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[GMCnet] A whole new world [message #316900]

Mon, 01 May 2017 12:08

glwgmc

Messages: 1014
Registered: June 2004

Karma: 10

Senior Member

Just about the time I thought I had a good handle on all things GMC, here I go climbing the learning curve getting to know this Prevost Country Coach conversion. It is interesting to me that the GMC experience is so much more helpful in this process than our previous full timing in a large diesel pusher. One would think it would be the other way around. The answer is that owning our two GMCs, and driving them so extensively, put me in a hands on position with nearly every system. With our diesel pusher that was not the case.

Most of the Prevost systems are similar to the GMC, only scaled way larger and often with more redundancy. As an example, the roof mounted heat pumps are very much the same as on our GMCs, only there are three of them, each zone controlled, and they are commonly ducted. The way they are implemented they are way quieter than in either of our two GMCs (neither of which had heat pumps, just AC with small electric heat strips). But, in addition to that there are two large engine driven AC compressors that supply evaporators located throughout the coach, each zone controlled by a thermostat, so the whole coach stays at set temp no matter how hot it is outside. As luxury tour busses it was imperative to keep all your passengers comfortable after all!

Interior heat is a very different in the Prevost from the GMC. In the Prevost the engine cooling fluid is also pumped throughout the coach, including the bay storage areas, where fan assisted radiators provide three zone even heat control even in very cold temperatures. Yes, the GMCs do that but only for the driver and passenger unless you add additional radiators and fans elsewhere. In addition, the Prevost has a diesel fired boiler (Webasto) that also heats that same fluid when needed like when you are parked so the even and controlled heat remains moving or not. The Webasto heating the engine cooling fluid means the engine is always warm started, even in cold weather. Finally, that same fluid passes through the water to water heat exchangers in two domestic water heaters (both about double the size of the GMC water heater) so you have continuous hot water whether plugged into shore power or not. Slick.

Both our GMC and the Prevost use air bags and auto ride height controllers. Both have about 4” up and 4” down travel for leveling while parked. The Prevost uses air bags all around while the GMCs obviously use air just in the rear. In the Prevost the air compressor is engine driven and of very high CMF output, but there is also a 120vac (Thomas in this case) air compressor to power such things as air doors and toilet flushing while parked. The Prevost also uses air to tension the belts that drive the huge side mounted fan (which itself uses a much larger version of the viscous coupled fan clutch employed in our GMCs) and the second AC compressor. One set of belts goes from the crank pulley to a 90 degree power take off unit and a second set of belts goes from that unit to the fan clutch. A third set of belts goes from that unit to the second AC compressor. With the engine running air pressure keeps all those belts properly tensioned. If a belt ever breaks, with the engine shut down you can release the air pressure and change belts by hand - no tools required.

The biggest difference between the systems on our GMCs and the systems in this Prevost is in the electrical systems. Our GMCs use 12vdc for both the chassis and house batteries and for starting the generator so it is easy to use combiners or isolators to make sure all batteries are charged from any charge source. Not so the Prevost. There the chassis uses 24vdc for most things (like starting) and also taps off 12vdc for things like the fluid recirculation pumps and light bulbs which are more widely available in 12vdc form than in 24vdc form. The house battery bank is all 12vdc as is the generator starting battery bank. The house and chassis batteries are completely isolated one from the other and each has its own independent charging systems. When the engine is running there is a belt driven, water cooled, 300 amp alternator that takes care of the 24vdc and 12vdc chassis battery bank. There also is a second belt driven air cooled alternator that charges the house and gen start batteries. When plugged in, the 50 amp main cord supplies power to the house, the house battery bank via two 2500 watt inverter/chargers and the gen start batteries via a combiner. But, it does not supply power to charge the chassis batteries. The idea was that as a luxury tour bus, the Prevost would be driven most every day so the large 300 amp alternator would take care of that duty. Country Coach did include a separate 10 amp 24vdc trickle charger, but it has to be plugged in separately from the 50 amp cord.

What was news to me is that the generator does not power the chassis battery charger unless you plug it into one of the dedicated shore/gen plugs that bypass the inverters. As an all electric coach, nearly everything runs off the inverters powered by a massive 1800 amp hour AGM battery bank. The exceptions are one of the roof heat pump units and the 220vac stove top. They only run if you are plugged into a 50 amp shore power plug or are running the 17.5kw four cylinder turbo charged Kabota generator which can supply as much as 145 amps (about the output of three of our GMC generators).

That interesting 24v/12v chassis electrical system requires the use of a device I did not know about called a battery equalizer. The 24vdc is achieved by using four 12vdc AGM batteries wired series/parallel. The two series wired groups make the 24vdc while tapping off of just one paralleled group provides the 12vdc. The battery equalizer makes sure that both groups carry the 12vdc load so they do not see significantly different amps while charging.

Some owners and some converters did add a dedicated 120vac plug in the engine compartment which is powered only by shore power or generator power but not by inverter power so the 24v charger would come on automatically but so far I have not found such a plug in this Country Coach conversion.

Having been so hands on with all the systems in our two GMCs has really helped speed up what otherwise would have been a much longer learning curve trying to figure out the systems in the Prevost. Not that it has been easy or fast, but just a lot easier and a lot faster because of that experience.

Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR

glwork@mac.com
http://jerrywork.com

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Jerry & Sharon Work
78 Royale
Kerby, OR