24 volt to 12 volt for a reailer brake controller

[billbunch47]

Have been told it is a easy thing to step down the volts. But no one here in Columbia seems to have a clue as to how or what pieces you need. Any help in this matter would be greatly put to good use, Thanks Bill

[Joe Cannarozzi]

You have 12 volts available both front and rear. The backside of the fuse panel door under the drivers window will tell you what # terminal is 12volt. Or your cigarette lighter and dash stereo are using 12 volts too.

A few places at the rear to tap in but someone else will be able to give you the correct place. Your trailer light plug is 12 volt and your Vanner battery equalizer has a terminal marked 12 volt and that should be mounted somewhere in the engine compartment.

An easy way to verify without a meter is with a simple circuit tester. The brightness of the bulb will be noticably dimmer when testing a 12 volt circuit compared to a 24.

[Kevin Erion]

Bill, if you are trying to install an electronic brake controller and you have 24 volts at the brake light switch, you have to use a relay for that. Anyone that installs these types of things should be able to draw a diagram for you.

[Jon Wehrenberg]

Bill,

I think your coach has 12 volt brake lights. As Kevin points out a relay should be used so you do not load the brake light circuit more than its wiring or CB will handle, and the power source for the trailer brake controller and thus the trailer brakes can come from the 12 volt post in the big electrical box over the engine. You can pick up the 12 volts directly from the coach brake light circuit, but if you prefer you can also pick it up from the toad brake light wiring receptacle.

I think only early 90s vintage or maybe earlier coaches had 24 volt coach lighting (except for headlights which always were 12 volts).

[billbunch47]

Kevin your right on ,I'm getting 24 volts on the brake light swith. Have already used the 12 volt post to power the controler and the big ground post in the electronic compartment under the driver. John my chassie is a 95, sure wish it was the later and just 12. Radio Shack seems to know what I'm trying to do but not the how to or the stuff to do it with, when you mention a relay will a bosch relay step down 24 in to 12 out?? This should not be as hard as I'm trying to make it. Bill

[JIM CHALOUPKA]

Bill said, when you mention a relay will a bosch relay step down 24v in to 12v out??

Bill, you do not understand what is going on nor the function of a relay.

A relay is not a device to change your voltage.

A relay is a device to switch the voltage applied to it, ON, or OFF.

It is primarily used to handle a heavy current draw (amps) that could not be handled by small wiring and switches.

For example a SMALL switch on a panel connected to activate a relay could have a control voltage of 24v @ the switch, the relay responds to the switch opening and closing and repeats this by opening and closing terminals of that relay that carry the load, say 240v @ 100 amps. (in your case 12v @ ?amps).

You must determine your control voltage, and find a supply point.
You must determine your controlled voltage, and ampere load on the circuit, and where you want it switched.
You must obtain a relay that will work within those voltages and ampere ratings, and connect it into the components circuit.

If you need more ask.

JIM:)

[Jon Wehrenberg]

Bill,

Jim has it right and rather than add to or confuse the issue I suggest you and he communicate via some simple wiring diagrams. I think you are not yet clear on how simple this is. All you are doing is using the signal circuit (whatever you pick, such as a brake light wire) to energize a coil that closes electric contacts to close the 12V brake controller circuit. Four wires. 2 to the relay coil (one of which is a ground wire), one 12V in from your 12V power source, and one 12V out to the brake controller.

[JIM CHALOUPKA]

Bill,

Jim has it right and rather than add to or confuse the issue I suggest you and he communicate via some simple wiring diagrams. I think you are not yet clear on how simple this is. All you are doing is using the signal circuit (whatever you pick, such as a brake light wire) to energize a coil that closes electric contacts to close the 12V brake controller circuit. Four wires. 2 to the relay coil (one of which is a ground wire), one 12V in from your 12V power source, and one 12V out to the brake controller.


Jon, I was only trying to help Bill understand the principal of what he was trying to do. (with the hope he could see the light and do it on his own)

As far as specific help about his bus, well, not having one of my own, I don't think I could do that in all practicality.

[Jon Wehrenberg]

Jim,

This is a case where bus specific information is not required. What Bill needs is a wiring diagram or even a relay part number and an associated diagram to suit his needs.

Where Bill opts to pick up his 12V and his 12V or 24V signal is entirely up to him because only Bill at this point knows to what extent he wants to fish wires or where he wants to locate his controller and relay.

Bill could locate the controller in the big electric box in the rear (but lose the opportunity to be able to adjust it as needed) or he could opt to locate it at the driver's area. Likelwise the relay can be located where convenient for his purposes. He can get signal power from the brake light switch if he wants to get it from the front, or he can pick it up from the rear from such sources as a brake light wire or even from the signal circuit from the brake light relay.

Where and how is unimportant. The only thing Bill needs now is a wiring diagram and maybe a part number for a relay.

[billbunch47]

I think a light bulb just went off. It seems to be going backwards but there is a spare wire close by , I was thinking at the source but somewhere in the system it has already been done for me because the brake light signal out to the trailer or toad is already 12 volts might as well try to use it. Will let you know, Thanks John & Jim, Bill

[ajducote]

There are a bunch of examples on the internet on wiring relays.
here are a few to look at.

http://www.the12volt.com/relays/relays.asp

www.installdr.com/TechDocs/999404.pdf

Andre Ducote
1999 Royale

[Jon Wehrenberg]

Bill,

That is why I mentioned the trailer receptacle earlier. On both my Prevost coaches the toad plug wiring had relays for each circuit (brake, park, turn signals) and the bus lights powered the relays which switched power from the 12 volt post.

You are correct in that it can likely handle the load. You may wish to follow your circuits however to make sure everything in there is sized to handle the extra load. You could have insufficient wire size, a circuit breaker or relay of inadequate size or you could have relays limited to the amperage you pull for the lights. You would not want to need a fast stop and then find the trailer brakes won't work because you tripped a breaker, or worse started cooking some wires. I can speak authoritatively about how ugly it gets when your Prevost is burning.