Is it possible to have the air conditioner, and outlets work off our batteries in our travel trailer? - RV-Dreams Community Forum

TheDigitalHippies · RV-Dreams Family Member

Is it possible to have the air conditioner, and outlets work off our batteries in our travel trailer?

GENECOP · RV-Dreams Family Member

Search Jack Mayer, read his electrical and solar page.....The AC is not really going to work off a basic solar system...

-- Edited by GENECOP on Saturday 26th of July 2014 08:56:37 PM

Sushidog · RV-Dreams Family Member

As my boss would say. The answer is always yes. Yes you can run your AC off of an inverter and batteries, but not 2 batteries - maybe a dozen or so batteries and a huge inverter if you want to run your AC for a few hours. However I recently made a post about high-efficiency mini-split, DC, ACs who lend themselves well to off-grid battery power. Here's a link: www.hotspotenergy.com/DC-air-conditioner/

If you go to this page, www.hotspotenergy.com/DC-air-conditioner/DC-AC-Complete-Systems.php you will see their minimal system that uses 4 - 12v 130ah Trojan bateries (about $800) and a high efficiency, 12,000 BTU, 48v DC AC for $1,795 that together will give you about 5 hours of AC before it needs recharging (by whatever means available.) So the answer is yes you can do it - for about $2,600.

Chip

-- Edited by Sushidog on Sunday 27th of July 2014 06:51:09 AM

TheDigitalHippies · RV-Dreams Family Member

Thanks guys. And Sushidog, that's about the price of a 320 watt solar kit www.amazon.com/Go-Power-Solar-Elite-Complete/dp/B0015398PE/ref=sr_1_5 that I found during searching. The solar kit doesn't include batteries though.

I was hoping it'd be cheaper to do the batteries alone, but it's not much, however I think the batteries suit my needs more right now. That's pretty expensive for us right now, but it does at least give me something to research. If We may just opt for fewer batteries, but that's only a $400 savings.

Thanks again, I may try something with the battery route if I can get it about 1/2 the price listed.

bjoyce · RV-Dreams Family Member

I will let the numbers talk.
30AMP at 120 volts = 3600 watts, so you need a 3000 watt inverter as a minimum. A 3000 watt inverter can run more than 3000 watts for short bursts. You would need at least 6 batteries, 100 AH or higher, to pull 3000 watts or the battery voltage will drop too low. One hour of 3000 watts is 3000 watt hours or 3 kilo-watt hours. At 12 volts this is 250 AH of battery. Since you can't run batteries below 50%, you would need at least 500 AH of battery to run one hour. Two hours would require 1000 AH of battery, or about 10 batteries. The solar would need to recharge 6000 watts. Solar is normally sized from 5 hours of full power (assuming tilting in the winter), so you need 1200 watts of tiltable solar panels to recharge or somewhere around 1800 or 2000 watts of flat panels.

To do even half of what you want would require at least a 2000 watt pure sinewave inverter and 6 batteries, but 3000 watts and 10 batteries would be better. If the campground power stayed up some of the time, the batteries would get recharged without solar.

12 volt fans, like an Endless Breeze, open windows on the shady side (you might have to create a shady side with fabric), and some tolerance from heat will be cheaper. You would still need 2 batteries to handle the load.

-- Edited by bjoyce on Sunday 27th of July 2014 09:58:17 AM

-- Edited by bjoyce on Sunday 27th of July 2014 09:59:09 AM

Technomadia · RV-Dreams Family Member

We built a Lithium Ion battery bank (500AH) that can run a single A/C for about 2.5 hrs when needed. Lithium has some unique advantages for running high capacity loads - such as little loss while under load, and the DoD is much lower than lead acid. For more information on LFP - www.technomadia.com/lithium .

Yes.. it's possible. But it's not cheap or straightforward :) A generator is probably a cheaper solution.

Sushidog · RV-Dreams Family Member

Lithium batteries offer a tremendous weight savings, and you can basically throw Peukert out the window (discharge at a high rate without affecting capacity.) But the biggest advantage is that you can discharge them down to 20% of capacity (vs 50% for a lead-acid) without affecting battery life (in cycles.) However an equivalent size lithium batery costs about 4 times as much as a quality lead acid battery (over 5 times an equiv. Sams Club battery.) When the added discharge capability is taken into account - a 100 ah lithuim ($620) has 80 usable AmpHrs, while 160ah of lead acid batteries (about $250 for quality batteries) to get the same 80 usable AH making the cost per usable AH only 2.5-3 times more than a lead acid. Then there's charging.... But if you're fighting a tight weight limit and must have the latest and best technology available, then they might be worth a look-see, if you can afford them.

For peons like me, counting my pennies, they are out of the question. I'm sure they are a must have for Prevost owners though - with all due respect. ;)

Chip

Technomadia · RV-Dreams Family Member

We're far from being 'Prevost Owners', and we count our pennies too. Well, maybe we round up to nickels. But we definitely don't have money to toss around like you're implying. We did a thorough cost analysis over the lifetime of the setup to determine this was the right choice for us.

Yes, the upfront cost acquisition was a bit higher (only 1.6x higher than the equivalent AGM setup we were considering)... but lifetime, it was cheaper. And factor in the Balqon cells now available actually bring that cost down and make them even more tempting (100AH at $440.. and get even cheaper at the larger capacities).

For high amp draws, maintenance and solar charging, LFP has advantages far beyond weight savings. And there are definitely downsides - like upfront costs and the more cutting edge nature of it.

- Cherie

Sushidog · RV-Dreams Family Member

No offense Cherie. You guys rule! I love your vids and give you guys props for breaking new ground. You know what they say, the pioneers may have first pick of the land, but they also have more arrows in their back too. ;)

Yes compared to high-end, AGM lead acid batteries the difference in cost is less, but compared to the cheapest conventional vented flooded lead acid batteries there's still quite a difference in initial cost - no matter that the lithiums might last over twice as long, if you can buy 3-4:1 they're still at a price disadvantage. I'd love to have a set though, because as you say, there is a definite upside. A $40,000 Mercedes may have three times the life of a $20,000 Honda, as well as being a better car overall, that most would rather drive and own. However you must first be able to afford the upfront costs and added insurance costs to be able to drive one.

Perhaps the price of Lithiums will continue to drop, (as solar has) making them something to watch for sure.

Chip

TheDigitalHippies · RV-Dreams Family Member

bjoyce wrote:
I will let the numbers talk.
30AMP at 120 volts = 3600 watts, so you need a 3000 watt inverter as a minimum. A 3000 watt inverter can run more than 3000 watts for short bursts. You would need at least 6 batteries, 100 AH or higher, to pull 3000 watts or the battery voltage will drop too low. One hour of 3000 watts is 3000 watt hours or 3 kilo-watt hours. At 12 volts this is 250 AH of battery. Since you can't run batteries below 50%, you would need at least 500 AH of battery to run one hour. Two hours would require 1000 AH of battery, or about 10 batteries. The solar would need to recharge 6000 watts. Solar is normally sized from 5 hours of full power (assuming tilting in the winter), so you need 1200 watts of tiltable solar panels to recharge or somewhere around 1800 or 2000 watts of flat panels.
To do even half of what you want would require at least a 2000 watt pure sinewave inverter and 6 batteries, but 3000 watts and 10 batteries would be better. If the campground power stayed up some of the time, the batteries would get recharged without solar.
12 volt fans, like an Endless Breeze, open windows on the shady side (you might have to create a shady side with fabric), and some tolerance from heat will be cheaper. You would still need 2 batteries to handle the load.

-- Edited by bjoyce on Sunday 27th of July 2014 09:58:17 AM

-- Edited by bjoyce on Sunday 27th of July 2014 09:59:09 AM

The programmer in me thanks you immensely. This is what I was looking for, but couldn't figure out on my own. You spelled everything out for me, and explained what is what, and why. I really appreciate it and will refer back to this again many times in the future.

TheDigitalHippies · RV-Dreams Family Member

Thanks Cherie, I'm off to read the post, and watch the video now.

bjoyce · RV-Dreams Family Member

We have 400 AH of the same Li-ion batteries as Cherie and Chris. We also changed to a 3000 watt Magnum hybrid inverter/charger. Both changes were an improvement for us. http://rv-dreams.activeboard.com/t57552584/our-new-batteries-and-invertercharger/ for more info.