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06-07-2018, 12:27 PM
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#1
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Mini-Skoolie
Join Date: Apr 2018
Location: Bristol Vermont
Posts: 13
Year: 2007
Engine: C7
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Inverter size for AC
I’m going to put 2 rooftop AC units on my Skoolie and power them with shore power or a generator. I have a 3000 watt inverter and I’m wondering if I need something bigger if the draw of the AC units is above 3000 Watts.
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06-07-2018, 12:56 PM
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#2
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Bus Crazy
Join Date: Feb 2017
Location: The West
Posts: 1,210
Year: 1998
Coachwork: MCI
Chassis: 102 EL3
Engine: DD 60
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Howdy and welcome Whalby!
Sometimes it helps to use "AC" for Alternating Current and "A/C" for Air Conditioning - just to keep everyone on the same page.
Roof air conditioners typically require 120VAC power (or 110VAC or 115VAC, whichever a person prefers).
Both shore power and generator provide 120VAC power (as in volts alternating current). There is no Inverter involved.
An Inverter "converts" DC 'power' to AC 'power.'
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06-07-2018, 01:01 PM
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#3
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Mini-Skoolie
Join Date: Apr 2018
Location: Bristol Vermont
Posts: 13
Year: 2007
Engine: C7
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Thanks! My shore power outlet will go through the inverter though is that ok or will the A/C units need a dedicated outlet that goes directly to them?
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06-07-2018, 01:09 PM
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#4
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Bus Crazy
Join Date: May 2016
Location: Grayson County, VA
Posts: 1,428
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: DT466
Rated Cap: 65
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Quote:
Originally Posted by Whalby
Thanks! My shore power outlet will go through the inverter though is that ok or will the A/C units need a dedicated outlet that goes directly to them?
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Your inverter may have an internal automatic transfer switch built in, which will run your A/C from the shore power and bypass the inverter.
Are you sure you need that much inverter? Reason I ask, is I saw another thread about solar and it seems 3000W can cause issues with solar panel/battery bank sizing.
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06-07-2018, 01:09 PM
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#5
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Bus Crazy
Join Date: Feb 2017
Location: The West
Posts: 1,210
Year: 1998
Coachwork: MCI
Chassis: 102 EL3
Engine: DD 60
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Quote:
Originally Posted by Whalby
Thanks! My shore power outlet will go through the inverter though is that ok or will the A/C units need a dedicated outlet that goes directly to them?
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Ahh! You have an Inverter with an internal transfer switch. Afraid I'm not sure if those transfer switches are limited (X amps) but someone here will know.
Personally, I would be inclined to install a panel in the shore power line before the Inverter and wire the A/C unit to it. That way there is no chance of accidentally running the A/C from battery (and depleting or possibly damaging them - demands on what you have there, of course).
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06-07-2018, 01:11 PM
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#6
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Bus Crazy
Join Date: May 2016
Location: Grayson County, VA
Posts: 1,428
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: DT466
Rated Cap: 65
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Quote:
Originally Posted by JDOnTheGo
Personally, I would be inclined to install a panel in the shore power line before the Inverter and wire the A/C unit to it. That way there is no chance of accidentally running the A/C from battery (and depleting or possibly damaging them - demands on what you have there, of course).
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Great point, JD. I accidentally ran my water heater from battery power and it drew them down from 100% to 70% in about 15-20 min.
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06-07-2018, 01:18 PM
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#7
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Mini-Skoolie
Join Date: Apr 2018
Location: Bristol Vermont
Posts: 13
Year: 2007
Engine: C7
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I got it that big so I have room to grow and it charges at 50amp which is nice. What did you hear could go wrong?
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06-07-2018, 01:23 PM
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#8
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Bus Crazy
Join Date: May 2016
Location: Grayson County, VA
Posts: 1,428
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: DT466
Rated Cap: 65
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Quote:
Originally Posted by Whalby
I got it that big so I have room to grow and it charges at 50amp which is nice. What did you hear could go wrong?
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There's some discussion of 3000W inverter here.
http://www.skoolie.net/forums/f49/so...s-22597-3.html
I haven't tried to wrap my head around it too much, I'm pretty dumb when it comes to electrical for some reason (it's a blind spot for me) but it made me start questioning my future solar setup.
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06-07-2018, 01:38 PM
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#9
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Bus Crazy
Join Date: Feb 2017
Location: The West
Posts: 1,210
Year: 1998
Coachwork: MCI
Chassis: 102 EL3
Engine: DD 60
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Basically boils down to lead-acid battery C rate for charge/discharge. You can certainly shorten the life of a battery bank by going too high or low - there is an ideal. I've always wondered where the line is between academic and real life on this topic. Clearly our (full-timers) use of our battery bank is rarely ideal.
For example (and these are made up numbers), assume you spend $500 for batteries and have less than ideal charge/discharge rates. Will they survive for 3 years instead of 4 (all other conditions being the same)? Or, will they survive 2 years instead of 10 years? I certainly do not know and would be curious to read something on that if anyone has a good link.
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06-07-2018, 01:42 PM
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#10
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Bus Geek
Join Date: Dec 2016
Location: Weeki Wachee, FL
Posts: 3,056
Year: 1997
Coachwork: Bluebird
Chassis: TC2000 FE
Engine: Cummins 5.9
Rated Cap: 72
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The Dometic 13500 rooftop air conditioner claims to consume 2800 watts. At 110V AC power that's over 25A, if you're doing it from 12V DC battery power through an inverter you're going to be pulling 234A! That's a LOT and doesn't take into consideration the inefficiencies of an inverter. You'll want Lithium batteries for that to be even remotely reasonable.
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06-07-2018, 01:48 PM
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#11
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Bus Crazy
Join Date: May 2016
Location: Grayson County, VA
Posts: 1,428
Year: 1996
Coachwork: Amtran
Chassis: International
Engine: DT466
Rated Cap: 65
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Quote:
Originally Posted by brokedown
if you're doing it from 12V DC battery power through an inverter you're going to be pulling 234A! That's a LOT and doesn't take into consideration the inefficiencies of an inverter. You'll want Lithium batteries for that to be even remotely reasonable.
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Just to clarify, I believe he's planning on running the A/C from shore/generator power, not batteries. The 3KW inverter is for other/future needs.
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06-14-2018, 07:13 AM
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#12
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Bus Nut
Join Date: Jan 2018
Location: Brevard County, FL
Posts: 911
Year: 1990
Coachwork: Bluebird
Chassis: Ford
Engine: 6.6 New Holland Diesel
Rated Cap: 60 kids, 10 window
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Which inverter do you have?
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