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Old 08-30-2016, 08:10 AM   #1
Mini-Skoolie
 
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Running Roof Air off Bus Generator

Does anyone have experience with running a roof Air Conditioner off of the bus alternator. We have been told by some people that with a 150 amp bus alternator you can run a 13,500 btu roof air from the alternator while you are going down the road. Others say that the AC would require to much wattage to run off the bus alternator. Who's right??
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Old 08-30-2016, 10:07 AM   #2
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I hasve experience with this.. I have a 200 amp alternatoir on my bus.. I do have a fully operational engine-driven air conditioner I built but also have a portable 2 hose A/C as well..

im running a 1500 watt pure sine-wave inverter.. at times in the trips ive made ive invoked the "3rd unit" which is running my portable unit along with my 2 engine units.

my portable pulls about 1100 watts running max.. it is a soft start unit and varies its power usage based on demand.. I have 2 group 31D AGM deep cycle batteries dedicated to the inverter and an isolator to charge them..plus the 2 main buys starting batteries

when I started out all 4 batteries were fully charged.. the isolator engages when my bus alternator is making power..

on the highway i found my alternator temperature got up there a bit and so its output dropped some.. I was able to break even with my 200 amp alternator running that 1100 watt A/C plus about 50 amps of the road A/C (coils, clutch, and indoor fans)...

slowing down at idle I lost a bit of power with everything maxxed out... I have good batteries so no issue...

in my case i wouldnt have done it with 150 amp alternator...

in my new york trip when i tossed off a compressor belt and lost my road A/C, i ran only my portable 12,000 btu unit (7 row bus stock insulation non-tinted windows).. and all it did was blow a little cool air in my face and kept me from sweating.. I was still pretty roasty till i got that belt on...

-Christopher
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Old 08-30-2016, 08:50 PM   #3
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Would it make any difference that we have a 3000 watt inverter and we don't have a bus air conditioner? We have gutted the bus and are going to insulate and tint the windows. Hoping that helps!
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Old 08-30-2016, 09:55 PM   #4
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not having a bus A/C means you arent pulling power for those fans.. but ultimately it comes down to Volts X amps = watts...

or amps = watts / volts so if your air conditioner pulls 1200 watts to run and your voltage is 12, thats 100 amps.. if you have 15% loss in your inverter you now are pulling 1380 watts instead of 1200 off your bus system.. so now you are at 115 amps just for your A/C.. and that assumes you have Zero loss in your wire going from the alternator to the battery and from the battery to the inverter..

thats a rough estinate with numbers for you.. someone else can correct me if ive buggered this up.. i been writing code all day so my brain might be number-crunched out..

-Christopher
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Old 09-21-2016, 05:28 PM   #5
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Wink Econo A/C

I made a stand alone A/C unit for under $200 that uses ice in a cooler(Walmart), a 12V water pump (Amazon), and an auxiliary heater from Summit Racing, which comes complete with all the wiring and a 3 speed switch.
Just fill it with ice and a little bit of water, plug it in and turn it on. Instant cold air (Really!).
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Old 09-21-2016, 05:46 PM   #6
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how do you catch the condensate from the cold coils?
-Christopher
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Old 09-21-2016, 09:12 PM   #7
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Cool idea (pun intended). About what run time do you get per ice fill and at what ambient temperature are you dealing with?
Thanks, Jack
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Old 09-21-2016, 11:04 PM   #8
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Interested in the cooler AC
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Old 09-22-2016, 09:01 AM   #9
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Too complicated, all you really need is the cooler with hole cut to mount a fan. There are plans all over the internet for these things.

http://www.kulr8.com/story/25928116/...er-for-8-bucks

Dick
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Old 09-22-2016, 10:30 AM   #10
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2 fans, one in one out.. and that solves the issue if the condensate... that hot-rod heater will make all tyour floors wet and those coils arent designed to be wet on the outside as its a heater.. theres no drain pan.. i suppose if you only use it in the desert you would be fine most of the time..

the cooler alone wont produce quite as much cold air but is surely much simpler...

BTU / hour is BTU / hour though so how long the ice lasts is much shorter than what you imagine it will be.. cooling takes energy...

if you are going on short outings and have access to a good freezer on-shore then this idea makes a lot of sense and is a viable option to expensive high power generators and A/C units..

-Christopher
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