Self Converters and Your Chassis Electrical?

[muddog16]

I'm in the process of staying out of the cold today and working inside and going through wiring and other systems, how on your buss if you changed out the 24 or 12 vdc chassis electrical system, did you switch the grounds , or did you switch the hot leads like in a normal electrical system! (normal is a non auto world electrical system)! I've been looking at the steering wheel and the schematics that came with it, I'm sure some of these are just taking the circuit to gnd like the horn! I'm open to suggestions! I've totally gutted my existing system and this will go back in the way I'm use to doing it or someone else's better idea! I did purchase Dave's book on Chassis electrical systems, and he has a great schematic in there on what he has suggested!  But before I go any further I'd just like to hear some other suggestions, one of these days I'm actually going to look inside another bus! I just finished making a call to the local electrical supplier and priced stuff for the automatic transfer switch and  neutral bonding device and they were not cheap.....ouch! I'm open to suggestions, comments, humor, or a nice home brewed bottle of hops!

Pat

[DavidInWilmNC]

This isn't a real answer to your question.  On my MC-8, the only items that were 12v when I bought it were the non-functioning stereo and the headlights.  Of course, the stereo was one of the first items to be tossed.  I left 24 volt items 24 volt and added 12 volt items.  All the lights, fans ('cept the dash fan), pumps, etc are standard 12 volt products.  I really only have a 24 volt system, but the equalizer gives me 80 amps of 12 volt power.  24 volt bulbs are not hard to find (I can hunt down a link, if you need it) and aren't expensive.  I ordered enough bulbs to replace just about everything on the bus when I first bought it, as many were burned out.  I kept the old ones that worked as spares and in some cases ordered extra spares (brake lights, for example).  Otherwise, you'll be having to up-size a lot of the wiring due to the greater current draw at 12 volts vs that at 24 volts.  Good luck.

David

[Len Silva]

David,

As a general rule, I like to use lots of relays (the standard automotive cubes) and locate them as needed, close to the load.  You can then use much smaller wire and low current switches to control them.  It is also much easier to have multiple control points with this arrangement (for instance, the water pump switch in the kitchen and bath, bedroom control of outside lights for those scary noises in the middle of the night, etc.)

Len

[H3Jim]

Len, do you use latching relays or just 3 or 4 way switches when you want to have mulitple switches control the same function? If so can yo provide  a model number of latching relay?

[DavidInWilmNC]

David,

As a general rule, I like to use lots of relays (the standard automotive cubes) and locate them as needed, close to the load.  You can then use much smaller wire and low current switches to control them.  It is also much easier to have multiple control points with this arrangement (for instance, the water pump switch in the kitchen and bath, bedroom control of outside lights for those scary noises in the middle of the night, etc.)

Len

Len,

I'm doing the same thing.  I hate to get out of bed and turn off lights in another room 30 feet away!  I have a wire and relay set aside with a timer for the block heater so I won't have to fumble around with that outside in the cold.  The water heater is on a relay so that it's disabled with the compressor on my 15K heat pump kicks in.  I can bypass this for when I have a 50 amp hook-up or am running the generator.  I've got outlets planned for each bay, one of which is controlled by a relay in the bus.  It makes it much easier to turn off those awning lights.  Like you said, they're also good for those 'scary noises in the middle of the night'.  Some of my controls are Intelletec that use a small three button panel, a four conductor cable, and have an LED to indicate when each circuit is on.  There can be multiple controls for this system wired in parallel.  To control a 110 volt load with them, just use another relay!  I'm leaning towards the relays with the round sockets and keeping a few spares on hand.  They are cheap and it's good insurance just in case.

David

edited to add... ronthebusnut has those Bosch-like automotive cube relays with 24 volt coils.  I bought several (and need to order more) and they're handy for using an original switch and wiring to control a 12 volt load.  I'll use the 'indirect lighting' switch to run some LED's for the steps, door light, and under the kick space under the base cabinets, etc.

[Stan]

Muddog: Your question seemed to be about switching grounds. If you visualize an automotive electric circuit, you have a wire coming from the battery to a device (light, horn, radio or whatever) and another wire going to ground. It doesn't matter which wire has the switch in it.

If you have a device which is internally connected to ground and completes the circuit when you bolt it to the vehicle frame, then you don't have any choice but to put the switch in the hot wire.

Many things on a bus are powered through a relay. In that case, you are switching the coil of the relay and the same thing applies. If both ends of the coil are available , you can switch either wire. If one end of the coil is tied to ground (many automotive relays are) then you have to switch the hot wire.

In the case of the horn relay, one end of the relay coil is connected to battery hot and you complete the circuit by connecting the other end to ground.

I hope this is what you were asking. If you were asking about four way switching, see the previous answers.

[prevost82]

Pat ... maybe you should go down to a truck wreakers and get a fuse and relay panel ... Then buy the electrical book for that make of the truck. This will give you an idea how to rewire the bus, and you should have enough fuse and relays to do all the circuits you require, all circuit fused and relayed. I mounted it inside the door at the top of the stairs if you want a pic, email me

I ripped all the old Prevost relays, tell-tales and alarms out of the front and rear juntion boxs and they became just that juntion boxes.

All alarms are in the new dash. I also ran a 1-0 ground with a ground stud at the following loctions, from the engine compartment (that where I moved the start bat'rys) to the rear panel and to the front panel and then into the front under the dash with a ground stud on each side of the bus. All grounds are terminated at the ground studs. This way I will never have a bad ground... and if I do it will be in 1 of 5 places.

Did you rip all the wire out running down the tunnel?

I also got rid of all the 24v and the coach and house systems are all 12v, 2- seperate systems, makes finding elec parts way cheeper and easier to find.

[NJT5047]

I ain't go no home-brew, but I got an opinion....    Maybe some of our electrical gurus could explain the rationale for switched grounds, but IMHO  switched grounds is gonna require a lot of extra wire and work. 
Until recently, the only commonly switched ground on most American made vehicles was the horn. 
Japanese and other asian cars and motorcycles have most electrical devices using switched grounds.  And they are a PITA to dx electrical problems.   I have assumed that since Jap cars are almost all plastic, there's no grounds available anyway.  And they like to &*## with American mechanics. 
I'd ground the component (load) and switch the hot lead.  Less "hot" wiring running all over the place letting smoke out. 
Regarding relays located near components.  That works fine, but will require running two leads to everything. 
The relay must be powered by a B+ of sufficient size either way, and it requires a control lead and ground wire.  The bus folk had it right with the relay panels and all relays near a dedicated power source.   
Using a truck fuse panel seems a good choice of protecting the chassis electricals.  It likely will have a relay for the headlights/running lights, horn, and probably the AC...which could be used for something. 
Unless the load requires a relay, why install one?  Be easier to break up the circuits into easily protected 10A, 12VDC circuits. 
The use of 12V LED tail/brake/turn and clearance lighting would allow use of the 24V wiring.  Or smaller replacement wiring. 
24V bus systems cost a right good bit to convert to 12V... unless you have some reason to scrap the starter, alternator, all HVAC systems, panels, relays...etc.   I believe Muddog has done this essentially removed everything.....I'd go to 12V truck style electrical system if I had to rewire the bus.   Otherwise, that 24V system looks like a keeper. 

My dos centavos, JR 

 

[muddog16]

There's an ice storm going on outside and I can't sleep anyway!  Ron and Jr, that is what I'm talking about, switching grounds.  I have  some pictures on my website of the bus, I've already built the panel, after all of this planning it just hit me that some one may have a better mouse trap!  Jr, I've wondered why the automobile industry used the chassis for ground for a long time, point in fact when I was stripping the baggage compartments out I noticed that "all" of the bolts for the hinges on the baggage doors and other brackets that electrolysis (sp) had eaten the end of everyone of them down to the nut! It was pretty apparent that it was not a great engineering feat, but I'm sure it was a cheaper way of doing things! And I'm not dissing engineers those guys earn their beans and take a lot of flak!  I'm sure no one expected these old buses to even be around today, considering how they were built I'm amazed at how well they have really weathered the storm of time!  With plastic being introduced in many new cars, I'm sure its a head ache with grounds.  I've considered running everything back to ground bars instead of grounding at the location, and I may very well do that, identifing each of them!

One of the things that really bothered me was while gutting the bus were the battery cables, the insulation just fell off in my hands when I pulled them out, that is so dangerous, and should be replace on any 20 year old bus!  Ron you mentioned 1/0 cable for your battery leads, for the chassis electrical system I'll probably use the same size or maybe even 2/0 depending on where I locate the batteries!  For the DN50 alternator feed to my SW 4024 Inverter I'm using 4/0 cables and keeping them as short as possilbe also! 

With the telltale that came with my dash, I'm realizing that I'm going to need some  sending units to actually activate these lights on the dash.  If anyone has a source for sending units I would appreciate that.  Again thanks for the input I do appreciate it!  As for the home brew Jr, I'll save that for warmer weather!

Pat

http://prevostlemirage.blogspot.com/

[Stan]

Muddog: I am still not sure what you are doing. Are you changing a 24 volt bus entirely over to 12 volts?

Why did you use high current relays for the Skinner valves? They use a nominal 10 watt coil which is less than one-half amp on 24 volts or one amp on 12 volts.

Dash idiot lights are switched by a sender that is just a switch which is not voltage sensitive. In some cases there is a relay in the circuit that will require the proper voltage on the coil.

I may not have beem clear enough in my treatise on switching ground wires or it may have been confusing. A simple explanation is to view it as a two wire system rather than one wire and chassis. It doesn't matter which wire the switch is in. If one of the wires is the chassis the switch has to be between the device and the chassis.

Troubleshooting a switched ground system is no different than a switched hot system. You use the battery hot (usually +) for the commom point to hook your meter and you probe with the negative meter lead.

[ChuckMC8]

My new engine was in a firetruck that started with 2 new 8D's at 12 volts. When I installed it in my bus and changed to 24volt (with 2 group 31' batts) the starter spins the engine MUCH faster, even with the smaller batteries.......I wouldnt change to 12 volts.....I'trying to change as much as possible to 24 volts. I've just bought a replacement fresh water pump in 24 volt as well as a 24 volt dash fan for the driver. I'm not concerned about finding replacement parts.
I run all 12 volts loads (including bus headlights and wiper motors)from my house battey bank (24 volt) and use Vanner equalizer. The 24 volt bus alternator charges the house batteries while underway.
24 vs 12 volt........same power for half the current draw..........makes sense to me!