How much battery/inverter to run AC overnight at a rest area

[khuffmanjr]

Hello everyone!

I use my Bighorn as my hotel room for business travel and I live pretty centrally in the country - Texas! - to make sure I can get to most of my usual work cities on a weekend. I tend to be no more than 15-18 hours away from work and usually just find a campground for the night on Saturday travel days. I've been tossing around the idea of spending some time in parts of the country that would require me to drive much longer on the weekends to get to those usual places. If I could run the bedroom AC on batteries on a Saturday night at a truck stop or rest area then I would feel a lot better about being 20+ hours from work for some of the year.

So my question is this: How much battery and inverter would I need to run the Bedroom AC continuously for 6-8 hours. I would also run the 12V/gas water heater and residential fridge and charge small electronics as well as run a 110v fan to move air as we sleep. The AC is 15k btu would seriously run continuously.

I'm really just looking for ballpark, but if you happen to know some numbers from your own ponderings then, by all means, share them. With the cost, and weight, of batteries I'm wondering if a generator wouldn't be a better option.

Thanks!
Ken

 

[Lynn1130]

Some one with much more battery knowledge than me will certainly jump in here but I'm just guessing that you don't have enough room for the batteries that this would take. On top of that getting them charged, on the road, again would seem like an impossibility. How about an RV park with hookups for the night?

 

[danemayer]

Say your A/C unit consumes 10 amps at 120V AC. That's 100 amps at 12V DC. And that's assuming 100% efficiency for the inverter to convert 12V DC to 120V AC.

I think a battery in good condition might deliver 100 amp hours before it dies. So I think that means you'd get a maximum of 1 hour of A/C use out of 1 battery.

But it's not good for your battery to be completely depleted, so you won't get that much run time.

If you want overnight A/C, you'll need a generator that's quiet enough to run overnight without annoying anyone. An on-board Onan 5500 propane unit is quiet enough, but you can go through a 40# tank of propane in a night. It'll be cheaper and easier to find a campground with power.

​

 

[wdk450]

Let's say that your Air Conditioner pulls 15 amps at 120 volts AC. With the 12 volt DC to 120 volt AC rule of thumb conversion, (10 to 1) you would need 150 amps of 12 volt DC current continuously for 8 hours. That comes in at 1200 amp hours. Since you can only run your batteries down to about 50% capacity before low voltage shutdown, that would give a ballpark figure of 2400 amp hours needed. A group 24 deep cycle battery has about 80 amp hours. So that would give us a battery bank of 30 group 24 deep cycle batteries to run the AC overnight. That is about 1500 lbs of battery at 50 lbs per battery.

A generator is a better option. That is why the larger Heartland 5th wheels have the generator option; for air conditioning. A 2000 watt portable generator would probably do the job, though it might have a problem with the huge Air Conditioner startup current pulse. Just check the gas tank size and full load fuel consumption figures to see if it will run all night. Chain it to your rear landing gear (if your sleeping are is in the front) with a motorcycle security chain and lock. Make sure your Carbon Monoxide alarm works. Many RV spaces will not allow you to run a generator overnight (even the quiet ones) due to the generator noise bothering other campers trying to sleep.

To all of the other experienced Heartlanders out there that want to challenge my figures, they are "best guesstimates", and just trying to get the idea across to the original poster.

 

[khuffmanjr]

Recharging them wouldn't be an issue. Since I generally travel the two weekend days and then I'm on full hookups the whole week, I wouldn't be concerned with a lengthy recharge.

In any case, this choice kind of stinks. I could get a 290lb Onan 6500 LP generator at ~$5500 plus have to pay for the 5er to be "prepped" for it - I have the front storage but it isn't prepped from Heartland - OR I can pay somewhere north of $2000 for the batteries but be way over weight. My impulsive side says to get the genny. My more sensible side - my god, when did that happen?! - says forget it all and just roll into a campground late at night about 20 Saturdays per year.

I don't know. It takes a lot of $40 nights in campgrounds to add up to the cost of getting the generator. And the batteries are stupidly heavy for what I'm trying to do. So thanks for talking it out with me, I guess. I'll leave this one alone for now.

Thanks!
Ken

 

[SNOKING]

Recharging them wouldn't be an issue. Since I generally travel the two weekend days and then I'm on full hookups the whole week, I wouldn't be concerned with a lengthy recharge.

In any case, this choice kind of stinks. I could get a 290lb Onan 6500 LP generator at ~$5500 plus have to pay for the 5er to be "prepped" for it - I have the front storage but it isn't prepped from Heartland - OR I can pay somewhere north of $2000 for the batteries but be way over weight. My impulsive side says to get the genny. My more sensible side - my god, when did that happen?! - says forget it all and just roll into a campground late at night about 20 Saturdays per year.

I don't know. It takes a lot of $40 nights in campgrounds to add up to the cost of getting the generator. And the batteries are stupidly heavy for what I'm trying to do. So thanks for talking it out with me, I guess. I'll leave this one alone for now.

Thanks!
Ken

What ^^^^^ you said. Inverters are good for small load over extended times, or large loads over short periods. Large loads over extended times = no way!

So that it is fully understood, here are some facts.

If you used 8 Dyno D260 (260 AmpHr) batteries, you would have 1040 amphrs or 520 usable, to the tune of 600+ lbs.

http://www.dynobattery.com/specd260.pdf

Attached is a spread sheet I created for boat owners that I installed battery banks for. It was design to help them manage a large battery bank. An Amp Hour meter is a great help in doing this.

As others have said this large heavy battery bank would run the AC for 4-5 hours.

Some truck stops have AC stations where a AC duck is placed in a window.

Chris

 

[carl.swoyer]

Hello everyone!

I use my Bighorn as my hotel room for business travel and I live pretty centrally in the country - Texas! - to make sure I can get to most of my usual work cities on a weekend. I tend to be no more than 15-18 hours away from work and usually just find a campground for the night on Saturday travel days. I've been tossing around the idea of spending some time in parts of the country that would require me to drive much longer on the weekends to get to those usual places. If I could run the bedroom AC on batteries on a Saturday night at a truck stop or rest area then I would feel a lot better about being 20+ hours from work for some of the year.

So my question is this: How much battery and inverter would I need to run the Bedroom AC continuously for 6-8 hours. I would also run the 12V/gas water heater and residential fridge and charge small electronics as well as run a 110v fan to move air as we sleep. The AC is 15k btu would seriously run continuously.

I'm really just looking for ballpark, but if you happen to know some numbers from your own ponderings then, by all means, share them. With the cost, and weight, of batteries I'm wondering if a generator wouldn't be a better option.

Thanks!
Ken

Inverters, although rated for so many amps and output are not designed for running the air-conditioning units. You will over temp the batteries. Not a good setup. Yes you can do it but, not a safe application. Looking into a genset such as the Onan 5500/6500 lp would be the best option.

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[dave10a]

Inverters, although rated for so many amps and output are not designed for running the air-conditioning units. You will over temp the batteries. Not a good setup. Yes you can do it but, not a safe application. Looking into a genset such as the Onan 5500/6500 lp would be the best option.

Sent from my XT1254 using Tapatalk

My motorhome had a 3KW inverter that ran on 4 Group 27 batteries with 1/0 cables from the batteries to the inverter. It was intended to run the microwave (briefly), TV and lighting. It would run an air conditioner for a several minutes before draining the batteries if they were on that power leg. The inverter would automatically shut down when the batteries drained to approx. 20% of charge to protect the batteries. Also please explain how the batteries would over temp when suppling the power. They could overheat while charging at a high rate if their internal resistance is high or overcharging in the case of equalization.

 

[carl.swoyer]

My motorhome had a 3KW inverter that ran on 4 Group 27 batteries with 1/0 cables from the batteries to the inverter. It was intended to run the microwave (briefly), TV and lighting. It would run an air conditioner for a several minutes before draining the batteries if they were on that power leg. The inverter would automatically shut down when the batteries drained to approx. 20% of charge to protect the batteries. Also please explain how the batteries would over temp when suppling the power. They could overheat while charging at a high rate if their internal resistance is high or overcharging in the case of equalization.

Normal supply of power would be coffee pot, TV, computer, fans and so on ... However the rooftop ac requirement is much higher. The higher amps being drawn off the batteries will cause a higher level of heat. The same as when you disconnect from shore power, the cord sometimes feels hot.
A friend of mine who had been running his RV AC unit did over temp his batteries. His Magnum Inverter has a battery temperature sensor and shut down for the over temp. Everyone has there own experiences. I saw the over temp personally so it can happen. Just sharing what I saw

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[esscobra]

a small inverter generator will run the fridge , inverter , and 1 a/c for overnight etc- you can get one easily handled by yourself for under 2k or you can get the onan for much less than you think and you could attach plug and plug your cord into it rather than do all the prep -