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Old 06-16-2019, 06:45 PM   #1
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Rooftop A/C power requirements

I know enough about electrical to do most basic jobs, but my knowledge doesn't extend much into AC vs DC. Therefore, I must ask the question...

When wiring a rooftop A/C unit such as a Coleman Mach series, does anyone know how much amperage / kwH these units require?
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Old 06-16-2019, 06:47 PM   #2
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In my experience A/C is not for off grid unless you got a good generator.
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Old 06-16-2019, 07:41 PM   #3
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Quote:
Originally Posted by CHEESE_WAGON View Post
When wiring a rooftop A/C unit such as a Coleman Mach series, does anyone know how much amperage / kwH these units require?
Specifications:
https://www.airxcel.com/docs/default...sn=cca90e6b_12


Looks like power draw for cooling is somewhere around 1200W-2000W depending on the climate.



So if you want to run that for 4 hours, you're looking at 4.8kWh - 8.0kWh.



This is why a mini-split makes a lot more sense from what I can tell. From single ton split benchmarks I've seen, they draw anywhere from 300W to 800W.
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Old 06-16-2019, 08:51 PM   #4
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Quote:
Originally Posted by CHEESE_WAGON View Post
I know enough about electrical to do most basic jobs, but my knowledge doesn't extend much into AC vs DC. Therefore, I must ask the question...

When wiring a rooftop A/C unit such as a Coleman Mach series, does anyone know how much amperage / kwH these units require?


As far as wiring for it, it is a 120V unit and you will need to run 12 AWG wire to it. The unit should use less than 20 amps but it will have a spike at startup that will go higher. Thatís why you need roughly a 3500 watt generator to run them. Shore power is more forgiving of temporary heavy loads.

If you are trying to run this from an inverter, youíre talking about 200 amps on the 12 volt side so you need very beefy wiring on the 12 V side. 2/0 welding wire is commonly used for this. Also a big battery bank...
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Old 06-16-2019, 09:20 PM   #5
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Figure an **extra** 100Ah @12V of battery bank per hour of runtime for a small aircon unit cooling a very small super-insulated space.

2-3kW of panels on the roof will help run it, but not recharge the bank at the same time, so double that.

Means you're parking in the full sunshine all day too.

So yes, in effect unrealistic and impractical, better to just run a genset.

Even better keep travelling, follow the 60's.
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Old 06-16-2019, 09:29 PM   #6
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Quote:
Originally Posted by CHEESE_WAGON View Post
I know enough about electrical to do most basic jobs, but my knowledge doesn't extend much into AC vs DC. Therefore, I must ask the question...

When wiring a rooftop A/C unit such as a Coleman Mach series, does anyone know how much amperage / kwH these units require?

The nameplate data is what to go by for figuring what cable you need etc, breaker too. Can't go wrong with that info. Same for any motors appliances etc. Well that and understanding Ohm's Law. Easy enough to look that up.


You sure know lots of other goodies though Cheese...


John
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Old 06-17-2019, 12:52 AM   #7
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The nameplate data is what to go by for figuring what cable you need etc, breaker too. Can't go wrong with that info. Same for any motors appliances etc. Well that and understanding Ohm's Law. Easy enough to look that up.
The nameplate on the unit in question seems to be missing, or perhaps because it is an original Coleman Mach 1 (1983 vintage), maybe they didn't have them?

Thanks for all the replies, folks. I'm currently in an older RV with an (I think) original Coleman Mach 1 unit. Innards appear to be straight from a refrigerator of the era, believe it runs R-22, so the unit posted here might actually be a tad more efficient, methinks. This one has been pretty rock-solid with the exception of spitting out a blower motor a couple years ago. However, roof is getting soft on the RV and considering using it as a donor for a future build. The replies here will certainly come in handy when sizing a battery bank or solar system.

I am well aware that this unit will pretty much require a genset, which is not a problem, the RV is equipped with a 3.0 kW Onan, I also have another junker with a 4.0 kW Onan, which has an identical Mach unit.

I'm simply kicking around a few alternate setup ideas, also want to make sure total power needs are met when off-grid. Sounds like a 3.0 kW genset may or may not be up to the task. I am also trying to calculate how much an electric bill might be when I am able to get my own property and my own service.


Can anyone explain the split system referred to herein? I've heard of these and not sure what the difference is...


Quote:
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You sure know lots of other goodies though Cheese...
Jack of all trades, master of none.

I'm also good at improvising. Necessity is the mother of invention, I always say. "If it looks stupid, but it works, it ain't stupid."

Former member here as well, I owned a Ford-chassis Blue Bird back then. I learned a lot in my tenure, and boy, you should see some of my posts from back then! My previous account was wiped out by attempts to wipe out spammers and bots. I was on hiatus for about ten years and changed email addresses, missing the warnings of impending account deletion. Therefore, as with others whose accounts suffered the same fate, there are a number of older threads that may not make sense where someone responded to a post I made that is no longer there. But I digress...

My father was an industrial/commercial HVAC controls contractor until he retired, also knew the nuts and bolts of such systems (I made a brief foray into the parent company he contracted from, didn't work out), and taught me quite a bit. I also have driven tractor-trailers for a few years, and have a good working knowledge of commercial vehicles. Also dealt with enough vehicle breakdowns and such to understand engines and at least the basics of control systems. I've also tended to mesh better with older folks than those my own age group, so I learned a lot more, and faster, than most my age. Richard Pryor said it best (as Mudbone) "You don't get to be old, being a fool."

My old man always told me, there's no excuse for not knowing something or being able to learn it if you can read. Maybe not true in all cases, but a good point, methinks. I have this uncanny ability to read a great many materials on a great many subjects, and thus have a good general knowledge level on a lot of things. Alternating current, however, is one I'm not sure I'll ever understand fully.

Not claiming to be a know-it-all, by any stretch of the imagination. No one knows everything, and anyone can be blindsided by incorrect or outdated information. I've been wrong before. However, I try to help others here where I feel I can.

Anyway, I guess you'd say some of my knowledge comes from experience, some of it comes from other's experience (I've learned that it's far easier and less expensive to learn from others' mistakes), and some of it comes from just knowing where to look for information.
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Old 06-17-2019, 10:33 AM   #8
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The mini splits are similar to a home a/c unit where you have a separate air handler and condenser. The air handler is a single unit that mounts on the wall and has a pipe run to the condenser. These are more efficient because of the low start up draw of the condenser. These condensers don't have that big kick to turn on the compressor that rooftop units do.
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Old 06-17-2019, 12:34 PM   #9
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The mini splits are similar to a home a/c unit where you have a separate air handler and condenser. The air handler is a single unit that mounts on the wall and has a pipe run to the condenser. These are more efficient because of the low start up draw of the condenser. These condensers don't have that big kick to turn on the compressor that rooftop units do.
Sounds like a swamp cooler?
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Old 06-17-2019, 12:54 PM   #10
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Maybe my description isn't the best.

It's just a two part system like HVAC in a house but on a smaller scale. They are made to cool a single room where an in he HVAC system is used to cool an entire house using air ducts.

You have the air handler and a compressor, yep separate items with a lineset of refrigerant between the two. The compressor cools the refrigerant and pumps it through the lineset to the air handler.
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Old 06-17-2019, 01:43 PM   #11
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Older ac units aren't as efficient as modern ones. I run an 15k btu old duo-therm unit that uses r22. Cools the back half of my bus well in 90+ degree heat. Start up spike is pretty big on my unit. I have a 2500 running watt 3250 peak watt gas honda generator that won't run it. This generator will, however, run a newer ac unit no problem fwiw. The generator I use now is a 6500 watt diesel unit and it powers everything easily.

Most manufacturers have a heat pump unit available. But they still take 15 or so amps to run. Not sure on the conversion between household ac units and rv ac units. What is a 1 ton household unit in btu's?

As far as running ac off solar or battery. Some on here have done it, but they are pretty heavily invested in inverters/panels/battery capacity. I don't use my bus or the ac enough to justify spending 1000's of dollars on that.
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Old 06-20-2019, 05:24 PM   #12
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Means you're parking in the full sunshine all day too.

That's a really good point.
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Old 06-26-2019, 03:51 PM   #13
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Sounds like a swamp cooler?
More like a home A/C unit here you have an inside unit (blows cold air, usually sits on top of your furnace) and an outside unit (which blows hot air) and two pipes and a power line running between them. A swamp cooler is one unit that sucks air through wet mats and blows it into the house.

The advantage of mini-split units is the compressor. It's almost always variable-speed, soft-start, which means it comes on gently and works only as hard as necessary. A rooftop RV unit's compressor generally comes on full-blast (regardless of the dial setting) and spins up so fast that it can suck 2x the rated power for several seconds, tripping breakers and causing generators to shutdown to save themselves.

There are "hard-start capacitor" kits that can be wired into the roof air unit. They are a big capacitor and some control electronics that store up power and deliver it to the compressor so that surge doesn't have to come from your generator. Good ones basically eliminate the startup surge and let you run two roof units on a 30A shore-power circuit.

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Old 06-26-2019, 03:57 PM   #14
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Most manufacturers have a heat pump unit available. But they still take 15 or so amps to run. Not sure on the conversion between household ac units and rv ac units. What is a 1 ton household unit in btu's?
From my research, 1 ton is about 12,000 BTU. These seem to run about 1200-1400W on high. I've found some in 110-120v models, but anything bigger is 220-240v.

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Old 06-26-2019, 04:04 PM   #15
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From my research, 1 ton is about 12,000 BTU. These seem to run about 1200-1400W on high. I've found some in 110-120v models, but anything bigger is 220-240v.

-S
Mine is 12k, next step would go to 15k, but it also jumps up to 220v.
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Old 06-26-2019, 05:35 PM   #16
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Electrical Help

I have an old ac unit off a 1987 Tiago that works. Iím hoping to run my ac unit and electric deep freeze I converted into a refrigerator while driving down the road. I have a Square D load center an inverter a converter also a 12 volt DC block. I was hoping someone out ther has information on how to wire it and set it up.
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Old 06-26-2019, 06:09 PM   #17
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I have an old ac unit off a 1987 Tiago that works. Iím hoping to run my ac unit and electric deep freeze I converted into a refrigerator while driving down the road. I have a Square D load center an inverter a converter also a 12 volt DC block. I was hoping someone out ther has information on how to wire it and set it up.
https://www.explorist.life/solarwiringdiagrams/
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Old 06-26-2019, 08:38 PM   #18
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Thanks for the link but I don’t have solar yet. Not until next year hopefully. I do have a bus battery oscillator thou. This is suppose to keep the bus and house batteries charged off the alternator while the bus is running. Thanks for any help with it.
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Old 06-26-2019, 08:40 PM   #19
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Sorry. Meant to type battery isolator.
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Old 06-26-2019, 08:46 PM   #20
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Darn... I was looking for a battery oscillator to hook up to my flux capacitor....
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