Converting a MC9 to 12v?

[Cecil The Diesel]

This may or may not be a complex series of questions, but I'm sure there are some of you that have done this.

I've got a 1982 MCI MC-9 that runs everything as far as I can tell on 24v except the headlights.

This bus is in the process of a conversion as an on the road live in coach for me, and my band so I'm about to wire it for 50 amp shore power. Is there a way to update this whole 24v system to something a little simpler and more geared toward a motorhome/coach instead of a charter bus?

I'm having a ground issue or something going on because some of my gauge lights flicker, or don't work at all depending on when they decide to or not. My volt, and temp gauges also fluctuate whenever I turn the headlights/running lights on or off. My two center side lights on top just don't work at all. Had a electrical guy do some tracing to a relay that was out in the control panel beside the driver seat wall. Wasn't sure that was the problem though. He found a replacement for about $80 we would have to order so I decided to hold off until I did some research.

I like the idea of it all being 12v except maybe the starter for ease of updating the gauges, lighting, accessories, etc...

Can someone give me some ideas on what would be the best option for my situation? 

[belfert]

You better have a set of wiring diagrams if you're going to even attempt this.  Do you have a Vanner Equalizer for any 12 volt stuff?  You're going to find a ton of stuff that needs to be changed to 12 volt.  Most exterior lights, gauges, some or all relays, starter, alternator, and other things will need to be replaced.  Changing things to fully 12 volt isn't going fix your bad grounds and such unless you plan to replace all of the wiring in the bus.

I started down this route once with my 1995 Dina thinking I might convert it to fully 12 volt.  I finally gave up because there are 40 pages of 11x17 wiring diagrams for my bus and I couldn't figure out how to deal with the transmission computer There is a couple on this board that have a Dina that was fully converted to 12 volt, but the previous owner worked as a mechanic at a truck shop if I recall correctly so he had access to parts.

Most commonly, the house and chassis systems are kept separate.  There is some movement towards using the house batteries to start the bus to eliminate a set of batteries.  Even then, the two systems are usually separate other than the batteries.

All the more power to you if you want to pursue this.  Personally, I would spend my time fixing the problems with the existing system.  If you have to pay someone to diagnose and fix the electrical system it could be less expensive to just rewire some of it, but keep it 24 volt.  Good luck whatever decision you make.

One other note, going from 24 down to 12 volt means most of your wires will need to be larger to handle more current.

[technomadia]

One other note, going from 24 down to 12 volt means most of your wires will need to be larger to handle more current.

This is very very important to keep in mind - and probably makes a switch from 24V to 12V completely impractical. It will double the current flowing down every wire, potentially overloading some.

Going the other direction is more practical - switching from 12V to 24V cuts the current demands in half.

I've sometimes wished that we had switched our 4106 from 12V to 24V for the alternator and starter, and I had then built a 24V house system.  You can get much bigger inverters at 24V than 12V.

Cheers,

  - Chris

[bevans6]

My MCI has almost nothing running on 12V, and I supply that from the 24 volt house bank using a Vanner equalizer.  Refrigerator computer, car radio in the dash, interior lights, the water pump.  That's about it.  24 volts is a far better system for a large vehicle wiring system, due to the reduced current requirement for the wiring.  A lot of the wiring in the bus is 16 gauge.

Brian

[Cecil The Diesel]

I don't have anything set up for equilizing yet. I have an old unit out of a motorhome I was gonna retrofit that will convert the shore power to 12v for interior lighting, and battery charging.

My main concern is updating everything. Some of the old relays are expensive, and/or hard to find, plus dash, gauge, radio, and cigarette lighter options are out of the question unless you put a 12 to 24 volt converter or reducer on everything. I can find a new ground source for it all I just don't want to have a relay blow while I'm on the road and it take 2 weeks to track it down, and have it shipped to me when I need to be at our next stop that night. I would like to design a setup to where I can keep one of everything extra I could possibly need without spending thousands in case of emergency.

My bus is a 5 speed manual, 8V71N and mechanical injection so no engine/tranny computer to worry with there. I'm ok with all internal lighting/power running off the house system if I can simply everything else. 

I am learning so bear with me.

[Len Silva]

You will almost certainly have to rewire the entire bus since, as mentioned, the current will double as will the wire size.  You would be much better off using a Vanner equalizer or converter to get the 12 volts needed for those few items that need it.

Relays don't "blow" and they are inexpensive to replace.

Your interior lights, radio, CB etc. can run off the 12 volt house system if that's what you want.  I think you would find converting the bus systems including lights, blower motors, starter, alternator, regulator, all the instruments, etc. to be prohibitively expensive.

[robertglines1]

Good chance in your relay situation you have unused /abandoned relays in the system that could be switched out for your bad one. You need also to realize while all electrical guys understand systems :these Bus systems are just a little special/different. Do you still have your stock AC system and Heat?  Also remember that a wire at 24 volts will only carry 1/2 the amps at 12 volts without over heating.  Would like one of the elect types to verify this for it's been awhile since I have worked all this out. Loose or dirty ground screws/wires are biggest prob with our systems.   Bob    Len posted as I was hope his was more clear than mine!

[Lee Bradley]

On a side note, the Odyssey crew is switching the boat they bought from 12 to 24 volt.

[belfert]

I don't have anything set up for equilizing yet. I have an old unit out of a motorhome I was gonna retrofit that will convert the shore power to 12v for interior lighting, and battery charging.

You are probably confusing an equalizer and a converter.  A converter takes 120 volts in and converts it to 12 volt.  An equalizer allows one to center tap a 24 volt battery bank to get 12 volts.  Without an equalizer you most likely don't have any 12 volt at all now.  Your 12 volt headlights may run in series on 24 volts.

I have separate house and chassis power systems.  My chassis system has both 24 volts and 12 volts.  You can power 12 volt stuff like cigarette lighters from your house system.  Gauges are pretty easy to get in 24 volt.  Most gauge manufacturers just add a resistor to a 12 volt gauge to make a 24 volt gauge.  (My bus has 24 volt gauges.)

[belfert]

On a side note, the Odyssey crew is switching the boat they bought from 12 to 24 volt.

Is there anything Sean doesn't completely rework/redo?  I know he did most/all of the electrical design on his bus, but his bus was a total gut and remodel.  I was actually thinking about Sean and Louise earlier today and meaning to visit their blog.

[Jeremy]

... plus dash, gauge, radio, and cigarette lighter options are out of the question...

Just to mention that these things aren't actually out of the question - in fact they are widely available if you know where to look (trucker's accessory shops for instance, either on-line or often at truckstops etc).

My bus has what looks like a 'normal' car stereo in the dashboard, but it's actually a 24v model. In fact there is a sticker on the bus door and one of the windows alerting potential thieves to the fact that the stereo is 24v and therefore not worth stealing!

Jeremy

[belfert]

The 12 volt at the front of my bus is not switched and the 24 volt is.  I installed a 15 amp 24 volt to 12 volt converter to power some of the 12 volt accessories that I only want running when the key is on.  You may be able to get a 24 volt radio, but it would be so much easier to get a 12 volt one.  I got the converter brand new on Ebay for maybe $25.

My radio is actually hooked to the house system so it can be run when the bus is not moving.

[Cecil The Diesel]

So far it sounds like a pretty big hassle to do this conversion, and probably best left at 24 volt.

I didn't think about having some extra relays that are unused since my a/c system is defunct, and I don't have overhead luggage bins anymore with a zillion lights in them.

I guess my question now since I'm leaning toward keeping the bus system the way it is this. Can I run a 24v source to a converter that drops it to 12v to charge the "house" system? What are my options for getting the house setup going?

I really appreciate all the input!

[Bill B /bus]

You should already have an equalizer installed with some 30-50 amp capacity. Will show up in the electrical schematics.

Terms to understand:

Converter - changes AC to DC, 102VAC to 12 or 24VDC.
Inverter - changes DC to AC. Comes in square wave or sine wave.
Equalizer - Enables half battery voltage without destroying a battery bank.

All the external lights on our MCI are 12V LED, except for the baggage bay lights. So the concern about wire ampacity is relieved due to low power draw of the LED.

Bill

[bevans6]

So good to explain the terms and the names of the common elements in the equation!  Took years for me to figure it all out.  Kudo's, even if actually growing familiar with the terms and what the pieces of equipment are will take longer.

Brian