Any way to test the brake magnet circuits?

[rbpru]

While replacing the bearings on my Pop-up, I discovered that one of the brake magnets was an open circuit and I only had one brake. The controller sensed the good circuit so it was happy.

Since the PUP was up on blocks, after I replaced the magnet and adjusted the brakes, I plugged in the 7 way and I spun each wheel while my wife stepped on the brake pedal.

My TT has four brake magnets and I was wondering how to test them short of jacking each wheel and spinning it.

I believe that each magnet has about 3.5 ohms resistance so four in parallel would be less than a ohm and difficult to read given the resistance of the trailer wiring.

Any suggestions?

[Golden_HVAC]

Sears used to sell a clamp on amp meter that detects DC amperage. Most all clamp on meters measure AC only, but this one is special. It is a reasonable price for a DC clamp on, about $90.

With this meter, you can clamp it over one of the brake wires and check each one by itself, or as stated above, clamp it on the main emergency box wire, pull the cable, and check the amperage to all 4 at once. If you get about 12 amps, then all 4 should be on. DO NOT leave them on for a long time (10 seconds), or you will have shorted coils. In normal use, the truck controller puts out only 4-9 volts and the coils will not get nearly as warm as applying the emergency 12 volts (or 14.5 volts if you are plugged into shore power) and there is no cooling air that normally happens while driving.

Fred.

[RCMAN46]

The prodigy P3 controller has a current read out. An open magnet can be detected.


I always check my current with full manual operation before each trip.

[time2roll]

With 12v applied you should get about 3 amps per wheel. Much more and you have a short. Much less and you have an open or poor connection.

[brulaz]

rbpru wrote:
While replacing the bearings on my Pop-up, I discovered that one of the brake magnets was an open circuit and I only had one brake. The controller sensed the good circuit so it was happy.
...

I use a Clamp-on Ammeter to check the brake current after pulling the emergency break-away plug. I think this would have detected your problem. The current should have been less than normal (by 1/2 if you only have two brakes).

Activating the brakes in the truck can be dicey. My built-in controller compensates for vehicle speed, so you will only get a very low current when at rest.

[spike99]

BTW….

Great in-depth Service manual at - click here -

Note: See its page 20+ for testing brake hub magnets.

[spike99]

.

If using a "timed" technology brake controller, jacking up the Trailer's wheels, spinning its tires and pressing the TV's brake pedal will work. Works great for each wheel.

If using an inertia (aka: "motion sensor") technology brake controller, spinning its wheels while on blocks won't work. Won't work because the Brake Controller's computer doesn't feel the "change of motion" need to send power down its blue wire.

What make/model of brake controller do you have?

For my many utility, boat and TT trailers, I remove its linear factory brake wiring and install much better STAR design - using thicker 10 gauge wiring. For more details about STAR design, surf:
- factory linear design - click here -
- STAR design - click here -

If it was my PUP, I'd upgrade to much better STAR design brake wiring.

[kaydeejay]

Golden_HVAC wrote:
I have heard that if you use a compass, and have someone activate the brakes from the truck, your compass will pound "North" toward the brake drum if it is working correctly.

Fred.

X2 - it works!

[Golden_HVAC]

I have heard that if you use a compass, and have someone activate the brakes from the truck, your compass will pound "North" toward the brake drum if it is working correctly.

Fred.