Solar Powered RV

Hi,

I agree that AGM would be a better power source for "quick" energy, with lower voltage drop. They also tolerate 80% deep discharge, so four group 31's would work, but eight would be better (assuming 48 volt banks).

Mark, you'd need too many marine batteries to accomplish this. Fewer, large Ah batteries will ultimately have a smaller footprint. Even though my L16's are tall, they have a much smaller footprint than the 8 T105's that you would need to "match" their Ah capacity with (actually 8 is more Ah but 6 is not enough). I would go with big Ah AGMs if trying to build a "cheap" system but lithium ion will charge an order of magnitude faster (how's 3-5C or more grab ya?) AND be 1/3 the weight. As far as inverters are concerned, that's no problem. Victron makes a 5kVA inverter with a 10kW surge (yes 10kW), can be had in 48V, AND they're stackable. We have discussed this seriously before and the consensus was that recharging in a timely manner was the real issue.

What about reducing the scale? A 5000 btu window unit draws much less than our roof air and could keep the bedroom cool. The lowest draw I found in a quick search was 4.5a at 120v and 462w.

Hi,

My 2500 watt msw Cobra has no problem running the air conditioner--but I won't do it because it is msw. I do have marine batteries.

I doubt that voltage drop would be much of a problem with a 48 volt or even 24 volt system.

It's nice to see the post turn into an exercise on a real world possibility.

A few problems not yet addressed from what I read here:

How do we handle the surge amps required to restart the air-conditioner's compressor? How deep will the voltage drop be on the battery-bank during this short start-up period? The battery-bank likely cannot get to get to even 50%soc and handle the load on "hot restart".

It seems to me since starting-batteries (many more thin plates) can handle high amp withdrawal, but little reserve, the ultimate battery may have to be marine-batteries. They fall between starting and true deep-cycle batteries, so we will loose the number of recycles possible, and need to replace the battery-bank more often.

And then the "biggest problem" of recharging the battery-bank in 20 minutes. Maybe we can be generous and go for (50% to 90%soc, or 50% to 80%soc).

My Schumacher SC-12000A speed-charger can handle a single deep-cycle (group 24, and maybe group 27) for a 50% to 80%soc in 1 hour. However; the voltage out-put to battery near end of that charge may approach 15.6 to 16.2 volts. That's to high to allow battery-bank to be connected to 12v circuit during charging.

Also this charger is multi-stage for 15 or 40 amps during charging. We will need a vary large scale up to handle the size battery-bank being discussed.

Hi mts,

You won't need as many batteries given the size of solar system. I would size the system based on 1.5 X the wattage of the air conditioner, so about 1800 watts.

That means that during the hottest part of the day the batteries will charge and the panels will directly run the air conditioner.

The panels could be on the roof in two layers. One that is fixed, and one that slides and then tilts to the optimum angle.

Battery system voltage at 48 means just a single controller is needed for 1800 watts. 12 volt needs could be from an ordinary converter such as a 55 amp PD unit with a single 12 volt battery as a "cushion".

Because, for most of the day, the panels will provide all power, the battery bank need not be quite so massive. Mena's bank, or mine might be large enough, if they were rewired for 48 volts.

A/C - no.
Microwave - yes, with big enough inverter (2000W?) and big enough battery bank (400 AH?).

A couple of 12V fans will make life a lot easier, you might not need A/C that often.

MW is the 3rd power-hungry item after A/C and 120V fridge. For MW and other items - assuming your fridge is propane - you need at least 400W total of panels. Better yet, max you roof space up and put as much solar wattage as you can, you won't regret it in a solar MH.

mena661 wrote:
. And I'd wire the bank for 48V so I wouldn't have to use 500MCM cables.

Yep. Much easier to work with than 12v.

pnichols wrote:

Probably the air conditioner run times they talk about are with their largest AGM battery bank option - eight AGM batteries for a total of 1600 amp hours.

Those AGMs look L16 sized. :) I wonder where they install them. Of course, my preference would be the LI batt option.

mlts22 wrote:

6000 Ah means I need 30 or so 12 volt batteries. At ~50 pounds, that is 1500 pounds of weight, and that's not including the very thick gauge cables needed in parallel, as well as the connectors and a very good crimp tool.

I was wondering how this thread would go. I would get a 4000Ah LI battery bank instead and save about ~1000 lbs or so of weight. And I'd wire the bank for 48V so I wouldn't have to use 500MCM cables.