PREVOST, The Ultimate Class



 

One of the most complex systems on a Prevost coach is the electrical system.  It is also one of the least understood systems on Prevost coaches.
 
This article is not meant to be a complete discussion of the electrical system, but rather an introduction to the system for most Prevost owners. 
 
Shell Electrical System
 
There are two systems supplied from Prevost, depending on your model year.  There is a 24v system, which is needed for the DDEC system in the engine, over-the-road-air in come coaches, and some lighting applications.  There is also a 12v system, primarily supplied for exterior lighting and other shell applications.
 
Both the 24v system and the 12v system run from the same set of batteries.
 
There are two different types of wiring harness hookups for the shell batteries and the type of configuration which your coach uses means different things:
 
One type of configuration is the 'jumper' system:
 
 
Usually batteries have multiple connections on terminals as the batteries are interconnected in order to produce postive and negative terminals for both 12v and 24v use.
 
The difficulty one may experience with a 'jumped' system is that at maximum loads, as much as 400 amperes of electricity may be pulled from the batteries over an extended period of time.  Should any of the 'stacked' terminals not have proper contact, they may arc or produce less than the desired amount of amperage.
 
The other system, referred to as a marine installation, is quite different:
 
 
In this application, each battery terminal has a single connection, each leading to both postive and negative electrical buses for distribution:
 
 
This is the positive terminal bus.
 
 
The above being the negative terminal bus.
 
From either of these two systems, the Prevost shell electrical system is connected, depending upon the conversion to the house or converted portion of your coach.
 
The House System
 
Each conversion company has its own way of setting up its electrical system to service all the many requirements of a Prevost conversion.
 
There are some very important considerations, however, which are general to all converions.
 
It is essential, due to the high load requirements of a Prevost conversion, to have fuses which completely close down a connection when they are tripped.  Klix on circuit breakers, such as shown below, do not.  They have bi-metal strips in them which may or may not completely terminate a shorted circuit:
  
What can happen with circuit breakers which look like this is seize in the closed position, when they should be open; resulting the potential of fire or serious appliance damage.
 
Instead, high-amperage fuses should be those which completely shut off the power from the batteries to the invertors, such as fuses, which may look like this:
 
 
These fuses work on a different principle than bi-metal breakers.  When the load is greater than the rated load on the fuse, a sandy material inside the fuse literally melts and creates a wall of glass inside the fuse itself, completely opening the circuit, thereby protecting anything beyond the fuse from damage.
 
Most coaches can be inspected carefully without taking too much apart to determine which types of fuses are used in your coach, and in many cases, thermal breakers can be replaced with properly rated Class T fuses.
 
They should be placed close to the source of power, i.e. battery.
 
Invertors have a variety of functions; to convert DC power to AC power &charge batteries in a variety of functions.   Most invertors today are 4000 watt invertors or higher.
 
Here's an example of just how much power your coach may be drawing.  Most coaches have at least 3 air conditioners.  If your invertor is wired to the 24v side of the power supply, each amp is multiplied by 5, in terms of battery amperage; so a single 20 amp roof air conditioner draws 100 battery amps.  Three air conditioners, then, are drawing 300 battery amps, and this does not include other battery drains, such as refrigerators, televisions, lighting and the other wide variety of electrical appliances on a Prevost coach.  So it is likely that that most coaches are routinely drawing 400 battery amps in regular use:  That's a powerful arc welder if the coach is not either wired properly or if not properly fused!
 
If your invertor is wired to the 12v side of the power supply system, battery amps are multiplied not by 5 but by 10.  (And demand very large cabling).  So instead of 300 amps being drawn by the air conditioners themselves, 600 amps are being drawn from the battery.
 
That is a very significant power draw, requiring batteries to be in great shape, wiring up to snuff, good fusing and proper operation of your coach.
 
Other Considerations
 
There is more, much more.  How appliances are wired and maintained is quite different, depending upon the age and conversion of your coach.  Older coaches, with manual systems such as the Bass panel, or newer systems such as Crestron or Lutron systems, manage the operations and circuit-breaking responsibilities for individual appliances and lighting.
 
Understanding the amount of power your coach may be using at a given time is a very important task for owners. 
 
There are some things owners can do on a routine basis to insure proper electrical operation of your coach.
 
First, know that constant replacement or resetting of fuses or circuit breakers should not be routine, especially if the coach has been debugged after construction.  Sometimes during a conversion, wires may be installed temporarily which may weaken a connection, requiring a new fuse to be installed; once.  After that, fuse or circuit breaker attention should be very infrequent.
 
Battery maintenance is something which is at least a yearly cleaning, tightening, inspection.  Most coach batteries should be replaced about every 4-6 years. 
 
Should your coach have a 'jumped' system, insure that all stacked terminals are tightened and clean.  Older Prevost coaches may have lead terminals which were much more prone to corrosion and loosening.
 
Inspect what wiring you can; remember your home on wheels is subject to vibration and movement; it is possible, even on the best conversions, to find wear on some insulation or loosening of connections.  These may ultimately result in short circuits or possible fuse blow-outs.  Part of your annual inspection by a qualified Prevost professional should include a close examination of your electrical system.
 
One of the beauties of having a Prevost coach is that it has all the amenities of a most luxurious lifestyle.  Much of that lifestyle, as we know, is electrically-powered in some fashion or another; keeping an operational electrical system in top condition is essential to the enjoyment of your coach.
 
Should you be shopping for a coach, you may wish to find out what kind of electrical system it has, how it is wired, what kind of fuses it has, what type of management system it uses, how it is configured.  The ins and outs of this article provide a mere introduction to the many complexities of the system, but hopefully wil help to provide most owners of an overview of how the system operates and the proper maintenance of an electrical system in a Prevost coach.
 
Happy motoring!
 
Writers note:  This article was prepared with the most helpful assistance Rick May, Parliament Coach, in Clearwater, Florida, a Prevost conversion firm Blue Bird dealer.  Thanks, Rick! ( Note : Rick is currently with Coachworx in Clearwater - JB 5/18/2012 )

Please credit John McKenna with adjustments to this article.