Running a 120v a/c unit off starter battery

msiminoff wrote:

jrnymn7 wrote:
My question is, would the vehicle's charging system be able to keep up???

I don't see any issue with running your window A/C from a 1000W inverter… Typically 1000W sine wave inverters will have a surge capacity of 2X the rated output. That's plenty to start the compressor in your 5000btu window A/C unit. The real question is; Is your current alternator and DC wiring is up to the task?

IF the alternator output is sufficient AND the inverter is mounted close to your starting battery AND the the power cables (from alternator to battery, and battery to inverter) are sized appropriately, then you're good to go. If your alternator is not able to provide the required continuous current, then replacing it with a high output one is a simple and relatively inexpensive undertaking. Adding a second alternator is a good solution as well, though this solution would be more expensive and complicated, especially if the 2nd alternator mounting componentry is not readily available. Take a look to see what DC Power Engineering has to offer.

As others have mentioned, you will probably be better off powering the inverter from your house battery bank and then run a pair (+ & -) of heavy (2ga or larger) charge cables from the alternator to the house battery (with appropriate fuses and disconnect of course). This will allow you to run the A/C for a short period of time while the engine isn't running, provide a source of 120V AC power in the coach, and prevent you from inadvertently discharging the starting battery if the inverter were to be left on.

By way of example; I replaced my alternator with a 180A model from DC Power and it will effortlessly operate my (8200BTU) roof A/C via my 2000W inverter, plus I can charge my battery bank while underway. I have 2ga wiring from my alternator to my house battery.

Cheers,
-Mark

so it is do-able. good to hear!

as you stated, there is the possibility of forgetting to shut off the inverter and killing the battery. that is definitely something to be mindful of in making my final decision. thank you.

on the other hand, i thought i read on a forum somewhere that a vehicle's charging system cannot charge a battery bank quick enough to make any real difference??? if so, that should also be true for keeping up with the a/c unit's load. and this is why i posed the question in the first place... will it keep up? does it all simply come down to the right alternator for the job???

i also know it doesn't take long for a dead starter battery to be brought back up to full charge by simply driving for a while. so there seems to be some disagreement as to the viability of charging a battery bank off the alternator. but again, don't some coaches do just that anyway?

the nice thing about charging the bank off the alternator is everything is already set up after the bank, i.e; wiring to inverter, wiring to a/c unit; and i wouldn't need to buy another inverter or a better starter battery... just a better alternator, wiring, etc.

on that note, i will need to learn how to properly wire that sort of set-up. any help from you folks would be greatly appreciated, and thanks for all your help so far!