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Old 07-03-2006, 03:07 PM   #1
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Air Conditioning/On Tour Part II

Well we lived through our first tour and we are doing another. The bus is still a work in progress.
We have no A.C. or Generator. I have a stupid huge converter/inverter (the mack daddy from camping world) and 4 batteries.
Is there any way to hook up a roof air to work while driving down the road?
We may surely perish doing a tour of the southwest with no A.C.
Then can we hook it up to shore power at parks?
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Old 07-03-2006, 04:38 PM   #2
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Year: 1993
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Chassis: International
Engine: 7.3 International diesel
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I'd imagine that you would need a bigger alternator at least. A/C's take a lot of power! Around 2000 watts for a 13,500 BTU's.
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Old 07-03-2006, 04:46 PM   #3
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2000 watts @ 12 volts would be 200 amps. You can get an alternator that big, but most skoolies do not come with one that size.

perhaps an engine driven compressor like most cars have would be better suited to your a/c while driving problem....although prob not the cheapest option. Ford vans with the ambulance package come with pretty intense A/C systems to keep both the cab and the modular box cool.

the simplest solution is to have an efficient geni you run while driving....which is prob a violation of NFPA regulations, but i know people do it.
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Old 07-03-2006, 05:08 PM   #4
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Voltage requirements for a RV AC unit

My Carrier roof mount RV AC unit uses about 13 amps at 120 Volts ac.
This use is about 1560 watts. Dividing 1560 watts into 12 dc equals about 130 amps. There are many alternators availablethat will produce 150 amps. A good plan would be to add a big power alternator driven by at least 2 belts.
The inverter should be at least a 2KW unit. Carefull consideration must be made for distances and wire sizes. A couple big 850-950 amp batteries should be good for transfering and storing some 12 volts. The roof ac unit will operate ok as long as the engine is making some high amps DC.
When the vehicle stops the ac unit will still run if the engine speed is high. The ac unit can then be plugged into any shore/house power. Frank
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Old 07-05-2006, 04:13 PM   #5
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I like the way your brain works frank. You seem like a highly intelligent person.

The big alternator and inverter sounds like a great idea. One more consideration is to make sure you have good ventilation to the inverter, because I would immagine it'll be giving off a lot of heat with 130 or more amps of continuous dc current flowing through it.

both of the buses i've owned came with leece neville alternators. They are pretty standard alternators when it comes to buses and big trucks. I know they offer at least 200 amp alternators. IF you have a leece neville it'll make mounting of the higher output unit very simple. The 2 belt idea is good too. At low engine speed speed it will require an incredible amount of torque to turn the alternator pully when the A/C is on.
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Old 07-15-2006, 10:15 AM   #6
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I would be woried about startup/surge when that A/C kicked on. When I installed a Xantrex Prosine 2.0 (2000 watt) inverter/charger in my last boat, they specified a size of wire that I had never heard of, 250 MCM. Turns out this wire is the size of a garden hose! They are also adament about the distance between the inverter and batteries being as short as possible. More can be read here:
http://www.xantrex.com/web/id/741/docserve.asp

These big inverters still draw power when in standby mode, so supplementing it with some cheaper/smaller models for modest uses would be help to save your batteries.

My new bus has an Onan diesel powering a factory-installed full-bus system. Think I should stay with this system? It takes up a lot of room, and can't be run on shore power. I'd like to remove it, and add a 6.5KW generator in place of the twin compressors. I'd stick a standard roof A/C in to get cool.

Where can you get 850 amp batteries? They must be huge!
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Old 07-15-2006, 11:47 AM   #7
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Bus electrical Suzi

Any person should not be concerned about the change from DC to AC with an inverter. Large wire sizes are often difficult to work with and very expensive.
In the electrical work, if a conductor is very large, it is common practice to use 2 or more conductors to do the same task. It is far easier to use 3 conductors of a #2 wire size in place of a single 250 MCM conductor size. DC wiring is less demanding than AC wiring.
Onan and Kohler companies are premium electrical power generator makers. In the past, the engines powering these units has not been great. Most all US companies who use diesel engines build very good units. The diesel gen sets are the ultimate power making machine. With any care, the units can produce power for a very long time.
Batteries of the 850-950 amps are very common and not especially large or heavy. The real power batteries can produce upwards of 1300-1500 amps.
Quick rule, the heavier the battery, the more lead. The more lead, the more power. The more power, the greater cost. New batteries can be priced by the weight as every pound of battery is about $1.50-2.00. Wallmart has some really good deals on batteries with great warranties.
I want a diesel gen set but I have a 7KW gas Kohler gen set. The unit has less than 850 hours as new. Anyone want to trade a diesel set of about 8KW? Frank
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Old 07-15-2006, 12:23 PM   #8
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<sound of hand slapping forehead>
Great idea about using multiple wires! The two 250 MCM wires, about 12' total, with connectors, was about $150 or so, as I remember. Had to go cross-town to find a place, as well.

I guess that you meant cold-cranking amps on the batteries, I was thinking amp-hour capacity.
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Old 07-16-2006, 08:07 PM   #9
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I use 00 welding cable. The guy who sold me my alternator and batteries custom makes battery cables out of this stuff. Not only does 00 welding cable do a great job of carrying current, it's tough, and very flexible.

remember that electricity is a lot like water.....

2 separate 1" pipes don't flow nearly as much water as a single 2" pipe. The same goes for wires.


The area of a pair of 1" circles would be 1.57 square inches
verses 3.14 square inches for a single 2" circle (r2xd)

It would take four 1 inch wires to flow as much current as a single 2 inch diameter wire.

obviously the copper cunductors you use are not going to be 2" in diameter, that number was just used as an example to keep the math simple.
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Old 07-16-2006, 10:35 PM   #10
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Welding leads sounds like a good idea- the cable that I used was outrageously stiff.
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