# Inverter Thought...



## Nathan (Jan 2, 2007)

Ok, I wasn't sure where to post this (Mods, tow vehicles, etc).
Has anyone run their A/C with an inverter? If so, was it a modified sine wave, or a pure sine wave?

Here is why I ask:
We don't use hookups all that often and when camping in the Mountains usually don't need them. However, getting out there and back usually means Walmart camping in an effort to save setup/takedown time and a few bucks. Unfortuantely the plains are not always the coolest place, and I won't even begin to talk about Utah last year







. Now, the trick is cooling off the trailer prior to going to bed and for a lunch or dinner stop. (Usually temps get low enough during the night for sleeping to be bearable)

So, with all of the Superduty talk, I was looking at available options and noticed that with the Dual Alternators on the Diesel, you get 320 Amps of capacity. That is an extra 2200 Watts of power over the standard alternator, and should be adequate to run a 2000W interter. So, what about hooking up an inverter and being able to power the A/C while hauling down the road?








It would allow you to cool off the trailer for say an hour before stopping for the night.








(If one wanted to get more extreme a couple 6V batteries in the bed of the tuck would also allow for short duration running when the engine is off like a lunch stop)

Now, can anyone come up with an issue with doing this? (I know, you have to have the engine running at a decent speed to make the power, and have to run 120V between the Truck and Trailer, but those are all little details.)


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## ED_RN (Jun 25, 2006)

I tried connecting our old pop-up to 600 watt inverter connected to the truck battery once to run a TV. It blew the fuse on the inverter every time. Someone told me something about a problem with the ground when you conect a inverter to a system with a converter. Don't know if that's true. Hopefully one of our members who really understand this stuff will chime in.


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## BoaterDan (Jul 1, 2005)

I think they're more than little details. I think you'd really have to dig into some of them. For example, do both alternators actually feed into the battery? I would think probably not. So, if not, then you have a major issue of where you would hook in to get the full amperage available. And what stops working (or getting slowly destroyed) if you start sucking off too many of them?

If they do feed into the battery, would the TV battery be able supply the necessary total amps required?

In any event, remember once you hook into shore power with the trailer, a bunch of things start kicking in... so you'd need to probably manually switch the fridge to stay on gas... but you'd still have the trailer converter/charger start trying to charge the batteries off the inverter hooked to the TV battery... each step losing some power along the way.

I have no idea whether it is technically possible, precisely because I don't know the answers to these "little details" questions you'd have to figure out.


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## Nathan (Jan 2, 2007)

BoaterDan said:


> I think they're more than little details. I think you'd really have to dig into some of them. For example, do both alternators actually feed into the battery? I would think probably not. So, if not, then you have a major issue of where you would hook in to get the full amperage available. And what stops working (or getting slowly destroyed) if you start sucking off too many of them?
> 
> If they do feed into the battery, would the TV battery be able supply the necessary total amps required?
> 
> ...


Good point on electrical feed off of the truck. I'd have to do some research there, but you can get a lot of info on the Superduty's since they are used by so many contractors. My main concern was burning up the A/C unit because I didn't spend a grand for a sine wave inverter.


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## Nathan (Jan 2, 2007)

ED_RN said:


> I tried connecting our old pop-up to 600 watt inverter connected to the truck battery once to run a TV. It blew the fuse on the inverter every time. Someone told me something about a problem with the ground when you conect a inverter to a system with a converter. Don't know if that's true. Hopefully one of our members who really understand this stuff will chime in.


I know you need to make sure most of the circuits on the converter are switched off (don't want to try to heat water, or keep the refridge cold on battery).

I don't have a generator for my house in case of power failures, but I do have trailer batteries and a 1700 Watt inverter. I can run my Fridge and deep freeze on the inverter (simultaneously) for around 4 hours before a fully charged group 27 battery drops to 11 volts. So this is what is pointing me in this direction. Perhaps I'll have to run an experiment one of these weeks.


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## sleecjr (Mar 24, 2006)

OK so the answer is yes and no. I have done this before on a few boats, but we had to install big bank of batts. Most of the time we added 2-4 6v batts to the boat. This just gives you a buffer as you go from shore power to shore power. I dont think you could run it off the stock alt. But here is the best place for that upgrade. ohiogen.com. Batts will work but is a lot of weight to add to a camper. Have you thought about a gen for the bed of the truck?


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## Ghosty (Jan 17, 2005)

Mathematically the numbers don't add up ... so i am going to say No

Previous experience will also led me to say NO...

In the long run... on your wallet.. on your truck... and on the environment... it would be better to simply purchase a generator ...

just my .02c


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## Nathan (Jan 2, 2007)

Ghosty said:


> Mathematically the numbers don't add up ... so i am going to say No
> 
> Previous experience will also led me to say NO...
> 
> ...


Ok, I'm trying to learn the numbers here. Assuming you have 2200 Watts of surplus power from the alternators, what prevents you from being able to use a inverter to power the A/C?








I'm not suggesting using the truck as a generator at the campsite, just using some extra power off of it as it tows the trailer. This can't be that bad.









I had been told that I couldn't run residential refrigerators on an inverter either, but it works great for short power outages (That's all we normally have around here in the midwest). I guess I'm just playing devils advocate here and looking for the reason why it won't work


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## GarethsDad (Apr 4, 2007)

Sorry to say this but it will work. Before I bought a backup house generator I used a 2000/4000 watt inverter to run the sump pump, the fridge the freezer and the boiler. I have a high idle solenoid on my winter diesel suburban ( idels at about 850 rpm ) I have the inverter mounted under the second row seat on the passenger side. It has 2 #2 ten strand wires that runs to the battery on the drivers side with a remote switch. I have a 230 amp alt in this setup. The engine will keep up but is not as efficient as a generator and it will take hours from the life of the engine. James


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## Nathan (Jan 2, 2007)

GarethsDad said:


> Sorry to say this but it will work. Before I bought a backup house generator I used a 2000/4000 watt inverter to run the sump pump, the fridge the freezer and the boiler. I have a high idle solenoid on my winter diesel suburban ( idels at about 850 rpm ) I have the inverter mounted under the second row seat on the passenger side. It has 2 #2 ten strand wires that runs to the battery on the drivers side with a remote switch. I have a 230 amp alt in this setup. The engine will keep up but is not as efficient as a generator and it will take hours from the life of the engine. James


Ahh Ha!!! Finally someone will say it will work!









Again, I'm not looking to use it as a stand alone generator (that would not be very efficient), but simply as an additional power source while driving. By the way, the base alternator is 135 amps and the dual alternator is 320 amps. Granted, I may never do this, but I'm an engineer, and therefore don't like being told that things won't work without a full analysis to prove it!








To convince myself, I think I'm going to have to hook up the inverter and try the A/C. Then all I will really need is a power source to keep up.









Look on the bright side everyone: You don't have to work with me every day!


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## N7OQ (Jun 10, 2006)

I would think it would work if it was a true sine wave Inverter but a Generator would much more efficient. A Honda, Kipor, or Yamaha inverter generator is proof tha tis would work. These generators are just a motor a alternator and a true sine wave Invertor.


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## johnp (Mar 15, 2004)

It would be nice if you can make it work but to get by the starting load of the A/C (Mine is 43 amps)you would need a 5000watt inverter and that would put you over the 320 amp alts capacity not to mention at an idle most alts don't put out near the rated capacity. Where are you planning on putting the inverter? I would also put a switch or turn off the breaker that feeds the converter in the trailer that way you are not trying to charge the truck and trailer batteries with the converter and the two alts. It can be done but it would be costly to do it correctly.

John


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## Insomniak (Jul 7, 2006)

Yeah, you could do it if you had a big enough inverter and alternator. The starting load of the A/C is what will kill your plans. I actually fiddled around with this, using an 1800 watt (3600 watt surge) inverter, and the A/C wouldn't even start without the inverter overloading and shutting off - but it was a MSW inverter. My Honda EU3000is generator will run the A/C, so you need somewhere around 2,500 watts continuous, with more for startup surge. That translates into roughly 250-300 DC amps (taking inverter inefficiency into account) to actually make things work. That would tax those alternators pretty hard in my opinion.

Two Honda 2000 watt generators connected in parallel will solve the problem! Other users have tried one generator and it won't work.....


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## Nathan (Jan 2, 2007)

Ok, so how does the A/C on mine start up when the trailer is plugged into a 15 amp outlet?








That 15 A circuit in my house is usually able to start the A/C while topping up the batteries after a few weeks in storage. Maybe the circuit breakers forgive the extra startup draw?

A couple $1000 gens are out of the question. First thing, I hate generators (yes even the quiet ones), and second I don't want to spend that kind of money on something like this. Again, it would only be used very rarely, so I'm not willing to drop a fortune on it. I was just thinking out loud...


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## GarethsDad (Apr 4, 2007)

Ok here is how the electrican explains it to the plumber. The elecrical system is based on 80%. A 15 amp breaker will give you 80% load before it trips or 12 amps. If the plug feeding your TT is in the garage it may be on a 20 amp breaker even though it's a 15 amp outlet giveing you 16 amps before the breaker trips. And this is how some can run the A/C and others can not. Also if you plug in the TT the converter will turn on right away unless the breaker is off. The converter will vary the charge to the batterys depending on how much of a charge they need. By the time you get into the TT to turn on the A/C the converter may have kicked down to trickel charge. These are just my thoughts on how things work. James


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## johnp (Mar 15, 2004)

The 15 amp breaker is also designed to allow the inrush of current the a/c will draw for a couple of seconds.

John


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## Rip (Jul 13, 2006)

No a 15 amp breaker is good for 15 amps and will trip at 15 amps you are only to figure the circuit load at 80% The Circuit-Breaker
Circuit breakers act to limit the current in a single circuit in most household applications. Typically a single circuit is limited to 20 amperes, although breakers come in many sizes. This means that 20 amps of current will heat the bimetallic strip to bend it downward and release the spring-loaded trip-lever. Since the heating is fairly slow, another mechanism is employed to handle large surges from a short circuit. A small electromagnet consisting of wire loops around a piece of iron will pull the bimetallic strip down instantly in case of a large current surge.


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## johnp (Mar 15, 2004)

OK this is why I stopped giving any advise. Yes a circuit should only be set up for 80% BUT the breaker will hold an inrush of current for a couple of seconds. WHY do you think with fuses you have a standard fuse and a dual element or slow-blow fuse. Try to start a motor that draws 12 amps with a standard fuse it will blow. Breakers are made to hold a little longer. Any motor load could draw up to 300% on start up. So maybe I should run a 40 amp circuit to run a table saw.

John


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## map guy (Jan 11, 2007)

Rip said:


> No a 15 amp breaker is good for 15 amps and will trip at 15 amps you are only to figure the circuit load at 80%


This is exactly right. But johnp2000 is also right that a breaker or fuse can be designed/engineered with certain characteristics for special applications.

Have you given thought to the size inverter and the wave form quality necessary to start/run your A/C without short or long term compressor damage? Simple electrical math says a 2000 W inverter will be needed but may not be enough for the start-up load. For this size inverter to run that size load you will need 400 + amp hours of battery bank to buffer the alternator charging. You would also need wiring from the alternator to the battery bank in the 2/0 gauge size for the distance / amperage plus the battery bank to inverter wiring would need to be 4/0 wiring be less than 3 feet of total + distance. A lot of challenges but yes it can be done. It would be easier/cheaper to use a small generator but this isn't cool "pun" intended for Walmart type camping.....

Have been studying inverter systems extensively lately due to our normal dry camping trips and the desire to minimize generator run time to 1-2 hours per day and still able to use some 110v appliances during the day -not including the A/C, refer and or hw tank.

Map Guy


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## bentpixel (Sep 2, 2006)

Powering the TT with an inverter can be tricky. Shore power and inverter power must never meet. Otherwise, everything frys. The large draw of the AC puts a strain on your battery/alternator. I wont say that this can't be done, but it will cost nearly the same as a generator.

I once worked on a News Gathering truck in the early 80's. The station tried to build a quite truck. It has 4 large batteries (about the same height and width as a standard battery but four *feet* long. They could handle a 6kw load fror one hour.







In practice, a half of that was reliable. 
That company abandoned the battery approach because the cost of alternator maintenance and the premature death of the batteries. I know that was then this is now. It's just story.

How about this alternative. Forget the A/C. Run a dedicated AC line from TT to TV/inverter. Tie down a portable evaporative cooler inside the TT.









I have one in my house (by Dyna-Cool) that I can dump a 5lb bag of ice for a quick cool down. I know there are condensation issues here, so this might only be a half a solution. Its only 75 watts.









my $.02's
Scott


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## Insomniak (Jul 7, 2006)

As mentioned, you're probably plugged into a 20 amp circuit. Most 15 amp circuits are used for lighting only. And, have you seen how much a 2000-3000 watt true sine wave inverter costs?



Nathan said:


> Ok, so how does the A/C on mine start up when the trailer is plugged into a 15 amp outlet?
> 
> 
> 
> ...


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## N7OQ (Jun 10, 2006)

On shore power you have a lot of available current and you would have be be using a 20 amp circuit breaker not a 15. Plus for very short periods you can pull a lot of current as much a 60+ amps for a short time plenty of current to get a good clean start. A circuit breaker is designed to hold indefinitely at rated current in free space at 40 Celsius. Now when you put it in a panel with other circuits it will loose some of its rating so this is way the load can only be 80% of the rating.


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## Nathan (Jan 2, 2007)

bentpixel said:


> How about this alternative. Forget the A/C. Run a dedicated AC line from TT to TV/inverter. Tie down a portable evaporative cooler inside the TT.
> 
> 
> 
> ...


Actually, they have evaporative coolers that mount over a roof vent of an RV and run on 12V. Only works well in dry areas though!









Something tells me I'm not going to be happy until I measure acutal amperage draw from the OB when the compressor starts








All things to do in time.

Of course the real solution is probably what I already do: Drive at night until it cools off and then stop... Or if it is over 90 deg acutally pay for camping for the night.


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## johnp (Mar 15, 2004)

I run the TurboMaxx-air vent on exhaust while driving and fire up the generator and a/c for food breaks. it only takes about ten minutes to get the temp down enough. Oh and watch as that 20 amp a/c breaker spikes over 40 amps when the compressor kicks in without tripping







At least the Carrier units run the fan for about ten seconds first before the compressor starts.

John


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