Bus Electrical Systems - DC

[VeldatheWonderbus]

Thanks, @roach711.

Unfortunately, the instructions on all of the 12V amp/gauge charts I've seen state to use the entire distance of the circuit, including the return via the chassis. To quote from the link I posted above:

1. calculate total length of wire from source to device and back again

Regarding the type of wire, I'm on board with using stranded copper, not Romex or other solid wire. That said, a spool of stranded copper from an auto store costs twice as much per foot as a spool of the same gauge stranded copper from a home improvement store. As long as it's run in conduit and isn't exposed to the elements (road grime etc.) I can't imagine why I'd need to pay twice as much for an auto-specific wire...if it can carry 120V it can carry 12V safely. Please let me know if I'm missing something here.

Thanks again!

[roach711]

What's the effective wire gauge of a steel bus body?

My 24' bus has a fiberglass body so all my wiring runs are "out and back" which gives me maximum effective circuit lengths of, say 48 feet including the horizontal and vertical run and the ground wire. Looking through the wiring I pulled out of the bus I see nothing larger than 14ga and a good bit of it is 16ga. (excluding the AC wiring, which used 8 & 10ga).

Bigger wire is safer wire so the only downside to oversized wiring is the cost.

[VeldatheWonderbus]

Ohhhhhh...so...since the bus body is essentially a giant wire, there isn't any impedance between the fixture (where's it's grounded to the body) and the neutral/ground return to the battery. Which means that I really only have to consider the half of the circuit which is running through the wire from the buss panel to the fixture when I'm looking at the distance and its effect on amperage drop. So even though it might be 45' from the panel to the furthest running light through the wire, and another 45' back via the body, I don't need to worry about the second half when computing distance because the "wire gauge" is a 32,000 pound chunk of metal.

Is that about right? This DC wiring thing is totally new to me, so I really appreciate the input.

Also, I'd like to point out that our discussion has already quadrupled the amount of information in this thread that is on-topic, instead of just about how to get a computer or TV to run on 12V. So thanks for that too, @roach711.

[roach711]

I was familiar with AC wiring before getting our bus, but understanding DC, and how to mix AC and DC circuits took a bit of time.

Your ground leg would be limited only by the size of the ground cables from body to frame and frame to engine. Those cables are typically pretty large so your ground leg (assuming the connections are clean) will be fairly hefty.

Clean ground connections are key, both device to body and body/frame frame/engine. Old vehicles, especially those from the rust belt often need those ground connections cleaned. A dab of dielectric grease on those connections is a good preventive measure. It keeps rust and corrosion at bay.

The DC wiring guide I have shows 14ga. with a 1 amp load good out to 105 feet. Your LED lights draw about a quarter amp each so that gives you about a half amp load total for two lights. I'd be very comfortable using 14ga.

[VeldatheWonderbus]

Rad. Thanks!

[mad_wolf]

Originally Posted by VeldatheWonderbus

Thanks, @roach711.

Unfortunately, the instructions on all of the 12V amp/gauge charts I've seen state to use the entire distance of the circuit, including the return via the chassis. To quote from the link I posted above:

1. calculate total length of wire from source to device and back again

Regarding the type of wire, I'm on board with using stranded copper, not Romex or other solid wire. That said, a spool of stranded copper from an auto store costs twice as much per foot as a spool of the same gauge stranded copper from a home improvement store. As long as it's run in conduit and isn't exposed to the elements (road grime etc.) I can't imagine why I'd need to pay twice as much for an auto-specific wire...if it can carry 120V it can carry 12V safely. Please let me know if I'm missing something here.

Thanks again!

I solved this issue on a sailboat by using old arc welding leads I had lying around and anywhere I needed to ground several things added a Copper wire buss bar This allowed me to attach 12 v grounds and with the 1/0 cable only need count the run length from the hot side as it was overkill on the return side .

We also ran 12 v + to a heavy bus bar in areas with multiple switched items lights ETC that have their own method of on / off at the location . In boats its a absolute that you want your 12 v and 120 ac bonding totally separate even then there is leakage that can eat up your sacrificial anodes or worse leak lethal amount of electric power to the water several kids have died from swimming near by at docks and on trying to get out of the water completed a circuit .

Not sure about now but years ago old used welding cables were cheap the fire / ems service I worked for we used a quick detach and ran same cables to rear bumpers and had the other half on a set of jumper cables that way no opening the hood to jump start from either end and no having to turn around to face traffic . Works great if you need to hook up a harbor freight cheap winch to pull your toad onto the trailer or any other number of things you might need a high draw 12 volt connection .

Unfortunately my bus dream is on hold due to lack of funds had a few things unexpected come up as I am sure everyone here has at some point .

Never overlook the marine equipment sailboats and ships have long history of needing to have stuff that holds up under adverse conditions and miles from the nearest shop .

[Piersg]

FWIW (I don't know much about 12v DC, YET), my bus has a common ground bar at the rear, right under all the marker lights and the top flashing lights. All the lights are grounded to that bar...

[roach711]

Originally Posted by Piersg

FWIW (I don't know much about 12v DC, YET), my bus has a common ground bar at the rear, right under all the marker lights and the top flashing lights. All the lights are grounded to that bar...

It makes sense to do it that way. Instead of each light (or whatever) grounded individually you just have one ground bar inside and out of the weather.

[VeldatheWonderbus]

I'm at a standstill on figuring out how to connect my new multi-function stop/turn/driving lights in the rear. Their turn and running light functions work just fine, but I can't figure out how to wire them to get brighter when the brake pedal is depressed. I've gone through the entire buss panel, but none of the connections become energized when the brakes are applied. I'm missing the relevant page (and all the even pages) of the electrical circuit diagram manual (for a DT 466e, if anyone has a copy around, or wants only the odd-numbered pages), so I can't review how the brake lights are connected to the brakes there.

Any advice would be appreciated. Thanks in advance!

(Same question also posted in DT466 forum)

[roach711]

Did your brake lights work before swapping out the tail lights?

There should be 4 wires (and maybe a green ground wire) going to each of the rear light clusters (brake, turn, running and reverse) One of them has to be powering the brake light.

An easy way to test a wire without taking the light apart is to stick a sewing pin through the wire then touch one voltmeter probe to the wire and the other to a good ground. Press the brake pedal and you'll see if the voltage changes. If not, test another wire. When done put some electrical tape over the holes.

[VeldatheWonderbus]

The brake lights worked, but that was four months and a complete gutting. The old wires were a combined mess of frayed, burned out, and cross-connected to all sorts of alarms and safety stuff we didn't want any more, so we took out all the wires for the rear lights, running lights, etc. The body had a lot of corrosion at the openings for the old lights, so we had to cut out and patch all of those spots anyway. Everything I cut out is labeled, but the wires that I labeled as having come from the tail lights are re-connected (as described below) and everything works except the brake light function.

I replaced the three-light-sets of Red/Amber/White (Running, Turn, Brake, & Flashing/Flashing/Backup) with two-light-sets of Red/White (Running, Turn, and Brake/Backup). The reds are multi-function LEDs that are supposed to be able to do running, turn, and "Stop", which I assume means "brake".

Everything else works, but the lights don't come on when we hit the brakes. There isn't another wire connection point on the lights for another wire anyway, even if I found another wire or connection in the buss panel which showed a current when the brakes were applied. I've tested all of the random wires which didn't seem to connect to anything we could figure out when we gutted the bus, and none of them show a current when the brakes are applied, either.

So, my thought is that either: 1) the (brand new) lights I bought are bunk; 2) the wire carrying the current to signal that the brakes have been applied is simply lost in Velda's brain box somewhere (photo); or, that's not how this system works, and I need to ____ the ___ to find the ____ in the ____ and then connect the lights via ___ and ___ through a reverse-wired relay*.


This is THE ONLY THING standing in the way of my getting her inspected and subsequently registered, so I'm kind of angsty about it. :/

*I couldn't leave the entire sentence composed of blanks, and a reverse-wired relay makes as much sense to me as anything else, so why not?

[VeldatheWonderbus]

This just in (diesel mechanic friend called me back right after I posted the last), for future reference of anyone who finds themselves in a similar situation:

Apparently, there is a device called a "treadle valve" which is directly attached to the brake pedal - most brake pedals come with their own treadle valve already attached. This valve controls the supply of air to the air brake, and has one or more pressure switches on it. One of those pressure switches will not have power to one side of it when the brakes are not applied, but as soon as pressure is applied the switch will provide power to the brake lights.

So now I know where to look, since I couldn't find the wire I needed in the buss panel. And now you know, in case you were wondering

[roach711]

So if I'm reading that right, no air pressure, no brake lights?

[family wagon]

Does (did) your bus have separate brake and turn signals? That is, red lamps for brake and separate amber (or red) blinking for turns? And now you want to install a single lamp to do double duty for turn and brake?

If the above is correct, you need two diodes per side. They can be had in a tidy little package from the trailer parts aisle in an auto supply place; they're used to adapt tow vehicles with separate brake and turn to the combined brake/turn setup used on most trailers.

If the above is incorrect... maybe my reading comprehension is suffering and I should have got to bed early, and feel free to disregard.

[VeldatheWonderbus]

@family wagon, I'm not exactly sure how they had the three-light array wired, and yes, I've gone to a two-light array as described above. The red lights are indeed multi-function, with three connections.

@roach711, I'm not sure of the exact relationship between air pressure and lights, but it does sound like you'd need to change the pressure with the brake pedal to turn the light on, which means that you'd have to have a pressurized system. Luckily, the air system on Velda is working, so that isn't the issue.

The other gem of information which my friend gave me (somewhat inadvertently) is that the parking brake will also turn the brake light on. This means that (since the parking brake is on) I wouldn't be able to find a change in voltage in the buss panel or see a difference in the tail lights when the brake pedal is applied, since the circuit is already energized. Jeeze. So, yeah, maybe I'm a bonehead. But it seems to me that 90% of the troubles I have had with Velda are the result of user error and simply not knowing what I'm doing, so maybe posting this information here will help someone else...

Oh, and here's the photo of Velda's electronic panel which I neglected to post above, in relation to why I HAD TO get some wires out of her before I could make sense of anything...

[daddyoften]

Holy rats nest Batman! =-O

[VeldatheWonderbus]

Yeah, and that's AFTER I removed all of the circuits described above. I had to put six new wires in to hook up the replacement lights, and I still have a couple of fans to re-connect, but it's still way better than it was originally. About 25-30% better. :/

I'd hoped to clean things out even more, but I don't know where most of the wires go or what they do, so I can't very well rip them out. The school district we bought her from did A LOT of after-market modifications, including Zonar sensors on just about everything but the seats, a camera system, GPS...

[VeldatheWonderbus]

Update! I'm going to keep this going in the DC wiring thread since it is related to DC, just the intricacies of a particular part of the DC system.

I finally found a site with some information that helped me figure out what the problem was: Brake light wiring with 3 wire turn signal help. | The H.A.M.B.

It turns out that even though the lights I bought are labeled as multi-function driving/turn/stop lights, they can only function as two of those at best - either driving and turn OR stop. And since they only have two wires (other than ground), you can't hook them up to three source circuits unless you use some fancy diodes or restrictors or something. So I bought another set of lights to use for brakes and used the first set for driving and turn signals.

I managed to find which connection on the buss panel is energized when the brakes are applied, but it was always hot if the brakes were on, so direct wiring to this connection would result in my brake lights being on whenever she was parked, even without the keys in the ignition. So that's a no-go.

I still had to figure out where to get the signal for the brakes, and the treadle valve on my brakes doesn't have any wires coming out of it at all, so that seemed to be a dead end. I followed a thin air hose from the treadle valve to the wiring panel, where it leads into a cylindrical device which has a set of four wires running out of it (no picture, it's so buried in the circuit box that I can barely see or touch the thing, let alone get a picture of it). I followed the wires to the computer for my KLAM electromagnetic brake retarder, and sure enough, they connected to the terminals for the brake light (among other things). One of the wires in that bundle from the cylindrical device did not connect to the KLAM computer, however; it doubled back to a relay and from there was connected to the switch in the control panel which turns the KLAM on. Which was connected to another wire which ran to a relay...

After some testing, I found that one of the terminals in that relay was only hot when the brakes were applied AND the ignition was turned on. However, as with everything in the circuit panel, the relay is rather inconveniently located, and I couldn't wire my new lights in directly. So I cut the wire I'd determined was the one I was looking for and spliced in my brake light circuit. The wire is only a #16 aluminum, which makes me a little nervous, but what else can I do? The brake lights work now, and I can have her inspected and (hopefully) get her registered!

What I still don't get is what happened to the original circuit? The wire I had labeled as the brake lights is directly wired to the buss panel, and is always hot if the brakes are applied - it lacks the relay which considers whether or not the ignition is on. I suppose that the eight-function flasher computer which I removed might have also been this relay; in fact, that's the only explanation I can think of.

The moral of the story? Label every single wire you cut, remove only what you have to or what is clearly useless, and expect that you'll still run into mysteries. Hopefully my "adventure" in this effort will help someone else avoid spending two months doing research and testing before they can fix their problem.

Cheers!

[VeldatheWonderbus]

Oh, another site I found helpful in making sure I had the right lights in the right places: https://www.fmcsa.dot.gov/regulation...section/393.11

This shows the requirements for color of light and reflector, placement, number, function, etc. Although some states may have different requirements for RVs (this site is for commercial vehicles), it's a good starting place to understand what will likely be required across the country, and it includes diagrams for RVs. Also note that I installed some extra clearance markers (two of the three amber lights along the side of Velda in the photo I posted above), and that several of the original clearance markers (along the top of the side) are burned out - I've got a bunch of new bulbs I'll be installing this morning.

[Piersg]

Thanks for the link to the lightings regs, it will come in handy!

I thought my electrical panel was bad, until i saw yours!