amp) when the brakes are fully activated.  .8 amps is not enough heat to melt that plastic.   An annual cleaning of the breakaway contacts still would not hurt.

 

[SuiteSuccess]

9 hours ago, NeverEasy said:

1. Slip a pared down popsicle stick between the contacts to let them cool for awhile, then quickly change with the plastic plunger. OR 2. Put an on/off switch on the 12 volt wire. (Not ideal but should work).  

Carl,

I agree that you should open the old breakaway and see if the plastic plug is melted.  Just consider this:  The original electric magnetic brakes used about 12.6 AMPS via the house battery(ies) to engage the brakes.  Read that, 4 brake magnets each have a resistance of 3.4 ohms.  Those in parallel work out to close enough to 1 ohm. 4/4 =1  Therefore, the AMPs required to engage those brakes are just about equal to the battery voltage  I=E/R or 12.6/1 - 12.6.

Ok, that's enough to generate heat if the contacts in the breakaway do not create a dead short across the contacts. On a system using electric brake magnets, it would be good to put some contact cleaner on your popsicle stick and push it in and out a few times.

Now, consider your system on Electric/Hydraulic.  The controller for that system only requires enough current to operate itself.  I have that system on my rig.  My testing shows no more than .8 amps (yes, 8/10s of an amp) when the brakes are fully activated.  .8 amps is not enough heat to melt that plastic.   An annual cleaning of the breakaway contacts still would not hurt.

 

Thanks Chet.  Always a teaching/learning experience with you. I so much appreciate it.

[SuiteSuccess]

Ok got my switch changed out.  Turns out the 0 ring on the plunger was hard and had glued itself to the housing.  Took a lot of effort to get the plunger to pull out but it was in good shape and not melted.  Would probably be a good idea to periodically lubricate the O ring to keep it supple.  I’m not so sure that it would not have broken the cable from the plunger if suddenly jerked.

[NeverEasy]

I did not think yours would have melted the plastic due to the low current you electric/hydraulic system pulls.

Don't use any petroleum-based oil or grease.  Silicone grease only on that "O" ring.

 

[SuiteSuccess]

14 hours ago, NeverEasy said:

I did not think yours would have melted the plastic due to the low current you electric/hydraulic system pulls.

Don't use any petroleum-based oil or grease.  Silicone grease only on that "O" ring.

 

Yep.  All I ever use.