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,
CoachWorX, in Clearwater,
Florida, Thanks, Rick!
Please credit John McKenna with
adjustments to this article.
