Okay guys, I am reluctant to ask as I am sure this topic has been beat to death, but alas, here goes. I have one Carrier AirV 13,500 BTU Roof Air that is brand new in the box. I mounted it, hooked it up to an extension cord off my shop and it cools wonderfully, you could hang meat inside now. However, I cannot get it to run off of either a 1575 watt inverter or a brand new 2500 watt Cobra Inverter I just bought at the truck stop. The fan will blow, but when it tries to kick the AC on, the inverter trips and shows power overload. This is wired to a 12V sytem with a bank of four batteries. I heard someone mention a hard start capacitor. Is this an option? Do I need a bigger inverter? A genset is not feasible as this is all that I want to run for now. I don't know what modified sine wave and pure sine wave is either. What can I say, I am not educated on such matters. Please help.
Thank you,
Josh Miller
You need a 3,000 watt Inverter minimum just to get the compressor to start
and then keep it running for the 15 minutes until the batteries are down to minimum
level and the inverter shuts down.
When I say 3,000 watts, I don't mean the cheap ones that have outragious claims either. More like a Heart/Xantrex/Prosine or similar.
You need to be able to handle 15 to 18 amp loads continous to run a 13,500 btu
a/c unit. Preferably a Pure Sine Wave ( Expen$ive ).
The inverters of that kind cost almost as much as a generator.
I doubt the cheapie inverters will even be worth the effort. Maybe a 2,500 running a small 5,000 btu window unit would work for a little while until the smoke escapes.
Fiftenn minutes? But if the engine is running, the inverter wont shut down right?
Josh,
I am not an electrical guru, like Sean or somebody, but it does sound like your inverter is too small. If you got a bigger inverter, then that would probably do it. We are only planning on running one or two of our roof airs off of our two inverters. We have to 4000 watt Trace inverters, that are Pure Sine wave. We will mostly be running our roof airs off of the generator, so not to tax our batteries and inverters, but I am sure that what you are trying to do will work.
BTW, are your four batteries the ones that your bus starts off of, or are they dedicated house? What size batteries are they?
God bless,
John
Josh,
Most ACs require a 20 amp circuit, that is 2400 watts (120 volts X 20 amps). 2400 watts divided by 12 volts equals 200 amps, so you will need to maintain 200 amps output from your alternator and this does not allow for inverter ineffeciencies or less than optimal alternator speed. If your coach is 24 volt and you install a 24 volt inverter, you would need a 100 amp alternator.
Wires from the inverter to the batteries should be 3-0 or 4-0 to allow enough power to flow from the batteries to the inverter. Jack
Modified sine wave has a wave form that is very square in steps, creating less then perfect A/C output. Pure sine wave, while still have square steps in the sine wave, have the steps much smaller and finer closer duplicating a true since wave form.
Call Dick Wright at Wrico International and he'll most likely suggest the Magnum inverter/charger pure sine wave. They make a 2800 which has good surge motor starting capability.
And yes you could get a hard start kit that includes a capacitor to ease with starting the compressor. Good Luck, TomC
Josh,
What everyone has said. The cheap inverters are rated by lawyers, not engineers. What lies can we get away with and which ones will cost us. That inverter is probably rated at 2500 watts into a resistive load like a toaster, not an inductive load like an air conditioner. They will never give you what you want.
The alternator (assuming a 50DN or equivalent) will work fine at road speed but idling through a 30 minute traffic jam will kill the batteries in no time.
Getting educated by buying the wrong stuff is very expensive. You could ask any one of us how we know that.
In layman's terms, motors and generators are almost the same thing. When a motor is running a normal speed, it's using some electricity, but it's also generating a lot of electricity that it sends back at the source. That is called counter electro-motice force, and the only reason it's interesting is that when the motor isn't turning, like when you first turn it on, or if it stalls, the CEMF isn't there and the motor the draws a TON of current, like three times normal. If your source can't supply that, the motor never gets going, and the breaker trips off. the capacitor kind of stores up some electricity and uses it like a little battery to help get the motor turning - as soon as it starts to turn, things get to normal really quickly.
the thing about modified sine wave and sine wave is that a lot of things take the electricity and immediately do something with it, like a TV or a radio puts it into a power supply that changes it to something else. They tend to run OK on modified sine wave output. A motor uses it directly as it comes. Since it is developing it's own electricity as CEMF, and for some other reasons, it runs really poorly on the square wave electricity that a modified sine wave inverter puts out and so it uses more electricity and can actually cause the motor to overheat and damage itself.
hopefully that made sense, it's been a lot of years since electric circuits 101...
Brian
The Carrier A/C units use a lot less than 20 amps of power. I would have to look it up for sure, but I believe my 15K BTU Carriers are rated at 13 or 14 amps. They need to be on a 20 amp circuit, but that is more for proper breaker and wire size. A 20 amp circuit should really have a sustained load of 16 amps.
LEN SILVA - you wrote -->
"...The alternator (assuming a 50DN or equivalent) will work fine at road speed but idling through a 30 minute traffic jam will kill the batteries in no time......"
Len - you need to do a little resarch before you make BLANKET statements like this
The typical gear driven 50DN is geared at 2.93 to 1 -
at an engine speed of 600 RPMs - a 50DN spins at approx 1800rpm and can produce a max REGULTED output of approx 4500 watts ( 165 amps at 28 volts)
at an engine speed of 1000RPMs - the max REGULATED output jumps to almost 7000 watts
even at IDLE - that's more than enough to overcome any inverter loses / still charge the bus batteries / and run a standard 13kbtu-15kbtu rooftop air conditioner
I'm just getting damn tired of all the MISINFORMATION
and yes I can back this up with my maintenance manual spec for the 50DN
Pete RTS/Daytona
Pete,
My Bad.
That was my experience with one 12 volt Eagle Entertainer, and I never got to fully check it out before it went out on another trip. Could have been a bad alternator, regulator, loose belts etc. Driver said he was stuck in traffic for an hour and the inverter kicked out for low bat. Came back when he got back up to speed.
So, I'm sorry for any mis-information I put out.
I don't know what kind of bus Josh has but he did say 12 volts.
Len
Come on Guy's...
The original poster said he was new to this and didn't know anything about inverters.
He asked if it would work. Which it didn't for reasons that the rest of us are aware.
He didn't specify if it was a bus, truck or golf cart for that matter.
He did say he bought off the display inverters which mostly are 12 volts.
Nobody needed to jump in and start a war over a 50DN alternator or why or how
something should/shouldn't, what output or anything else that I saw.
The bottom line is simple: He is using 12 volts, He needs enough battery amperage
to handle a 2400 to 3000 watt inverter to run his A/C ( Theoretically ).
A standard Automotive type alternator might not have enough output to run
with a large load. Since he didn't say what he has and how big the alternator is
we are in a blind spot here.
A Bus alternator or big truck alternator may be of
sufficient capacity to operate his rig, But there are way too many other things
that must be considered.
So, That said ... Have a Nice Day and Be Nicer Please....
Hi ojgetaway32,
Welcome!
Just to add to all the great replys you recieved,, you also have to remember that these units use more current/amps as the outside ambiant
temp rises.. 14 amps is normal at 80 degrees. Here in N.J. today, it's 92 degrees and my 1- 15,000 btu unit is drawing 18 amps. Two days ago it
was 96 degrees and it drew 19 amps. Just doubble that for start up power.. This should give you a good idea what your power needs should be.
Good Luck
Nick-
Just to set the record straight - Dave - I responded to some misinformation about a typical 50DN - and that's the way I framed my response
I doubt it will pan out but I am looking for a surplus rotary aircraft inverter that might do the job. I think that most of them were 400hz. I will see what I can come up with. I sure hope you can get it working I have had my share of troubles in the AC dept, mostly self inflicted ;D
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.
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
Quote from: ojgetaway32 on August 20, 2009, 11:20:27 AM
... 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 (http://ourodyssey.blogspot.com)
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
I have a Honeywell rotary inverter. If you give me the specs, I will see if it will suit your needs.
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
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.
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
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
You have a bus, your certainly misguided lol, no question about it.
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.
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
Quote from: jjrbus on August 21, 2009, 08:51:03 AM
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.
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....
Quote from: belfert on August 21, 2009, 08:06:50 AM
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.
Quote from: ojgetaway32 on August 21, 2009, 08:20:48 AM
... 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.
Quote from: jjrbus on August 21, 2009, 08:51:03 AM
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 (http://ourodyssey.blogspot.com)
Question for NICK
Will increasing the size of the "start Capacitor" and or "run Capacitor"" help a 13kbtu or 15kbtu RV roof top Air Conditioner start easier on a smaller inverter ??
what sizes would you recommend ??
Here's my simple math reason for using my diesel generator for powering my A/C's when driving:
My reasoning assumes your going to have a generator anyway, I use a small inverter only for small loads and my refrigerator when stopped.
Using some of Seans numbers, which I thank him for as I was curious of 50DN loading vs fuel usage would be.
.4gph using 50DN, .6gph using diesel generator
To make it simple I am looking at 1000 hours usage
.6 X 1000 hours=600 gal, .4 X 1000=400, 600-400=200 difference, 200 X $2.60(current diesel price)=$520.00
Premium MSW inverter, 3000 watt min and batteries=$3000.00 (my figures)
3000/520=5.769 5.769 X 1000=5769 hours generator needs to run to equal cost of inverter/batteries alone.
5769/8 = 721 You would have to drive 8 hours a day for 721 days to get this many hours. Or basically 2 years straight @ 8 hours a day.
I did not include any incidental maintenace costs (oil, filters or battery replacements. etc) for the sake of this discussion.
Now, maybe you travel this way, maybe you don't.
I just took a two week trip to Minnesota and ran the generator only around 60 hours. If your a weekender, its going to take along time to get to almost 6000 hours. On the other hand if your criss crossing the country like Sean does, or do a lot of serious boondocking, then its another story.
Just my way of thinking on this,
Cliff
I dry camp/boondock all of the time so I needed an inverter and battery bank anyhow unless I run the generator pretty much 24x7 for my household fridge.
I bought my Prosine 3000 inverter for $900. With two sets of batteries and the cables and such I am right about $3000. My golf cart batteries didn't work the best so I went to different batteries.
Another factor that I considered, which may not to that big of a deal, is that any horsepower that is being used to turn that big alternator is not available to the rear wheels when going up those hills. Jack
Another thing to consider is possibly rising costs of fuel. We have a lot more than 3K invested in our battery/inverter setup, but we rarely have to run the generator. We can even survive off of a supplemental 20amp sure power (if the airs aren't running).
We would like to sometime hook up to our alternator (50DN)to the house batteries (especially since we stripped the OTR air), but we are going to need to know how to safely do it. We are thinking that we will use isolator, but that is another post.
God bless,
John
Quote from: JackConrad on August 21, 2009, 12:09:00 PM
Another factor that I considered, which may not to that big of a deal, is that any horsepower that is being used to turn that big alternator is not available to the rear wheels when going up those hills. Jack
Jack,
When we're in the hills, I turn the intertie off on the big upgrades, which gives that ~10hp back for climbing, then turn it back on for the downgrades, where it makes electricity for free.
In fact, the 0.3-0.4 I mentioned earlier was at fast idle. In real-world driving, it works out to be more like 0.2, because its almost always free on the downgrades, and we are seldom cranking out the full ~200 amps across the tie.
-Sean
http://OurOdyssey.BlogSpot.com (http://ourodyssey.blogspot.com)
I this is for your big rig, then I highly recommend an APU. Now if you already have the roof top air mounted, you could get the Powertech APU which is just a 2 cylinder Diesel (either Kubota or Caterpillar) running a 5kw generator. It clamp mounts onto the frame, and just needs fuel, 12v and cab mounted controls, and then you can hook up directly to your own generator. You'll then have endless power. Good Luck, TomC
Okay, Tell me why a 2200 watt gasoline generator will run the darn thing but a brand new 3000w MSW inverter won't. Ugh! F*** it! I'm gonna move where its cold.
Josh
Quote from: ojgetaway32 on August 26, 2009, 07:15:35 AM
Okay, Tell me why a 2200 watt gasoline generator will run the darn thing but a brand new 3000w MSW inverter won't. Ugh! F*** it! I'm gonna move where its cold.
Josh
Josh,
That question has been answered multiple times already. It's MSW, it won't work. Now, somebody here could post a 20 page explanation of AC theory which would explain why it won't work, but it won't alter the facts.
A 2200 watt generator has a sine-wave output, the MSW inverter does not.
Now, even modified sine wave can vary considerably, usually related to the cost of the inverter.
One thing you can try is to monitor the 12 volt battery voltage as you try to turn on the air conditioner. If it drops much below 11 volts, then you may just not have enough battery for it to work.
Here are a couple of pictures that may help to explain it.
many of the better "modified sine wave" inverters - design thier waveforms to provide the same RMS voltage (area under the curves).
more like the picture provided
Okay, that makes sense about the generator vs the MSW inverter. Funny how I have a couple of generators laying around that will run it but no PSW inverter. Gotta love it.
Josh
Okay, here is what I did: I took a shot on eBay on a brand new 6000-12000W MSW inverter. I hooked it up to my batteries when it came and the darn thing worked!!! I ran the truck engine on low idle for an hour or so and everything seems to be fine. The cab and sleeper sure are cold! I paid $426 with shipping from Michigan to Wheeling, WV. If things start to go awry, I will upgrade my alternator. All looks good now though. Funny, the LED indicator on the inverter says 2200W while running so the inverter is barely even working. The startup must be a killer draw!
Thanks to all who advised, counseled and chastised. I needed it all.
Josh
Thats great, what brand is it,thanks for the update