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Old 02-29-2024, 02:25 PM   #1
ShrimpBurrito
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Default 12-volt air conditioner

With battery technology rapidly advancing with the development of various lithium chemistries, it seems of little surprise that Dometic now makes a 12-volt ~6,800 BTU air conditioner, the Dometic RTX 2000. According to the specs, it consumes just 19 amps while in "Eco" mode.

https://www.dometic.com/en-us/outdoo...tx-2000-262673

Looks like it costs about $2,500.

Dave
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Old 03-01-2024, 10:02 AM   #2
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I guess I am very confused about this - more than usual! I can't come close to making sense of the numbers. And reading the descriptions and specs is like listening to someone reading Alice in Wonderland with a mouthful of marbles. Dometic normally does a much better job with descriptions and specs.

I would welcome any other engineering types to help me out. Meanwhile, don't write your check just yet.

Bill
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Old 03-01-2024, 10:43 AM   #3
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Third party websites can offer more info. For example:

https://rackupgo.com/products/dometi...12v-9600028490
https://gearjunkie.com/motors/aston-...oadster-reveal

Dave
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Old 03-01-2024, 02:30 PM   #4
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Default Here's my take

This will b a little techie. If you're not up for techie, feel free to skip it.
---------------------------------
Dave -

The RTX2000 specs say "2000 watts/6800 BTU @ 12Volts". What does that mean?

At 12 VDC, 2000 watts is 167 amps. That is a whopper of a current draw! But 2000 watts can't mean 167 amps of current, since the unit's fuse is only 80 amps. In fact, the spec says that the unit 's max draw is 58 amps at 12 VDC. This means that the max electrical power used is 58 X 12 = 696 watts from the power supply, not 2000 watts. And running 58 amps through an 80-amp fuse is a reasonable number, so I tend to believe it.

At the same time, it is worth noting that Dometic also offers several 13,500 BTU RV rooftop air conditioners, operating from AC power, for about $1000-1200. These units provides twice as much cooling as the RTX2000 (13,500 BTU vs 6800 BTU), for laboutn half the cost - about $1100 lower cost.

So the "big difference", the "new technology", is that the RTX2000 unit operates directly from 12 volts DC, while an ordinary Dometic RV air conditioner operates from 120 volts AC. This might be useful if you always operate solely from solar and batteries. On the other hand, you could buy a 3000-watt Renogy pure-sine power inverter for about $400, run the ordinary RV air conditioner from 12 volts, and save several hundred dollars. You could run the A/C on LOW COOL and get similar cooling capacity at a bit lower power consumption, or on HIGH COOL to get twice as much cooling at higher power consumption. Your choice.

The bottom line is that electrical watts are not the same as thermal (cooling) watts. Dometic's description is poorly written and confusing at best, and I am not sure where they are trying to go with this product. It is definitely an interesting device - thanks for flagging it to us, Dave. For TM use, though, I see no advantage in the RTX2000, and substantial added cost. According to the write-up, Dometic's target audience for the RTX2000 is long-haul trucks, where it might be worthwhile. I find it interesting, though, that most long haul trucks have 24-volt or even 48-volt electrical systems, not 12 volts.

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Old 03-03-2024, 09:35 PM   #5
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Hi Bill,

Yea, I'm not sure what the advantage is of running a 12VDC A/C unit directly through the battery vs a 120VAC A/C unit through an inverter. Clearly, you'd avoid the 10-20% inverter loss, which is important if you're running it alot, but other than that I'm not sure what the cost premium gets you.

Interesting too about your power calculations....I'm not sure where the 2kw number comes from.

But, broadly speaking, I think this is a sign of the way things boondocker units are headed. I saw a van conversion recently that was 100% electric / battery. Zero propane. Induction cooktop, electric water heater, electric furnace (of some sort), DC fridge, etc. I think they had something like an 800Ah battery bank, and 600W of solar, and found that to provide essentially unlimited power for their needs. Dropping two 20-lb tanks of propane frees up about 100 lb, which is enough for over 300Ah in batteries alone, so the additional weight really isn't even that much.

Dave
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Old 03-04-2024, 09:35 AM   #6
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Dave -

I agree with you. Now that better batteries and better solar panels are becoming available, the future looks interesting.

As I read the Dometic ad, I wondered if the unit actually operates on 12 VDC, or if it has an internal inverter. No way to know, but a 58-amp 12-VDC motor would be a beast.

I also thought about the several feet of BIG wires that would be needed to carry 58 amps from the batteries, wherever they are, to the A/C, presumably in the middle of the roof. Probably #2 wires at best. Wires the size of your index finger are difficult to install.

Still, an interesting development. I will be curious to see where Dometic goes with it.

Bill
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Old 03-04-2024, 01:30 PM   #7
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Great, questions, Bill! I'm sure someone has done an install of one on YouTube -- I may look it up at some point.

Dave
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Old 03-12-2024, 07:40 PM   #8
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2000 W of heat transfer is not the same as 2000 W of electrical power draw. Heat Pumps move more heat energy than they consume in electrical energy. This ratio is called the Coefficient of Performance (CoP). A unit with a CoP of 2 would move 2 watts of heat for every electrical watt consumed.

For real world AC's, the theoretical max CoP is around 14ish. A world class unit might be around 10. A good unit would be around 5-8. An average unit is around 3. This Dometic is around to 2.8. I would not call this a very energy efficient AC.
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