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Old 02-12-2005, 05:34 PM   #29
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Two types of switches...

Over59,

There are two types of automatic resetting breakers: Type I (cycling) and Type II (non-cycling).
More information on these breakers can be found here:
http://www.1firsttech.com/products.asp

The particular breaker I used, (Type I) can be found here:
http://www.1firsttech.com/data_sheets_pdfs/ext_300.pdf

PS I usually hang around a discussion until I see the general consensus and then agree with the masses!
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Old 02-12-2005, 06:43 PM   #30
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Quote:
Originally Posted by pattersontoo
...PS I usually hang around a discussion until I see the general consensus and then agree with the masses!
Perhaps you should make include that sentiment in your signature so that everyone has the proper perspective on your advice.

Tom
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Old 02-12-2005, 11:16 PM   #31
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Quote:
Originally Posted by pattersontoo
It takes EVERYTHING in the way of supplied power and sends it to your brakes. Guaranteed that if you have a fuse in that path it will surely blow and release the trailer brakes.
That's just plain wrong. Each brake magnet has a set resistance (around 3 ohms, I think), so it doesn't matter at all how big the battery is, or how many amps it will put out, each magnet can only draw about 4 amps at 13 volts. I=V/R. So if you have four magnets, a 20 circuit breaker would be sufficient to handle every possible ounce of power that the magnets can use. It won't blow the fuse or circuit breaker unless there is also a short in the system.

And if you have a short in the brake line, you won't be getting any juice to the brakes. Electricity will follow the path of least resistance, direct to ground. Believing that running without a fuse or circuit breaker will allow more juice to flow around the short, and reach the magnets anyway, is not correct.
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Old 02-13-2005, 01:36 AM   #32
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Plain wrong....

http://www.warnernet.com/pdf/819-0090_P1377.pdf

I had originally typed out a long dissertation on Electrically Safe Working Practices and how it applies to not fusing safety circuits. The link above will show you that even the manufacturers of the breakaway switch do not show a fuseable link between their switch and the power source.
I was also going to explain how Ohm's Law is affected by heat.
I stopped myself because I figured that it is not worth it.
This is SUPPOSED to be a place where people help people.
Suffice it to say that in my 20 years designing, building and repairing industrial automation that you never fuse a safety device. The NEC states that you never fuse a safety device. If you would like the chapter and sub-section of the 2002 NEC Handbook I will go get it for you. I am a member of the IAEI for a number of years. I bet I can find it quickly. Does anyone else out here have the Handbook so you can check me on it? I do not want to be called a liar.
In retrospect I feel that maybe I should have left it at saying that no trailer manufacturer has fused their breakaway switches.
I will not say anything that I cannot back up without third party documentation.


PS Sorry I could not agree with the masses on this.
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Old 02-13-2005, 01:41 AM   #33
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Quote:
Originally Posted by TomW
Perhaps you should make include that sentiment in your signature so that everyone has the proper perspective on your advice.

Tom
Why is it that everyone here wants to exchange barbs? Are we suffering from cabin fever?
That was considered a joke. Maybe even a pun.
I am just talking about the things I have documentation on. If you read my posts you will see that I usually have a useful link that is helpful and/or insightful.
At least I am trying to be helpful.
Relax, man.
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Old 02-13-2005, 06:43 AM   #34
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don etal,

if there was a short in a brake wire it would be in parallel with the magnets.

there would still be some current going to the magnets no matter what the resistance of the short. ohm's law.

i think that is what andy was trying to get at all along.

some brakes no matter how little, are better than no brakes. as i pointed out earlier my truck's brake line is fused. but, since it is "slugged" with a 60 amp mega fuse i would expect the wire to burn in the clear before it would blow.

even though everyone here need not agree on this subject, remember, andy adjusted insurance claims on airstreams for many years and has seen the results "doing things the other way" first hand. just ask him.

and if you think about it, anyone in his position would naturally opt for the safest advice.

other than the current crop of ford f150s that burst into flames from electrical problems caused by faulty antilock wiring, when was the last time you heard of tow vehicles spontainiously igniting?

i think the possibility of losing your brakes at the worst possible moment is a larger risk.

john
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Old 02-13-2005, 07:30 AM   #35
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Quote:
Originally Posted by john hd
if there was a short in a brake wire it would be in parallel with the magnets.

there would still be some current going to the magnets no matter what the resistance of the short. ohm's law.
It will only be in parallel if the short is in the wire to an individual magnet. If it is in the main wire that feeds all the magnets it will be in series. This will very, very quickly burn in half and there will still be no brakes. But you do have an uprotected relatively light wire that is part of a harness burning end to end.

Andy might have 39 years of experience, been an insurance adjuster, et al, but he hasn't thought this through. He needs to take a piece of 10 ga. wire 30 ft. long and lay it across a set of battery terminals and report the results.

John
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Old 02-13-2005, 07:30 AM   #36
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Thanks Lou. I had them all mixed up. Type III is manual.

http://order.waytekwire.com/IMAGES/M37/catalog/217_068

I a 100 amp fuse a good size for the battery main.
http://order.waytekwire.com/IMAGES/M37/catalog/217_066

www.waytekwire.com
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Old 02-13-2005, 09:42 AM   #37
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I said I wouldn't post again on this topic, but I need to re-emphasize one thing I stated in my last post. Then I'll shut up and let everyone do whatever they want, because I don't want to get into a nasty debate.

Anyway, an unfused wire in your tow vehicle represents a risk of a short circuits 24/7/365 - i.e. all the time. This fact alone would make me want this wire fused. It does not matter whether a trailer is hooked up. Since most times that most vehicles are driven, a trailer is not attached, does it seem surprising that people haven't seen too many cases of a tow vehile burning? Most such shorts probably do occur when a trailer is not attached. And if the circuit is fused (by fused I mean with a fuse or circuit breaker), as I suspect most are, the short will eventually be found and repaired and the vehicle will not haven insurance claim for burning down.

When towing a trailer you should be checking that your trailer brakes actually work frequently and monitoring the display on the controller even more frequently for indications of a problem. Thus, with due care, your "un-fused" circuit should only make any difference if that short circuit were to actually occur when pulling down that mountain. Of course a dead short in parallel with two or four or six brake magnets (4 ohms - 3 Amps each I think), will mean that most current will still go thru the short, with little to no measurable braking performance. But you still would be "letting the smoke" out of a wire somewhere.

And, I guess I'll agree with some of the other thoughts mentioned in this thread. The fuse (again fuse or circuit breaker as you prefer) is to protect the wire from the Battery to the Brake Controller. A short after the controller will likely do one of two things. It'll either cause the controller to shut down it's output to the brakes and report a fault or I suppose if the Brake Controller is more basic, it could damage the brake controller. Either way, this is likely to happen faster than a fuse or circuit breaker would open.

I will not discuss the Breakaway Switch wire in trailer, because I have no idea of how trailer manufacturers handle this (fused or not?), but I will say that if it were up to me, I'd consider that fact that that wire respresents an opportunity for a short 24/7/365, not just when the breakaway switch is used.
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Old 02-13-2005, 10:42 AM   #38
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we ain't talking christmas lights here!

john

with much respect i do not agree about the series explanation.

it is clearly a parallel circuit. otherwise it would not operate if one magnet were to fail.

i have included a very crude drawing to explain my point. as you can see any fault to ground along the entire braking system would be in parallel with the brake magnet coils.

the thing everyone needs to remember about parallel circuits is that the voltage drop across a resistance is the same. only the current varies. that is why with even a low resistance (read BAD) short the brake magnets will still receive some current.

hence, the some is better than none point of view. again this is what andy is getting at.

perhaps the best solution would be a way of deenergizing the braking circuit when not in use! but then that could lead to human error.

here is my attachment for what it is worth.

john
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Old 02-13-2005, 11:56 AM   #39
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As I stated earlier:
Fuses are a no-no.
Automatic-reset breakers are required by the brake controller manufacturer. They reset so quickly you would be hard-pressed to even see the change even on a DMM, (maybe on a VOM). These breakers open and close in milliseconds. The breaker manufacturer supplies the reset times in the literature that comes with the breaker.
If you have a factory-installed brake controller, (like in the 2005 Ford F-250), or a factory-installed pre-wired option then it has this built into the fuse panel. This is why they are sometimes confused with fuses. Mine is installed on the firewall and then ran to the battery.
As stated before, this is considered a safety circuit by automakers. Fuses are not present in safety circuits. This is the reason electronics manufacturers have been manufacturing automatic-reset breakers for quite a long time now.
As for the breakaway switch, there should never be a fuse between it and the power source. A fuse is considered the "weak link" in an electrical circuit. It is designed to protect equipment from damage or personnel from a dangerous electrcial shock. The NFPA and NEC considers anything over 50V, AC or DC, to be a hazardous voltage. I do not see how your system would have hazardous voltage at the levels we are dealing with in a 12VDC system. This rules out using a fuse to protect personnel.
Now, to use a fuse to protect the switch. These are just plain switches. When the insulator, (the part that is hooked to the tether), is pulled out, (when the trailer goes walk-about), then the two conductors touch. Two simple little pieces of metal hooked to two simple little pieces of wire. The alternative path to ground is completed and power is passed from the trailer's battery to the trailer brake circuit. What would you need to protect from damage in this circuit at that time?
Remember, there are only two reasons you use a fuse in a circuit:
1. To protect personnel from injury or death.
2. To protect equipment from damage.
I teach these in the Electrician Apprenticeship program I do for a number of automotive plants.
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Old 02-13-2005, 12:24 PM   #40
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Quote:
Originally Posted by john hd
john

with much respect i do not agree about the series explanation.

it is clearly a parallel circuit. otherwise it would not operate if one magnet were to fail.
Ok, I see your point, all that training wasted. But I still think with E=IR when R=0 that you are asking for trouble with no breaker. My only hope would be the controller failed open. Either way I don't think you will have braking for more than a second or two and the problems it could cause aren't worth the little time it will work.

John
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Old 02-13-2005, 01:01 PM   #41
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Great schematic, john hd!

Quote:
Originally Posted by john hd
john

here is my attachment for what it is worth.

john
If you ever need a job drawing electrical diagrams look me up!
Good job, buddy. IEEE would be proud of you.

What was this thread about anyway? Man, it has gone on and on and on...

I guess I am just adding to it.
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Old 02-13-2005, 02:06 PM   #42
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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
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