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-   -   Brake fuse (https://www.airforums.com/forums/f37/brake-fuse-15450.html)

Over59 02-07-2005 08:28 AM

Brake fuse
 
Does one fuse the brakes. The wiring diagrams don't show fusing for any of the trailer running lights, ect. While some of these curcuits may fuse in the TW it looks like the brake line comes unfused off the tw control panel aux post to the Brake controller then on to the brakes. Should a fuse be in there somewhere to protect the brake controller. I was thinking an inline fuse at the connector box in the trailer for each axel.

Inland RV Center, In 02-07-2005 08:48 AM

Protecting an electrical brake line with a fuse or circuit breaker is taboo.

The idea is to have some kind of brakes, even though a short or partial short developed.

Partial shorts usually come from worn out brake magnets.

Andy

Over59 02-07-2005 09:01 AM

Thanks Andy. Kind of thought that may be the case. Better to have brakes with smokin wire than good wire and no brakes.

markdoane 02-07-2005 09:45 AM

Isn't there supposed to be a fuse or circuit breaker in front of the brake controller?

Inland RV Center, In 02-07-2005 10:14 AM

Don.

Absoluely not.

The theory is that even with most shorts, you will still have some braking.

It is far better to be able to stop, than to be worried about some smoking wires.

The short can be fixed. Your life cannot.

Andy

markdoane 02-07-2005 10:57 AM

I'm just repeating what I see in the installation instructions for brake controllers. Most specify a 20a circuit breaker.

I don't follow your logic about being able to stop, rather than worry about smoking wires. If the brake circuit is grounded enough to trip a 20 amp breaker, then there's probably nothing getting through to the magnets anyway. And if you have a short on one side only, feeding full amps to the other side could cause the trailer to trip sideways.

I think you should have a fuse or breaker in front of the breakaway switch too.

Just my personal opinion, not a theory.

Safari Tim 02-07-2005 11:11 AM

I agree Don, a fuse or circuit breaker is needed. At least you won't be on FIRE when you can't stop ;-)

To clarify, the circuit breaker/fuse is in the tow vehicle on the wire that feeds the brake controller. And all fusing is done right next to the battery positive post, as close as possible.

There is no fuse for the brakes on the trailer itself.

87MH 02-07-2005 12:13 PM

Breakaway Switch Fuse/Breaker
 
Quote:

Originally Posted by markdoane
.....I think you should have a fuse or breaker in front of the breakaway switch too.....

Having become quite intimate with the electric panel on the '78 Sovereign, I know for a fact that there is a 50 amp breaker on the line feeding the breakaway switch (this line is common to the electric tongue jack). The feed line from the breaker to the front (jack/breakaway switch) is only 12 gauge wire.....

The phrase "too hot to handle" comes to mind, quickly followed by "lit up like a Christmas tree".

I agree with Inland Andy - on the breakaway - since you have no way to monitor the trailer (breakaway) system, it would be unwise to install a fuse on the breakaway system.

Inland RV Center, In 02-07-2005 12:15 PM

Dealing with theories, opinions, guesses, or logic, is not the same as factual proof.

First of all, a fire will not start if you have a magnet shorted.

Secondly, controller manufacturers, because of liability, suggest fusing.

Third, all of us have choices to make.

If you wish to have no brakes, because you had a short, just to save some wiring, that's your choice.

Most owners, want the security of knowing that even with a short, they will still have some brakes.

Lastly, since power will not be applied to the brakes for more than a few seconds, that is not enough time to overheat the wires.

Also, the wires themselves offer some resistance in addition to the magnets resistance. Therefore, it is impossible to get a "dead" short.

That being the case, the heavy wires will get hot, but they won't burn.

Bottom line is how well someone choses to be as safe as they can, regardless of the circumstances.

Ask any pilot.

Andy

markdoane 02-07-2005 12:31 PM

I would certainly encourage anybody to think very carefully about the advice given in the above posting by Inland RV. If you don't have enough experience to figure it out, ask someone you trust.

I ain't no fool. I'm going with what feels right, which means every wire should have circuit protection. That means a resettable breaker ahead of the brake controller, and a fusible link or breaker on the breakaway switch.

Inland RV Center, In 02-07-2005 12:52 PM

There is a marked difference between somones opinion, and 39 years of dealing with any specific problem.

That becomes factas well as experience, our ageless teacher.

Anyone, I am sure, that had to stop quickly, would readily agree that to have some brakes, gives them a chance.

To have no brakes, gives a person, a big fat zero chance.

Don, the choice is yours, as well as theirs.

Leading anyone down a road with zero brakes, is not my idea of safety.

But, again, that's your choice. My only advice would be don't lose your brakes, and hit someone, or, get into a sway, and find out you have zero brakes.

That's not a good situation for anyone to get into.

Stopping a trailer, at all costs, when necessary, is the object. What it may cost to do that, very quickly, becomes insignificant, under the circunstances.

Safety, when dealing with lives, has no cost.

I have been there and done that, personally, with test trailers, single as well as tandem axles.

But the real bottom line, is convert to disc brakes, and then the fuse question becomes meaningless.

Andy

markdoane 02-07-2005 02:26 PM

So once again, 39 years experience means that you have all the answers, and everyone else is wrong.

Happy for ya.

Safari Tim 02-07-2005 02:31 PM

Quote:

Originally Posted by Inland RV Center, In

But the real bottom line, is convert to disc brakes, and then the fuse question becomes meaningless.

Andy

Ahh....

Like they always say, 'Follow the money'.

Most tow vehicles come prewired today with a brake controller pigtail and fuse in the glove box to be installed by the brake contoller installer. There is a fused brake controller feed built into the tow vehcile fuse box.

The AS, even my '71 has 40 amp fuse which leaves the battery location to the tow vehicle where it is tapped off there to the electric jack and break away switch.

Power should always be fused or breakered at the battery positive post. And if two batteries are connected together as in a trailer/tow vehicle, they need to be fused at both ends.

One more note. The short may not occur in the brake itself, it may occur anywhere along the length of wire and with no fuse protection you have a very real chance of a fire starting.

TomW 02-07-2005 02:42 PM

Quote:

Originally Posted by Inland RV Center, In
...But the real bottom line, is convert to disc brakes, and then the fuse question becomes meaningless.

The hydraulic pump (aka a possible failure point with disk brakes which drum brakes do not have) will need a healthy chunk of power to do its job.

Following the "don't put a fuse on the controller" argument, it would appear that the pump falls into the same frame of reasoning.

Tom

87MH 02-07-2005 02:49 PM

Breakaway Circuit Protection and Test
 
Quote:

Originally Posted by TomW
Following the "don't put a fuse on the controller" argument, it would appear that the pump falls into the same frame of reasoning...

I think I have have been enlightened to the wisdom of the Airstream way of doing things.....

Yes, the breakaway circuit is on a very heavy breaker, and yes, the magnets will fail if a short circuit should occur,

but....

the circuit is tested each and every time you hook the tow vehicle to the trailer....with the operation of the electric jack!

Power to the jack means power to the breakaway switch!

A failproof circuit test each and every time you hook up.

Eureka!

TomW 02-07-2005 02:52 PM

I put a 30 amp self-reseting breaker on the input power lead to my Prodigy controller because Tekonsha recommended it AND because I reasoned that the only thing that would trip it would be a dead short.

If a dead short is present, no power will make it to your brakes because it will all go to the short.

A fuse would not be a good idea because once it goes, its gone. With a self-reseting breaker, you get multiple chances to see if the short is intermittent.

Tom

Ga Pockets 02-07-2005 02:54 PM

The auto reset circuit breaker( 20 or 30 amp depending on # of axles) is between your Tow Vehicle's 12 volt system and the controller. If your charging system were to have a voltage spike or over current draw your system, your controller is still intact and will be workable in a few seconds after breaker cools and resets. If your controller gets fried..........a fuse down stream is a non-issue as you won't have brakes.






Wiring Instructions For Electronic Brake Controls
ELECTRONIC BRAKE CONTROL INSTALLATIO


3. Connect BLACK (+) wire through an



automatic reset circuit breaker (20 amp for
1-2 axles, 30 amp for 3-4 axles) to the

POSITIVE (+) terminal of the battery.

The BLACK wire is the power supply

line to the brake control.







5.
The BLUE (brake output) wire must be



connected to the trailer connector’s brake wire. (no fuse)











Inland RV Center, In 02-07-2005 03:11 PM

Don.

No, I do not have all the answers.

But I do have the background of seeing almost any type of Airstream problem that someone can dream up.

What I try to report, is that experience factor, of what and why, and the fix.

The choice is still up to the individual owner.

All coins have two sides. Some are OK, some are less than OK. Each individual makes their own choices, of describing safety.

Safety issues are far removed from liability issues.

The only arguement is in the case of a brake line short, almost always caused by a worn out magnet, is it safer to have some brakes, or no brakes?

My 39 years with customers and insureds, say they would rather have the former, namely some brakes.

Andy

john hd 02-07-2005 04:37 PM

not to jump in here and stir things up.

however, with your average battery in a tow vehicle being able to produce 650 amps, most wiring will become the fuse itself.

all in all, i'm with andy on this one. even though my rig is fused from the factory. 60 amp fuse, it will destroy the wires before blowing.

i think a good comprimise is a self resetting circuit breaker.

john

Over59 02-07-2005 09:33 PM

Well I guess I asked a good question. There is a resetting breaker between the controller and the power when I looked more carefully. Installed by the dealer with the controller. So if the controller lights are on I have juice going aft. I'll be running separate lines to the axles from the connection block, one for each axle. I'll fuse the hitch jack inline. I will not fuse the breakaway switch and don't see any reason to do so. I wouldn't want a damaged fuse / breaker to go unnoticed and then not have power available to the switch if needed. Using the same line as the jack would help but I've blown that line fuse with a bad switch and had to use the hand crank when I ran out of fuses. I guess I would have the same concerns about fusing brakes aft of the controller, wouldn't know if they were bad. I'm not sure I would notice the difference between one and two axles braking until I really needed them both. Seems like something could be built into the controller to indicate there is a short on the system. This part of the technology has a long way to go. You would think that the new units would have something different than my 59.
I have another question but I think I'll save it.
PS. Still obsessing over the Duramax and 8.1L. If only diesel wasn't more than premium gas.

66Overlander 02-08-2005 05:27 AM

First, I can pretty much assure you that prewired vehicles will have a fuse or circuit breaker from the factory (Ford, Chevy, Dodge, etc.) because while a wire "will act as it's own fuse" if it shorts out, it may do so in an inconvenient location, start a fire, and burn the vehicle down in the process. Therefore, any wiring done by the tow vehicle manufacturer will have provisions for a fuse or circuit breaker so that the fuse "open" occurs in such a way as to protect the rest of the vehicle.

Second, every set of trailer brake installation instructions I have seen indicates that the makers of the brake controllers also see this as a requirement and specify a fuse or circuit breaker in the power feed wire.

To do anything else is taking unnecessary chances. In most situations with a loss of trailer brakes you should be able to eventually get the rig stopped (but it'll take longer), as long as your dash or other part of your tow vehicle is not "on fire" or smoking heavily.

And in case you're wondering why I'm disagreeing with Inland Andy on this one, I've been an engineer in the Auto Industry for many years and am familiar with their circuit protection practices. Andy is a valuable resource to this Forum and he may be right on many issues, but there is definitely room to disagree on this one. If you add an unfused brake control circuit, you are (as Andy might say) asking to become a statistic. Luckily shorted wires are probably much rarer events than trailer sway, and most people may never experience one. But why take your chances when peace of mind is as close as the addition of a fuse or circuit breaker?

Inland RV Center, In 02-08-2005 09:56 AM

Joe.

Come down a 7000 foot mountain with a 31 foot trailer without brakes.

Then tell us how foolish we are to not have fuse in a brake line. Tell us how your going to stop this rig on a narrow two lane winding down hill highway, and fix the problem.

Things being things, when in an emergency, "ANY" help is good.
Having a blown fuse, is not a good excuse, for not having brakes.

Engineers or not, coming down a mountain, such as we have here, is no fun, even when everything is OK.

Peace of mind? What really is peace of mind when it comes to brakes? Know that you have something instead of perhaps nothing, describes a peaceful mind.

There has never been a known fire from a trailer brake line being shorted.

Bottom line is everyone can make their choices.

The issue of what is ideal becomes useless, when we must have the brakes, and we don't.

Fusing any electrical circuit is a very wise thing to do. "BUT" there are a very few exceptions.

Each owner can decide for themselves, which way they want to go. But when they are posed the question of no brakes to some brakes, seldom would anyone say "I will go with the no brakes."

It's not a matter of whats right or who is right, it's much more of a matter of
what do you do, if your faced with a "got to."

Some people drive over the edge. Fortunately, most use good common sense, and have prepared their equipment and themselves accordingly.

Andy

Chuck 02-08-2005 10:50 AM

Quote:

Originally Posted by Over59
Seems like something could be built into the controller to indicate there is a short on the system.....


There is on mine. something I need to investigate before next season. My brake controller is indicating a short in the system somewhere, when the trailer is NOT attached, and I step on the brake. (light flashes rapidly). However, when the trailer is attached, the indicator shows that everything is normal, with my foot on and off the brake. ??

(tekonsha voyager, plugged into a factory trailer-package equipped Dodge.)

Over59 02-08-2005 04:37 PM

Chuck, I think it's telling you you forgot the trailer. :p

66Overlander 02-08-2005 05:40 PM

Andy,
This will be my last post on this issue, so you need not debate the issue with me further. You cannot prove that a Trailer Brake wire has not cause a fire anymore than I can prove it has. In the aftermath of a fire it is often hard to pinout the cause. By the way, an unfused wire represents a risk 24/7/365, not just whenever you have a trailer hooked up.

In any case, I chose to follow proper circuit protection practices to minimize the chance of such events. Each owner can chose to do as they wish and take any chances they wish. I was just trying to provide the information necessary for them to make an informed decision.

Anon 02-12-2005 12:53 PM

Quote:

Originally Posted by markdoane
I'm just repeating what I see in the installation instructions for brake controllers. Most specify a 20a circuit breaker.

I don't follow your logic about being able to stop, rather than worry about smoking wires. If the brake circuit is grounded enough to trip a 20 amp breaker, then there's probably nothing getting through to the magnets anyway. And if you have a short on one side only, feeding full amps to the other side could cause the trailer to trip sideways.

I think you should have a fuse or breaker in front of the breakaway switch too.

Just my personal opinion, not a theory.


The breaker that the instructions are referring to is an automatic-reset breaker. They are small and metal-encased. This is absolutely essential to have to isolate the brake controller from being shorted. It has to be a fast-acting automatic reset type. This way you will have brakes no matter what. Sometimes the breaker will trip and reset without you even knowing that it happened. DO NOT use a fuse or a manual-rest breaker. As Andy said, you will have no brakes then.
Do not put a fuse in front of the break-away switch. If the break-away is triggered it is because of a MAJOR problem, like the trailer and tow vehicle are no longer travelling together. When that happens and your break-away trips it sends power from your trailer battery to the brakes. 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.

Anon 02-12-2005 12:59 PM

https://65.196.229.70/pdf/N5100.pdf

This link will show you that Draw-Tite requires a automatic-reset breaker. It is an Adobe Acrobat file so you can save it to your PC for reference.

Over59 02-12-2005 02:00 PM

Thanks Lou.

You managed to agree with everyone. I think that's the setup the dealer did on mine. The DIYer needs to get the right type resetting breaker. Would that be a Type I or III? I think Type II is manual? Type I is autoreset with power on and Type III is auto reset when the power is turned off. I may have them backwards.

Anon 02-12-2005 04:34 PM

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:
https://www.1firsttech.com/products.asp

The particular breaker I used, (Type I) can be found here:
https://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!

TomW 02-12-2005 05:43 PM

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

markdoane 02-12-2005 10:16 PM

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.

Anon 02-13-2005 12:36 AM

Plain wrong....
 
https://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.

Anon 02-13-2005 12:41 AM

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.

john hd 02-13-2005 05:43 AM

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

74Argosy24MH 02-13-2005 06:30 AM

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

Over59 02-13-2005 06:30 AM

Thanks Lou. I had them all mixed up. Type III is manual.

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

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

www.waytekwire.com

66Overlander 02-13-2005 08:42 AM

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.

john hd 02-13-2005 09:42 AM

we ain't talking christmas lights here!
 
1 Attachment(s)
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

Anon 02-13-2005 10:56 AM

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.

74Argosy24MH 02-13-2005 11:24 AM

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

Anon 02-13-2005 12:01 PM

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.

Inland RV Center, In 02-13-2005 01:06 PM

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

66Overlander 02-13-2005 01:29 PM

Quote:

Originally Posted by pattersontoo
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.

Lou,
A fuse or circuit brakers IS a "designed in" weak link, done on purpose to make sure that a circuit fails in a "safe" manner if a short circuit to ground occurs.

At least in automotive (i.e. 12V) applications, a fuse or curcuit breaker is not used to protect personnel which, in any case, are of too high a resistance to trip such a circuit protection device. And in most cases in automotive applications (there may be few exceptions), the sole purpose of the fuse or circuit breaker is to protect the wiring, nothing more, nothing less. A shorted wire that is not protected by a fuse or circuit breaker may overheat with all of the negative side effects that can come from such overheating.

In the case of a short circuit in the wiring the wire resistance which can be much less than one ohm (depending upon the nature of the short) represents the only resistance to current flow. As an example only, let's say the short is 1/10th of an ohm: 12 volts divided by 0.1 ohm = 120 Amps. A typical brake control circuit will not last very long at this current level.

This is my final word on this message string (really). I will no longer point out incorrect theories about the need for (or purposes of) circuit protection devices. Each person that reads this message string can decide which "facts" they choose to beleive and wire their tow vehicle or trailer in a manner consistent with those choices.

john hd 02-13-2005 04:10 PM

"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 "

andy.

you are correct in the strictest sense on this one. it is a series parallel circuit when you consider the resistance of the wires and connections.

that is my lineman training showing through, we are taught to consider only the resistance of devices. and not the wires connected to circuits because of the extremely high voltages i work with AND because the conductors are usually the size of your arm (not kidding!)

however, if you were to consider only the magnets as you suggest in a pure parallel circuit. there would be the same voltage drop across each magnet with only the current varying with the resistance.

the end result is the same, shorted magnet produces no braking. the remaining magnets get "some" current.

obviously the entire circuit would be in a state of overload at this point, AND adding a fuse would be a recipie for disaster if you were screaming up to a crosswalk full of kids!

john:)

gsymes 02-13-2005 06:18 PM

More or less
 
Maybe, more or less to this than we are seeing. Obviously the technical issues have been covered for the electrically challenged. Have you ever bought a old boat and had to replace all the wiring because of inline splices and corrosion. Not to speak of the PO thinking that speaker wire makes a good system because that’s all he had at a moments notice. Fishing being the priority LOL.
If I built brake controllers any amateur, was going to install in his vehicle, I would definitely recommend a intermittent breaker. Actually I would recommend they take it to Inland RV if they were in California. Smooth HUH Andy.
I have seen some horrible installation jobs locally, for this reason I decided to do it myself. Also breakers do fail, a friend of mine just had this happen.
Did I use a intermittent, the answer is NO. I encased the wiring from the battery to the trailer in flexible conduit. I made sure that this wiring would not see daylight in my time, nor would it see any sharp metal object on my Dodge truck.
After 32 years in aviation I have seen many a burnt wire that never gave a indication by “popping” a circuit breaker. I take that back, smoke in the cockpit or cabin is always a good indicator. Protect the wires properly.
I don’t enter this issue lightly, there is a time and place for “fused” circuits and if you doubt your, or your manufactures installation, I think you should have a intermittent breaker. If you trust the installation then I would rather see smoke, than see my family in the hospital or at the grave yard.


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