Trailer breakaway switch operation, and inverter questions

Trailer breakaway switch operation, and inverter questions

gary-736Dear Gary,
I have several questions about the breakaway switch on a travel trailer. First, thank you so much for all of your time at the Hershey Shows. You always go way beyond what is expected to answer questions. My wife, Jayme, and I have attended several of your sessions over the years. I have always learned something from each session, even when I attended the same session two days in a row! 
 
Now for the questions concerning a breakaway switch on a travel trailer. Is the power to the brakes directly from the battery or is it routed through the converter distribution box? Should a travel trailer be stored with the pin in or out of the breakaway switch? With the breakaway pin out, do the switch and the brakes consume much power from the battery? If you have the ability to keep the batteries charged during storage, should you remove the breakaway pin? Is it best for the trailer brakes to be set (pin out) or open (pin in) during a month or more of storage? 
 
Also, I had an inverter installed with an automatic transfer switch so that all of the 120V outlets and systems will work in the trailer. It is not powerful enough to run the microwave or air conditioner, but can power anything else in the trailer. Besides using the TV while boondocking, my main use is so I can run the absorption refrigerator using electric during travel. I have to engage the battery disconnect switch before I turn on the inverter and keep it disconnected while the inverter is on. If I have the inverter on and the battery disconnect switch engaged during travel, will this affect the operation of my breakaway switch? 
 
Thanks for you help in understanding the breakaway switch and the impact on the batteries and brakes. —Graham and Jayme M.

Dear Graham and Jayme,
It was good to have you at the seminars in Hershey!

The breakaway switch on a towable RV is always powered by the battery bank on the trailer. That way, if the tow vehicle and trailer ever part company, the brakes will be activated and remain fully applied. It should not be connected through the converter since the converter is only activated with the application of 120-volt AC power.

Always leave the pin in the switch. Once a year, jack up one or two tires on each axle, spin the tires and pull the pin to be sure the brakes are fully activated. The tire/wheel assembly should immediately stop with the pin pulled. 

While the pin is out, spray electrical contact cleaner inside the switch housing to keep those contacts fresh, then fully reinsert the pin. When the pin is out or not fully inserted, the brake magnets will continue to draw power and eventually drain the battery bank. The brakes can draw a lot of current – upwards of 3 amps or so for each magnet, depending on the size of the brakes. So the bottom line is never remove the pin except once a year for cleaning and testing.

While driving, you’ll want the alternator of the tow vehicle engine to keep charging the battery bank on the trailer. If you disconnect the battery, it won’t be able to accept that charge. I’m not sure why you need to disconnect the battery to activate the inverter while traveling. You should be able charge the battery while driving AND operate the inverter to power the AC side of the refrigerator. In this manner, nothing will affect the breakaway switch. Even with the disconnect activated, the breakaway switch should still be able to power the brakes in an emergency. Easy to test – activate the disconnect switch, spin the tires and pull the pin. You might need to have your tow wiring evaluated.

Besides using the inverter, you could also run the refrigerator to get it cold overnight, and turn the whole refrigerator off while driving. Without opening the door often, the contents will typically still stay cold enough as you drive. Once you stop, light it on propane, turn on the inverter, or plug into shore power. A couple different options to consider.

Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.

##RVT842

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5 thoughts on “Trailer breakaway switch operation, and inverter questions

  1. PennyPA

    We found out the hard way that our break-away switch worked. Pulled into a campground and, after registering, went to drive to our campsite…but the trailer wouldn’t move! I got out and checked the wheels for blockages. Checked the brakes…nothing. Then happened to glance up (we have a fiver) and noted the break-away cable plug was just dangling. Evidently it had been pulled out during a VERY sharp turn into the campground. Reinserted the plug and off we went!

  2. Tommy Molnar

    I just thought of something. We had our electric drum brakes converted to electric over hydraulic disc brakes. I’ve never checked to see how the breakaway switch reacts now that we’ve made the change. Gonna have to go out today and see what happens with a spinning wheel test. Or, just pull the pin out and see if I can move the trailer.

    1. Wolfe

      SHOULD work the same. If your brakes can stop the trailer while towing, they stop it now too. The switch just slams on maximum braking, and doesnt know what type brakes you have. I don’t know if literally all it is (?), but the breakaway switch electrically acts as a shunt between the +12 and e-brake pins on the 7wire.

  3. Jeff

    Here’s a little secret. Always leave the Break Away Switch Plug or Plunger plugged in. If you remove the Plunger, the switch is active and will begin sending current to your electric brakes. After a Very Short Period of time the BRAKE AWAY Switch will become very HOT and eventually MELT. Yes, I said MELT and it will destroy the switch.

    1. Wolfe

      I don’t think your switch should ever melt. That indicates dirty (high resistance) contacts, and resistance + high amps makes a heating element.

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