I'm new to RVing so been doing some research and creative thinking. Over on RV.net I came across a post that made me think.

When discussing running the AC off of batteries, someone posted this -

http://www.rv.net/forum/index.cfm/fu...g/1/page/2.cfm

"Its not a matter of running amps on your AC. Its the startup amps that kill the deal. Startup amperage will be two to three times the running amperage on any appliance that has an AC motor.

When using an inverter, it is all about watts. If you have an AC Unit that runs on 10 amps (10*120) you are using 1200 watts. Since your inverter is converting that 1200 watts from 12 volts (1200/12)gives you an amperage draw of 100 amps from your 12 volt battery. Depending on the AC, startup wattage can vary from 2400 all the way up to 3600 watts for a few seconds. By the numbers, that can be up to 300 amps from a 12 volt source. Now, if you had that much amperage available, your wiring would likely not handle 300 amps without smoke and fire.

With your generators, you have the same issue: wattage. Those who have decent AC units that are of recent manufacture and energy star compliant will have units that will start with about 1.5 times the running amperage. Those with older units that require up to 3 times the running amperage need a bigger generator. Most small AC generators have a running amperage(watts=amps*volts) and a surge amperage for starting surge loads like an AC. Check the numbers on the plate on your AC unit and on your generator. You can then calculate whether the generator will handle the load.

I have built my own system using a 200 amp 12 volt alternator mounted to a Briggs Engine. This charges a bank of four 12 volt deep cycle batteries which are connected to a 2000 watt running 4000 watt surge inverter. I use this setup because the engine does not have to run at 3600 rpm to produce clean AC power like on small generators. I use less fuel and make less noise. And, often, I do not have to start the engine for hours to have plenty of power. When the batteries do need charging, the engine only has to run a couple of hours to fully charge the batteries on a normal basis. If I am going to run the AC cooling, I do start the engine to produce power though."

I understand that conventional wisdom suggests a generator to run the AC, microwave, etc. but I like the idea of running EVERYTHING off of a battery bank thru an inverter and having a small high-amp alternator on a very economical motor charge the batteries. Has anyone here done anything similar? Report on your success or failure.

 

Very big expensive rigs with huge 12 or 24V battery banks have this capability. They also have 10 or 15kw diesel generators that can run everything.
Perhaps your idea will work, but most people get a 5000 watt gas generator and hook up. At the end of the day it takes a lot of power to run the AC, 13-15 amps for 1 13,500 btu unit. Diesel if you have the money, is better.
It would seem that if there was a better way, someone would be selling it.
Let us know how it turns out! Good luck!

 

I have a 3 bank 4-6Volt, 2-12V battery system in my toyhauler with a 3000Watt Inverter. It will run the Micro for a bag of popcorn, but no more. It will fire up the AC but the load will burn down the battery bank in no time so I won't even try that. I spent well over a thousand dollars on the system I have, so you better be ready to carry a HUGE bank of batterys to run a AC unit for anytime at all. You'll drag them down before the coach gets cold.
When it gets hot enough to want the AC unit.............I fire up the Onan 5.5 generator.
This is just the start of what you'll need.

 

Geez, Joe, you're a pretty handy guy to have around!

 

12valve,

You can pretty easily come up with a system to start the AC but the hour after hour power draw will have to be equaled with charging. If not you'll kill even a big bank of bats before you want to turn the AC off. And when drawing high amps you get less out of the battery. Bats are fine for an inverter running a microwave, a coffee grinder and even 120 volt lights or a TV if you want. But AC is a big power draw and it is a draw that just goes on and on. Once the bats are down you have a long recharge time to bring them back up properly.

I built a 2250 watt diesel generator and am able to run my AC, that usually requires about 3500 watts to start, by installing a starter kit. It's a big capacitor that helps the compressor motor to start with much fewer amps.

If you had a bank of PV panels on the roof it would help offset the electrical load and would keep some sun off the roof to lower the cooling load.


John

 

Juz,

It looks like your charger is powered by your inverter?


John

 

It does look like that Wetspirit, but it's not. I have it setup so the line at the main switch can backfeed to the charger to power it up, I just throw a switch to go from inverter to charger. The schematic makes it look more complicated than it really is.
These help (solar panels), and wasn't part of the schematic. It's a lot of work just to make coffee and watch TV without the generator, but late at night when dry camping it's well worth it. Powering the AC unit, thats a whole nother story.

 

I was afraid I had just spent all the money I had on an Onan 5.5 for nothing. I looked at many options and decided the Onan was the best way to go. I hope to get it set up and wired this weekend.

As my 5er is not designed for an onboard generator I am building my own set up like the Juicebox but using the 5.5 rather than the 4.0 that Onan uses.

 

here's some good information on the subject.
http://www.phrannie.org/phredex.html

 

I have been doing a lot of research myself on AC units for truck campers and from what I have found is that most AC units even in trailers are overkill and that the best unit out there for truck campers and most trailers is the PolarCub by Coleman. Depending on the year of production they range from 7800-9200 btu and can be run by a Honda 2000 genny with power to spare. I have read that these units are more efficient in cooling because they cool more consistently by staying on longer rather than a blast of cold air, shut down, another blast of cold air, shut down, so on and so forth. I have also read that for trailers that have 2 AC units it is better to have 2 PolarCubs instead of the 11,000 or 13,500 btu units to cool because of the cycling on and off effect. Because these larger units cycle on and off a lot, condensation builds up more in the camper or trailer, probably not a really big problem for us folks out in the west but maybe for those in more humid climates. Just food for thought.

 

I've been into the alt. energy thing for over 30 yrs , and I'm a full time RVer , the biggest problem with alt. energy & mobile , is the capacity to carry a battery bank big enough to handle the larger loads [ Like AC - large load for a long time ] 2nd is enough roof space to put enough solar panels .
My batteries weigh 135lbs before adding acid [ forget - but at least 3-4 gal=20-30lbs ] , my set up has 4 of these [ Trojan 225s 6v , 2 in series , making 2 sets =12v, then in parallel for longer run time ] , this in a bus , I do not think you could get a RV trailer to carry that load , with out being in the middle of the trailer & frame , now you need to seal it in a box to vent gases .
So there is a compromise with my Airstream , fewer , smaller batteries , use a generator for large , long time runs , AC , furnace & micro .
If anybody wants to do it right with inverters , you realy need to buy sine wave inverters , more efficient , the cheaper, square wave & modified sine wave inverters will either shorten the life or kill a lot of equipment ,
The basics are learning math & Ohms law , you can not have your cake & eat it too .
Heres a good source .


http://www.backwoodssolar.com/