running a 5000 btu AC unit

[onthego]

How much battery AH would i need to run a 5000 BTU AC unit for about 8 hours?

[rsilvers]

The AC uses about 560 watts. So 4.7 amps for 8 hours is 4560 watt hours.

But the inverter may be 90% efficient, so 5066 WH.

And then even a deep-cycle battery you want to discharge to about no less than 1/2 full, so double that to 10133 WH.

And then note that batteries lose capacity over time, so I would say 12000 WH.

At lease in this case, you don't have to worry about cold-weather effects.

[inetdog]

When converting from AC (for A/C) draw to DC capacity it is most straightforward to keep everything in Watt-hours (Wh) or kilowatt hours (kWh) until you get to the DC side. Than make one conversion from kWh to Ah based on nominal or actual battery voltage.

Bottom line is that it going to be very expensive. And high enough power that you do NOT want to be using 12V.
Finally, discharging your battery bank to 50% every day is going to reduce its life significantly.
You would be better with at least twice the battery calculated by rsilvers.
So, 24000 watt hours. At 48V that is 500AH. You cannot do that with 12 or 6V batteries without running them in parallel, and you do not want to do that.
That leaves using twenty four 2V 500AH batteries in series.

[rsilvers]

While it is true that double the capacity will make the battery last almost twice as long, it will cost twice as much to do so. And a 50% discharge should still last about four years. So he could do a 50% discharge and see how long it lasts, and then replace as needed, and be no worse off but with lower upfront costs.

[sensij]

One problem with designing to 50% discharge means that if anything happens to disrupt the charging strategy, the subsequent day will over-discharge the battery, or the system needs to be taken offline. By designing to a safer discharge level of 25-30%, you have some ability to ride through any loss of availability of charge.

[rsilvers]

That's true. If this is solar power, and the solar is not greatly oversized, then you should double the battery from what I said.

[onthego]

its fine if the battery only last a year or 2, thanks for the help

[SunEagle]

IMO a battery system big enough to run an AC system that lasts only 2 years would be a big expense and a lot of money down the drain. But the money is yours to burn if you so choose.

[onthego]

IMO a battery system big enough to run an AC system that lasts only 2 years would be a big expense and a lot of money down the drain. But the money is yours to burn if you so choose.

its in a cargo trailer conversion that i plan on using maybe one time to go across the country. you think 2 of he vmax 125's would be a good choice? i have 300 watts of solar and can always run the vehicle to charge them