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Old 04-19-2018, 07:37 PM   #1
Bus Crazy
 
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Join Date: Oct 2017
Location: Virginia
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Year: 1971
Coachwork: Wayne
Chassis: International Loadstar 1700
Engine: 345 international V-8
rooftop a/c running off alternator

Maybe I am nuts, but.... I am thinking when driving why not run at least one of the roof top a/c units using an inverter from the alternator on the bus engine. I need to change the alternator anyway, and there are some really big ones up to 300 amps out there. I am thinking that a 200 amp alternator would be more then enough if I have done my math right.

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Old 06-17-2021, 04:42 PM   #2
Mini-Skoolie
 
Join Date: Jun 2019
Location: Arizona
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Year: 2002
Coachwork: Thomas
Chassis: GMC Savana 3500
Engine: 6.5 L 395 CID V8 Diesel
were you able to tackle this project ? mulling over the task now myself
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Old 06-17-2021, 05:55 PM   #3
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Year: 1971
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Chassis: International Loadstar 1700
Engine: 345 international V-8
Ended up using an Onan rv generator to run rooftop a/c. Have a curtain behind the front unit, that keeps the front reasonably cool.


I am helping a friend wire his bus, and his inverter ( 2000 watt)has no trouble powering a rooftop a/c. We tried it yesterday. The house batteries are not connected to the alternator, although if it where it should pull about 125 amps running the a/c
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Old 06-17-2021, 09:41 PM   #4
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Join Date: Aug 2019
Location: Auburn, WA
Posts: 682
Year: 2000
Coachwork: IC / Amtran
Chassis: 3000 / 33' Flat Nose
Engine: IC T444E / Allison MT643
Rated Cap: 72 Kids / 48 Adults
Why not a DC (alternator) to DC charging of the house batteries and then use the inverter to run the AC?
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Old 06-18-2021, 02:13 AM   #5
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Location: Bly Oregon
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Year: 1986
Coachwork: Crown
Chassis: Supercoach
Engine: Cummins 350 big cam
Rated Cap: 86 passengers?
I have already got a second alternator mounted on the engine of the new Crown. It is rated for 250 amps which equals 3000 watts at 12 volts and 3500 watts running with 14 volts. This alternator will provide current flow to a DC bus that will also be charged from a 1 kw solar array. I believe this will provide for running at least one roof top AC while going down the road. Keep in mind that alternators are not designed to run at the full current rating for extended time. I don't expect to pull high amps except maybe when the AC compressor starts up. The DC bus will be used to operate a 3 kw sine wave inverter (which handles 4 kw surges). All of this provides AC going down the road. Nothing is free and I expect I will take a hit to fuel economy though.
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Old 06-18-2021, 07:35 AM   #6
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Join Date: May 2009
Location: Columbus Ohio
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Year: 1991
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Chassis: International 3800
Engine: DTA360 / MT643
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someone else here installed a second alternator just to run their rooftop A/C.. Native is his screen name.. he said it works great.. a rooftop A/C isa undersized for on the road but it helps and gives you the ability to also run that A/C when parked on shore power or generator.
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