what size, and how many A/C's do you have?

I have one 15K A/C and am carrying 2 honda 2K's with the parallel cable. I doubt an inverter would handle to startup current of the A/C compressor.

I got the two generators from Mayberry's +parallel cable for under 2 thousand bucks. They also included a quart of oil and 1 set of battery charging cable for free.

Suppose your AC only requires 12 amp hours to run. Then to use it for 8 hours it could draw as much as 120 amps with cycling and constant use for AC only. Thats a pretty strong draw for an battery bank.

Our motor home has 6 6 volts in a parallel, series setup adding up to 660 reserve hours. Does the battery bank last for 8 hours? Yes at a minimum draw. Does it recharge quickly? No.

The battery volts will drop rather quickly under load; from 12.6 (nominal full charge under load) to 11.5 (about 80%) in a few hours of use. Hooked up to 50 amps, it took more than 7 hours to restore the battery bank from 11.0 volts to full charge.

While charging the DC amps can read as high as 100 amps charging. At the FMCA rally running the genset 5-6 hours a day with AC running, did not bring the level back to full charge. I suspect the same conditions that make you want the AC also slow the charging/inverter system somewhat. Seems like the Interstate battery guy said something about 70 degrees as normal for amp hour readings. Heat and humidity is never a good situation.

We have a 7500 watt gen set (about .6 gallons diesel per hour), 2000 watt converter and 6 NEW house batteries.

As Robert Heinlein used to say TANSTAAFL. I suspect that includes inverters and generators also. Remember the math works under "ideal" circumstances. Practical circumstances will vary and usually downward.

That being said, we will go to Quartzite in January and boondock for at least a week or until the tanks fill.

Your mileage will vary,
Mike

Technically a large invertor combined with a genset can work to get past the start up.  However they must be linked to assure they are in phase and they must be compatible in waveform to be efficient.  I am assuming you are going to use the AC generated by the generator directly to the air conditioner.  Using the generator to charge the batteries and the invertor to power the air conditioner is a lose, lose, lose situation with an efficiency loss at the generator, and efficiency loss at the charger/converter, an efficiency loss due to heating the over used batteries, and finally an efficiency loss at the inverter.  I believe Yamaha and Onan both make a package that will allow you to overcome the start up current on air conditioners which is only a few seconds each time it cycles on.  Some use a synchronised pair of Honda 2000's when AC is needed.

Not so simple is it.  We just go to hook ups when it is too hot and stay in the mountains mostly in the summer.  Our Honda 1000 runs about an hour a month for ironing the quilting work.  Solar provides the rest of our needs.

I would recommend a large generator, an enhanced package, or a synchronized pair but I don't recommend the pain, weight, expensive, and inefficiency of the invertor route to get air conditioning.

Of course that is only my opinion.

Larry

k&c:
This is an idea near and dear to my heart as I prefer being an "unplugged" kind of guy. As you have read - technically very do-able, but practically not worth it to cobble the pieces together today. Yes, some high end class A MHs will invert the front AC unit while driving and power it with a 300+amp upgraded alternator. The issue with your lower amp genset idea (something I would love to be able to do in my rig) as has been said above is to synch everyting including the charger. It is just a matter of technology and an "integrated" solution is finally almost available - though currently on a slightly larger scale than you desire. The brand new not even really released Onan Hybrid Quiet Diesel system does just what you are suggesting (using an underpowered genset and an inverter to handle the peaks). I would bet that a smaller solution a. la. using a single 1,000 or 2,000 watt generator to power bigger loads solution might be coming out soon. I see a demand for such a solution as a dual 1k or 2k genset setup, though excellent, is a little overkill during the lower amp run times.


-- Edited by RVDude at 09:25, 2007-08-21

Look what I found !!

Little pricey but seem to fit the bill, its designed to help the small generators on boats to start AC's and such with a boost from the batteries.
http://www.pkys.com/Victron/multi_plus.htm