Off grid AC with 960watts + 870Ah

[BradKW]

Building an RV in southern FL and AC is a must due to the heat. I have (3) new Suniva panels, 320w @ 24v, total 960w in theory. Outback80 MPPT.

The battery bank I am looking at setting up is (4) 6v Trojans, 435Ah each, series/parallel for an 870 Ah bank. Alternate charging and system power from a Honda (or Yamaha) 2000i.

The AC I wish to power is 410w peak operation...startup surge unknown... https://www.amazon.com/gp/product/B0...=ATVPDKIKX0DER With extensive (for an RV) insulation (spray foam + polyIso), I expect lower setting and economy mode to be sufficient to keep Peukert from killing this project before it leaves the gate. Hopefully something to the tune of 2.75A 20min per hour.

With other 110-120v requirements being microwave, computer, tool chargers, and toying with trying to mimic a ultra low draw 110 'fridge setup I saw, I wish to get a 3000w pure sine inverter. Magnum is out of my budget, so looking hard at a GoPower with a 0.5A idle: https://www.amazon.com/gp/product/B0...=ATVPDKIKX0DER ...would certainly appreciate other suggestions.

I've read through the "stickys" and see that I'm designing a system that exceeds what Sunking suggests for a 12v system. If I understand correctly though, moving to 24v would require doubling an already huge (for RV) battery bank to maintain the Ah needed to stand a chance at useful operation using no more than 50% capacity. I believe I understand the over-sized cabling and connections necessary to prevent this from being a fire hazard. Whether it turns out to be an expensive failed experiment is, however, something I feel willing to attempt. Any advice on any aspect would be great!

It's still in the very early stages, but if you're interested in the platform, build thread is here: http://www.cheaprvliving.com/forums/...-RV-Conversion

[sensij]

I've read through the "stickys" and see that I'm designing a system that exceeds what Sunking suggests for a 12v system. If I understand correctly though, moving to 24v would require doubling an already huge (for RV) battery bank to maintain the Ah needed to stand a chance at useful operation using no more than 50% capacity. I believe I understand the over-sized cabling and connections necessary to prevent this from being a fire hazard. Whether it turns out to be an expensive failed experiment is, however, something I feel willing to attempt. Any advice on any aspect would be great!

The energy capacity is the same at 12 V or 24 V. It sounds like you are letting the Ah concept mislead you.

6v * 435 Ah * 4 batteries = 10440 Wh
12v * 870 Ah * 2 batteries = 10440 Wh
24v * 435 Ah * 1 battery = 10440 Wh

Your 50% capacity is 5220 Wh. Check your total expected load against that.

If you are drawing 410 W from a 12 V battery, that is 34 A, less than C/20 for the battery you've suggested so not bad (no other loads considered).
410 W from a 24 V battery is 17 A, so you can get away with smaller conductors (less copper) for the same load.

[Logan5]

If you are planning on doing a system with air conditioning, Forget 12 or 24 volts. You will want a 48 volts system without any question. You will also want as small of a bedroom space as feasible. the smaller the better, so as to only cool the space you actually sleep. You could also consider The "Hot Spot" 4812 vrf split unit already designed to run directly from battery and solar. Using an inverter to run a window AC through and inverter will be very limited especially at 24 volt. You will also want a solar array that is over sized to insure you get to float everyday, on cloudy days and less than ideal solar conditions you will need to run a generator to maintain, condition and properly take advantage of your solar energy production.

[Logan5]

For refrigeration you should be looking at 24 VDC top load models, they require no inverter and use much less power and can be run from your 48 volt bank with simple step down. This way you only need to run a much smaller inverter and mostly for the microwave. Not running inverter 24hrs 7 for any critical loads is crucial when living true off grid, with all the high power modern conveniences.

[BradKW]

That sounds very helpful! You are right, I have based everything on my understanding of the Ah concept as it applies to needing two 6v batteries to = 12v and the Ah rating stays the same. In fact, even though you've explained it clearly, I'm having trouble getting my head around it because I'm used to only seeing it in one way. Much appreciated.

[Sunking]

That sounds very helpful! You are right, I have based everything on my understanding of the Ah concept as it applies to needing two 6v batteries to = 12v and the Ah rating stays the same. In fact, even though you've explained it clearly, I'm having trouble getting my head around it because I'm used to only seeing it in one way. Much appreciated.

Quit working with Amp Hours would solve all your problems and eliminate errors. Use Watt Hours.

I can tell you this, buy a good generator because solar is not going to work out for you. Get a generator and a good Electronic Battery Isolator. The Isolator will charge the batteries when the engine is running. One hour engine time will generate more power than the panels can generate in several days. You will need the genny for days you do not drive.

Plan on parking that tin can where it is exposed to the blistering hott sun without any shade from dawn to dusk with the panels oriented due Solar South? That is what it will take, and even then the panels will not generate enough power for what you intend to use them for. You won't have to worry about cooking, just set the food out and the Solar RV Oven will cook it.

[BradKW]

If you are planning on doing a system with air conditioning, Forget 12 or 24 volts. You will want a 48 volts system without any question. You will also want as small of a bedroom space as feasible. the smaller the better, so as to only cool the space you actually sleep. You could also consider The "Hot Spot" 4812 vrf split unit already designed to run directly from battery and solar. Using an inverter to run a window AC through and inverter will be very limited especially at 24 volt. You will also want a solar array that is over sized to insure you get to float everyday, on cloudy days and less than ideal solar conditions you will need to run a generator to maintain, condition and properly take advantage of your solar energy production.

Thanks Logan, that's a nice AC unit. I did look at it once before when doing searches...and unfortunately the price hasn't changed

Fair to say tho, if it works well enough to forego a generator, it's certainly worth considering...

[MetricAmerica]

For refrigeration you should be looking at 24 VDC top load models, they require no inverter and use much less power and can be run from your 48 volt bank with simple step down. This way you only need to run a much smaller inverter and mostly for the microwave. Not running inverter 24hrs 7 for any critical loads is crucial when living true off grid, with all the high power modern conveniences.

Ok I have to say, a chest refrigerator is not good in humid areas, unless your running a dehumidifier in the kitchen full time! I live on Lake Erie, so only have semi humid summers and still it causes trouble with mold as water pools at the bottom. But please do look at any 15 cm thick insulation refrigerators! This only 2.5 cm thick insulation stuff is extremely inadequate!

[BradKW]

So with a better understanding, I thinking that 24v would be the best way to go for me...fits with plan for (4) 6v battery bank. And the 24v version of the inverter is more efficient, so even better: https://www.amazon.com/Go-Power-GP-S...1+GP-SW3000-24. Any recommendations for other inverters that are in the 3000W and $1,000 ranges?

Also, what's a good quality step down 24v to 12v for some existing 12v items I may wish to use?

TY!