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Old 05-05-2022, 08:56 AM   #1
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Default 12V vs 120V A/C why?

Hey folks. I know very little about this subject and I'm trying to learn and understand the why. If I'm building out a van that will have a lithium battery system with a 3000-watt inverter/charger, why would I want to consider a 12V rooftop A/C unit (Dometic RTX2000. 20-40 amps) instead of a 120V (Coleman Mach 10 NDQ. 10-15 amps)? The math, both in dollars and running time, seems to strongly support the 120V system. Am I missing something? Thanks in advance.

Also, if there's a thread about this issue can someone direct me to it? I couldn't locate one.
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Old 05-05-2022, 09:50 AM   #2
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Hey folks. I know very little about this subject and I'm trying to learn and understand the why. If I'm building out a van that will have a lithium battery system with a 3000-watt inverter/charger, why would I want to consider a 12V rooftop A/C unit (Dometic RTX2000. 20-40 amps) instead of a 120V (Coleman Mach 10 NDQ. 10-15 amps)? The math, both in dollars and running time, seems to strongly support the 120V system. Am I missing something? Thanks in advance.

Also, if there's a thread about this issue can someone direct me to it? I couldn't locate one.
The inverter uses electricity to convert 12 to 120volts. I believe it is around 10 percent loss. So with a 12 volt system, you will not lose these to inefficiency.
Not familiar with the Dometic RTX2000. Have you looked at the Pro air or Truma 12 volt systems? I have read the Pro air makes a lot noise on the exterior.

Noise from air conditioning is a major issue inside the van. I have read the Coleman Mach 10 NDQ is better than most but not as quiet as the newer units. Personally I have the Houghton Belaire unit.
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Old 05-05-2022, 09:59 AM   #3
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Thank you. At a 20% loss wouldn't a 120V unit still only use about 18, maybe 20, amps? That seems well below 30-40 amps at 12V. Again, I'm not as up to speed on this as most and I'm trying to understand if I'm missing something.
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Old 05-05-2022, 10:18 AM   #4
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Thank you. At a 20% loss wouldn't a 120V unit still only use about 18, maybe 20, amps? That seems well below 30-40 amps at 12V. Again, I'm not as up to speed on this as most and I'm trying to understand if I'm missing something.
I am not familiar with 30-40 amps at 12v. It is usually a lot more. I have checked with the Pro Air people. When ambient temps are 100 F. The unit will use over 100amps to run at full tilt. 100amps X 12 = 1200watts.

120 volt AC will use about 10amps X 120 = 1200watts plus the inverter consumption. I have read the motors on 120 volt ac are more efficient?

Also if you get a 120 volt unit. Make sure it has a soft start built in or add on after. This will increase the life of your inverter. A 3000 watt can struggle on the start up of the air conditioner.
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Old 05-05-2022, 10:31 AM   #5
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Ah, ok. Hadn't considered the AMPS x Volts equation. Good points. Thank you...
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Old 05-05-2022, 10:48 AM   #6
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Ah, ok. Hadn't considered the AMPS x Volts equation. Good points. Thank you...
Amp hours are something in rv terms. Actually, we really need to look at watts or actually KW for air conditioning use.

I have 800ah of lithium with a Victron 12/3000 inverter. Yes, I run my Houghton on battery power. I can run for awhile. Never really run it until bank was 20 percent but I estimate it will probably run 5 hours or more.

If I need that much ac time, I will run genny. Just upgraded to Onan 2800i inverter genny. Really like it because it is way less noisy and vibrates much less. Actually can stay inside van and carry a conversation with wife and not have to elevate voices to be heard.
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Old 05-05-2022, 12:47 PM   #7
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The Dometic is quite small at about 6800 btu/hr so would be tough to keep many class b models cool in hot sunny weather, I think. Dometic shows it at 58 amps on the high end, but my guess is starting is much higher than that.


Most rooftops are much higher Btu/hr than that and the NDQ lools to be 13500 but/hr.


So the Dometic will use half the power at least and give half the cooling and not run directly off shore power so you need a big charger/converter for shore or genny use plus very large cabling to the roof.


Personally, I would choose the AC unit.
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Old 05-05-2022, 05:52 PM   #8
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The Dometic is quite small at about 6800 btu/hr so would be tough to keep many class b models cool in hot sunny weather, I think. Dometic shows it at 58 amps on the high end, but my guess is starting is much higher than that.


Most rooftops are much higher Btu/hr than that and the NDQ lools to be 13500 but/hr.


So the Dometic will use half the power at least and give half the cooling and not run directly off shore power so you need a big charger/converter for shore or genny use plus very large cabling to the roof.


Personally, I would choose the AC unit.
Do you know much about the Pro Air unit? It is suppose to be 20K BTU running on 12 volt. Coachmen uses it in the Beyond. I have heard it is really loud for people outside?
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Old 05-05-2022, 05:54 PM   #9
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Do you know much about the Pro Air unit? It is suppose to be 20K BTU running on 12 volt. Coachmen uses it in the Beyond. I have heard it is really loud for people outside?

About all I know about it is the same info about it being loud outside.


At 2K BTU/hr it would probably pull near 200 amps of DC 12v though, and more starting, so a big cable needed.
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Old 05-12-2022, 04:00 PM   #10
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This isn't what you asked, so if it doesn't apply please ignore it.

Do you know what time of year you will be camping? Have you considered no air conditioner at all? We bought our Road Trek (Sprinter 2005 van chassis) and it came with rooftop AC. We've never used it. Actually, I tried it, but it doesn't work. So far we've never even considered getting it fixed or replaced.

For the most part all of our camping has been in the spring thru June or the fall. We use the fans for air circulation and that's it. Nighttime has always been cool enough for sleeping. Camping wouldn't be much fun if we were confined to the van during the daytime, even if we did have AC. Anyway, just my $.02 worth!
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Old 05-12-2022, 05:42 PM   #11
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This isn't what you asked, so if it doesn't apply please ignore it.

Do you know what time of year you will be camping? Have you considered no air conditioner at all? We bought our Road Trek (Sprinter 2005 van chassis) and it came with rooftop AC. We've never used it. Actually, I tried it, but it doesn't work. So far we've never even considered getting it fixed or replaced.

For the most part all of our camping has been in the spring thru June or the fall. We use the fans for air circulation and that's it. Nighttime has always been cool enough for sleeping. Camping wouldn't be much fun if we were confined to the van during the daytime, even if we did have AC. Anyway, just my $.02 worth!
Like you I try to avoid camping in hot climates. We live in Southern California. Most of the Summer and late spring and early fall are still in the 80-90's. Inside the van will be at least another 10 degrees hotter. We have camped in places where it was 70 degrees at midnight. AC helps make the inside of van comfortable. Most of time, we look for places with some water so we can cool off but not always possible.
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