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Old 04-01-2017, 11:59 PM   #1
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Help using 120VAC to power 12VDC Air Conditioner

Hi everyone!

I have a Champion shuttle bus that I'm doing a conversion on. The bus has a Thermo King AC unit. The unit operates without the engine running, meaning it has an electrical compressor.

What I'd like to do is power this air conditioner using the power pole at a campsite.

I plan to run some testes with a clamp amp meter to determine the 12vdc amps required.

Can I just purchase the right sized converter and connect it directly to the starting batteries and thus operate all of the 12vdc items in the bus that are connected to the starting batteries?

Thanks...and I love this website!
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Old 04-02-2017, 12:31 AM   #2
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Join Date: Feb 2012
Location: Salt Lake City Utah
Posts: 1,633
Year: 2000
Chassis: Blue Bird
Engine: ISC 8.3
There'll definitely be fans powered by 12 V dc on the condenser and evaporator. But take a closer look for the compressor. It'd be rather uncommon for the compressor to be electric-driven rather than belt-driven off the engine.

In any case yes, converters (which to me implies it's a battery charger too) and power supplies can be had in a variety of sizes/wattage to power 12 V electrical systems from the "shore power" campground pedestal.
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Old 04-02-2017, 10:13 AM   #3
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Location: Spring Valley AZ
Posts: 1,343
Year: 2000
Coachwork: Bluebird
Engine: 5.9 Cummins
Rated Cap: 2 elderly children, 1 cat
"testes with a clamp"
Don, Mary and Spooky the cat.
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Old 04-02-2017, 10:53 AM   #4
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Location: Willamina, Oregon
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Coachwork: 97 Bluebird TC1000 5.9
Don't run your appliances from your vehicle starter battery. There's not enough power there and you will likely run your battery down and not be able to go home. Get house batteries to run appliances.
Nobody's Business
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Old 04-02-2017, 10:48 PM   #5
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Hi guys, "testes with a clamp" yes that is quite the typo!

I do plan to get house batteries later down the road. I have just started my conversion so first phase is to get somewhat operational so I can start having fun. I've read enough and watched enough videos to see that this is a multi year project...as they say "there is always something to be done on the bus"

I don't want to damage anything so I think I will find the power connection to the independent AC unit and connect it to its own manual transfer switch. On the other side of that transfer switch I'll put a 12v battery to handle expected peak amps when the compressor kicks on. I'll put the convertor to that battery as well.

That way I don't put the starting batteries nor the entire electrical system of the bus at risk.

Thanks guys!
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Old 04-03-2017, 07:15 AM   #6
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Location: hills of sw virginia
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Year: 1996
Chassis: thomas
Engine: 8.3 cummins
Rated Cap: 11 window
test to see if you have an ac powered compressor. turn the key to the on position without starting the bus, does the ac unit get cold? if not you have an engine driven ac compressor under the hood, look and see.
living in a bus down by the river.
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Old 04-03-2017, 02:01 PM   #7
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Location: So Cal
Posts: 2,965
Year: 1935
Coachwork: Superior
Chassis: Chevy
Engine: 317 ci/tid / Isuzu
Find the TK data placard on the unit and see what it tells you. If there is still a question in your mind jot down the serial # and contact the mfg. Better safe than sorry. Jack
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Old 10-23-2017, 03:55 PM   #8
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I was wrong!

Sorry for wasting everyone's time. I was wrong about the AC unit working with the engine off. Turns out you guys were right, there is a compressor connected to the engine.

So I'm stuck with this big head knocker AC unit inside the bus that only works with the engine running. I guess I will have to put in another AC unit for when I'm parked at the campground.
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