How to power a Carrier AirV Roof top AC

[Chuck Newman]

Pete,

Thank you for the 50DN information.  That's great new for my planned A/C operation.  It's the best news I've had all day.

[pvcces]

For a little more 50DN information, our generator puts out 70 amps at a dead slow idle and it puts out 220 amps on fast idle, around 1,000 engine RPM. These readings come directly off of our Link 2000, so we have little reason to doubt them.

220 amps at 14 volts equals 3,080 watts. With fair sized house batteries to handle time while sitting in traffic, this will work for a while. We run a Heart 2500 inverter, and our air conditioner has never failed to start on the inverter.

We bought our 2500 because we had a 2000 that started the air conditioner only once out out of many tries. We do run 4/0 wiring to reduce the losses.

Two ratings will help on deciding on an inverter; the maximum surge current and the search current. Less expensive inverters will not do as well on these ratings.

For what it's worth.

Tom Caffrey

[Sean]

... I am sure this topic has been beat to death, ...  I don't know what modified sine wave and pure sine wave is either. 

Josh,

Welcome to the forum.  As you can see, sometimes a simple question can result in some interesting discussion.

When you are certain a topic has been "beat to death," that's a sure bet that the very next thing you should do is search the archives.  For example, a quick search for "modified sine wave" (with the quotes included) will turn up dozens of posts discussing and explaining the difference, and even a few posts about what is needed to run an air conditioner from an inverter.

As you've heard, to run a 13.5 kBTU/hr air conditioner, you will need a true sine wave inverter with at least 2,700 watts of continuous output, and 5,400 watts of "surge" capacity.  Practically speaking, that means a quality 3,000-watt model.

BTW, a setup to run an air conditioner using inverters and batteries will almost always cost more than a generator capable of doing the same thing.  There are lots of good reasons to want to do it, but saving capital cost is usually not one of them.  A 3kW sine wave inverter capable of starting and running a roof air will cost you in the neighborhood of a grand or so, and then you'll need to invest in 0000 battery cables to run it (for a 12-volt system), heavy crimps, class-T fuses, not to mention lots of batteries, and possibly an alternator upgrade if yours does not put out the required ~225 amps or so.  To give you some sense, we have over $3,000 worth of batteries weighing more than half a ton, and that lets us run one 13.5 roof air for about six solid hours -- if nothing else at all is running.  That's enough to go overnight if we have it set to cycle the compressor off periodically, but in the daytime it will last us barely four hours.

Once you've used up all the battery power, you still need some way to recharge, which usually means a generator.

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com

[bevans6]

I'd be really interested to know how much horsepower a 50DN alternator takes to run, at idle and at speed, putting out maximum amperage.  Anybody have that sort of information or formula?

Brian

[bottomacher]

I have a Honeywell rotary inverter. If you give me the specs, I will see if it will suit your needs.

[TomC]

Brian- 1 horsepower=750watts.  Usually with a generator, they size the engine at almost 2hp per kilowatt.  A 300amp @ 12v (14.1v running)=4230watts÷750=5.64hp.  270amp @ 24v (28.2v)=7614watts÷750=10.2hp.  Course this is at maximum output-still not bad considering what you're getting.  Good Luck, TomC

[belfert]

Am I going to save any fuel by running one A/C unit off my DN50 instead of running my 8KW generator?  Now, I often run both front and rear A/C units so it would be a moot point in those cases since the rear requires the generator.  My inverter can't handle both at once.

My Series 60 can be challenged a bit on some hills out west and taking away even 5 HP could be an issue at times.  I have the smaller 11.1L S60 so it is closer to a 6V2 in HP than an 8V92.

[lostagain]

Going up a steep hill in MC5s, 7s, 8s and 9s whith 8V71s, we used to turn the AC off to gain HP. It made a noticeable difference.

JC

[ojgetaway32]

Wow!  Thank you all for the information and posts!  I apologize for starting a blog skirmish.  I guess I should add some info.  I have a 1983 MC 9 which I love, however the AC unit we are discussing is on a International 9300 truck tractor with a Cummins Big Cam III @ 400+hp.  I put the roof AC on the roof of the sleeper because I have been doing some relief driver work for my company which is local, low speed work that has required me to be on the job 14 hours per day.  Loading and chaining the load is a sweaty affair.  With no AC and no air movement while travelling because of low road speed, I have been dying from the heat.  The AC unit was brand new and just sitting in my warehouse.  I mounted it thinking it would not be such a $@^%!##^%$#&$* ordeal!  It mounted easily and runs great off an extension cord from the shop.  You could hang meat in my sleeper now.  Here is what I have learned:  I should have shut up and drank more fluids and not worried about AC or stayed in the damn office and out of the truck.

But alas, I've got to do something now because I can't let a perfectly good Roof Air Unit just ride along.  I propose the following:  Upgrade my stock 130 amp alternator with a 200 amp one.  Get an 3000W pure sine wave inverter.  Hook them together, turn on the AC and go trucking!

Kindly advise if I you believe I am misguided.

Thanks again,

Josh

[cody]

 You have a bus, your certainly misguided lol, no question about it.

[BG6]

Two things to consider:

1)  the load amps given are RUNNING amps, not STARTING amps

2)  if the compressor uses an induction ("brushless") motor, startup can be DOUBLE the running amps -- even more if you don't have a pure sine wave power feed, because poles fight each other until there is a stable rotation.

[jjrbus]

All the rich guys and purists will insist that you use a true sine wave inverter. I used a Trace Dr 3624 modified sinewave inverter full time for 10 years. I think Dallas also used a MSW? The only problem I had was the clock in the microwave would not keep proper time.  It powered battery chargers, cell phones, LCD TV's, household appliances, computers, ink jet printers all types of lights with no problems!!   I also used it over the road to power 1 dometic roof top air. And in the real world I could idle for ages with the 50DN alternator without drawing down the batterys.

                                                        JIm

[BG6]

All the rich guys and purists will insist that you use a true sine wave inverter. I used a Trace Dr 3624 modified sinewave inverter full time for 10 years. I think Dallas also used a MSW? The only problem I had was the clock in the microwave would not keep proper time.  It powered battery chargers, cell phones, LCD TV's, household appliances, computers, ink jet printers all types of lights with no problems!!   I also used it over the road to power 1 dometic roof top air. And in the real world I could idle for ages with the 50DN alternator without drawing down the batterys.

I'm neither a "rich guy" nor a "purist."  I just happen to know about things like electricity and motors, having spent some time in the aerospace industry and having done broadcast and communications engineering -- both fields where an understanding of loads can come in handy.

Different motors have different characteristics, some will work where others (even with the same HP and amps ratings) won't.

[Hartley]

Josh,

I think the real answer is for you to find someone who is getting their
truck repo-ed and see if they will part with the "Pony Engine" system
that is used on trucks to make power and run a/c when parked.

They also call them APU, Usually a small diesel 2 or 3 cylinder engine
with a generator section (6.5kw?), A/C compressor, Radiator and stuff
all in a box that frame mounts under the sleeper. Long Haul trucks will
be the most probable to have them. With the new anti-idle rules many
truckers have installed the new APU systems.

A Buddy of mine just got a deal on one for $800 complete, The guy that
had it spent $8,000 new, Wanted $1,600 for his take off and negotiated
to $800 cash. I think this idea (My Buddy) is to install it in one of his
buses, Use the A/C compressor to run his Dash air, The generator section
to power the rest of his bus and make hot water.

Oh.. And to Pete,

I keep trying Aleve for the Inflamed Fingers but it doesn't do that much
to squelch keyboard outbursts I have found. Have a Great Day...
Sure glad I don't have to worry about Hurricanes anymore...

Dave....

[Sean]

Am I going to save any fuel by running one A/C unit off my DN50 instead of running my 8KW generator?

Definitely.

At max load, our DN50 adds between 0.3 and 0.4 GPH to our over-the-road fuel consumption vs. when we have the house intertie turned off.  And that's about 7kw, enough to run two air conditioners and still be charging the batteries.  If you are only running one A/C, your incremental consumption will be lower.

By contrast, your 8kW genny probably uses between 0.5 and 0.6 GPH to do the same work.

...  I propose the following:  Upgrade my stock 130 amp alternator with a 200 amp one.  Get an 3000W pure sine wave inverter.  Hook them together, turn on the AC and go trucking!

That will work under most circumstances.  On really hot days, when the A/C starts pulling close to 20 amps, the 200-amp alternator may be marginal.  Also, make sure you get an alternator that is rated for those amps continuously, and will produce them at idle or fast-idle rpm.  Lastly, remember you will still need some hefty batteries to cover the start-up surge for the A/C, as 200 amps is only enough to cover the running amps.

All the rich guys and purists will insist that you use a true sine wave inverter. I used a Trace Dr 3624 modified sinewave inverter full time for 10 years.

How about just us practical guys?

Using an MSW to run induction motors is penny-wise and pound-foolish.  You might just as easily have written that rich guys and purists insist on using that expensive diesel-rated oil, or coolant, or even fuel, whereas you've been running just fine for years on inexpensive unrated stuff.  This is the sort of thing that looks like it works great, right up until it doesn't, when it fails catastrophically, and then you wonder what happened.

MSW kills induction motors, slowly.  The motor will run much hotter internally.  A related downside is that the device, whether it is an air conditioner, fridge, air compressor, or whatever, will run much less efficiently.  That means you will be using more juice to do the same work, and if that's from a battery bank, the bank will have to be that much larger to get the same run time, virtually instantly negating the savings from MSW.  But the more insidious issue is that the extra internal heat will eventually ruin the induction motor, and so you will be replacing that roof air, fridge, or compressor much sooner than you would by using true sine wave.  You may not notice this for a long time (maybe as long as you own the bus), because we could be talking the difference between 8 years and 12 years, or between 15 years and 20 years.  But rest assured, you are slowly damaging the motors by running them on MSW.

If you live in your rig full time, as we do, and run all your motors off the inverter nearly 100% of the time, and have several such motors, the chances become much greater that one will fail in a mere matter of a few years.  Bottom line: true sine wave is actually more cost-effective in the long run for motor applications, due to increased efficiency and extended life.

If you don't need to run induction motors on the inverter, and all you have are "battery chargers, cell phones, LCD TV's, household appliances, computers, ink jet printers all types of lights" then MSW is a fine choice, and I, too, would choose to save the money and weight over a true sine wave model.  None of those items cares one whit about the incoming waveform (household appliances generally use "universal" motors, which will run on anything, including DC, and electronics run on DC internally and use switching-mode power supplies to generate it, where the incoming power is rectified anyway).

FWIW.

-Sean
http://OurOdyssey.BlogSpot.com