Johnhd
Your suggestion has nothing to do with brake magnets that are wired in parallel, as you now have a series parallel circuit. Your suggested set up, is only a single series circuit.
All wires have some resistance. The larger the wire, the smaller the resistance.
Additionally, as any wire heats up, it's resistance increases, which will make the initial current drain reduce. Same as a light bulb. As the element becomes hot, it's resistance increases, therefore the current decreases
Shorts in electric brake systems seldom come from the wiring or breakaway switches.
Shorts do happen, "very often" in the brake magnets.
Normally at 12 volts DC a
12 volt magnet will draw 3 amps, but at 13.5 volts DC (when towing) that same magnet now draws 3.37 amps. So for the single axle owner, not bad, as that trailer will only draw 6.74 amps. On a tandem trailer the draw will be 13.48 amps. Since fuses should not be used more than 75 percent of their capacity (for safety) thats getting very close to the maximum that a 20 amp fuse should be used at.
Now lets talk about a tri-axle owner. He will be at 20.22 amps, at maximum.
He does not have a chance with a 20 amp fuse. He also will be very close to the limit of drawing no more than 75 percent through a 30 amp fuse, which is 22.5 amps.
These are examples that have not considered any resistance from the wires or connections.
Owners usually are not aware that a brake magnet contains a coil of wire.
When the magnet has been in service way after it's design limit, a short will develop when the magnet is energized and firmly touches the armature plate.
Therefore the short will not be zero resistance, but can be low enough to cause a fuse or circuit breaker to open.
Tests have been made, many years ago, duplicating what I just described.
On any trailer, that has two or more brakes, if one magnet shorts out (having a lower resistance) because of wear, the other wheels will still operate almost at normal. Simple series parallel circuit set up is the reason that
happens.
Practical experience, is far removed from theories, thoughts, ought-to-be's, and the like. Regardless of documentation, there will always be those that will disagree, with most anything.
My sole purpose is to be helpful. If someone choses otherwise, so be it. My only suggestion, is to prove otherwise, not by theories or I believe's, but go do the tests.
They have the trailers, so what's stopping them from doing a test themselves? Is it easier to argue than it is to set up and run tests? Perhaps so.
But the bottom line is that many newcomers come to this site to learn, since they are new to Rving.
Lets give them a shot at learning the right stuff, so that they too can join the rest of us who enjoy "safe Rving".
Differences of opinions, are always welcome. But facts can only be refuted with other facts, not by opinions.
It is in that context that, as time permits, I offer answers that came from factual experience, not theories, or guesses.
Hopefully, the next post on this subject will be from someone that has duplicated the setup and has run the tests.
Whoever that may be, make sure you use one magnet that clearly has the wire coil of the magnet exposed.
But the bottom line that dooms all the theories, as well as practical experience with electric trailer brakes, is "disc brakes".
Wow, no brake current drain. No worn magnets to cause problems. State of the "art" in braking systems? You bet. Superior to electric brakes? Hands down. And another "wow" is that a rotor is miuch closer to being in balance than a hub and drum. Therefore if you balanced only the tire and wheel, you most likely will be in great shape.
But, there are those that will disagree and will still feel that there is no real motive to change from electric brakes.
Airstream has always been the innovator. Why then, have they chosen to make disc brakes standard on all the classic models? Surely, we can't accuse them of being "dumb. They want the best, for the best owner/customer in the RV industry, namely the Airstream owner.
New or used, that's you.
Andy
Linear Mode
