Wiring brake controller

lostagain · January 14, 2011, 12:12:53 PM

The instructions show how I should use a 10 ga wire to send the current from the controller (mounted at the front by the driver), to the trailer plug. I am using existing spare wires that run from the front panel to the rear panel. There are 4 or 5 unused ones. They don't look thick enough to be near 10 ga, more like 14, 16 ga.

Could I use 2 spare wires tied together from fr. panel to rear panel? Wouldn't it be like doubling the size of one wire?

I am using 10 ga from controller to fr. panel, and from rear panel to trailer plug.

JC

bevans6 · January 14, 2011, 01:15:07 PM

They are mostly 14 or 16 gauge in there. You can figure out the ampacity of them and add that together. I ran wires from the AC condenser bay to the back inside the old freon tubing, as a conduit. Thinking about this further, I think I might mount the controller at the back in the engine bay and not worry about it. Depends on how big the trailer is I think.

Brian

Len Silva · January 14, 2011, 01:24:43 PM

Keep in mind that those instructions are intended for a car or pickup where the controller is 15 feet or so from the hitch. You may want to go to 8 ga. for the additional length of the bus.

I would find out what the maximum current of your electric brakes are to calculate the wire size. If, for instance, you are pulling a three axle trailer with full brakes, it may not be enough.

lostagain · January 14, 2011, 04:46:22 PM

Brian, I thought about mounting the controller in the back, but then I wouldn't be able to adjust it. It is a small trailer ( 7' X 16', 2 axle). I can't see it in the bus mirrors or feel it anyway. I mounted the controller by the driver anyway...

Len, if I wanted 8 gauge, can I assume that 2 of the existing wires together ( 14 to 16 gauge each) would make 7 to 8 gauge wired together? Sorry guys, I am electrically challenged and rather clueless...

JC

brando4905 · January 15, 2011, 05:33:47 AM

FWIW, I have my brake controller mounted in the engine compartment. Once you get the controller adjusted you never have to touch it again. When I set mine up, I just had to stop a couple of times and go back there and dial it in to where it felt comfortable. This works for me since the trailer load stays pretty much the same all the time.

Also never felt like I needed to use the manual brake switch on the controller while towing with the bus. Same trailer being towed with pick-up, I would want the controller where I could reach it.

Brandon

bevans6 · January 15, 2011, 05:44:41 AM

Like I said, for a little wee trailer like that I would probably be happy with the controller in the back. My trailer is 30' ball to bumper and can weigh in excess of 8K lbs, so I went with the front mounted controller.

The rule of thumb is 10 amps per axle with brakes. The controller instructions are usually for up to 3 axles, so they want 10 gauge wire and an 30 amp breaker. Feel free to act like an engineer and downgrade/make your own decision, use the wire you want or have, and fuse accordingly with the appropriate breaker. It's equally valid to design for the actual use as opposed to worst possible case. Don't go over 30 amps because that is the limit of the controller as well as the wire, but if you go under 30 amps, fuse for the ampacity of the wire you are using.

The ampacity (ability of a wire to carry current) is available in various charts. About the most conservative is NEC, which is for insulated wire in bundles and at 600 volts. It calls for 10 gauge wire for 30 amps, in the distance you are looking at (40 or 50 feet is not really all that long, you run those currents inside your house all the time over longer distances). 12 gauge wire carries 20 amps, 14 gauge wire carries 15 amps and even though it's not in the NEC chart. 16 gauge wire carries 10 amps. Just look in your manual to find out what gauge the wires you are thinking of using are (each circuit is identified and the wire gauge called out in my MC-5 manual, anyway) and just add up the number of amps you decide to use. Two 14 gauge wires are good for 30 amps, three 16 gauge wires likewise.

Brian

Chopper Scott · January 15, 2011, 06:13:19 AM

Check your trailer also. My trailer is a 102 x 16' double axle but only has brakes on 1 axle. I have 12 gauge wiring for what it's worth.

lostagain · January 15, 2011, 06:58:32 AM

Thank you guys,

as mentioned earlier, I mounted the controller by the driver. I got the 12V to it without much difficulty with a 30A fuse.

I'll look up the wires in the manual as Brian said.

Sounds like 2 wires to the back will do. I ran a 10 ga. from the contr. to the front panel with a 30A breaker. And a 10 ga. from the rear panel to the trailer plug.

I got the brake light signal from a 24V to 12V converter that the PO had installed in the back for a trailer plug. (It didn't have anything for brakes). Running that signal up another spare wire to the front.

I also installed a high mounted LED stop light bar on the back of the bus while I am in the wiring mode. At least now I have something to show for a couple days work.

JC

Joe Camper · January 15, 2011, 07:11:27 AM

I just did his project.

Here is where one sees just how well he has engineered the conversion. I ran a new 10 gauge wire to the front and took advantage of all the accessability to wiring chases that I built in. Left the spares for future spares.

Piece of cake.

Len Silva · January 15, 2011, 08:20:23 AM

Quote from: bevans6 on January 15, 2011, 05:44:41 AM
Like I said, for a little wee trailer like that I would probably be happy with the controller in the back. My trailer is 30' ball to bumper and can weigh in excess of 8K lbs, so I went with the front mounted controller.

The rule of thumb is 10 amps per axle with brakes. The controller instructions are usually for up to 3 axles, so they want 10 gauge wire and an 30 amp breaker. Feel free to act like an engineer and downgrade/make your own decision, use the wire you want or have, and fuse accordingly with the appropriate breaker. It's equally valid to design for the actual use as opposed to worst possible case. Don't go over 30 amps because that is the limit of the controller as well as the wire, but if you go under 30 amps, fuse for the ampacity of the wire you are using.

The ampacity (ability of a wire to carry current) is available in various charts. About the most conservative is NEC, which is for insulated wire in bundles and at 600 volts. It calls for 10 gauge wire for 30 amps, in the distance you are looking at (40 or 50 feet is not really all that long, you run those currents inside your house all the time over longer distances). 12 gauge wire carries 20 amps, 14 gauge wire carries 15 amps and even though it's not in the NEC chart. 16 gauge wire carries 10 amps. Just look in your manual to find out what gauge the wires you are thinking of using are (each circuit is identified and the wire gauge called out in my MC-5 manual, anyway) and just add up the number of amps you decide to use. Two 14 gauge wires are good for 30 amps, three 16 gauge wires likewise.

Brian

Brian,

A slight disagreement with your numbers. The NEC calculations are correct for 120 VAC, but don't work as well when you get down to 12 volts. It's not that the loss is any different, it's just that the voltage drop as a percentage of the available voltage is much higher.

For example, 30 amps through 40 feet of 10 Ga. wire will result in a voltage drop of 1.23 volts. That is insignificant at 120 volts but a 10% drop at 12 volts.

In addition, you must include the length of wire from the batteries to the controller and then to the trailer brakes as the total length, perhaps as much as 70-80 feet.

The 10 ga. will work fine for a light trailer, but in the example of a heavy three axle unit, I would go with 8 Ga. I would also be sure there was an 8 Ga. or better copper ground connection from the trailer to the bus.

I would use an auto reset breaker and not a fuse.

bioVenture · January 15, 2011, 08:39:31 AM

Len is absolutely right!! Auto-resetting breaker, Not a fuse, and go with the 8ga. wire.

The last thing u want to be dealing with on any trip are brake problems

Joe

belfert · January 15, 2011, 12:41:54 PM

A fuse should never blow except if you're pulling too much current or you end up with a direct short. How does an auto reset breaker help if it just keeps blowing due to a short or over current?

zubzub · January 15, 2011, 01:03:40 PM

oh oh oh!! I know the answer to this one ( and I almost never do with 'lectricathingamee stuff) the auto reset breaker will trip....letting you know there is a problem, but will reset allowing to keep using the circuit i.e. the brakes until you have corrected the problem. My bus has a bunch of them and they are great trouble shooters that allow you to proceed a short distance to safety. Fer instance I had a to ground short in the front headlight wiring....pulled mucho current, breaker tripped, lights when out....very dark out there at 60 mph....lights turned back on before I had pulled over, fixed the problem. FWIW I also enjoy not pulling 15 fuses to see which one has blown.

bevans6 · January 15, 2011, 01:29:33 PM

It's funny - I said "fuse with the appropriate breaker". I wonder why I never think of saying "breaker with the appropriate breaker" or maybe "protect with the appropriate breaker". I always use "fuse" as the verb, I have no idea why and it's obviously confusing. yes, the instructions do say to use an auto-reset breaker. The comment about voltage drop is no doubt correct, but the actual current level (yeah, I actually do think in terms of actual as opposed to worst case when i think about current and voltage drops, goes back to lab work in college and that was how we were taught to do it) is likely no more than 8 or 10 amps, and the voltage output is variable and adjustable anyway. On the other hand, if you are parallelling up a bunch of 16 gauge wires to get the capacity anyway, why not add another one if it's there not being used?

Brian

Highway Yacht · January 15, 2011, 01:35:19 PM

Quote from: belfert on January 15, 2011, 12:41:54 PM
A fuse should never blow except if you're pulling too much current or you end up with a direct short. How does an auto reset breaker help if it just keeps blowing due to a short or over current?

I like the Breakers too... That way you can easily tell which one is tripped and search for the problem instead of pulling fuses.. Once you think you have the problem fixed, you can reset the breaker. If the problem isn't fixed, it will only trip the breaker again and you can start all over with the trouble shooting without having to keep replacing fuses.